X-Git-Url: http://nitlanguage.org

diff --git a/src/modelize/modelize_property.nit b/src/modelize/modelize_property.nit
index d2625cd..6f7f209 100644
--- a/src/modelize/modelize_property.nit
+++ b/src/modelize/modelize_property.nit
@@ -42,6 +42,28 @@ redef class ModelBuilder
 	# Public clients need to use `mpropdef2node` to access stuff.
 	private var mpropdef2npropdef = new HashMap[MPropDef, APropdef]
 
+	# Associate a `npropdef` with its `mpropdef`
+	#
+	# Be careful, this method is unsafe, no checking is done when it's used.
+	# The safe way to add method it's to use the `build_property`
+	#
+	# See `mpropdef2npropdef`
+	fun unsafe_add_mpropdef2npropdef(mpropdef: MPropDef,npropdef: APropdef)
+	do
+		mpropdef2npropdef[mpropdef] = npropdef
+	end
+
+	# Associate a `nclassdef` with its `mclassdef`
+	#
+	# Be careful, this method is unsafe, no checking is done when it's used.
+	# The safe way to add mclass it's to use the `build_property`
+	#
+	# See `mclassdef2nclassdef`
+	fun unsafe_add_mclassdef2nclassdef(mclassdef: MClassDef, nclassdef: AClassdef)
+	do
+		mclassdef2nclassdef[mclassdef] = nclassdef
+	end
+
 	# Retrieve the associated AST node of a mpropertydef.
 	# This method is used to associate model entity with syntactic entities.
 	#
@@ -55,10 +77,9 @@ redef class ModelBuilder
 			toolcontext.run_phases_on_npropdef(res)
 			return res
 		end
-		if mpropdef isa MMethodDef and mpropdef.mproperty.is_root_init then
-			res = mclassdef2nclassdef.get_or_null(mpropdef.mclassdef)
-			if res != null then return res
-		end
+		# Fall back to the class node if any.
+		res = mclassdef2nclassdef.get_or_null(mpropdef.mclassdef)
+		if res != null then return res
 		return null
 	end
 
@@ -80,7 +101,6 @@ redef class ModelBuilder
 	end
 
 	# Build the properties of `nclassdef`.
-	# REQUIRE: all superclasses are built.
 	private fun build_properties(nclassdef: AClassdef)
 	do
 		# Force building recursively
@@ -103,6 +123,25 @@ redef class ModelBuilder
 				npropdef.build_signature(self)
 			end
 			for npropdef in nclassdef2.n_propdefs do
+				if not npropdef isa ATypePropdef then continue
+				# Check circularity
+				var mpropdef = npropdef.mpropdef
+				if mpropdef == null then continue
+				if mpropdef.bound == null then continue
+				if not check_virtual_types_circularity(npropdef, mpropdef.mproperty, mclassdef.bound_mtype, mclassdef.mmodule) then
+					# Invalidate the bound
+					mpropdef.is_broken = true
+					mpropdef.bound = new MErrorType(mclassdef.mmodule.model)
+				end
+			end
+			for npropdef in nclassdef2.n_propdefs do
+				# Check ATypePropdef first since they may be required for the other properties
+				if not npropdef isa ATypePropdef then continue
+				npropdef.check_signature(self)
+			end
+
+			for npropdef in nclassdef2.n_propdefs do
+				if npropdef isa ATypePropdef then continue
 				npropdef.check_signature(self)
 			end
 		end
@@ -121,28 +160,26 @@ redef class ModelBuilder
 		var mclassdef = nclassdef.mclassdef.as(not null)
 
 		# Are we a refinement
-		if not mclassdef.is_intro then return
+		if not mclassdef.is_intro then
+			# Set the default_init of the mclassdef with the intro default_init
+			mclassdef.default_init = mclassdef.mclass.intro.default_init
+			return
+		end
 
 		# Look for the init in Object, or create it
 		if mclassdef.mclass.name == "Object" and the_root_init_mmethod == null then
 			# Create the implicit root-init method
-			var mprop = new MMethod(mclassdef, "init", mclassdef.mclass.visibility)
+			var mprop = new MMethod(mclassdef, "init", nclassdef.location, mclassdef.mclass.visibility)
 			mprop.is_root_init = true
 			var mpropdef = new MMethodDef(mclassdef, mprop, nclassdef.location)
 			var mparameters = new Array[MParameter]
 			var msignature = new MSignature(mparameters, null)
 			mpropdef.msignature = msignature
-			mpropdef.new_msignature = msignature
 			mprop.is_init = true
-			nclassdef.mfree_init = mpropdef
 			self.toolcontext.info("{mclassdef} gets a free empty constructor {mpropdef}{msignature}", 3)
 			the_root_init_mmethod = mprop
-			return
 		end
 
-		# Is the class forbid constructors?
-		if not mclassdef.mclass.kind.need_init then return
-
 		# Is there already a constructor defined?
 		var defined_init: nullable MMethodDef = null
 		for mpropdef in mclassdef.mpropdefs do
@@ -151,76 +188,76 @@ redef class ModelBuilder
 			if mpropdef.mproperty.is_root_init then
 				assert defined_init == null
 				defined_init = mpropdef
-			else if mpropdef.mproperty.name == "init" then
-				# An explicit old-style init named "init", so return
+			else if mpropdef.name == "defaultinit" then
 				return
 			end
 		end
 
-		if not nclassdef isa AStdClassdef then return
+		if mclassdef.default_init != null then return
+
+		# If the class is not AStdClassdef or it's an enum just return. No defaultinit is need.
+		if not nclassdef isa AStdClassdef or nclassdef.n_classkind isa AEnumClasskind then return
 
 		# Collect undefined attributes
 		var mparameters = new Array[MParameter]
 		var initializers = new Array[MProperty]
 		for npropdef in nclassdef.n_propdefs do
 			if npropdef isa AMethPropdef then
-				if npropdef.mpropdef == null then return # Skip broken attribute
-				var at = npropdef.get_single_annotation("autoinit", self)
-				if at == null then continue # Skip non tagged init
-
-				var sig = npropdef.mpropdef.msignature
+				if not npropdef.is_autoinit then continue # Skip non tagged autoinit
+				var mpropdef = npropdef.mpropdef
+				if mpropdef == null then return # Skip broken method
+				var sig = mpropdef.msignature
 				if sig == null then continue # Skip broken method
-
-				if not npropdef.mpropdef.is_intro then
-					self.error(at, "Error: `autoinit` cannot be set on redefinitions")
-					continue
-				end
-
-				for param in sig.mparameters do
-					var ret_type = param.mtype
-					var mparameter = new MParameter(param.name, ret_type, false)
-					mparameters.add(mparameter)
-				end
-				initializers.add(npropdef.mpropdef.mproperty)
-				npropdef.mpropdef.mproperty.is_autoinit = true
+				mparameters.add_all sig.mparameters
+				initializers.add(mpropdef.mproperty)
+				mpropdef.mproperty.is_autoinit = true
 			end
 			if npropdef isa AAttrPropdef then
-				if npropdef.mpropdef == null then return # Skip broken attribute
+				var mreadpropdef = npropdef.mreadpropdef
+				if mreadpropdef == null then return # Skip broken attribute
+				var msignature = mreadpropdef.msignature
+				if msignature == null then return # Skip broken attribute
 				if npropdef.noinit then continue # Skip noinit attribute
-				var atautoinit = npropdef.get_single_annotation("autoinit", self)
-				if atautoinit != null then
-					# For autoinit attributes, call the reader to force
+				var atlateinit = npropdef.get_single_annotation("lateinit", self)
+				if atlateinit != null then
+					# For lateinit attributes, call the reader to force
 					# the lazy initialization of the attribute.
-					initializers.add(npropdef.mreadpropdef.mproperty)
-					npropdef.mreadpropdef.mproperty.is_autoinit = true
+					initializers.add(mreadpropdef.mproperty)
+					mreadpropdef.mproperty.is_autoinit = true
 					continue
 				end
-				if npropdef.has_value then continue
-				var paramname = npropdef.mpropdef.mproperty.name.substring_from(1)
-				var ret_type = npropdef.mpropdef.static_mtype
-				if ret_type == null then return
-				var mparameter = new MParameter(paramname, ret_type, false)
-				mparameters.add(mparameter)
+				if npropdef.has_value and not npropdef.is_optional then continue
 				var msetter = npropdef.mwritepropdef
 				if msetter == null then
-					# No setter, it is a old-style attribute, so just add it
+					# No setter, it is a readonly attribute, so just add it
+					var paramname = mreadpropdef.mproperty.name
+					var ret_type = msignature.return_mtype
+					if ret_type == null then return
+					var mparameter = new MParameter(paramname, ret_type, false)
+					mparameters.add(mparameter)
+
 					initializers.add(npropdef.mpropdef.mproperty)
 					npropdef.mpropdef.mproperty.is_autoinit = true
 				else
 					# Add the setter to the list
+					mparameters.add_all msetter.msignature.mparameters
 					initializers.add(msetter.mproperty)
 					msetter.mproperty.is_autoinit = true
 				end
 			end
 		end
 
+		var the_root_init_mmethod = self.the_root_init_mmethod
 		if the_root_init_mmethod == null then return
 
 		# Look for most-specific new-stype init definitions
-		var spropdefs = the_root_init_mmethod.lookup_super_definitions(mclassdef.mmodule, mclassdef.bound_mtype)
-		if spropdefs.is_empty then
-			toolcontext.error(nclassdef.location, "Error: {mclassdef} does not specialize {the_root_init_mmethod.intro_mclassdef}. Possible duplication of the root class `Object`?")
-			return
+		var spropdefs = new ArraySet[MMethodDef]
+
+		for x in mclassdef.get_direct_supermtype do
+			var y = x.mclass.intro.default_init
+			if y == null then continue
+			if y.is_broken or y.msignature == null then return
+			spropdefs.add y
 		end
 
 		# Look at the autoinit class-annotation
@@ -236,14 +273,14 @@ redef class ModelBuilder
 			end
 
 			if autoinit.n_args.is_empty then
-				error(autoinit, "Syntax error: `autoinit` expects method identifiers, use `noautoinit` to clear all autoinits.")
+				error(autoinit, "Syntax Error: `autoinit` expects method identifiers, use `noautoinit` to clear all autoinits.")
 			end
 
 			# Get and check each argument
 			for narg in autoinit.n_args do
 				var id = narg.as_id
 				if id == null then
-					error(narg, "Syntax error: `autoinit` expects method identifiers.")
+					error(narg, "Syntax Error: `autoinit` expects method identifiers.")
 					return
 				end
 
@@ -268,35 +305,51 @@ redef class ModelBuilder
 				if pd isa MMethodDef then
 					# Get the signature resolved for the current receiver
 					var sig = pd.msignature.resolve_for(mclassdef.mclass.mclass_type, mclassdef.bound_mtype, mclassdef.mmodule, false)
-					mparameters.add_all sig.mparameters
+					mparameters.add_all(sig.mparameters)
 				else
 					# TODO attributes?
 					abort
 				end
 			end
-		else if noautoinit != null then
-			if initializers.is_empty then
-				warning(noautoinit, "useless-noautoinit", "Warning: the list of autoinit is already empty.")
+		else if spropdefs.not_empty then
+			# Search for inherited manual defaultinit
+			var manual = null
+			for s in spropdefs do
+				if mpropdef2npropdef.has_key(s) then
+					self.toolcontext.info("{mclassdef} inherits a manual defaultinit {s}", 3)
+					manual = s
+				end
 			end
-			# Just clear initializers
-			mparameters.clear
-			initializers.clear
-		else
 			# Search the longest-one and checks for conflict
 			var longest = spropdefs.first
 			if spropdefs.length > 1 then
-				# Check for conflict in the order of initializers
-				# Each initializer list must me a prefix of the longest list
 				# part 1. find the longest list
 				for spd in spropdefs do
 					if spd.initializers.length > longest.initializers.length then longest = spd
+
+					if spd != manual and manual != null then
+						self.toolcontext.info("{mclassdef} conflict between manual defaultinit {manual} and automatic defaultinit {spd}.", 3)
+					end
+				end
+				# conflict with manual autoinit?
+				if longest != manual and manual != null then
+					self.error(nclassdef, "Error: conflict between manual defaultinit {manual} and automatic defaultinit {longest}.")
 				end
 				# part 2. compare
-				for spd in spropdefs do
+				# Check for conflict in the order of initializers
+				# Each initializer list must me a prefix of the longest list
+				# If `noautoinit` is set, just ignore conflicts
+				if noautoinit == null then for spd in spropdefs do
 					var i = 0
 					for p in spd.initializers do
 						if p != longest.initializers[i] then
-							self.error(nclassdef, "Error: conflict for inherited inits {spd}({spd.initializers.join(", ")}) and {longest}({longest.initializers.join(", ")})")
+							var proposal = new ArraySet[MProperty]
+							for spd2 in spropdefs do
+								proposal.add_all spd2.initializers
+							end
+							proposal.add_all initializers
+							self.error(nclassdef, "Error: cannot generate automatic init for class {mclassdef.mclass}. Conflict in the order in inherited initializers {spd}({spd.initializers.join(", ")}) and {longest}({longest.initializers.join(", ")}). Use `autoinit` to order initializers. eg `autoinit {proposal.join(", ")}`")
+							# TODO: invalidate the initializer to avoid more errors
 							return
 						end
 						i += 1
@@ -304,41 +357,35 @@ redef class ModelBuilder
 				end
 			end
 
-			# Can we just inherit?
-			if spropdefs.length == 1 and mparameters.is_empty and defined_init == null then
-				self.toolcontext.info("{mclassdef} inherits the basic constructor {longest}", 3)
-				mclassdef.mclass.root_init = longest
-				return
-			end
-
-			# Combine the inherited list to what is collected
-			if longest.initializers.length > 0 then
-				mparameters.prepend longest.new_msignature.mparameters
-				initializers.prepend longest.initializers
+			if noautoinit != null then
+				# If there is local or inherited initializers, then complain.
+				if initializers.is_empty and longest.initializers.is_empty then
+					warning(noautoinit, "useless-noautoinit", "Warning: the list of autoinit is already empty.")
+				end
+				# Just clear initializers
+				mparameters.clear
+				initializers.clear
+			else
+				# Combine the inherited list to what is collected
+				if longest.initializers.length > 0 then
+					mparameters.prepend longest.msignature.mparameters
+					initializers.prepend longest.initializers
+				end
 			end
 		end
 
-		# If we already have a basic init definition, then setup its initializers
-		if defined_init != null then
-			defined_init.initializers.add_all(initializers)
+		# Create a specific new autoinit constructor
+		do
+			var mprop = new MMethod(mclassdef, "defaultinit", nclassdef.location, public_visibility)
+			mprop.is_init = true
+			var mpropdef = new MMethodDef(mclassdef, mprop, nclassdef.location)
+			mpropdef.initializers.add_all(initializers)
 			var msignature = new MSignature(mparameters, null)
-			defined_init.new_msignature = msignature
-			self.toolcontext.info("{mclassdef} extends its basic constructor signature to {defined_init}{msignature}", 3)
-			mclassdef.mclass.root_init = defined_init
-			return
+			mpropdef.msignature = msignature
+			mclassdef.default_init = mpropdef
+			self.toolcontext.info("{mclassdef} gets a free auto constructor `{mpropdef}{msignature}`. {spropdefs}", 3)
+			mclassdef.mclass.the_root_init_mmethod = the_root_init_mmethod
 		end
-
-		# Else create the local implicit basic init definition
-		var mprop = the_root_init_mmethod.as(not null)
-		var mpropdef = new MMethodDef(mclassdef, mprop, nclassdef.location)
-		mpropdef.has_supercall = true
-		mpropdef.initializers.add_all(initializers)
-		var msignature = new MSignature(mparameters, null)
-		mpropdef.new_msignature = msignature
-		mpropdef.msignature = new MSignature(new Array[MParameter], null) # always an empty real signature
-		nclassdef.mfree_init = mpropdef
-		self.toolcontext.info("{mclassdef} gets a free constructor for attributes {mpropdef}{msignature}", 3)
-		mclassdef.mclass.root_init = mpropdef
 	end
 
 	# Check the visibility of `mtype` as an element of the signature of `mpropdef`.
@@ -351,15 +398,21 @@ redef class ModelBuilder
 		# It is a case-by case
 		var vis_type: nullable MVisibility = null # The own visibility of the type
 		var mmodule_type: nullable MModule = null # The original module of the type
-		mtype = mtype.as_notnullable
+		mtype = mtype.undecorate
 		if mtype isa MClassType then
 			vis_type = mtype.mclass.visibility
-			mmodule_type = mtype.mclass.intro.mmodule
+			mmodule_type = mtype.mclass.intro_mmodule
 		else if mtype isa MVirtualType then
 			vis_type = mtype.mproperty.visibility
 			mmodule_type = mtype.mproperty.intro_mclassdef.mmodule
 		else if mtype isa MParameterType then
 			# nothing, always visible
+		else if mtype isa MNullType then
+			# nothing to do.
+		else if mtype isa MBottomType then
+			# nothing to do.
+		else if mtype isa MErrorType then
+			# nothing to do.
 		else
 			node.debug "Unexpected type {mtype}"
 			abort
@@ -369,10 +422,10 @@ redef class ModelBuilder
 			assert mmodule_type != null
 			var vis_module_type = mmodule.visibility_for(mmodule_type) # the visibility of the original module
 			if mproperty.visibility > vis_type then
-				error(node, "Error: The {mproperty.visibility} property `{mproperty}` cannot contain the {vis_type} type `{mtype}`")
+				error(node, "Error: the {mproperty.visibility} property `{mproperty}` cannot contain the {vis_type} type `{mtype}`.")
 				return
 			else if mproperty.visibility > vis_module_type then
-				error(node, "Error: The {mproperty.visibility} property `{mproperty}` cannot contain the type `{mtype}` from the {vis_module_type} module `{mmodule_type}`")
+				error(node, "Error: the {mproperty.visibility} property `{mproperty}` cannot contain the type `{mtype}` from the {vis_module_type} module `{mmodule_type}`.")
 				return
 			end
 		end
@@ -388,6 +441,71 @@ redef class ModelBuilder
 			for t in mtype.arguments do check_visibility(node, t, mpropdef)
 		end
 	end
+
+	# Detect circularity errors for virtual types.
+	fun check_virtual_types_circularity(node: ANode, mproperty: MVirtualTypeProp, recv: MType, mmodule: MModule): Bool
+	do
+		# Check circularity
+		# Slow case: progress on each resolution until we visit all without getting a loop
+
+		# The graph used to detect loops
+		var mtype = mproperty.mvirtualtype
+		var poset = new POSet[MType]
+
+		# The work-list of types to resolve
+		var todo = new List[MType]
+		todo.add mtype
+
+		while not todo.is_empty do
+			# The visited type
+			var t = todo.pop
+
+			if not t.need_anchor then continue
+
+			# Get the types derived of `t` (subtypes and bounds)
+			var nexts
+			if t isa MNullableType then
+				nexts = [t.mtype]
+			else if t isa MGenericType then
+				nexts = t.arguments
+			else if t isa MVirtualType then
+				var vt = t.mproperty
+				# Because `vt` is possibly unchecked, we have to do the bound-lookup manually
+				var defs = vt.lookup_definitions(mmodule, recv)
+				if defs.is_empty then return false
+				nexts = new Array[MType]
+				for d in defs do
+					var next = defs.first.bound
+					if next == null then return false
+					nexts.add next
+				end
+			else if t isa MClassType then
+				# Basic type, nothing to to
+				continue
+			else if t isa MParameterType then
+				# Parameter types cannot depend on virtual types, so nothing to do
+				continue
+			else
+				abort
+			end
+
+			# For each one
+			for next in nexts do
+				if poset.has_edge(next, t) then
+					if mtype == next then
+						error(node, "Error: circularity of virtual type definition: {next} <-> {t}.")
+					else
+						error(node, "Error: circularity of virtual type definition: {mtype} -> {next} <-> {t}.")
+					end
+					return false
+				else
+					poset.add_edge(t, next)
+					todo.add next
+				end
+			end
+		end
+		return true
+	end
 end
 
 redef class MPropDef
@@ -399,18 +517,13 @@ end
 redef class AClassdef
 	# Marker used in `ModelBuilder::build_properties`
 	private var build_properties_is_done = false
-
-	# The free init (implicitely constructed by the class if required)
-	var mfree_init: nullable MMethodDef = null
 end
 
 redef class MClass
 	# The base init of the class.
-	# Used to get the common new_msignature and initializers
 	#
-	# TODO: Where to put this information is not clear because unlike other
-	# informations, the initialisers are stable in a same class.
-	var root_init: nullable MMethodDef = null
+	# TODO: merge with `root_init` and `ModelBuilder::the_root_init_mmethod` if possible
+	var the_root_init_mmethod: nullable MMethod = null
 end
 
 redef class MClassDef
@@ -440,17 +553,17 @@ redef class MClassDef
 
 			# SELF must be declared in Object, otherwise this will create conflicts
 			if intro_mclassdef.mclass.name != "Object" then
-				modelbuilder.error(nintro, "Error: the virtual type SELF must be declared in Object.")
+				modelbuilder.error(nintro, "Error: the virtual type `SELF` must be declared in `Object`.")
 			end
 
 			# SELF must be public
 			if mprop.visibility != public_visibility then
-				modelbuilder.error(nintro, "Error: the virtual type SELF must be public.")
+				modelbuilder.error(nintro, "Error: the virtual type `SELF` must be public.")
 			end
 
 			# SELF must not be fixed
 			if intro.is_fixed then
-				modelbuilder.error(nintro, "Error: the virtual type SELF cannot be fixed.")
+				modelbuilder.error(nintro, "Error: the virtual type `SELF` cannot be fixed.")
 			end
 
 			return
@@ -479,17 +592,17 @@ redef class APropdef
 		if nvisibility != null then
 			mvisibility = nvisibility.mvisibility
 			if mvisibility == intrude_visibility then
-				modelbuilder.error(nvisibility, "Error: intrude is not a legal visibility for properties.")
+				modelbuilder.error(nvisibility, "Error: `intrude` is not a legal visibility for properties.")
 				mvisibility = public_visibility
 			end
 		end
 		if mclassdef.mclass.visibility == private_visibility then
 			if mvisibility == protected_visibility then
 				assert nvisibility != null
-				modelbuilder.error(nvisibility, "Error: The only legal visibility for properties in a private class is private.")
+				modelbuilder.error(nvisibility, "Error: `private` is the only legal visibility for properties in a private class.")
 			else if mvisibility == private_visibility then
 				assert nvisibility != null
-				modelbuilder.advice(nvisibility, "useless-visibility", "Warning: private is superfluous since the only legal visibility for properties in a private class is private.")
+				modelbuilder.advice(nvisibility, "useless-visibility", "Warning: `private` is superfluous since the only legal visibility for properties in a private class is private.")
 			end
 			mvisibility = private_visibility
 		end
@@ -503,7 +616,7 @@ redef class APropdef
 			var mdoc = ndoc.to_mdoc
 			mpropdef.mdoc = mdoc
 			mdoc.original_mentity = mpropdef
-		else if mpropdef.is_intro and mpropdef.mproperty.visibility >= protected_visibility then
+		else if mpropdef.is_intro and mpropdef.mproperty.visibility >= protected_visibility and mpropdef.name != "new" then
 			modelbuilder.advice(self, "missing-doc", "Documentation warning: Undocumented property `{mpropdef.mproperty}`")
 		end
 
@@ -525,38 +638,29 @@ redef class APropdef
 		if nvisibility == null then return
 		var mvisibility = nvisibility.mvisibility
 		if mvisibility != mprop.visibility and mvisibility != public_visibility then
-				modelbuilder.error(nvisibility, "Error: redefinition changed the visibility from a {mprop.visibility} to a {mvisibility}")
+				modelbuilder.error(nvisibility, "Error: redefinition changed the visibility from `{mprop.visibility}` to `{mvisibility}`.")
 		end
 	end
 
 	private fun check_redef_keyword(modelbuilder: ModelBuilder, mclassdef: MClassDef, kwredef: nullable Token, need_redef: Bool, mprop: MProperty): Bool
 	do
 		if mclassdef.mprop2npropdef.has_key(mprop) then
-			modelbuilder.error(self, "Error: A property {mprop} is already defined in class {mclassdef.mclass} at line {mclassdef.mprop2npropdef[mprop].location.line_start}.")
-			return false
-		end
-		if mprop isa MMethod and mprop.is_toplevel != (parent isa ATopClassdef) then
-			if mprop.is_toplevel then
-				modelbuilder.error(self, "Error: {mprop} is a top level method.")
-			else
-				modelbuilder.error(self, "Error: {mprop} is not a top level method.")
-			end
+			modelbuilder.error(self, "Error: a property `{mprop}` is already defined in class `{mclassdef.mclass}` at line {mclassdef.mprop2npropdef[mprop].location.line_start}.")
 			return false
-
 		end
 		if mprop isa MMethod and mprop.is_root_init then return true
 		if kwredef == null then
 			if need_redef then
-				modelbuilder.error(self, "Redef error: {mclassdef.mclass}::{mprop.name} is an inherited property. To redefine it, add the redef keyword.")
+				modelbuilder.error(self, "Redef Error: `{mclassdef.mclass}::{mprop.name}` is an inherited property. To redefine it, add the `redef` keyword.")
 				return false
 			end
 
-			# Check for full-name conflicts in the project.
-			# A public property should have a unique qualified name `project::class::prop`.
+			# Check for full-name conflicts in the package.
+			# A public property should have a unique qualified name `package::class::prop`.
 			if mprop.intro_mclassdef.mmodule.mgroup != null and mprop.visibility >= protected_visibility then
 				var others = modelbuilder.model.get_mproperties_by_name(mprop.name)
 				if others != null then for other in others do
-					if other != mprop and other.intro_mclassdef.mmodule.mgroup != null and other.intro_mclassdef.mmodule.mgroup.mproject == mprop.intro_mclassdef.mmodule.mgroup.mproject and other.intro_mclassdef.mclass.name == mprop.intro_mclassdef.mclass.name and other.visibility >= protected_visibility then
+					if other != mprop and other.intro_mclassdef.mmodule.mgroup != null and other.intro_mclassdef.mmodule.mgroup.mpackage == mprop.intro_mclassdef.mmodule.mgroup.mpackage and other.intro_mclassdef.mclass.name == mprop.intro_mclassdef.mclass.name and other.visibility >= protected_visibility then
 						modelbuilder.advice(self, "full-name-conflict", "Warning: A property named `{other.full_name}` is already defined in module `{other.intro_mclassdef.mmodule}` for the class `{other.intro_mclassdef.mclass.name}`.")
 						break
 					end
@@ -564,13 +668,15 @@ redef class APropdef
 			end
 		else
 			if not need_redef then
-				modelbuilder.error(self, "Error: No property {mclassdef.mclass}::{mprop.name} is inherited. Remove the redef keyword to define a new property.")
+				modelbuilder.error(self, "Error: no property `{mclassdef.mclass}::{mprop.name}` is inherited. Remove the `redef` keyword to define a new property.")
 				return false
 			end
 		end
 		return true
 	end
 
+	# Checks for useless type in redef signatures.
+	private fun check_repeated_types(modelbuilder: ModelBuilder) do end
 end
 
 redef class ASignature
@@ -591,21 +697,20 @@ redef class ASignature
 	# Visit and fill information about a signature
 	private fun visit_signature(modelbuilder: ModelBuilder, mclassdef: MClassDef): Bool
 	do
-		var mmodule = mclassdef.mmodule
 		var param_names = self.param_names
 		var param_types = self.param_types
 		for np in self.n_params do
 			param_names.add(np.n_id.text)
 			var ntype = np.n_type
 			if ntype != null then
-				var mtype = modelbuilder.resolve_mtype(mmodule, mclassdef, ntype)
+				var mtype = modelbuilder.resolve_mtype_unchecked(mclassdef, ntype, true)
 				if mtype == null then return false # Skip error
 				for i in [0..param_names.length-param_types.length[ do
 					param_types.add(mtype)
 				end
 				if np.n_dotdotdot != null then
 					if self.vararg_rank != -1 then
-						modelbuilder.error(np, "Error: {param_names[self.vararg_rank]} is already a vararg")
+						modelbuilder.error(np, "Error: `{param_names[self.vararg_rank]}` is already a vararg")
 						return false
 					else
 						self.vararg_rank = param_names.length - 1
@@ -615,7 +720,7 @@ redef class ASignature
 		end
 		var ntype = self.n_type
 		if ntype != null then
-			self.ret_type = modelbuilder.resolve_mtype(mmodule, mclassdef, ntype)
+			self.ret_type = modelbuilder.resolve_mtype_unchecked(mclassdef, ntype, true)
 			if self.ret_type == null then return false # Skip error
 		end
 
@@ -623,24 +728,25 @@ redef class ASignature
 		return true
 	end
 
-	# Build a visited signature
-	fun build_signature(modelbuilder: ModelBuilder): nullable MSignature
+	private fun check_signature(modelbuilder: ModelBuilder, mclassdef: MClassDef): Bool
 	do
-		if param_names.length != param_types.length then
-			# Some parameters are typed, other parameters are not typed.
-			modelbuilder.error(self.n_params[param_types.length], "Error: Untyped parameter `{param_names[param_types.length]}'.")
-			return null
+		var res = true
+		for np in self.n_params do
+			var ntype = np.n_type
+			if ntype != null then
+				if modelbuilder.resolve_mtype(mclassdef, ntype) == null then
+					res = false
+				end
+			end
 		end
-
-		var mparameters = new Array[MParameter]
-		for i in [0..param_names.length[ do
-			var mparameter = new MParameter(param_names[i], param_types[i], i == vararg_rank)
-			self.n_params[i].mparameter = mparameter
-			mparameters.add(mparameter)
+		var ntype = self.n_type
+		if ntype != null then
+			if modelbuilder.resolve_mtype(mclassdef, ntype) == null then
+				res = false
+			end
 		end
-
-		var msignature = new MSignature(mparameters, ret_type)
-		return msignature
+		if not res then is_broken = true
+		return res
 	end
 end
 
@@ -652,6 +758,8 @@ end
 redef class AMethPropdef
 	redef type MPROPDEF: MMethodDef
 
+	# Is the method annotated `autoinit`?
+	var is_autoinit = false
 
 	# Can self be used as a root init?
 	private fun look_like_a_root_init(modelbuilder: ModelBuilder, mclassdef: MClassDef): Bool
@@ -687,22 +795,27 @@ redef class AMethPropdef
 	do
 		var n_kwinit = n_kwinit
 		var n_kwnew = n_kwnew
-		var is_init = n_kwinit != null or n_kwnew != null
+		var is_new = n_kwnew != null
+		var is_init = n_kwinit != null or is_new
 		var name: String
 		var amethodid = self.n_methid
 		var name_node: ANode
+		var is_old_style_init = false
 		if amethodid == null then
-			if not is_init then
-				name = "main"
-				name_node = self
-			else if n_kwinit != null then
+			if n_kwinit != null then
 				name = "init"
 				name_node = n_kwinit
+				var old_style_annot = get_single_annotation("old_style_init", modelbuilder)
+				if  old_style_annot != null or self.n_signature.n_params.not_empty then
+					name = "defaultinit"
+					if old_style_annot != null then is_old_style_init = true
+				end
 			else if n_kwnew != null then
 				name = "new"
 				name_node = n_kwnew
 			else
-				abort
+				name = "main"
+				name_node = self
 			end
 		else if amethodid isa AIdMethid then
 			name = amethodid.n_id.text
@@ -712,14 +825,25 @@ redef class AMethPropdef
 			name = amethodid.collect_text
 			name_node = amethodid
 
-			if name == "-" and self.n_signature.n_params.length == 0 then
+			var arity = self.n_signature.n_params.length
+			if name == "+" and arity == 0 then
+				name = "unary +"
+			else if name == "-" and arity == 0 then
 				name = "unary -"
+			else if name == "~" and arity == 0 then
+				name = "unary ~"
+			else
+				if amethodid.is_binary and arity != 1 then
+					modelbuilder.error(self.n_signature, "Syntax Error: binary operator `{name}` requires exactly one parameter; got {arity}.")
+				else if amethodid.min_arity > arity then
+					modelbuilder.error(self.n_signature, "Syntax Error: `{name}` requires at least {amethodid.min_arity} parameter(s); got {arity}.")
+				end
 			end
 		end
 
 		var look_like_a_root_init = look_like_a_root_init(modelbuilder, mclassdef)
 		var mprop: nullable MMethod = null
-		if not is_init or n_kwredef != null then mprop = modelbuilder.try_get_mproperty_by_name(name_node, mclassdef, name).as(nullable MMethod)
+		if not is_init or n_kwredef != null or look_like_a_root_init then mprop = modelbuilder.try_get_mproperty_by_name(name_node, mclassdef, name).as(nullable MMethod)
 		if mprop == null and look_like_a_root_init then
 			mprop = modelbuilder.the_root_init_mmethod
 			var nb = n_block
@@ -729,17 +853,21 @@ redef class AMethPropdef
 		end
 		if mprop == null then
 			var mvisibility = new_property_visibility(modelbuilder, mclassdef, self.n_visibility)
-			mprop = new MMethod(mclassdef, name, mvisibility)
+			mprop = new MMethod(mclassdef, name, self.location, mvisibility)
 			if look_like_a_root_init and modelbuilder.the_root_init_mmethod == null then
 				modelbuilder.the_root_init_mmethod = mprop
 				mprop.is_root_init = true
 			end
 			mprop.is_init = is_init
-			mprop.is_new = n_kwnew != null
-			if mprop.is_new then mclassdef.mclass.has_new_factory = true
-			if parent isa ATopClassdef then mprop.is_toplevel = true
-			self.check_redef_keyword(modelbuilder, mclassdef, n_kwredef, false, mprop)
+			mprop.is_new = is_new
+			if is_new then mclassdef.mclass.has_new_factory = true
+			if name == "sys" then mprop.is_toplevel = true # special case for sys allowed in `new` factories
+			if not self.check_redef_keyword(modelbuilder, mclassdef, n_kwredef, false, mprop) then
+				mprop.is_broken = true
+				return
+			end
 		else
+			if mprop.is_broken then return
 			if not self.check_redef_keyword(modelbuilder, mclassdef, n_kwredef, not self isa AMainMethPropdef, mprop) then return
 			check_redef_property_visibility(modelbuilder, self.n_visibility, mprop)
 		end
@@ -748,7 +876,10 @@ redef class AMethPropdef
 		if is_init then
 			for p, n in mclassdef.mprop2npropdef do
 				if p != mprop and p isa MMethod and p.name == name then
-					check_redef_keyword(modelbuilder, mclassdef, n_kwredef, false, p)
+					if not check_redef_keyword(modelbuilder, mclassdef, n_kwredef, false, p) then
+						mprop.is_broken = true
+						return
+					end
 					break
 				end
 			end
@@ -757,6 +888,15 @@ redef class AMethPropdef
 		mclassdef.mprop2npropdef[mprop] = self
 
 		var mpropdef = new MMethodDef(mclassdef, mprop, self.location)
+		if mpropdef.name == "defaultinit" and mclassdef.is_intro then
+			assert mclassdef.default_init == null
+			mpropdef.is_old_style_init = is_old_style_init
+			mclassdef.default_init = mpropdef
+			# Set the initializers with the mproperty.
+			# This point is need when a super class define this own default_init and inherited class use the default_init generated automaticlely.
+			mpropdef.initializers.add mprop
+			mpropdef.is_calling_init = true
+		end
 
 		set_doc(mpropdef, modelbuilder)
 
@@ -773,19 +913,13 @@ redef class AMethPropdef
 	do
 		var mpropdef = self.mpropdef
 		if mpropdef == null then return # Error thus skiped
+		var mproperty = mpropdef.mproperty
 		var mclassdef = mpropdef.mclassdef
 		var mmodule = mclassdef.mmodule
 		var nsig = self.n_signature
 
-		if mpropdef.mproperty.is_root_init and not mclassdef.is_intro then
-			var root_init = mclassdef.mclass.root_init
-			if root_init != null then
-				# Inherit the initializers by refinement
-				mpropdef.new_msignature = root_init.new_msignature
-				assert mpropdef.initializers.is_empty
-				mpropdef.initializers.add_all root_init.initializers
-			end
-		end
+		var accept_special_last_parameter = self.n_methid == null or self.n_methid.accept_special_last_parameter
+		var return_is_mandatory = self.n_methid != null and self.n_methid.return_is_mandatory
 
 		# Retrieve info from the signature AST
 		var param_names = new Array[String] # Names of parameters from the AST
@@ -804,7 +938,7 @@ redef class AMethPropdef
 		# FIXME: do not inherit from the intro, but from the most specific
 		var msignature: nullable MSignature = null
 		if not mpropdef.is_intro then
-			msignature = mpropdef.mproperty.intro.msignature
+			msignature = mproperty.intro.msignature
 			if msignature == null then return # Skip error
 
 			# The local signature is adapted to use the local formal types, if any.
@@ -814,14 +948,14 @@ redef class AMethPropdef
 			if param_names.length != msignature.arity then
 				var node: ANode
 				if nsig != null then node = nsig else node = self
-				modelbuilder.error(node, "Redef error: {mpropdef} redefines {mpropdef.mproperty.intro} with {param_names.length} parameter(s), {msignature.arity} expected. Signature is {mpropdef}{msignature}")
+				modelbuilder.error(node, "Redef Error: expected {msignature.arity} parameter(s) for `{mproperty.name}{msignature}`; got {param_names.length}. See introduction at `{mproperty.full_name}`.")
 				return
 			end
-		else if mpropdef.mproperty.is_init and not mpropdef.mproperty.is_new then
+		else if mproperty.is_init and not mproperty.is_new then
 			# FIXME UGLY: inherit signature from a super-constructor
 			for msupertype in mclassdef.supertypes do
 				msupertype = msupertype.anchor_to(mmodule, mclassdef.bound_mtype)
-				var candidate = modelbuilder.try_get_mproperty_by_name2(self, mmodule, msupertype, mpropdef.mproperty.name)
+				var candidate = modelbuilder.try_get_mproperty_by_name2(self, mmodule, msupertype, mproperty.name)
 				if candidate != null then
 					if msignature == null then
 						msignature = candidate.intro.as(MMethodDef).msignature
@@ -846,7 +980,7 @@ redef class AMethPropdef
 
 		if param_names.length != param_types.length then
 			# Some parameters are typed, other parameters are not typed.
-			modelbuilder.error(nsig.n_params[param_types.length], "Error: Untyped parameter `{param_names[param_types.length]}'.")
+			modelbuilder.error(nsig.n_params[param_types.length], "Error: untyped parameter `{param_names[param_types.length]}'.")
 			return
 		end
 
@@ -858,7 +992,15 @@ redef class AMethPropdef
 		end
 
 		# In `new`-factories, the return type is by default the classtype.
-		if ret_type == null and mpropdef.mproperty.is_new then ret_type = mclassdef.mclass.mclass_type
+		if ret_type == null and mproperty.is_new then ret_type = mclassdef.mclass.mclass_type
+
+		# Special checks for operator methods
+		if not accept_special_last_parameter and mparameters.not_empty and mparameters.last.is_vararg then
+			modelbuilder.error(self.n_signature.n_params.last, "Error: illegal variadic parameter `{mparameters.last}` for `{mproperty.name}`.")
+		end
+		if ret_type == null and return_is_mandatory then
+			modelbuilder.error(self.n_methid, "Error: mandatory return type for `{mproperty.name}`.")
+		end
 
 		msignature = new MSignature(mparameters, ret_type)
 		mpropdef.msignature = msignature
@@ -868,7 +1010,18 @@ redef class AMethPropdef
 
 		# Check annotations
 		var at = self.get_single_annotation("lazy", modelbuilder)
-		if at != null then modelbuilder.error(at, "Syntax error: `lazy` must be used on attributes.")
+		if at != null then modelbuilder.error(at, "Syntax Error: `lazy` must be used on attributes.")
+
+		var atautoinit = self.get_single_annotation("autoinit", modelbuilder)
+		if atautoinit != null then
+			if not mpropdef.is_intro then
+				modelbuilder.error(atautoinit, "Error: `autoinit` cannot be set on redefinitions.")
+			else if not mclassdef.is_intro then
+				modelbuilder.error(atautoinit, "Error: `autoinit` cannot be used in class refinements.")
+			else
+				self.is_autoinit = true
+			end
+		end
 	end
 
 	redef fun check_signature(modelbuilder)
@@ -878,9 +1031,18 @@ redef class AMethPropdef
 		var mclassdef = mpropdef.mclassdef
 		var mmodule = mclassdef.mmodule
 		var nsig = self.n_signature
-		var mysignature = self.mpropdef.msignature
+		var mysignature = mpropdef.msignature
 		if mysignature == null then return # Error thus skiped
 
+		# Check
+		if nsig != null then
+			if not nsig.check_signature(modelbuilder, mclassdef) then
+				mpropdef.msignature = null # invalidate
+				mpropdef.is_broken = true
+				return # Forward error
+			end
+		end
+
 		# Lookup for signature in the precursor
 		# FIXME all precursors should be considered
 		if not mpropdef.is_intro then
@@ -890,7 +1052,9 @@ redef class AMethPropdef
 			var precursor_ret_type = msignature.return_mtype
 			var ret_type = mysignature.return_mtype
 			if ret_type != null and precursor_ret_type == null then
-				modelbuilder.error(nsig.n_type.as(not null), "Redef Error: {mpropdef.mproperty} is a procedure, not a function.")
+				modelbuilder.error(nsig.n_type, "Redef Error: `{mpropdef.mproperty}` is a procedure, not a function.")
+				mpropdef.msignature = null
+				mpropdef.is_broken = true
 				return
 			end
 
@@ -901,7 +1065,9 @@ redef class AMethPropdef
 					var prt = msignature.mparameters[i].mtype
 					var node = nsig.n_params[i]
 					if not modelbuilder.check_sametype(node, mmodule, mclassdef.bound_mtype, myt, prt) then
-						modelbuilder.error(node, "Redef Error: Wrong type for parameter `{mysignature.mparameters[i].name}'. found {myt}, expected {prt} as in {mpropdef.mproperty.intro}.")
+						modelbuilder.error(node, "Redef Error: expected `{prt}` for parameter `{mysignature.mparameters[i].name}'; got `{myt}`.")
+						mpropdef.msignature = null
+						mpropdef.is_broken = true
 					end
 				end
 			end
@@ -913,12 +1079,14 @@ redef class AMethPropdef
 					# Inherit the return type
 					ret_type = precursor_ret_type
 				else if not modelbuilder.check_subtype(node, mmodule, mclassdef.bound_mtype, ret_type, precursor_ret_type) then
-					modelbuilder.error(node, "Redef Error: Wrong return type. found {ret_type}, expected {precursor_ret_type} as in {mpropdef.mproperty.intro}.")
+					modelbuilder.error(node, "Redef Error: expected `{precursor_ret_type}` for return type; got `{ret_type}`.")
+					mpropdef.msignature = null
+					mpropdef.is_broken = true
 				end
 			end
 		end
 
-		if mysignature.arity > 0 then
+		if nsig != null then
 			# Check parameters visibility
 			for i in [0..mysignature.arity[ do
 				var nt = nsig.n_params[i].n_type
@@ -927,22 +1095,107 @@ redef class AMethPropdef
 			var nt = nsig.n_type
 			if nt != null then modelbuilder.check_visibility(nt, nt.mtype.as(not null), mpropdef)
 		end
+		check_repeated_types(modelbuilder)
+	end
+
+	# For parameters, type is always useless in a redef.
+	# For return type, type is useless if not covariant with introduction.
+	redef fun check_repeated_types(modelbuilder) do
+		var mpropdef = self.mpropdef
+		if mpropdef == null then return
+		if mpropdef.is_intro or n_signature == null then return
+		# check params
+		for param in n_signature.n_params do
+			if param.n_type != null then
+				modelbuilder.advice(param.n_type, "useless-signature", "Warning: useless type repetition on parameter `{param.n_id.text}` for redefined method `{mpropdef.name}`")
+			end
+		end
+		# get intro
+		var intro = mpropdef.mproperty.intro
+		var n_intro = modelbuilder.mpropdef2npropdef.get_or_null(intro)
+		if n_intro == null or not n_intro isa AMethPropdef then return
+		# check return type
+		var ret_type = n_signature.ret_type
+		if ret_type != null and ret_type == n_intro.n_signature.ret_type then
+			modelbuilder.advice(n_signature.n_type, "useless-signature", "Warning: useless return type repetition for redefined method `{mpropdef.name}`")
+		end
 	end
 end
 
+redef class AMethid
+	# Is a return required?
+	#
+	# * True for operators and brackets.
+	# * False for id and assignment.
+	fun return_is_mandatory: Bool do return true
+
+	# Can the last parameter be special like a vararg?
+	#
+	# * False for operators: the last one is in fact the only one.
+	# * False for assignments: it is the right part of the assignment.
+	# * True for ids and brackets.
+	fun accept_special_last_parameter: Bool do return false
+
+	# The minimum required number of parameters.
+	#
+	# * 1 for binary operators
+	# * 1 for brackets
+	# * 1 for assignments
+	# * 2 for bracket assignments
+	# * 0 for ids
+	fun min_arity: Int do return 1
+
+	# Is the `self` a binary operator?
+	fun is_binary: Bool do return true
+end
+
+redef class AIdMethid
+	redef fun return_is_mandatory do return false
+	redef fun accept_special_last_parameter do return true
+	redef fun min_arity do return 0
+	redef fun is_binary do return false
+end
+
+redef class ABraMethid
+	redef fun accept_special_last_parameter do return true
+	redef fun is_binary do return false
+end
+
+redef class ABraassignMethid
+	redef fun return_is_mandatory do return false
+	redef fun min_arity do return 2
+	redef fun is_binary do return false
+end
+
+redef class AAssignMethid
+	redef fun return_is_mandatory do return false
+	redef fun is_binary do return false
+end
+
 redef class AAttrPropdef
 	redef type MPROPDEF: MAttributeDef
 
+	# The static type of the property (declared, inferred or inherited)
+	# This attribute is also used to check if the property was analyzed and is valid.
+	var mtype: nullable MType
+
 	# Is the node tagged `noinit`?
 	var noinit = false
 
 	# Is the node tagged lazy?
 	var is_lazy = false
 
-	# Has the node a default value?
-	# Could be through `n_expr` or `n_block`
+	# Is the node tagged optional?
+	var is_optional = false
+
+	# Does the node have a default value?
+	# Could be through `n_expr`, `n_block` or `is_lazy`
 	var has_value = false
 
+	# The name of the attribute
+	# Note: The name of the attribute is in reality the name of the mreadpropdef
+	var name: String = n_id2.text is lazy
+
 	# The guard associated to a lazy attribute.
 	# Because some engines does not have a working `isset`,
 	# this additional attribute is used to guard the lazy initialization.
@@ -957,48 +1210,20 @@ redef class AAttrPropdef
 	redef fun build_property(modelbuilder, mclassdef)
 	do
 		var mclass = mclassdef.mclass
-		var nid2 = n_id2
-		var name = nid2.text
 
 		var atabstract = self.get_single_annotation("abstract", modelbuilder)
-		if atabstract == null then
-			if mclass.kind == interface_kind then
-				modelbuilder.error(self, "Error: Attempt to define attribute {name} in the interface {mclass}.")
-			else if mclass.kind == enum_kind then
-				modelbuilder.error(self, "Error: Attempt to define attribute {name} in the enum class {mclass}.")
-			else if mclass.kind == extern_kind then
-				modelbuilder.error(self, "Error: Attempt to define attribute {name} in the extern class {mclass}.")
-			end
 
-			var mprop = new MAttribute(mclassdef, "_" + name, private_visibility)
-			var mpropdef = new MAttributeDef(mclassdef, mprop, self.location)
-			self.mpropdef = mpropdef
-			modelbuilder.mpropdef2npropdef[mpropdef] = self
-		end
+		if atabstract == null then build_attribute_property(modelbuilder, mclassdef)
 
-		var readname = name
-		var mreadprop = modelbuilder.try_get_mproperty_by_name(nid2, mclassdef, readname).as(nullable MMethod)
-		if mreadprop == null then
-			var mvisibility = new_property_visibility(modelbuilder, mclassdef, self.n_visibility)
-			mreadprop = new MMethod(mclassdef, readname, mvisibility)
-			if not self.check_redef_keyword(modelbuilder, mclassdef, n_kwredef, false, mreadprop) then return
-		else
-			if not self.check_redef_keyword(modelbuilder, mclassdef, n_kwredef, true, mreadprop) then return
-			check_redef_property_visibility(modelbuilder, self.n_visibility, mreadprop)
-		end
-		mclassdef.mprop2npropdef[mreadprop] = self
+		# Construction of the read property. If it's not correctly built just return.
+		if not build_read_property(modelbuilder, mclassdef) then return
 
-		var mreadpropdef = new MMethodDef(mclassdef, mreadprop, self.location)
-		self.mreadpropdef = mreadpropdef
-		modelbuilder.mpropdef2npropdef[mreadpropdef] = self
-		set_doc(mreadpropdef, modelbuilder)
-		if mpropdef != null then mpropdef.mdoc = mreadpropdef.mdoc
 		if atabstract != null then mreadpropdef.is_abstract = true
 
 		has_value = n_expr != null or n_block != null
 
 		if atabstract != null and has_value then
-			modelbuilder.error(atabstract, "Error: `abstract` attributes cannot have an initial value")
+			modelbuilder.error(atabstract, "Error: `abstract` attributes cannot have an initial value.")
 			return
 		end
 
@@ -1007,45 +1232,120 @@ redef class AAttrPropdef
 		if atnoinit != null then
 			noinit = true
 			if has_value then
-				modelbuilder.error(atnoinit, "Error: `noautoinit` attributes cannot have an initial value")
+				modelbuilder.error(atnoinit, "Error: `noautoinit` attributes cannot have an initial value.")
 				return
 			end
 			if atabstract != null then
-				modelbuilder.error(atnoinit, "Error: `noautoinit` attributes cannot be abstract")
-				return
+				modelbuilder.warning(atnoinit, "useless-noautoinit", "Warning: superfluous `noautoinit` on abstract attribute.")
 			end
 		end
 
-		var atlazy = self.get_single_annotation("lazy", modelbuilder)
-		var atautoinit = self.get_single_annotation("autoinit", modelbuilder)
-		if atlazy != null or atautoinit != null then
-			if atlazy != null and atautoinit != null then
-				modelbuilder.error(atlazy, "Error: lazy incompatible with autoinit")
-				return
-			end
+		# Construction of the read property. If it's not correctly built just return.
+		if not build_lazy_property(modelbuilder, mclassdef) then return
+
+		var atoptional = self.get_single_annotation("optional", modelbuilder)
+		if atoptional != null then
 			if not has_value then
-				if atlazy != null then
-					modelbuilder.error(atlazy, "Error: a lazy attribute needs a value")
-				else if atautoinit != null then
-					modelbuilder.error(atautoinit, "Error: a autoinit attribute needs a value")
-				end
-				return
+				modelbuilder.error(atoptional, "Error: `optional` attributes need a default value.")
 			end
-			is_lazy = true
-			var mlazyprop = new MAttribute(mclassdef, "lazy _" + name, none_visibility)
-			var mlazypropdef = new MAttributeDef(mclassdef, mlazyprop, self.location)
-			self.mlazypropdef = mlazypropdef
+			is_optional = true
 		end
 
 		var atreadonly = self.get_single_annotation("readonly", modelbuilder)
 		if atreadonly != null then
 			if not has_value then
-				modelbuilder.error(atreadonly, "Error: a readonly attribute needs a value")
+				modelbuilder.error(atreadonly, "Error: `readonly` attributes need a value.")
 			end
 			# No setter, so just leave
 			return
 		end
 
+		if not mclassdef.is_intro and not has_value and not noinit then
+			modelbuilder.advice(self, "attr-in-refinement", "Warning: attributes in refinement need a value or `noautoinit`.")
+		end
+
+		# Construction of the read property. If it's not correctly built just return.
+		if not build_write_property(modelbuilder, mclassdef, false) then return
+
+		if atabstract != null then mwritepropdef.is_abstract = true
+
+		var atautoinit = self.get_single_annotation("autoinit", modelbuilder)
+		if atautoinit != null then
+			if has_value then
+				modelbuilder.error(atautoinit, "Error: `autoinit` attributes cannot have an initial value.")
+			else if not mwritepropdef.is_intro then
+				modelbuilder.error(atautoinit, "Error: `autoinit` attributes cannot be set on redefinitions.")
+			else if not mclassdef.is_intro then
+				modelbuilder.error(atautoinit, "Error: `autoinit` attributes cannot be used in class refinements.")
+			else if atabstract == null then
+				modelbuilder.warning(atautoinit, "useless-autoinit", "Warning: superfluous `autoinit` on attribute.")
+			end
+		else if atabstract != null then
+			# By default, abstract attribute are not autoinit
+			noinit = true
+		end
+	end
+
+	# Build the attribute property
+	fun build_attribute_property(modelbuilder: ModelBuilder, mclassdef: MClassDef)
+	do
+		var mclass = mclassdef.mclass
+		var attribute_name = "_" + name
+
+		if not mclass.kind.need_init then
+			modelbuilder.error(self, "Error: attempt to define attribute `{name}` in the {mclass.kind} `{mclass}`.")
+		end
+		var mprop = new MAttribute(mclassdef, "_" + name, self.location, private_visibility)
+		var mpropdef = new MAttributeDef(mclassdef, mprop, self.location)
+		self.mpropdef = mpropdef
+		modelbuilder.mpropdef2npropdef[mpropdef] = self
+	end
+
+	# Build the read method property to get the value of the attribute
+	# Return `true` if the property was correctly created else return `false`.
+	# Warning the signature of the property is not set. This step is done by `build_signature`.
+	fun build_read_property(modelbuilder: ModelBuilder, mclassdef: MClassDef): Bool
+	do
+		var mclass = mclassdef.mclass
+
+		var readname = name
+		var mreadprop = modelbuilder.try_get_mproperty_by_name(self, mclassdef, readname).as(nullable MMethod)
+		if mreadprop == null then
+			var mvisibility = new_property_visibility(modelbuilder, mclassdef, self.n_visibility)
+			mreadprop = new MMethod(mclassdef, readname, self.location, mvisibility)
+			if not self.check_redef_keyword(modelbuilder, mclassdef, n_kwredef, false, mreadprop) then
+				mreadprop.is_broken = true
+				return false
+			end
+		else
+			if mreadprop.is_broken then return false
+			if not self.check_redef_keyword(modelbuilder, mclassdef, n_kwredef, true, mreadprop) then return false
+			check_redef_property_visibility(modelbuilder, self.n_visibility, mreadprop)
+		end
+		mclassdef.mprop2npropdef[mreadprop] = self
+
+		var attr_mpropdef = mpropdef
+		if attr_mpropdef != null then
+			mreadprop.getter_for = attr_mpropdef.mproperty
+			attr_mpropdef.mproperty.getter = mreadprop
+		end
+
+		var mreadpropdef = new MMethodDef(mclassdef, mreadprop, self.location)
+		self.mreadpropdef = mreadpropdef
+		modelbuilder.mpropdef2npropdef[mreadpropdef] = self
+		set_doc(mreadpropdef, modelbuilder)
+		if mpropdef != null then mpropdef.mdoc = mreadpropdef.mdoc
+
+		return true
+	end
+
+	# Build the write method property to set the attribute value
+	# Return `true` if the property was correctly created else return `false`.
+	# Warning the signature of the property is not set.
+	fun build_write_property(modelbuilder: ModelBuilder, mclassdef: MClassDef, is_same_visibility: Bool): Bool
+	do
+		var mclass = mclassdef.mclass
+
 		var writename = name + "="
 		var atwritable = self.get_single_annotation("writable", modelbuilder)
 		if atwritable != null then
@@ -1053,7 +1353,7 @@ redef class AAttrPropdef
 				writename = atwritable.arg_as_id(modelbuilder) or else writename
 			end
 		end
-		var mwriteprop = modelbuilder.try_get_mproperty_by_name(nid2, mclassdef, writename).as(nullable MMethod)
+		var mwriteprop = modelbuilder.try_get_mproperty_by_name(self, mclassdef, writename).as(nullable MMethod)
 		var nwkwredef: nullable Token = null
 		if atwritable != null then nwkwredef = atwritable.n_kwredef
 		if mwriteprop == null then
@@ -1061,24 +1361,64 @@ redef class AAttrPropdef
 			if atwritable != null then
 				mvisibility = new_property_visibility(modelbuilder, mclassdef, atwritable.n_visibility)
 			else
-				mvisibility = private_visibility
+				mvisibility = mreadpropdef.mproperty.visibility
+				# By default, use protected visibility at most
+				if mvisibility > protected_visibility and not is_same_visibility then mvisibility = protected_visibility
+			end
+			mwriteprop = new MMethod(mclassdef, writename, self.location, mvisibility)
+			if not self.check_redef_keyword(modelbuilder, mclassdef, nwkwredef, false, mwriteprop) then
+				mwriteprop.is_broken = true
+				return false
 			end
-			mwriteprop = new MMethod(mclassdef, writename, mvisibility)
-			if not self.check_redef_keyword(modelbuilder, mclassdef, nwkwredef, false, mwriteprop) then return
-			mwriteprop.deprecation = mreadprop.deprecation
+			mwriteprop.deprecation = mreadpropdef.mproperty.deprecation
 		else
-			if not self.check_redef_keyword(modelbuilder, mclassdef, nwkwredef or else n_kwredef, true, mwriteprop) then return
+			if mwriteprop.is_broken then return false
+			if not self.check_redef_keyword(modelbuilder, mclassdef, nwkwredef or else n_kwredef, true, mwriteprop) then return false
 			if atwritable != null then
 				check_redef_property_visibility(modelbuilder, atwritable.n_visibility, mwriteprop)
 			end
 		end
 		mclassdef.mprop2npropdef[mwriteprop] = self
 
+		var attr_mpropdef = mpropdef
+		if attr_mpropdef != null then
+			mwriteprop.setter_for = attr_mpropdef.mproperty
+			attr_mpropdef.mproperty.setter = mwriteprop
+		end
+
 		var mwritepropdef = new MMethodDef(mclassdef, mwriteprop, self.location)
 		self.mwritepropdef = mwritepropdef
 		modelbuilder.mpropdef2npropdef[mwritepropdef] = self
 		mwritepropdef.mdoc = mreadpropdef.mdoc
-		if atabstract != null then mwritepropdef.is_abstract = true
+
+		return true
+	end
+
+	# Build the lazy attribute property
+	# Return `true` if the property was correctly created else return `false`.
+	fun build_lazy_property(modelbuilder: ModelBuilder, mclassdef: MClassDef): Bool
+	do
+		var mclass = mclassdef.mclass
+
+		var atlazy = self.get_single_annotation("lazy", modelbuilder)
+		var atlateinit = self.get_single_annotation("lateinit", modelbuilder)
+		if atlazy != null or atlateinit != null then
+			if atlazy != null and atlateinit != null then
+				modelbuilder.error(atlazy, "Error: `lazy` incompatible with `lateinit`.")
+				return false
+			end
+			if not has_value then
+				if atlazy != null then
+					modelbuilder.error(atlazy, "Error: `lazy` attributes need a value.")
+				else if atlateinit != null then
+					modelbuilder.error(atlateinit, "Error: `lateinit` attributes need a value.")
+				end
+				has_value = true
+				return false
+			end
+			create_lazy
+		end
+		return true
 	end
 
 	redef fun build_signature(modelbuilder)
@@ -1093,7 +1433,7 @@ redef class AAttrPropdef
 
 		var ntype = self.n_type
 		if ntype != null then
-			mtype = modelbuilder.resolve_mtype(mmodule, mclassdef, ntype)
+			mtype = modelbuilder.resolve_mtype_unchecked(mclassdef, ntype, true)
 			if mtype == null then return
 		end
 
@@ -1113,35 +1453,12 @@ redef class AAttrPropdef
 		var nexpr = self.n_expr
 		if mtype == null then
 			if nexpr != null then
-				if nexpr isa ANewExpr then
-					mtype = modelbuilder.resolve_mtype(mmodule, mclassdef, nexpr.n_type)
-				else if nexpr isa AIntExpr then
-					var cla = modelbuilder.try_get_mclass_by_name(nexpr, mmodule, "Int")
-					if cla != null then mtype = cla.mclass_type
-				else if nexpr isa AFloatExpr then
-					var cla = modelbuilder.try_get_mclass_by_name(nexpr, mmodule, "Float")
-					if cla != null then mtype = cla.mclass_type
-				else if nexpr isa ACharExpr then
-					var cla = modelbuilder.try_get_mclass_by_name(nexpr, mmodule, "Char")
-					if cla != null then mtype = cla.mclass_type
-				else if nexpr isa ABoolExpr then
-					var cla = modelbuilder.try_get_mclass_by_name(nexpr, mmodule, "Bool")
-					if cla != null then mtype = cla.mclass_type
-				else if nexpr isa ASuperstringExpr then
-					var cla = modelbuilder.try_get_mclass_by_name(nexpr, mmodule, "String")
-					if cla != null then mtype = cla.mclass_type
-				else if nexpr isa AStringFormExpr then
-					var cla = modelbuilder.try_get_mclass_by_name(nexpr, mmodule, "String")
-					if cla != null then mtype = cla.mclass_type
-				else
-					modelbuilder.error(self, "Error: Untyped attribute {mreadpropdef}. Implicit typing allowed only for literals and new.")
-				end
-
+				mtype = infer_static_type(modelbuilder, nexpr, mclassdef, mmodule, mreadpropdef)
 				if mtype == null then return
 			end
 		else if ntype != null and inherited_type == mtype then
 			if nexpr isa ANewExpr then
-				var xmtype = modelbuilder.resolve_mtype(mmodule, mclassdef, nexpr.n_type)
+				var xmtype = modelbuilder.resolve_mtype_unchecked(mclassdef, nexpr.n_type, true)
 				if xmtype == mtype then
 					modelbuilder.advice(ntype, "useless-type", "Warning: useless type definition")
 				end
@@ -1149,32 +1466,206 @@ redef class AAttrPropdef
 		end
 
 		if mtype == null then
-			modelbuilder.error(self, "Error: Untyped attribute {mreadpropdef}")
+			modelbuilder.error(self, "Error: untyped attribute `{mreadpropdef}`.")
 			return
 		end
 
+		self.mtype = mtype
+
 		if mpropdef != null then
 			mpropdef.static_mtype = mtype
 		end
 
-		do
-			var msignature = new MSignature(new Array[MParameter], mtype)
-			mreadpropdef.msignature = msignature
-		end
+		build_read_signature
 
-		var mwritepropdef = self.mwritepropdef
-		if mwritepropdef != null then
-			var name: String
-			name = n_id2.text
-			var mparameter = new MParameter(name, mtype, false)
-			var msignature = new MSignature([mparameter], null)
-			mwritepropdef.msignature = msignature
-		end
+		if self.mwritepropdef != null then build_write_signature
 
 		var mlazypropdef = self.mlazypropdef
 		if mlazypropdef != null then
-			mlazypropdef.static_mtype = modelbuilder.model.get_mclasses_by_name("Bool").first.mclass_type
+			mlazypropdef.static_mtype = mmodule.bool_type
+		end
+		check_repeated_types(modelbuilder)
+	end
+
+	# Build the read method signature
+	# `except`: mreadpropdef != null
+	# `expect`: mtype != null
+	fun build_read_signature
+	is
+		expect(mreadpropdef != null and mtype != null)
+	do
+		var msignature = new MSignature(new Array[MParameter], mtype)
+		mreadpropdef.msignature = msignature
+	end
+
+	# Build the write method signature
+	# `except`: mwritepropdef != null
+	# `expect`: mtype != null
+	fun build_write_signature
+	is
+		expect(mwritepropdef != null and mtype != null)
+	do
+		var mwritetype = mtype.as(not null)
+		if is_optional then
+			mwritetype = mwritetype.as_nullable
+		end
+		var mparameter = new MParameter(name, mwritetype, false)
+		var msignature = new MSignature([mparameter], null)
+		mwritepropdef.msignature = msignature
+	end
+
+	# Create a new setter for the attribute.
+	#
+	# `modelbuilder`: It's used to link the new `mwritepropdef` and `self`
+	# `visibility`: Is the setter has the same visibilty of the `mreadpropdef`.
+	#	If `not is_same_visibility and mreadpropdef.mproperty.visibility > protected_visibility` the `mwritepropdef` visibility will be set to protected.
+	fun create_setter(modelbuilder: ModelBuilder, is_same_visibility: nullable Bool): AAttrPropdef
+	is
+		expect(mreadpropdef != null) # Use to define the visibility, the mclassdef and the doc of the `mwritepropdef`
+	do
+		if mwritepropdef != null then return self # Self already has a `mwritepropdef`
+		var same_visibility = false
+		if is_same_visibility != null then same_visibility = is_same_visibility
+
+		self.build_write_property(modelbuilder, mreadpropdef.mclassdef, same_visibility)
+		self.build_write_signature
+		return self
+	end
+
+	# Set the default `self` value
+	#
+	# `expr`: Represents the default value of the attribute. If `expr isa ABlockExpr` `self.n_block` will be set.
+	fun define_default(expr: AExpr): AAttrPropdef
+	do
+		self.has_value = true
+		if expr isa ABlockExpr then
+			self.n_block = expr
+		else
+			self.n_expr = expr
+		end
+		return self
+	end
+
+	# Set `self` as optional
+	fun define_as_optional: AAttrPropdef
+	is
+		expect(has_value)
+	do
+		is_optional = true
+		return self
+	end
+
+	# Create the lazy attribute.
+	#
+	# see `mlazypropdef` for more information about this property.
+	fun create_lazy: AAttrPropdef
+	is
+		expect(has_value and mpropdef != null) # The only way to get a null `mpropdef` is when the attribute is defined as `abstract`. But if the attribute has a value, it cannot be abstract.
+	do
+		if self.mlazypropdef != null then return self # Self already has a `mlazypropdef`
+		is_lazy = true
+		var mlazyprop = new MAttribute(mpropdef.mclassdef, "lazy _" + name, self.location, none_visibility)
+		mlazyprop.is_fictive = true
+		var mlazypropdef = new MAttributeDef(mpropdef.mclassdef, mlazyprop, self.location)
+		mlazypropdef.is_fictive = true
+		self.mlazypropdef = mlazypropdef
+		return self
+	end
+
+	# Detect the static type from the value assigned to the attribute `self`
+	#
+	# Return the static type if it can be safely inferred.
+	private fun infer_static_type(modelbuilder: ModelBuilder, nexpr: AExpr,
+		mclassdef: MClassDef, mmodule: MModule, mreadpropdef: MPropDef): nullable MType
+	do
+		var mtype = null
+		if nexpr isa ANewExpr then
+			mtype = modelbuilder.resolve_mtype_unchecked(mclassdef, nexpr.n_type, true)
+		else if nexpr isa AAsCastExpr then
+			mtype = modelbuilder.resolve_mtype_unchecked(mclassdef, nexpr.n_type, true)
+		else if nexpr isa AIntegerExpr then
+			var cla: nullable MClass = null
+			if nexpr.value isa Int then
+				cla = modelbuilder.try_get_mclass_by_name(nexpr, mmodule, "Int")
+			else if nexpr.value isa Byte then
+				cla = modelbuilder.try_get_mclass_by_name(nexpr, mmodule, "Byte")
+			else if nexpr.value isa Int8 then
+				cla = modelbuilder.try_get_mclass_by_name(nexpr, mmodule, "Int8")
+			else if nexpr.value isa Int16 then
+				cla = modelbuilder.try_get_mclass_by_name(nexpr, mmodule, "Int16")
+			else if nexpr.value isa UInt16 then
+				cla = modelbuilder.try_get_mclass_by_name(nexpr, mmodule, "UInt16")
+			else if nexpr.value isa Int32 then
+				cla = modelbuilder.try_get_mclass_by_name(nexpr, mmodule, "Int32")
+			else if nexpr.value isa UInt32 then
+				cla = modelbuilder.try_get_mclass_by_name(nexpr, mmodule, "UInt32")
+			else
+				# Should not happen, and should be updated as new types are added
+				abort
+			end
+			if cla != null then mtype = cla.mclass_type
+		else if nexpr isa AFloatExpr then
+			var cla = modelbuilder.try_get_mclass_by_name(nexpr, mmodule, "Float")
+			if cla != null then mtype = cla.mclass_type
+		else if nexpr isa ACharExpr then
+			var cla: nullable MClass
+			if nexpr.is_code_point then
+				cla = modelbuilder.try_get_mclass_by_name(nexpr, mmodule, "Int")
+			else
+				cla = modelbuilder.try_get_mclass_by_name(nexpr, mmodule, "Char")
+			end
+			if cla != null then mtype = cla.mclass_type
+		else if nexpr isa ABoolExpr then
+			var cla = modelbuilder.try_get_mclass_by_name(nexpr, mmodule, "Bool")
+			if cla != null then mtype = cla.mclass_type
+		else if nexpr isa ASuperstringExpr then
+			var cla = modelbuilder.try_get_mclass_by_name(nexpr, mmodule, "String")
+			if cla != null then mtype = cla.mclass_type
+		else if nexpr isa AStringFormExpr then
+			var cla: nullable MClass
+			if nexpr.is_bytestring then
+				cla = modelbuilder.try_get_mclass_by_name(nexpr, mmodule, "Bytes")
+			else if nexpr.is_re then
+				cla = modelbuilder.try_get_mclass_by_name(nexpr, mmodule, "Regex")
+			else if nexpr.is_string then
+				cla = modelbuilder.try_get_mclass_by_name(nexpr, mmodule, "String")
+			else
+				abort
+			end
+			if cla != null then mtype = cla.mclass_type
+		else if nexpr isa AArrayExpr and nexpr.n_type == null and nexpr.n_exprs.not_empty then
+			# Non-empty arrays without an explicit type
+
+			var item_mtypes = new Set[MType]
+			var fails = false
+			for node in nexpr.n_exprs do
+				var item_mtype = infer_static_type(modelbuilder, node, mclassdef, mmodule, mreadpropdef)
+				if item_mtype == null then
+					fails = true
+				else
+					item_mtypes.add item_mtype
+				end
+			end
+
+			if fails then return null # Failed to infer some types
+
+			if item_mtypes.length > 1 then
+				modelbuilder.error(self, "Type Error: ambiguous array type {item_mtypes.join(" ")}")
+			end
+
+			mtype = mmodule.array_type(item_mtypes.first)
+		else if nexpr isa AUminusExpr and (nexpr.n_expr isa AIntegerExpr or nexpr.n_expr isa AFloatExpr) then
+			# The Int and Float unary - is defined in `kernel`, so this may
+			# result in an invalid behavior when using a custom kernel.
+			# A workaround is to declare the attribute static type.
+			# This is still very useful, especially to novice programmers.
+			mtype = infer_static_type(modelbuilder, nexpr.n_expr, mclassdef, mmodule, mreadpropdef)
+		else if nexpr isa AOnceExpr then
+			mtype = infer_static_type(modelbuilder, nexpr.n_expr, mclassdef, mmodule, mreadpropdef)
+		else
+			modelbuilder.error(self, "Error: untyped attribute `{mreadpropdef}`. Implicit typing allowed only for literals and new.")
 		end
+		return mtype
 	end
 
 	redef fun check_signature(modelbuilder)
@@ -1182,9 +1673,21 @@ redef class AAttrPropdef
 		var mpropdef = self.mpropdef
 		if mpropdef == null then return # Error thus skipped
 		var ntype = self.n_type
-		var mtype = self.mpropdef.static_mtype
+		var mtype = self.mtype
 		if mtype == null then return # Error thus skipped
 
+		var mclassdef = mpropdef.mclassdef
+		var mmodule = mclassdef.mmodule
+
+		# Check types
+		if ntype != null then
+			if modelbuilder.resolve_mtype(mclassdef, ntype) == null then return
+		end
+		var nexpr = n_expr
+		if nexpr isa ANewExpr then
+			if modelbuilder.resolve_mtype(mclassdef, nexpr.n_type) == null then return
+		end
+
 		# Lookup for signature in the precursor
 		# FIXME all precursors should be considered
 		if not mpropdef.is_intro then
@@ -1192,7 +1695,7 @@ redef class AAttrPropdef
 			if precursor_type == null then return
 
 			if mtype != precursor_type then
-				modelbuilder.error(ntype.as(not null), "Redef Error: Wrong static type. found {mtype}, expected {precursor_type}.")
+				modelbuilder.error(ntype.as(not null), "Redef Error: expected `{precursor_type}` type as a bound; got `{mtype}`.")
 				return
 			end
 		end
@@ -1231,7 +1734,7 @@ redef class AAttrPropdef
 			if mysignature.arity != msignature.arity then
 				var node: ANode
 				if nsig != null then node = nsig else node = self
-				modelbuilder.error(node, "Redef Error: {mysignature.arity} parameters found, {msignature.arity} expected. Signature is {mpropdef}{msignature}")
+				modelbuilder.error(node, "Redef Error: expected {msignature.arity} parameter(s) for `{mpropdef.mproperty.name}{msignature}`; got {mysignature.arity}. See introduction at `{mpropdef.mproperty.full_name}`.")
 				return
 			end
 			var precursor_ret_type = msignature.return_mtype
@@ -1239,7 +1742,7 @@ redef class AAttrPropdef
 			if ret_type != null and precursor_ret_type == null then
 				var node: ANode
 				if nsig != null then node = nsig else node = self
-				modelbuilder.error(node, "Redef Error: {mpropdef.mproperty} is a procedure, not a function.")
+				modelbuilder.error(node, "Redef Error: `{mpropdef.mproperty}` is a procedure, not a function.")
 				return
 			end
 
@@ -1251,7 +1754,7 @@ redef class AAttrPropdef
 					var node: ANode
 					if nsig != null then node = nsig else node = self
 					if not modelbuilder.check_sametype(node, mmodule, mclassdef.bound_mtype, myt, prt) then
-						modelbuilder.error(node, "Redef Error: Wrong type for parameter `{mysignature.mparameters[i].name}'. found {myt}, expected {prt}.")
+						modelbuilder.error(node, "Redef Error: expected `{prt}` type for parameter `{mysignature.mparameters[i].name}'; got `{myt}`.")
 					end
 				end
 			end
@@ -1262,11 +1765,32 @@ redef class AAttrPropdef
 					# Inherit the return type
 					ret_type = precursor_ret_type
 				else if not modelbuilder.check_subtype(node, mmodule, mclassdef.bound_mtype, ret_type, precursor_ret_type) then
-					modelbuilder.error(node, "Redef Error: Wrong return type. found {ret_type}, expected {precursor_ret_type}.")
+					modelbuilder.error(node, "Redef Error: expected `{precursor_ret_type}` return type; got `{ret_type}`.")
 				end
 			end
 		end
 	end
+
+	# Type is useless if the attribute type is the same thant the intro.
+	redef fun check_repeated_types(modelbuilder) do
+		var mreadpropdef = self.mreadpropdef
+		if mreadpropdef == null then return
+		if mreadpropdef.is_intro or n_type == null then return
+		# get intro
+		var intro = mreadpropdef.mproperty.intro
+		var n_intro = modelbuilder.mpropdef2npropdef.get_or_null(intro)
+		if n_intro == null then return
+		# get intro type
+		var ntype = null
+		if n_intro isa AMethPropdef then
+			ntype = n_intro.n_signature.ret_type
+		else if n_intro isa AAttrPropdef and n_intro.n_type != null then
+			ntype = n_intro.n_type.mtype
+		end
+		# check
+		if ntype == null or ntype != n_type.mtype or mpropdef == null then return
+		modelbuilder.advice(n_type, "useless-signature", "Warning: useless type repetition on redefined attribute `{mpropdef.name}`")
+	end
 end
 
 redef class ATypePropdef
@@ -1274,31 +1798,33 @@ redef class ATypePropdef
 
 	redef fun build_property(modelbuilder, mclassdef)
 	do
-		var name = self.n_id.text
-		var mprop = modelbuilder.try_get_mproperty_by_name(self.n_id, mclassdef, name)
+		var name = self.n_qid.n_id.text
+		var mprop = modelbuilder.try_get_mproperty_by_name(self.n_qid, mclassdef, name)
 		if mprop == null then
 			var mvisibility = new_property_visibility(modelbuilder, mclassdef, self.n_visibility)
-			mprop = new MVirtualTypeProp(mclassdef, name, mvisibility)
+			mprop = new MVirtualTypeProp(mclassdef, name, self.location, mvisibility)
 			for c in name.chars do if c >= 'a' and c<= 'z' then
-				modelbuilder.warning(n_id, "bad-type-name", "Warning: lowercase in the virtual type {name}")
+				modelbuilder.warning(n_qid, "bad-type-name", "Warning: lowercase in the virtual type `{name}`.")
 				break
 			end
-			if not self.check_redef_keyword(modelbuilder, mclassdef, self.n_kwredef, false, mprop) then return
 		else
-			if not self.check_redef_keyword(modelbuilder, mclassdef, self.n_kwredef, true, mprop) then return
+			if mprop.is_broken then return
 			assert mprop isa MVirtualTypeProp
 			check_redef_property_visibility(modelbuilder, self.n_visibility, mprop)
 		end
-		mclassdef.mprop2npropdef[mprop] = self
 
 		var mpropdef = new MVirtualTypeDef(mclassdef, mprop, self.location)
 		self.mpropdef = mpropdef
-		modelbuilder.mpropdef2npropdef[mpropdef] = self
 		if mpropdef.is_intro then
 			modelbuilder.toolcontext.info("{mpropdef} introduces new type {mprop.full_name}", 4)
 		else
 			modelbuilder.toolcontext.info("{mpropdef} redefines type {mprop.full_name}", 4)
 		end
+		if not self.check_redef_keyword(modelbuilder, mclassdef, self.n_kwredef, not mpropdef.is_intro, mprop) then
+			mpropdef.is_broken =true
+		end
+		mclassdef.mprop2npropdef[mprop] = self
+		modelbuilder.mpropdef2npropdef[mpropdef] = self
 		set_doc(mpropdef, modelbuilder)
 
 		var atfixed = get_single_annotation("fixed", modelbuilder)
@@ -1312,11 +1838,10 @@ redef class ATypePropdef
 		var mpropdef = self.mpropdef
 		if mpropdef == null then return # Error thus skipped
 		var mclassdef = mpropdef.mclassdef
-		var mmodule = mclassdef.mmodule
 		var mtype: nullable MType = null
 
 		var ntype = self.n_type
-		mtype = modelbuilder.resolve_mtype(mmodule, mclassdef, ntype)
+		mtype = modelbuilder.resolve_mtype_unchecked(mclassdef, ntype, true)
 		if mtype == null then return
 
 		mpropdef.bound = mtype
@@ -1328,7 +1853,7 @@ redef class ATypePropdef
 		var mpropdef = self.mpropdef
 		if mpropdef == null then return # Error thus skipped
 
-		var bound = self.mpropdef.bound
+		var bound = mpropdef.bound
 		if bound == null then return # Error thus skipped
 
 		modelbuilder.check_visibility(n_type, bound, mpropdef)
@@ -1337,39 +1862,26 @@ redef class ATypePropdef
 		var mmodule = mclassdef.mmodule
 		var anchor = mclassdef.bound_mtype
 
-		# Check circularity
-		if bound isa MVirtualType then
-			# Slow case: progress on each resolution until: (i) we loop, or (ii) we found a non formal type
-			var seen = [self.mpropdef.mproperty.mvirtualtype]
-			loop
-				if seen.has(bound) then
-					seen.add(bound)
-					modelbuilder.error(self, "Error: circularity of virtual type definition: {seen.join(" -> ")}")
-					return
-				end
-				seen.add(bound)
-				var next = bound.lookup_bound(mmodule, anchor)
-				if not next isa MVirtualType then break
-				bound = next
-			end
+		var ntype = self.n_type
+		if modelbuilder.resolve_mtype(mclassdef, ntype) == null then
+			mpropdef.bound = null
+			return
 		end
 
 		# Check redefinitions
-		bound = mpropdef.bound.as(not null)
 		for p in mpropdef.mproperty.lookup_super_definitions(mmodule, anchor) do
 			var supbound = p.bound
-			if supbound == null then break # broken super bound, skip error
+			if supbound == null or supbound isa MBottomType or p.is_broken then break # broken super bound, skip error
 			if p.is_fixed then
-				modelbuilder.error(self, "Redef Error: Virtual type {mpropdef.mproperty} is fixed in super-class {p.mclassdef.mclass}")
+				modelbuilder.error(self, "Redef Error: virtual type `{mpropdef.mproperty}` is fixed in super-class `{p.mclassdef.mclass}`.")
 				break
 			end
 			if p.mclassdef.mclass == mclassdef.mclass then
-				# Still a warning to pass existing bad code
-				modelbuilder.warning(n_type, "refine-type", "Redef Error: a virtual type cannot be refined.")
+				modelbuilder.error(n_type, "Redef Error: a virtual type cannot be refined.")
 				break
 			end
 			if not modelbuilder.check_subtype(n_type, mmodule, anchor, bound, supbound) then
-				modelbuilder.error(n_type, "Redef Error: Wrong bound type. Found {bound}, expected a subtype of {supbound}, as in {p}.")
+				modelbuilder.error(n_type, "Redef Error: expected `{supbound}` bound type; got `{bound}`.")
 				break
 			end
 		end