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

diff --git a/src/modelize/modelize_property.nit b/src/modelize/modelize_property.nit
index a4d1141..aadfb5c 100644
--- a/src/modelize/modelize_property.nit
+++ b/src/modelize/modelize_property.nit
@@ -86,7 +86,8 @@ redef class ModelBuilder
 		# Force building recursively
 		if nclassdef.build_properties_is_done then return
 		nclassdef.build_properties_is_done = true
-		var mclassdef = nclassdef.mclassdef.as(not null)
+		var mclassdef = nclassdef.mclassdef
+		if mclassdef == null then return # skip error
 		if mclassdef.in_hierarchy == null then return # Skip error
 		for superclassdef in mclassdef.in_hierarchy.direct_greaters do
 			if not mclassdef2nclassdef.has_key(superclassdef) then continue
@@ -102,6 +103,25 @@ 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 = mclassdef.mmodule.model.null_type
+				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
@@ -139,9 +159,6 @@ redef class ModelBuilder
 			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
@@ -163,18 +180,11 @@ redef class ModelBuilder
 		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
-
+				if not npropdef.is_autoinit then continue # Skip non tagged autoinit
+				if npropdef.mpropdef == null then return # Skip broken method
 				var sig = npropdef.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)
@@ -184,25 +194,26 @@ redef class ModelBuilder
 				npropdef.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 or mreadpropdef.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
+				var paramname = mreadpropdef.mproperty.name
+				var ret_type = mreadpropdef.msignature.return_mtype
 				if ret_type == null then return
 				var mparameter = new MParameter(paramname, ret_type, false)
 				mparameters.add(mparameter)
 				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
 					initializers.add(npropdef.mpropdef.mproperty)
 					npropdef.mpropdef.mproperty.is_autoinit = true
 				else
@@ -218,7 +229,7 @@ redef class ModelBuilder
 		# 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`?")
+			toolcontext.error(nclassdef.location, "Error: `{mclassdef}` does not specialize `{the_root_init_mmethod.intro_mclassdef}`. Possible duplication of the root class `Object`?")
 			return
 		end
 
@@ -235,14 +246,14 @@ 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
 
@@ -267,35 +278,35 @@ 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.")
-			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
 				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
@@ -303,17 +314,27 @@ 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
+			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
+				# 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
+				# Combine the inherited list to what is collected
+				if longest.initializers.length > 0 then
+					mparameters.prepend longest.new_msignature.mparameters
+					initializers.prepend longest.initializers
+				end
 			end
 		end
 
@@ -350,15 +371,17 @@ 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
 			node.debug "Unexpected type {mtype}"
 			abort
@@ -368,10 +391,10 @@ 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
@@ -387,6 +410,72 @@ 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)
+				# TODO something to manage correctly bound conflicts
+				assert not defs.is_empty
+				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
@@ -439,17 +528,17 @@ 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
@@ -478,17 +567,17 @@ 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
@@ -524,38 +613,29 @@ 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
@@ -563,13 +643,15 @@ 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
@@ -597,14 +679,14 @@ redef class ASignature
 			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(mmodule, 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
@@ -614,7 +696,7 @@ 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(mmodule, mclassdef, ntype, true)
 			if self.ret_type == null then return false # Skip error
 		end
 
@@ -622,24 +704,25 @@ 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.mmodule, 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.mmodule, 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
 
@@ -651,6 +734,8 @@ 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
@@ -711,8 +796,19 @@ 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
 
@@ -735,9 +831,16 @@ redef class AMethPropdef
 			end
 			mprop.is_init = is_init
 			mprop.is_new = n_kwnew != null
-			if parent isa ATopClassdef then mprop.is_toplevel = true
-			self.check_redef_keyword(modelbuilder, mclassdef, n_kwredef, false, mprop)
+			if mprop.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
+			end
 			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
@@ -746,7 +849,10 @@ 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
@@ -785,6 +891,9 @@ redef class AMethPropdef
 			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
 		var param_types = new Array[MType] # Types of parameters from the AST
@@ -812,7 +921,7 @@ 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 `{mpropdef.mproperty.name}{msignature}`; got {param_names.length}. See introduction at `{mpropdef.mproperty.full_name}`.")
 				return
 			end
 		else if mpropdef.mproperty.is_init and not mpropdef.mproperty.is_new then
@@ -844,7 +953,7 @@ 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
 
@@ -858,6 +967,14 @@ redef class AMethPropdef
 		# 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
 
+		# 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 `{mpropdef.mproperty.name}`.")
+		end
+		if ret_type == null and return_is_mandatory then
+			modelbuilder.error(self.n_methid, "Error: mandatory return type for `{mpropdef.mproperty.name}`.")
+		end
+
 		msignature = new MSignature(mparameters, ret_type)
 		mpropdef.msignature = msignature
 		mpropdef.is_abstract = self.get_single_annotation("abstract", modelbuilder) != null
@@ -866,7 +983,18 @@ 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)
@@ -876,9 +1004,18 @@ 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
@@ -888,7 +1025,9 @@ 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.as(not null), "Redef Error: `{mpropdef.mproperty}` is a procedure, not a function.")
+				mpropdef.msignature = null
+				mpropdef.is_broken = true
 				return
 			end
 
@@ -899,7 +1038,9 @@ 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
@@ -911,7 +1052,9 @@ 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
@@ -925,12 +1068,88 @@ 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
+		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
 
@@ -960,12 +1179,8 @@ redef class AAttrPropdef
 
 		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}.")
+			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, private_visibility)
@@ -996,7 +1211,7 @@ redef class AAttrPropdef
 		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
 
@@ -1005,28 +1220,28 @@ 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")
+		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
 			end
 			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")
+					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
 			end
 			is_lazy = true
@@ -1038,12 +1253,16 @@ redef class AAttrPropdef
 		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
+
 		var writename = name + "="
 		var atwritable = self.get_single_annotation("writable", modelbuilder)
 		if atwritable != null then
@@ -1059,7 +1278,9 @@ redef class AAttrPropdef
 			if atwritable != null then
 				mvisibility = new_property_visibility(modelbuilder, mclassdef, atwritable.n_visibility)
 			else
-				mvisibility = private_visibility
+				mvisibility = mreadprop.visibility
+				# By default, use protected visibility at most
+				if mvisibility > protected_visibility then mvisibility = protected_visibility
 			end
 			mwriteprop = new MMethod(mclassdef, writename, mvisibility)
 			if not self.check_redef_keyword(modelbuilder, mclassdef, nwkwredef, false, mwriteprop) then return
@@ -1077,6 +1298,22 @@ redef class AAttrPropdef
 		modelbuilder.mpropdef2npropdef[mwritepropdef] = self
 		mwritepropdef.mdoc = mreadpropdef.mdoc
 		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
 
 	redef fun build_signature(modelbuilder)
@@ -1091,7 +1328,7 @@ redef class AAttrPropdef
 
 		var ntype = self.n_type
 		if ntype != null then
-			mtype = modelbuilder.resolve_mtype(mmodule, mclassdef, ntype)
+			mtype = modelbuilder.resolve_mtype_unchecked(mmodule, mclassdef, ntype, true)
 			if mtype == null then return
 		end
 
@@ -1112,9 +1349,27 @@ redef class AAttrPropdef
 		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")
+					mtype = modelbuilder.resolve_mtype_unchecked(mmodule, 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")
@@ -1132,14 +1387,14 @@ redef class AAttrPropdef
 					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.")
+					modelbuilder.error(self, "Error: untyped attribute `{mreadpropdef}`. Implicit typing allowed only for literals and new.")
 				end
 
 				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(mmodule, mclassdef, nexpr.n_type, true)
 				if xmtype == mtype then
 					modelbuilder.advice(ntype, "useless-type", "Warning: useless type definition")
 				end
@@ -1147,10 +1402,12 @@ 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
@@ -1173,6 +1430,7 @@ redef class AAttrPropdef
 		if mlazypropdef != null then
 			mlazypropdef.static_mtype = modelbuilder.model.get_mclasses_by_name("Bool").first.mclass_type
 		end
+		check_repeated_types(modelbuilder)
 	end
 
 	redef fun check_signature(modelbuilder)
@@ -1180,9 +1438,21 @@ 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(mmodule, mclassdef, ntype) == null then return
+		end
+		var nexpr = n_expr
+		if nexpr isa ANewExpr then
+			if modelbuilder.resolve_mtype(mmodule, 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
@@ -1190,7 +1460,7 @@ 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
@@ -1229,7 +1499,7 @@ 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
@@ -1237,7 +1507,7 @@ 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
 
@@ -1249,7 +1519,7 @@ 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
@@ -1260,11 +1530,30 @@ 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
+		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 then return
+		modelbuilder.advice(n_type, "useless-signature", "Warning: useless type repetition on redefined attribute `{mpropdef.name}`")
+	end
 end
 
 redef class ATypePropdef
@@ -1278,7 +1567,7 @@ redef class ATypePropdef
 			var mvisibility = new_property_visibility(modelbuilder, mclassdef, self.n_visibility)
 			mprop = new MVirtualTypeProp(mclassdef, name, 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_id, "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
@@ -1314,7 +1603,7 @@ redef class ATypePropdef
 		var mtype: nullable MType = null
 
 		var ntype = self.n_type
-		mtype = modelbuilder.resolve_mtype(mmodule, mclassdef, ntype)
+		mtype = modelbuilder.resolve_mtype_unchecked(mmodule, mclassdef, ntype, true)
 		if mtype == null then return
 
 		mpropdef.bound = mtype
@@ -1326,7 +1615,7 @@ 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)
@@ -1335,30 +1624,18 @@ 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(mmodule, 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 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
@@ -1367,7 +1644,7 @@ redef class ATypePropdef
 				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