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

diff --git a/src/modelize/modelize_property.nit b/src/modelize/modelize_property.nit
index faaf149..9924245 100644
--- a/src/modelize/modelize_property.nit
+++ b/src/modelize/modelize_property.nit
@@ -17,10 +17,11 @@
 # Analysis and verification of property definitions to instantiate model element
 module modelize_property
 
-import modelize_class
+intrude import modelize_class
 private import annotation
 
 redef class ToolContext
+	# Run `AClassdef::build_property` on the classdefs of each module
 	var modelize_property_phase: Phase = new ModelizePropertyPhase(self, [modelize_class_phase])
 end
 
@@ -36,18 +37,24 @@ private class ModelizePropertyPhase
 end
 
 redef class ModelBuilder
-	# Register the npropdef associated to each mpropdef
-	# FIXME: why not refine the `MPropDef` class with a nullable attribute?
-	var mpropdef2npropdef = new HashMap[MPropDef, APropdef]
+	# Registration of the npropdef associated to each mpropdef.
+	#
+	# Public clients need to use `mpropdef2node` to access stuff.
+	private var mpropdef2npropdef = new HashMap[MPropDef, APropdef]
 
 	# Retrieve the associated AST node of a mpropertydef.
 	# This method is used to associate model entity with syntactic entities.
 	#
-	# If the property definition is not associated with a node, returns node.
+	# If the property definition is not associated with a node, returns `null`.
 	fun mpropdef2node(mpropdef: MPropDef): nullable ANode
 	do
-		var res: nullable ANode = mpropdef2npropdef.get_or_null(mpropdef)
-		if res != null then return res
+		var res
+		res = mpropdef2npropdef.get_or_null(mpropdef)
+		if res != null then
+			# Run the phases on it
+			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
@@ -55,6 +62,23 @@ redef class ModelBuilder
 		return null
 	end
 
+	# Retrieve all the attributes nodes localy definied
+	# FIXME think more about this method and how the separations separate/global and ast/model should be done.
+	fun collect_attr_propdef(mclassdef: MClassDef): Array[AAttrPropdef]
+	do
+		var res = new Array[AAttrPropdef]
+		var n = mclassdef2nclassdef.get_or_null(mclassdef)
+		if n == null then return res
+		for npropdef in n.n_propdefs do
+			if npropdef isa AAttrPropdef then
+				# Run the phases on it
+				toolcontext.run_phases_on_npropdef(npropdef)
+				res.add(npropdef)
+			end
+		end
+		return res
+	end
+
 	# Build the properties of `nclassdef`.
 	# REQUIRE: all superclasses are built.
 	private fun build_properties(nclassdef: AClassdef)
@@ -62,7 +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
@@ -78,6 +103,24 @@ 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.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
@@ -139,7 +182,7 @@ 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
+				if npropdef.mpropdef == null then return # Skip broken method
 				var at = npropdef.get_single_annotation("autoinit", self)
 				if at == null then continue # Skip non tagged init
 
@@ -147,40 +190,45 @@ redef class ModelBuilder
 				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")
+					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)
+					var mparameter = new MParameter(param.name, ret_type, false, ret_type isa MNullableType)
 					mparameters.add(mparameter)
 				end
 				initializers.add(npropdef.mpropdef.mproperty)
+				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
 					# the lazy initialization of the attribute.
-					initializers.add(npropdef.mreadpropdef.mproperty)
+					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)
+				var mparameter = new MParameter(paramname, ret_type, false, ret_type isa MNullableType)
 				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
 					# Add the setter to the list
 					initializers.add(msetter.mproperty)
+					msetter.mproperty.is_autoinit = true
 				end
 			end
 		end
@@ -190,43 +238,110 @@ 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
 
-		# 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
-				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(", ")})")
-						return
+		# Look at the autoinit class-annotation
+		var autoinit = nclassdef.get_single_annotation("autoinit", self)
+		var noautoinit = nclassdef.get_single_annotation("noautoinit", self)
+		if autoinit != null then
+			# Just throws the collected initializers
+			mparameters.clear
+			initializers.clear
+
+			if noautoinit != null then
+				error(autoinit, "Error: `autoinit` and `noautoinit` are incompatible.")
+			end
+
+			if autoinit.n_args.is_empty then
+				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.")
+					return
+				end
+
+				# Search the property.
+				# To avoid bad surprises, try to get the setter first.
+				var p = try_get_mproperty_by_name(narg, mclassdef, id + "=")
+				if p == null then
+					p = try_get_mproperty_by_name(narg, mclassdef, id)
+				end
+				if p == null then
+					error(narg, "Error: unknown method `{id}`")
+					return
+				end
+				if not p.is_autoinit then
+					error(narg, "Error: `{p}` is not an autoinit method")
+					return
+				end
+
+				# Register the initializer and the parameters
+				initializers.add(p)
+				var pd = p.intro
+				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)
+					# Because the last parameter of setters is never default, try to default them for the autoinit.
+					for param in sig.mparameters do
+						if not param.is_default and param.mtype isa MNullableType then
+							param = new MParameter(param.name, param.mtype, param.is_vararg, true)
+						end
+						mparameters.add(param)
+					end
+				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
+					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(", ")})")
+							# TODO: invalidate the initializer to avoid more errors
+							return
+						end
+						i += 1
 					end
-					i += 1
 				end
 			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
+			# 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
 
 		# If we already have a basic init definition, then setup its initializers
@@ -262,7 +377,7 @@ 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
@@ -271,6 +386,8 @@ redef class ModelBuilder
 			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
@@ -280,10 +397,10 @@ 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
@@ -299,6 +416,72 @@ 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
@@ -308,7 +491,8 @@ redef class MPropDef
 end
 
 redef class AClassdef
-	var build_properties_is_done = false
+	# 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
@@ -350,17 +534,17 @@ 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
@@ -380,26 +564,26 @@ redef class APropdef
 	# The associated propdef once build by a `ModelBuilder`
 	var mpropdef: nullable MPROPDEF is writable
 
-	private fun build_property(modelbuilder: ModelBuilder, mclassdef: MClassDef) is abstract
-	private fun build_signature(modelbuilder: ModelBuilder) is abstract
-	private fun check_signature(modelbuilder: ModelBuilder) is abstract
+	private fun build_property(modelbuilder: ModelBuilder, mclassdef: MClassDef) do end
+	private fun build_signature(modelbuilder: ModelBuilder) do end
+	private fun check_signature(modelbuilder: ModelBuilder) do end
 	private fun new_property_visibility(modelbuilder: ModelBuilder, mclassdef: MClassDef, nvisibility: nullable AVisibility): MVisibility
 	do
 		var mvisibility = public_visibility
 		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
@@ -435,33 +619,37 @@ 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}.")
+			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
-			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`.
+			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
+						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
+				end
+			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
@@ -495,14 +683,14 @@ 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
@@ -512,7 +700,7 @@ 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
 
@@ -520,24 +708,24 @@ 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
+		return res
 	end
 end
 
@@ -609,8 +797,19 @@ 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
 
@@ -633,12 +832,24 @@ redef class AMethPropdef
 			end
 			mprop.is_init = is_init
 			mprop.is_new = n_kwnew != null
-			if parent isa ATopClassdef then mprop.is_toplevel = true
+			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
 			self.check_redef_keyword(modelbuilder, mclassdef, n_kwredef, false, mprop)
 		else
-			if not mprop.is_root_init and not self.check_redef_keyword(modelbuilder, mclassdef, n_kwredef, not self isa AMainMethPropdef, mprop) 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
+
+		# Check name conflicts in the local class for constructors.
+		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)
+					break
+				end
+			end
+		end
+
 		mclassdef.mprop2npropdef[mprop] = self
 
 		var mpropdef = new MMethodDef(mclassdef, mprop, self.location)
@@ -672,6 +883,9 @@ 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
@@ -692,11 +906,14 @@ redef class AMethPropdef
 			msignature = mpropdef.mproperty.intro.msignature
 			if msignature == null then return # Skip error
 
+			# The local signature is adapted to use the local formal types, if any.
+			msignature = msignature.resolve_for(mclassdef.mclass.mclass_type, mclassdef.bound_mtype, mmodule, false)
+
 			# Check inherited signature arity
 			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
@@ -728,13 +945,19 @@ 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
 
 		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)
+			var is_default = false
+			if vararg_rank == -1 and param_types[i] isa MNullableType then
+				if i < param_names.length-1 or accept_special_last_parameter then
+					is_default = true
+				end
+			end
+			var mparameter = new MParameter(param_names[i], param_types[i], i == vararg_rank, is_default)
 			if nsig != null then nsig.n_params[i].mparameter = mparameter
 			mparameters.add(mparameter)
 		end
@@ -742,11 +965,23 @@ 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
 		mpropdef.is_intern = self.get_single_annotation("intern", modelbuilder) != null
 		mpropdef.is_extern = self.n_extern_code_block != null or self.get_single_annotation("extern", modelbuilder) != null
+
+		# 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.")
 	end
 
 	redef fun check_signature(modelbuilder)
@@ -759,6 +994,14 @@ redef class AMethPropdef
 		var mysignature = self.mpropdef.msignature
 		if mysignature == null then return # Error thus skiped
 
+		# Check
+		if nsig != null then
+			if not nsig.check_signature(modelbuilder, mclassdef) then
+				self.mpropdef.msignature = null # invalidate
+				return # Forward error
+			end
+		end
+
 		# Lookup for signature in the precursor
 		# FIXME all precursors should be considered
 		if not mpropdef.is_intro then
@@ -768,7 +1011,8 @@ 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.")
+				self.mpropdef.msignature = null
 				return
 			end
 
@@ -777,18 +1021,23 @@ redef class AMethPropdef
 				for i in [0..mysignature.arity[ do
 					var myt = mysignature.mparameters[i].mtype
 					var prt = msignature.mparameters[i].mtype
-					if not myt.is_subtype(mmodule, mclassdef.bound_mtype, prt) or
-							not prt.is_subtype(mmodule, mclassdef.bound_mtype, myt) then
-						modelbuilder.error(nsig.n_params[i], "Redef Error: Wrong type for parameter `{mysignature.mparameters[i].name}'. found {myt}, expected {prt} as in {mpropdef.mproperty.intro}.")
+					var node = nsig.n_params[i]
+					if not modelbuilder.check_sametype(node, mmodule, mclassdef.bound_mtype, myt, prt) then
+						modelbuilder.error(node, "Redef Error: expected `{prt}` for parameter `{mysignature.mparameters[i].name}'; got `{myt}`.")
+						self.mpropdef.msignature = null
 					end
 				end
 			end
 			if precursor_ret_type != null then
+				var node: nullable ANode = null
+				if nsig != null then node = nsig.n_type
+				if node == null then node = self
 				if ret_type == null then
 					# Inherit the return type
 					ret_type = precursor_ret_type
-				else if not ret_type.is_subtype(mmodule, mclassdef.bound_mtype, precursor_ret_type) then
-					modelbuilder.error(nsig.n_type.as(not null), "Redef Error: Wrong return type. found {ret_type}, expected {precursor_ret_type} as in {mpropdef.mproperty.intro}.")
+				else if not modelbuilder.check_subtype(node, mmodule, mclassdef.bound_mtype, ret_type, precursor_ret_type) then
+					modelbuilder.error(node, "Redef Error: expected `{precursor_ret_type}` for return type; got `{ret_type}`.")
+					self.mpropdef.msignature = null
 				end
 			end
 		end
@@ -805,6 +1054,56 @@ redef class AMethPropdef
 	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
 
@@ -832,32 +1131,27 @@ redef class AAttrPropdef
 	redef fun build_property(modelbuilder, mclassdef)
 	do
 		var mclass = mclassdef.mclass
+		var nid2 = n_id2
+		var name = nid2.text
 
-		var name: String
-		name = self.n_id2.text
+		var atabstract = self.get_single_annotation("abstract", modelbuilder)
+		if atabstract == null then
+			if not mclass.kind.need_init then
+				modelbuilder.error(self, "Error: attempt to define attribute `{name}` in the {mclass.kind} `{mclass}`.")
+			end
 
-		if mclass.kind == interface_kind or mclassdef.mclass.kind == enum_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}.")
+			var mprop = new MAttribute(mclassdef, "_" + name, private_visibility)
+			var mpropdef = new MAttributeDef(mclassdef, mprop, self.location)
+			self.mpropdef = mpropdef
+			modelbuilder.mpropdef2npropdef[mpropdef] = self
 		end
 
-		# New attribute style
-		var nid2 = self.n_id2
-		var mprop = new MAttribute(mclassdef, "_" + name, private_visibility)
-		var mpropdef = new MAttributeDef(mclassdef, mprop, self.location)
-		self.mpropdef = mpropdef
-		modelbuilder.mpropdef2npropdef[mpropdef] = self
-
 		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
-			mreadprop.deprecation = mprop.deprecation
 		else
 			if not self.check_redef_keyword(modelbuilder, mclassdef, n_kwredef, true, mreadprop) then return
 			check_redef_property_visibility(modelbuilder, self.n_visibility, mreadprop)
@@ -868,15 +1162,26 @@ redef class AAttrPropdef
 		self.mreadpropdef = mreadpropdef
 		modelbuilder.mpropdef2npropdef[mreadpropdef] = self
 		set_doc(mreadpropdef, modelbuilder)
-		mpropdef.mdoc = mreadpropdef.mdoc
+		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.")
+			return
+		end
+
 		var atnoinit = self.get_single_annotation("noinit", modelbuilder)
+		if atnoinit == null then atnoinit = self.get_single_annotation("noautoinit", modelbuilder)
 		if atnoinit != null then
 			noinit = true
 			if has_value then
-				modelbuilder.error(atnoinit, "Error: `noinit` 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
 			end
 		end
@@ -885,15 +1190,16 @@ redef class AAttrPropdef
 		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")
+				modelbuilder.error(atlazy, "Error: `lazy` incompatible with `autoinit`.")
 				return
 			end
 			if not has_value then
 				if atlazy != null then
-					modelbuilder.error(atlazy, "Error: a lazy attribute needs a value")
+					modelbuilder.error(atlazy, "Error: `lazy` attributes need a value.")
 				else if atautoinit != null then
-					modelbuilder.error(atautoinit, "Error: a autoinit attribute needs a value")
+					modelbuilder.error(atautoinit, "Error: `autoinit` attributes need a value.")
 				end
+				has_value = true
 				return
 			end
 			is_lazy = true
@@ -905,12 +1211,16 @@ 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
@@ -930,7 +1240,7 @@ redef class AAttrPropdef
 			end
 			mwriteprop = new MMethod(mclassdef, writename, mvisibility)
 			if not self.check_redef_keyword(modelbuilder, mclassdef, nwkwredef, false, mwriteprop) then return
-			mwriteprop.deprecation = mprop.deprecation
+			mwriteprop.deprecation = mreadprop.deprecation
 		else
 			if not self.check_redef_keyword(modelbuilder, mclassdef, nwkwredef or else n_kwredef, true, mwriteprop) then return
 			if atwritable != null then
@@ -942,39 +1252,44 @@ redef class AAttrPropdef
 		var mwritepropdef = new MMethodDef(mclassdef, mwriteprop, self.location)
 		self.mwritepropdef = mwritepropdef
 		modelbuilder.mpropdef2npropdef[mwritepropdef] = self
-		mwritepropdef.mdoc = mpropdef.mdoc
+		mwritepropdef.mdoc = mreadpropdef.mdoc
+		if atabstract != null then mwritepropdef.is_abstract = true
 	end
 
 	redef fun build_signature(modelbuilder)
 	do
+		var mreadpropdef = self.mreadpropdef
 		var mpropdef = self.mpropdef
-		if mpropdef == null then return # Error thus skipped
-		var mclassdef = mpropdef.mclassdef
+		if mreadpropdef == null then return # Error thus skipped
+		var mclassdef = mreadpropdef.mclassdef
 		var mmodule = mclassdef.mmodule
 		var mtype: nullable MType = null
 
-		var mreadpropdef = self.mreadpropdef
 
 		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
 
 		var inherited_type: nullable MType = null
 		# Inherit the type from the getter (usually an abstract getter)
-		if mreadpropdef != null and not mreadpropdef.is_intro then
+		if not mreadpropdef.is_intro then
 			var msignature = mreadpropdef.mproperty.intro.msignature
 			if msignature == null then return # Error, thus skipped
 			inherited_type = msignature.return_mtype
-			if mtype == null then mtype = inherited_type
+			if inherited_type != null then
+				# The inherited type is adapted to use the local formal types, if any.
+				inherited_type = inherited_type.resolve_for(mclassdef.mclass.mclass_type, mclassdef.bound_mtype, mmodule, false)
+				if mtype == null then mtype = inherited_type
+			end
 		end
 
 		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)
+					mtype = modelbuilder.resolve_mtype_unchecked(mmodule, mclassdef, nexpr.n_type, true)
 				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
@@ -994,14 +1309,14 @@ 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 {mpropdef}. 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
@@ -1009,13 +1324,15 @@ redef class AAttrPropdef
 		end
 
 		if mtype == null then
-			modelbuilder.error(self, "Error: Untyped attribute {mpropdef}")
+			modelbuilder.error(self, "Error: untyped attribute `{mreadpropdef}`.")
 			return
 		end
 
-		mpropdef.static_mtype = mtype
+		if mpropdef != null then
+			mpropdef.static_mtype = mtype
+		end
 
-		if mreadpropdef != null then
+		do
 			var msignature = new MSignature(new Array[MParameter], mtype)
 			mreadpropdef.msignature = msignature
 		end
@@ -1024,7 +1341,7 @@ redef class AAttrPropdef
 		if mwritepropdef != null then
 			var name: String
 			name = n_id2.text
-			var mparameter = new MParameter(name, mtype, false)
+			var mparameter = new MParameter(name, mtype, false, false)
 			var msignature = new MSignature([mparameter], null)
 			mwritepropdef.msignature = msignature
 		end
@@ -1043,6 +1360,18 @@ redef class AAttrPropdef
 		var mtype = self.mpropdef.static_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
@@ -1050,7 +1379,7 @@ 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
@@ -1089,7 +1418,7 @@ 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
@@ -1097,7 +1426,7 @@ 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
 
@@ -1106,22 +1435,21 @@ redef class AAttrPropdef
 				for i in [0..mysignature.arity[ do
 					var myt = mysignature.mparameters[i].mtype
 					var prt = msignature.mparameters[i].mtype
-					if not myt.is_subtype(mmodule, mclassdef.bound_mtype, prt) or
-							not prt.is_subtype(mmodule, mclassdef.bound_mtype, myt) then
-						var node: ANode
-						if nsig != null then node = nsig else node = self
-						modelbuilder.error(node, "Redef Error: Wrong type for parameter `{mysignature.mparameters[i].name}'. found {myt}, expected {prt}.")
+					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: expected `{prt}` type for parameter `{mysignature.mparameters[i].name}'; got `{myt}`.")
 					end
 				end
 			end
 			if precursor_ret_type != null then
+				var node: ANode
+				if nsig != null then node = nsig else node = self
 				if ret_type == null then
 					# Inherit the return type
 					ret_type = precursor_ret_type
-				else if not ret_type.is_subtype(mmodule, mclassdef.bound_mtype, precursor_ret_type) then
-					var node: ANode
-					if nsig != null then node = nsig else node = self
-					modelbuilder.error(node, "Redef Error: Wrong return type. found {ret_type}, expected {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: expected `{precursor_ret_type}` return type; got `{ret_type}`.")
 				end
 			end
 		end
@@ -1139,7 +1467,7 @@ 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
@@ -1153,6 +1481,11 @@ redef class ATypePropdef
 		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
 		set_doc(mpropdef, modelbuilder)
 
 		var atfixed = get_single_annotation("fixed", modelbuilder)
@@ -1170,7 +1503,7 @@ 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
@@ -1182,7 +1515,7 @@ 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)
@@ -1191,30 +1524,18 @@ 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
@@ -1222,8 +1543,8 @@ redef class ATypePropdef
 				modelbuilder.warning(n_type, "refine-type", "Redef Error: a virtual type cannot be refined.")
 				break
 			end
-			if not bound.is_subtype(mmodule, anchor, supbound) then
-				modelbuilder.error(n_type, "Redef Error: Wrong bound type. Found {bound}, expected a subtype of {supbound}, as in {p}.")
+			if not modelbuilder.check_subtype(n_type, mmodule, anchor, bound, supbound) then
+				modelbuilder.error(n_type, "Redef Error: expected `{supbound}` bound type; got `{bound}`.")
 				break
 			end
 		end