Add generic restrictions

src/compiler/crystal/semantic/top_level_visitor.cr

@@ -72,6 +72,16 @@ class Crystal::TopLevelVisitor < Crystal::SemanticVisitor
               node.raise "type vars must be #{type_type_vars.join ", "}, not #{type_vars.join ", "}"
             end
           end
+          if restriction = node.generic_restriction
+            type_restriction = type.restriction
+            if type_restriction
+              if restriction != type_restriction
+                restriction.raise "generic restriction must be '#{type_restriction}', not '#{restriction}'"
+              end
+            else
+              restriction.raise "#{type.type_desc} #{name} doesn't have a generic restriction"
+            end
+          end
         else
           node.raise "#{name} is not a generic #{type.type_desc}"
         end
@@ -81,6 +91,7 @@ class Crystal::TopLevelVisitor < Crystal::SemanticVisitor
       if type_vars = node.type_vars
         type = GenericClassType.new @program, scope, name, nil, type_vars, false
         type.splat_index = node.splat_index
+        type.restriction = node.generic_restriction
       else
         type = NonGenericClassType.new @program, scope, name, nil, false
       end
@@ -221,10 +232,36 @@ class Crystal::TopLevelVisitor < Crystal::SemanticVisitor
       end
 
       type = type.as(ModuleType)
+
+      if type_vars = node.type_vars
+        if type.is_a?(GenericType)
+          type_type_vars = type.type_vars
+          if type_vars != type_type_vars
+            if type_type_vars.size == 1
+              node.raise "type var must be #{type_type_vars.join ", "}, not #{type_vars.join ", "}"
+            else
+              node.raise "type vars must be #{type_type_vars.join ", "}, not #{type_vars.join ", "}"
+            end
+          end
+          if restriction = node.generic_restriction
+            type_restriction = type.restriction
+            if type_restriction
+              if restriction != type_restriction
+                restriction.raise "generic restriction must be '#{type_restriction}', not '#{restriction}'"
+              end
+            else
+              restriction.raise "#{type.type_desc} #{name} doesn't have a generic restriction"
+            end
+          end
+        else
+          node.raise "#{name} is not a generic #{type.type_desc}"
+        end
+      end
     else
       if type_vars = node.type_vars
         type = GenericModuleType.new @program, scope, name, type_vars
         type.splat_index = node.splat_index
+        type.restriction = node.generic_restriction
       else
         type = NonGenericModuleType.new @program, scope, name
       end

src/compiler/crystal/syntax/ast.cr

@@ -1284,7 +1284,7 @@ module Crystal
 
   # Class definition:
   #
-  #     'class' name [ '<' superclass ]
+  #     'class' name [ '<' superclass ] [ 'where' generic restriction ]
   #       body
   #     'end'
   #
@@ -1293,14 +1293,15 @@ module Crystal
     property body : ASTNode
     property superclass : ASTNode?
     property type_vars : Array(String)?
+    property generic_restriction : ASTNode?
     property name_location : Location?
     property doc : String?
     property splat_index : Int32?
     property? abstract : Bool
     property? struct : Bool
     property visibility = Visibility::Public
 
-    def initialize(@name, body = nil, @superclass = nil, @type_vars = nil, @abstract = false, @struct = false, @splat_index = nil)
+    def initialize(@name, body = nil, @superclass = nil, @type_vars = nil, @generic_restriction = nil, @abstract = false, @struct = false, @splat_index = nil)
       @body = Expressions.from body
     end
 
@@ -1310,30 +1311,31 @@ module Crystal
     end
 
     def clone_without_location
-      clone = ClassDef.new(@name, @body.clone, @superclass.clone, @type_vars.clone, @abstract, @struct, @splat_index)
+      clone = ClassDef.new(@name, @body.clone, @superclass.clone, @type_vars.clone, @generic_restriction.clone, @abstract, @struct, @splat_index)
       clone.name_location = name_location
       clone
     end
 
-    def_equals_and_hash @name, @body, @superclass, @type_vars, @abstract, @struct, @splat_index
+    def_equals_and_hash @name, @body, @superclass, @type_vars, @generic_restriction, @abstract, @struct, @splat_index
   end
 
   # Module definition:
   #
-  #     'module' name
+  #     'module' name [ 'where' generic restriction ]
   #       body
   #     'end'
   #
   class ModuleDef < ASTNode
     property name : Path
     property body : ASTNode
     property type_vars : Array(String)?
+    property generic_restriction : ASTNode?
     property splat_index : Int32?
     property name_location : Location?
     property doc : String?
     property visibility = Visibility::Public
 
-    def initialize(@name, body = nil, @type_vars = nil, @splat_index = nil)
+    def initialize(@name, body = nil, @type_vars = nil, @generic_restriction = nil, @splat_index = nil)
       @body = Expressions.from body
     end
 
@@ -1342,12 +1344,12 @@ module Crystal
     end
 
     def clone_without_location
-      clone = ModuleDef.new(@name, @body.clone, @type_vars.clone, @splat_index)
+      clone = ModuleDef.new(@name, @body.clone, @type_vars.clone, @generic_restriction.clone, @splat_index)
       clone.name_location = name_location
       clone
     end
 
-    def_equals_and_hash @name, @body, @type_vars, @splat_index
+    def_equals_and_hash @name, @body, @type_vars, @generic_restriction, @splat_index
   end
 
   # Annotation definition:

src/compiler/crystal/syntax/lexer.cr

@@ -1139,8 +1139,13 @@ module Crystal
         when 'h'
           case next_char
           when 'e'
-            if next_char == 'n'
+            case next_char
+            when 'n'
               return check_ident_or_keyword(:when, start)
+            when 'r'
+              if next_char == 'e'
+                return check_ident_or_keyword(:where, start)
+              end
             end
           when 'i'
             if next_char == 'l' && next_char == 'e'

src/compiler/crystal/syntax/parser.cr

@@ -1566,9 +1566,16 @@ module Crystal
           superclass = parse_ident
         end
       end
+
+      generic_restriction = nil
+      if type_vars && @token.keyword?(:where)
+        next_token_skip_space_or_newline
+        generic_restriction = parse_expression
+      end
+
       skip_statement_end
 
-      body = push_visbility { parse_expressions }
+      body = push_visibility { parse_expressions }
 
       end_location = token_end_location
       check_ident :end
@@ -1578,7 +1585,7 @@ module Crystal
 
       @type_nest -= 1
 
-      class_def = ClassDef.new name, body, superclass, type_vars, is_abstract, is_struct, splat_index
+      class_def = ClassDef.new name, body, superclass, type_vars, generic_restriction, is_abstract, is_struct, splat_index
       class_def.doc = doc
       class_def.name_location = name_location
       class_def.end_location = end_location
@@ -1641,9 +1648,16 @@ module Crystal
       skip_space
 
       type_vars, splat_index = parse_type_vars
+
+      generic_restriction = nil
+      if type_vars && @token.keyword?(:where)
+        next_token_skip_space_or_newline
+        generic_restriction = parse_expression
+      end
+
       skip_statement_end
 
-      body = push_visbility { parse_expressions }
+      body = push_visibility { parse_expressions }
 
       end_location = token_end_location
       check_ident :end
@@ -1653,7 +1667,7 @@ module Crystal
 
       @type_nest -= 1
 
-      module_def = ModuleDef.new name, body, type_vars, splat_index
+      module_def = ModuleDef.new name, body, type_vars, generic_restriction, splat_index
       module_def.doc = doc
       module_def.name_location = name_location
       module_def.end_location = end_location
@@ -5164,7 +5178,7 @@ module Crystal
       name_location = @token.location
       next_token_skip_statement_end
 
-      body = push_visbility { parse_lib_body_expressions }
+      body = push_visibility { parse_lib_body_expressions }
 
       check_ident :end
       end_location = token_end_location
@@ -5844,7 +5858,7 @@ module Crystal
       name == "self" || @def_vars.last.includes?(name)
     end
 
-    def push_visbility
+    def push_visibility
       old_visibility = @visibility
       @visibility = nil
       value = yield

src/compiler/crystal/types.cr

@@ -1456,6 +1456,9 @@ module Crystal
     # The type variable names (K and V in Hash).
     getter type_vars : Array(String)
 
+    # The optional generic restriction specified with `where`.
+    property restriction : ASTNode?
+
     # The index of the `*` in the type variables.
     property splat_index : Int32?
 
@@ -1477,7 +1480,10 @@ module Crystal
         return instance
       end
 
+      # Used for instantiating the generic type
       instance_type_vars = {} of String => ASTNode
+      # Passed to the macro interpreter checking the generic restriction
+      restriction_check_vars = {} of String => TypeVar
       type_var_index = 0
       self.type_vars.each_with_index do |name, index|
         if splat_index == index
@@ -1486,9 +1492,11 @@ module Crystal
             types << type_vars[type_var_index]
             type_var_index += 1
           end
-          var = Var.new(name, program.tuple_of(types))
+          type_var = program.tuple_of(types)
+          var = Var.new(name, type_var)
           var.bind_to(var)
           instance_type_vars[name] = var
+          restriction_check_vars[name] = type_var
         else
           type_var = type_vars[type_var_index]
           case type_var
@@ -1499,11 +1507,24 @@ module Crystal
           when ASTNode
             instance_type_vars[name] = type_var
           end
+          restriction_check_vars[name] = type_var
           type_var_index += 1
         end
       end
 
       instance = self.new_generic_instance(program, self, instance_type_vars)
+
+      # Don't check the generic restriction unless the type is fully instantiated
+      if restriction && !instance.unbound?
+        unless macro_expression_truthy?(program, restriction.not_nil!, self, free_vars: restriction_check_vars)
+          if type_vars.size == 1
+            raise TypeException.new "type var #{type_vars.first} doesn't satisfy restriction '#{restriction}' of #{type_desc} #{name}"
+          else
+            raise TypeException.new "type vars #{type_vars.join ", "} don't satisfy restriction '#{restriction}' of #{type_desc} #{name}"
+          end
+        end
+      end
+
       generic_types[type_vars] = instance
 
       if instance.is_a?(GenericClassInstanceType) && !instance.superclass
@@ -3333,3 +3354,10 @@ private def add_instance_var_initializer(including_types, name, value, meta_vars
     end
   end
 end
+
+private def macro_expression_truthy?(program, node : Crystal::ASTNode, scope : Crystal::Type, free_vars = nil)
+  interpreter = Crystal::MacroInterpreter.new program, scope, scope, node.location, in_macro: false
+  interpreter.free_vars = free_vars
+  node.accept interpreter
+  interpreter.last.truthy?
+end