Refactor restriction mechanism for autocasting (#12014)

src/compiler/crystal/semantic/ast.cr

@@ -49,34 +49,6 @@ module Crystal
         end
       end
     end
-
-    def can_autocast_to?(other_type)
-      self_type = self.type
-
-      case {self_type, other_type}
-      when {IntegerType, IntegerType}
-        self_min, self_max = self_type.range
-        other_min, other_max = other_type.range
-        other_min <= self_min && self_max <= other_max
-      when {IntegerType, FloatType}
-        # Float32 mantissa has 23 bits,
-        # Float64 mantissa has 52 bits
-        case self_type.kind
-        when .i8?, .u8?, .i16?, .u16?
-          # Less than 23 bits, so convertable to Float32 and Float64 without precision loss
-          true
-        when .i32?, .u32?
-          # Less than 52 bits, so convertable to Float64 without precision loss
-          other_type.kind.f64?
-        else
-          false
-        end
-      when {FloatType, FloatType}
-        self_type.kind.f32? && other_type.kind.f64?
-      else
-        false
-      end
-    end
   end
 
   class Var
@@ -859,22 +831,6 @@ module Crystal
     end
   end
 
-  class NumberLiteral
-    def can_autocast_to?(other_type)
-      case {self.type, other_type}
-      when {IntegerType, IntegerType}
-        min, max = other_type.range
-        min <= integer_value <= max
-      when {IntegerType, FloatType}
-        true
-      when {FloatType, FloatType}
-        true
-      else
-        false
-      end
-    end
-  end
-
   # Fictitious node to mean a location in code shouldn't be reached.
   # This is used in the implicit `else` branch of a case.
   class Unreachable < ASTNode

src/compiler/crystal/semantic/restrictions.cr

@@ -1346,68 +1346,72 @@ module Crystal
     end
   end
 
-  class NumberAutocastType
+  class AutocastType
+    # Returns true if the AST node associated with `self` denotes a value of the
+    # given *type*.
+    def matches_exactly?(type : Type) : Bool
+      false
+    end
+
+    # Returns true if the AST node associated with `self` denotes a value that
+    # may be interpreted in the given *type*, but is itself not of that type.
+    def matches_partially?(type : Type) : Bool
+      false
+    end
+
     def restrict(other, context)
-      if other.is_a?(IntegerType) || other.is_a?(FloatType)
-        # Check for an exact match, which can't produce an ambiguous call
-        if literal.type == other
+      if other.is_a?(Type)
+        if matches_exactly?(other)
           set_exact_match(other)
-          other
-        elsif !exact_match? && literal.can_autocast_to?(other)
+          return other
+        elsif !exact_match? && matches_partially?(other)
           add_match(other)
-          other
-        else
-          literal.type.restrict(other, context)
+          return other
         end
-      else
-        type = literal.type.restrict(other, context) ||
-               super(other, context)
-        if type == self
-          type = @match || literal.type
-        end
-        type
       end
+
+      literal_type = literal.type?
+      type = literal_type.try(&.restrict(other, context)) || super(other, context)
+      if type == self
+        # if *other* is an AST node (e.g. `Path`) or a complex type (e.g.
+        # `UnionType`), `@match` may be set from recursive calls to `#restrict`,
+        # so we propagate any exact matches found during those calls
+        type = @match || literal_type
+      end
+      type
     end
 
     def compatible_with?(type)
-      literal.type == type || literal.can_autocast_to?(type)
+      matches_exactly?(type) || matches_partially?(type)
     end
   end
 
-  class SymbolAutocastType
-    def restrict(other, context)
-      case other
-      when SymbolType
-        set_exact_match(other)
-        other
-      when EnumType
-        if !exact_match? && other.find_member(literal.value)
-          add_match(other)
-          other
-        else
-          literal.type.restrict(other, context)
-        end
-      else
-        type = literal.type.restrict(other, context) ||
-               super(other, context)
-        if type == self
-          type = @match || literal.type
-        end
-        type
-      end
+  class NumberAutocastType
+    def matches_exactly?(type : IntegerType | FloatType) : Bool
+      literal.type == type
     end
 
-    def compatible_with?(type)
-      case type
-      when SymbolType
-        true
-      when EnumType
-        !!(type.find_member(literal.value))
+    def matches_partially?(type : IntegerType | FloatType) : Bool
+      literal = self.literal
+
+      if literal.is_a?(NumberLiteral)
+        literal.representable_in?(type)
       else
-        false
+        literal_type = literal.type
+        (literal_type.is_a?(IntegerType) || literal_type.is_a?(FloatType)) && literal_type.subset_of?(type)
       end
     end
   end
+
+  class SymbolAutocastType
+    def matches_exactly?(type : SymbolType) : Bool
+      true
+    end
+
+    def matches_partially?(type : EnumType) : Bool
+      !type.find_member(literal.value).nil?
+    end
+  end
 end
 
 private def get_generic_type(node, context)

src/compiler/crystal/syntax/ast.cr

@@ -336,6 +336,25 @@ module Crystal
       end
     end
 
+    # Returns true if this literal is representable in the *other_type*. Used to
+    # define number literal autocasting.
+    #
+    # TODO: if *other_type* is a `FloatType` then precision loss and overflow
+    # may occur (#11710)
+    def representable_in?(other_type)
+      case {self.type, other_type}
+      when {IntegerType, IntegerType}
+        min, max = other_type.range
+        min <= integer_value <= max
+      when {IntegerType, FloatType}
+        true
+      when {FloatType, FloatType}
+        true
+      else
+        false
+      end
+    end
+
     def clone_without_location
       NumberLiteral.new(@value, @kind)
     end

src/compiler/crystal/types.cr

@@ -1336,6 +1336,31 @@ module Crystal
         raise "Bug: called 'range' for non-integer literal"
       end
     end
+
+    # Returns true if every _finite_ member of this type is also exactly
+    # representable in the *other_type*. Used to define legal autocasts of
+    # number-typed variables
+    def subset_of?(other_type : IntegerType) : Bool
+      self_min, self_max = self.range
+      other_min, other_max = other_type.range
+      other_min <= self_min && self_max <= other_max
+    end
+
+    # :ditto:
+    def subset_of?(other_type : FloatType) : Bool
+      # Float32 mantissa has 23 bits,
+      # Float64 mantissa has 52 bits
+      case kind
+      when .i8?, .u8?, .i16?, .u16?
+        # Less than 23 bits, so convertable to Float32 and Float64 without precision loss
+        true
+      when .i32?, .u32?
+        # Less than 52 bits, so convertable to Float64 without precision loss
+        other_type.kind.f64?
+      else
+        false
+      end
+    end
   end
 
   class FloatType < PrimitiveType
@@ -1359,6 +1384,18 @@ module Crystal
         raise "Bug: called 'range' for non-float literal"
       end
     end
+
+    # Returns true if every _finite_ member of this type is also exactly
+    # representable in the *other_type*. Used to define legal autocasts of
+    # number-typed variables.
+    def subset_of?(other_type : IntegerType) : Bool
+      false
+    end
+
+    # :ditto:
+    def subset_of?(other_type : FloatType) : Bool
+      kind.f32? && other_type.kind.f64?
+    end
   end
 
   class SymbolType < PrimitiveType