Fixed issue 22348 - Specify forward referencing of MixinDeclaration (#3513)

* Fixed issue 22348 - Specify forward referencing of MixinDeclaration

Signed-off-by: Robert Grancsa <[email protected]>

* fixed indentation

Signed-off-by: Robert Grancsa <[email protected]>

* fixed indentation

Signed-off-by: Robert Grancsa <[email protected]>

* fixed indentation

Signed-off-by: Robert Grancsa <[email protected]>

* Fix Issue 22348 - Specify forward referencing of MixinDeclaration

Signed-off-by: Robert Grancsa <[email protected]>

---------

Signed-off-by: Robert Grancsa <[email protected]>

Author: RobertGrancsa

spec/module.dd

@@ -626,14 +626,31 @@ $(GNAME MixinDeclaration):
     $(D mixin) $(D $(LPAREN)) $(GLINK2 expression, ArgumentList) $(D $(RPAREN)) $(D ;)
 )
 
-    $(P Each $(GLINK2 expression, AssignExpression) in the $(I ArgumentList) is
-        evaluated at compile time, and the result must be representable
-        as a string.
-        The resulting strings are concatenated to form a string.
-        The text contents of the string must be compilable as a valid
-        $(GLINK DeclDefs), and is compiled as such.
-        )
+$(P Each $(GLINK2 expression, AssignExpression) in the $(I ArgumentList) is
+    evaluated at compile time, and the result must be representable
+    as a string.
+    The resulting strings are concatenated to form a string.
+    The text contents of the string must be compilable as a valid
+    $(GLINK DeclDefs), and is compiled as such.)
 
+$(P The content of a mixin cannot be forward referenced by other DeclDefs of
+    the same scope because it is not yet pulled in the AST.)
+
+---------
+class B : A {}      // Error: undefined identifier `A`
+mixin ("class A {}");
+---------
+
+$(P Forward references may only work in function bodies because they
+    are processed after the declarations)
+
+---------
+void v()
+{
+    class B : A {}
+}
+mixin ("class A {}");
+---------
 
 $(H2 $(LEGACY_LNAME2 PackageModule, package-module, Package Module))