d: Merge UDAs between function prototype and definitions (PR90136)

This change fixes the symbol merging in get_symbol_decl to also consider
prototypes.  This allows the ability to set user defined attributes on
the prototype of a function, which then get applied to the definition,
if found later in the compilation.

The lowering of UDAs to GCC attributes has been commonized into a single
function called apply_user_attributes.

gcc/d/ChangeLog:

	PR d/90136
	* d-attribs.cc: Include dmd/attrib.h.
	(build_attributes): Redeclare as static.
	(apply_user_attributes): New function.
	* d-tree.h (class UserAttributeDeclaration): Remove.
	(build_attributes): Remove.
	(apply_user_attributes): Declare.
	(finish_aggregate_type): Remove attrs argument.
	* decl.cc (get_symbol_decl): Merge declaration prototypes with
	definitions.  Use apply_user_attributes.
	* modules.cc (layout_moduleinfo_fields): Remove last argument to
	finish_aggregate_type.
	* typeinfo.cc (layout_classinfo_interfaces): Likewise.
	* types.cc (layout_aggregate_members): Likewise.
	(finish_aggregate_type): Remove attrs argument.
	(TypeVisitor::visit (TypeEnum *)): Use apply_user_attributes.
	(TypeVisitor::visit (TypeStruct *)): Remove last argument to
	finish_aggregate_type.  Use apply_user_attributes.
	(TypeVisitor::visit (TypeClass *)): Likewise.

gcc/testsuite/ChangeLog:

	PR d/90136
	* gdc.dg/pr90136a.d: New test.
	* gdc.dg/pr90136b.d: New test.
	* gdc.dg/pr90136c.d: New test.

1 files changed, 29 insertions, 20 deletions

diff --git a/gcc/d/decl.cc b/gcc/d/decl.cc
index 053d553..042c10c 100644
--- a/gcc/d/decl.cc
+++ b/gcc/d/decl.cc
@@ -1110,7 +1110,10 @@ get_symbol_decl (Declaration *decl)
       /* Set function type afterwards as there could be self references.  */
       TREE_TYPE (decl->csym) = build_ctype (fd->type);
 
-      if (!fd->fbody)
+      /* Set DECL_INITIAL now if the function has a definition.  */
+      if (fd->fbody)
+	DECL_INITIAL (decl->csym) = error_mark_node;
+      else
 	DECL_EXTERNAL (decl->csym) = 1;
     }
   else
@@ -1151,26 +1154,38 @@ get_symbol_decl (Declaration *decl)
 							 mangled_name);
       /* The frontend doesn't handle duplicate definitions of unused symbols
 	 with the same mangle.  So a check is done here instead.  */
-      if (!DECL_EXTERNAL (decl->csym))
+      if (IDENTIFIER_DSYMBOL (mangled_name))
 	{
-	  if (IDENTIFIER_DSYMBOL (mangled_name))
-	    {
-	      Declaration *other = IDENTIFIER_DSYMBOL (mangled_name);
+	  Declaration *other = IDENTIFIER_DSYMBOL (mangled_name);
+	  tree olddecl = decl->csym;
+	  decl->csym = get_symbol_decl (other);
 
-	      /* Non-templated variables shouldn't be defined twice.  */
-	      if (!decl->isInstantiated ())
-		ScopeDsymbol::multiplyDefined (decl->loc, decl, other);
-
-	      decl->csym = get_symbol_decl (other);
+	  /* The current declaration is a prototype or marked extern, merge
+	     applied user attributes and return.  */
+	  if (DECL_EXTERNAL (olddecl) && !DECL_INITIAL (olddecl))
+	    {
+	      apply_user_attributes (decl, decl->csym);
 	      return decl->csym;
 	    }
-
+	  /* The previous declaration is a prototype or marked extern, set the
+	     current declaration as the main reference of the symbol.  */
+	  else if (DECL_EXTERNAL (decl->csym) && !DECL_INITIAL (decl->csym))
+	    {
+	      IDENTIFIER_DSYMBOL (mangled_name) = decl;
+	      DECL_EXTERNAL (decl->csym) = 0;
+	    }
+	  /* Non-extern, non-templated decls shouldn't be defined twice.  */
+	  else if (!decl->isInstantiated ())
+	    ScopeDsymbol::multiplyDefined (decl->loc, decl, other);
+	}
+      else
+	{
 	  IDENTIFIER_PRETTY_NAME (mangled_name)
 	    = get_identifier (decl->toPrettyChars (true));
 	  IDENTIFIER_DSYMBOL (mangled_name) = decl;
-	}
 
-      SET_DECL_ASSEMBLER_NAME (decl->csym, mangled_name);
+	  SET_DECL_ASSEMBLER_NAME (decl->csym, mangled_name);
+	}
     }
 
   DECL_LANG_SPECIFIC (decl->csym) = build_lang_decl (decl);
@@ -1358,13 +1373,7 @@ get_symbol_decl (Declaration *decl)
     }
 
   /* Apply any user attributes that may affect semantic meaning.  */
-  if (decl->userAttribDecl)
-    {
-      Expressions *attrs = decl->userAttribDecl->getAttributes ();
-      decl_attributes (&decl->csym, build_attributes (attrs), 0);
-    }
-  else if (DECL_ATTRIBUTES (decl->csym) != NULL)
-    decl_attributes (&decl->csym, DECL_ATTRIBUTES (decl->csym), 0);
+  apply_user_attributes (decl, decl->csym);
 
   /* %% Probably should be a little more intelligent about setting this.  */
   TREE_USED (decl->csym) = 1;