c++: subst failure in attribute argument [PR95192]

Another SFINAE issue: we weren't propagating substitution failure in
attributes back up.  And tsubst_function_decl needs to check substitution
before register_specialization.  I thought about moving the other error
returns up as well, but they aren't SFINAE cases, so they can stay where
they are.

This change caused pr84630.C to stop giving an error; this was because
partial instantiation of the lambda failed silently, and before the change
that meant error_mark_node passed to decl_attributes, which complained about
there being an argument at all.  With the change the partial instantiation
fails, but no error was ever given, because push_template_decl silently
failed if current_template_parms wasn't set.  So let's set c_t_p
appropriately.  lambda-uneval13.C is a valid testcase to exercise this.

gcc/cp/ChangeLog:

	PR c++/95192
	* pt.c (tsubst_attribute): Handle error.
	(apply_late_template_attributes): Return false on error.
	(tsubst_function_decl): Check its return value.
	(tsubst_decl): Likewise.
	(push_template_decl): Assert current_template_parms.
	(tsubst_template_decl): Set current_template_parms.

gcc/testsuite/ChangeLog:

	PR c++/95192
	* g++.dg/cpp0x/pr84630.C: Call b().
	* g++.dg/cpp2a/lambda-uneval13.C: New test.
	* g++.dg/ext/attr-expr1.C: New test.

gcc/cp/pt.c

@@ -11571,6 +11571,8 @@ tsubst_attribute (tree t, tree *decl_p, tree args,
     val = tsubst_expr (val, args, complain, in_decl,
 		       /*integral_constant_expression_p=*/false);
 
+  if (val == error_mark_node)
+    return error_mark_node;
   if (val != TREE_VALUE (t))
     return build_tree_list (TREE_PURPOSE (t), val);
   return t;
@@ -11617,9 +11619,10 @@ tsubst_attributes (tree attributes, tree args,
 
 /* Apply any attributes which had to be deferred until instantiation
    time.  DECL_P, ATTRIBUTES and ATTR_FLAGS are as cplus_decl_attributes;
-   ARGS, COMPLAIN, IN_DECL are as tsubst.  */
+   ARGS, COMPLAIN, IN_DECL are as tsubst.  Returns true normally,
+   false on error.  */
 
-static void
+static bool
 apply_late_template_attributes (tree *decl_p, tree attributes, int attr_flags,
 				tree args, tsubst_flags_t complain, tree in_decl)
 {
@@ -11628,12 +11631,12 @@ apply_late_template_attributes (tree *decl_p, tree attributes, int attr_flags,
   tree *p;
 
   if (attributes == NULL_TREE)
-    return;
+    return true;
 
   if (DECL_P (*decl_p))
     {
       if (TREE_TYPE (*decl_p) == error_mark_node)
-	return;
+	return false;
       p = &DECL_ATTRIBUTES (*decl_p);
       /* DECL_ATTRIBUTES comes from copy_node in tsubst_decl, and is identical
          to our attributes parameter.  */
@@ -11668,9 +11671,11 @@ apply_late_template_attributes (tree *decl_p, tree attributes, int attr_flags,
 	  t = *p;
 	  if (ATTR_IS_DEPENDENT (t))
 	    {
+	      *q = tsubst_attribute (t, decl_p, args, complain, in_decl);
+	      if (*q == error_mark_node)
+		return false;
 	      *p = TREE_CHAIN (t);
 	      TREE_CHAIN (t) = NULL_TREE;
-	      *q = tsubst_attribute (t, decl_p, args, complain, in_decl);
 	      while (*q)
 		q = &TREE_CHAIN (*q);
 	    }
@@ -11680,6 +11685,7 @@ apply_late_template_attributes (tree *decl_p, tree attributes, int attr_flags,
 
       cplus_decl_attributes (decl_p, late_attrs, attr_flags);
     }
+  return true;
 }
 
 /* The template TMPL is being instantiated with the template arguments TARGS.
@@ -14048,6 +14054,10 @@ tsubst_function_decl (tree t, tree args, tsubst_flags_t complain,
 			     tsubst (DECL_FRIEND_CONTEXT (t),
 				     args, complain, in_decl));
 
+  if (!apply_late_template_attributes (&r, DECL_ATTRIBUTES (r), 0,
+				       args, complain, in_decl))
+    return error_mark_node;
+
   /* Set up the DECL_TEMPLATE_INFO for R.  There's no need to do
      this in the special friend case mentioned above where
      GEN_TMPL is NULL.  */
@@ -14127,8 +14137,6 @@ tsubst_function_decl (tree t, tree args, tsubst_flags_t complain,
       && !processing_template_decl)
     defaulted_late_check (r);
 
-  apply_late_template_attributes (&r, DECL_ATTRIBUTES (r), 0,
-				  args, complain, in_decl);
   if (flag_openmp)
     if (tree attr = lookup_attribute ("omp declare variant base",
 				      DECL_ATTRIBUTES (r)))
@@ -14228,7 +14236,9 @@ tsubst_template_decl (tree t, tree args, tsubst_flags_t complain,
   /* The template parameters for this new template are all the
      template parameters for the old template, except the
      outermost level of parameters.  */
+  auto tparm_guard = make_temp_override (current_template_parms);
   DECL_TEMPLATE_PARMS (r)
+    = current_template_parms
     = tsubst_template_parms (DECL_TEMPLATE_PARMS (t), args,
 			     complain);
 
@@ -14491,8 +14501,9 @@ tsubst_decl (tree t, tree args, tsubst_flags_t complain)
             if (!DECL_TEMPLATE_PARM_P (r))
               DECL_ARG_TYPE (r) = type_passed_as (type);
 
-	    apply_late_template_attributes (&r, DECL_ATTRIBUTES (r), 0,
-					    args, complain, in_decl);
+	    if (!apply_late_template_attributes (&r, DECL_ATTRIBUTES (r), 0,
+						 args, complain, in_decl))
+	      return error_mark_node;
 
             /* Keep track of the first new parameter we
                generate. That's what will be returned to the
@@ -14581,8 +14592,9 @@ tsubst_decl (tree t, tree args, tsubst_flags_t complain)
 	       finish_member_declaration.  */
 	    DECL_CHAIN (r) = NULL_TREE;
 
-	    apply_late_template_attributes (&r, DECL_ATTRIBUTES (r), 0,
-					    args, complain, in_decl);
+	    if (!apply_late_template_attributes (&r, DECL_ATTRIBUTES (r), 0,
+						 args, complain, in_decl))
+	      return error_mark_node;
 
 	    if (vec)
 	      TREE_VEC_ELT (vec, i) = r;
@@ -14901,9 +14913,10 @@ tsubst_decl (tree t, tree args, tsubst_flags_t complain)
 
 	DECL_CHAIN (r) = NULL_TREE;
 
-	apply_late_template_attributes (&r, DECL_ATTRIBUTES (r),
-					/*flags=*/0,
-					args, complain, in_decl);
+	if (!apply_late_template_attributes (&r, DECL_ATTRIBUTES (r),
+					     /*flags=*/0,
+					     args, complain, in_decl))
+	  return error_mark_node;
 
 	/* Preserve a typedef that names a type.  */
 	if (is_typedef_decl (r) && type != error_mark_node)

gcc/testsuite/g++.dg/cpp0x/pr84630.C

@@ -5,3 +5,4 @@ template <typename...> struct c {
   template <int> __attribute__((noinline([] {}))) int b();  // { dg-error "wrong number of arguments" }
 };
 c<> a;
+int i = a.b<42>();

gcc/testsuite/g++.dg/cpp2a/lambda-uneval13.C

@@ -0,0 +1,11 @@
+// { dg-do compile { target c++20 } }
+
+template <class U> struct A
+{
+  template <class T> void spam(decltype([]{}) *s = nullptr) { }
+};
+
+void foo()
+{
+  A<int>().spam<int>();
+}

gcc/testsuite/g++.dg/ext/attr-expr1.C

@@ -0,0 +1,9 @@
+// PR c++/95192
+
+template<typename T>
+__attribute__((assume_aligned(sizeof(int(T()))))) // { dg-message "function type" }
+T *f();
+
+void test21() {
+  void *p = f<void>()		// { dg-error "no match" }
+}