My r11-2202 was trying to enforce [dcl.type.auto.deduct]/4, which says
"If the placeholder-type-specifier is of the form type-constraint[opt]
decltype(auto), T shall be the placeholder alone." But this made us
reject 'constexpr decltype(auto)', which, after clarification from CWG,
should be valid. [dcl.type.auto.deduct]/4 is supposed to be a syntactic
constraint, not semantic, so it's OK that the constexpr marks the object
as const.
As a consequence, checking TYPE_QUALS in do_auto_deduction is too late,
and we have a FIXME there anyway. So in this patch I'm attempting to
detect 'const decltype(auto)' earlier. If I'm going to use TYPE_QUALS,
it needs to happen before we mark the object as const due to constexpr,
that is, before grokdeclarator's
/* A `constexpr' specifier used in an object declaration declares
the object as `const'. */
if (constexpr_p && innermost_code != cdk_function)
...
Constrained decltype(auto) was a little problem, hence the TYPENAME
check. But in a typename context you can't use decltype(auto) anyway,
I think.
Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk/11?
PR c++/102229
gcc/cp/ChangeLog:
* decl.c (check_decltype_auto): New.
(grokdeclarator): Call it.
* pt.c (do_auto_deduction): Don't check decltype(auto) here.
gcc/testsuite/ChangeLog:
* g++.dg/cpp1y/decltype-auto5.C: New test.
---
gcc/cp/decl.c | 58 ++++++++++++++-------
gcc/cp/pt.c | 13 -----
gcc/testsuite/g++.dg/cpp1y/decltype-auto5.C | 35 +++++++++++++
3 files changed, 74 insertions(+), 32 deletions(-)
create mode 100644 gcc/testsuite/g++.dg/cpp1y/decltype-auto5.C
diff --git a/gcc/cp/decl.c b/gcc/cp/decl.c
index 56f80775ca0..196eac287eb 100644
--- a/gcc/cp/decl.c
+++ b/gcc/cp/decl.c
@@ -11354,6 +11354,33 @@ name_unnamed_type (tree type, tree decl)
gcc_assert (!TYPE_UNNAMED_P (type));
}
+/* Check that decltype(auto) was well-formed: only plain decltype(auto)
+ is allowed. TYPE might contain a decltype(auto). Returns true if
+ there was a problem, false otherwise. */
+
+static bool
+check_decltype_auto (location_t loc, tree type)
+{
+ if (tree a = type_uses_auto (type))
+ {
+ if (AUTO_IS_DECLTYPE (a))
+ {
+ if (a != type)
+ {
+ error_at (loc, "%qT as type rather than plain "
+ "%<decltype(auto)%>", type);
+ return true;
+ }
+ else if (TYPE_QUALS (type) != TYPE_UNQUALIFIED)
+ {
+ error_at (loc, "%<decltype(auto)%> cannot be cv-qualified");
+ return true;
+ }
+ }
+ }
+ return false;
+}
+
/* Given declspecs and a declarator (abstract or otherwise), determine
the name and type of the object declared and construct a DECL node
for it.
@@ -12702,25 +12729,9 @@ grokdeclarator (const cp_declarator *declarator,
"allowed");
return error_mark_node;
}
- /* Only plain decltype(auto) is allowed. */
- if (tree a = type_uses_auto (type))
- {
- if (AUTO_IS_DECLTYPE (a))
- {
- if (a != type)
- {
- error_at (typespec_loc, "%qT as type rather than "
- "plain %<decltype(auto)%>", type);
- return error_mark_node;
- }
- else if (TYPE_QUALS (type) != TYPE_UNQUALIFIED)
- {
- error_at (typespec_loc, "%<decltype(auto)%> cannot be "
- "cv-qualified");
- return error_mark_node;
- }
- }
- }
+
+ if (check_decltype_auto (typespec_loc, type))
+ return error_mark_node;
if (ctype == NULL_TREE
&& decl_context == FIELD
@@ -13080,6 +13091,15 @@ grokdeclarator (const cp_declarator *declarator,
id_loc = declarator ? declarator->id_loc : input_location;
+ if (innermost_code != cdk_function
+ /* Don't check this if it can be the artifical decltype(auto)
+ we created when building a constraint in a compound-requirement:
+ that the type-constraint is plain is going to be checked in
+ cp_parser_compound_requirement. */
+ && decl_context != TYPENAME
+ && check_decltype_auto (id_loc, type))
+ return error_mark_node;
+
/* A `constexpr' specifier used in an object declaration declares
the object as `const'. */
if (constexpr_p && innermost_code != cdk_function)
diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index 9834baf34db..6d5da17b9d0 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -29912,19 +29912,6 @@ do_auto_deduction (tree type, tree init, tree
auto_node,
return error_mark_node;
targs = make_tree_vec (1);
TREE_VEC_ELT (targs, 0) = deduced;
- /* FIXME: These errors ought to be diagnosed at parse time. */
- if (type != auto_node)
- {
- if (complain & tf_error)
- error ("%qT as type rather than plain %<decltype(auto)%>", type);
- return error_mark_node;
- }
- else if (TYPE_QUALS (type) != TYPE_UNQUALIFIED)
- {
- if (complain & tf_error)
- error ("%<decltype(auto)%> cannot be cv-qualified");
- return error_mark_node;
- }
}
else
{
diff --git a/gcc/testsuite/g++.dg/cpp1y/decltype-auto5.C
b/gcc/testsuite/g++.dg/cpp1y/decltype-auto5.C
new file mode 100644
index 00000000000..01cc54fb71d
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1y/decltype-auto5.C
@@ -0,0 +1,35 @@
+// PR c++/102229
+// { dg-do compile { target c++14 } }
+
+struct S {
+ constexpr static decltype(auto) x = 42;
+ const constexpr static decltype(auto) y = 42; // { dg-error "cannot be
cv-qualified" }
+
+ constexpr decltype(auto) mfn1 () { return 0; }
+ const constexpr decltype(auto) mfn2 () { return 0; } // { dg-error "cannot
be cv-qualified" }
+};
+
+constexpr decltype(auto) i = 42;
+const constexpr decltype(auto) j = 42; // { dg-error "cannot be cv-qualified" }
+
+constexpr decltype(auto) fn() { return 42; }
+const decltype(auto) fn2() { return 42; } // { dg-error "cannot be
cv-qualified" }
+
+auto constexpr foo() -> const decltype(auto) // { dg-error "cannot be
cv-qualified" }
+{
+ return 0;
+}
+
+#if __cpp_concepts
+template<typename>
+concept C = true;
+
+constexpr C decltype(auto) x1 = 0;
+const constexpr C decltype(auto) x2 = 0; // { dg-error "cannot be
cv-qualified" "" { target c++20 } }
+
+constexpr C decltype(auto) fn3() { return 0; }
+const constexpr C decltype(auto) fn4() { return 0; } // { dg-error "cannot be
cv-qualified" "" { target c++20 } }
+#endif
+
+template<const decltype(auto) = 42> // { dg-error "cannot be cv-qualified" }
+void g ();
base-commit: 1e2eee7b29ed2afbc7edea6f3da7e6c8f70b1a4e
--
2.33.1
