Hi!
cp_parser_range_for temporarily reverts IDENTIFIER_BINDING changes
to hide the decls from the structured bindings from lookup during
parsing of the expression after :
If there are 2 or more name independent decls, we undo IDENTIFIER_BINDING
for the same name multiple times, even when just one has been added
(with a TREE_LIST inside of it as decl).
The following patch fixes it by handling the _ name at most once, the
later loop will DTRT then and just reinstall the temporarily hidden
binding with the TREE_LIST in there.
Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
2025-02-06 Jakub Jelinek <ja...@redhat.com>
PR c++/115586
* parser.cc (cp_parser_range_for): For name independent decls in
structured bindings, only push the name/binding once per
structured binding.
* g++.dg/cpp26/name-independent-decl9.C: New test.
* g++.dg/cpp26/name-independent-decl10.C: New test.
--- gcc/cp/parser.cc.jj 2025-02-04 21:14:50.000000000 +0100
+++ gcc/cp/parser.cc 2025-02-06 11:01:49.018050841 +0100
@@ -14570,9 +14570,19 @@ cp_parser_range_for (cp_parser *parser,
decomp = &decomp_d;
decomp->count = tree_to_uhwi (TREE_OPERAND (v, 1)) + 1;
decomp->decl = d;
+ bool seen_name_independent_decl = false;
for (unsigned int i = 0; i < decomp->count;
i++, d = DECL_CHAIN (d))
{
+ if (name_independent_decl_p (d))
+ {
+ /* If there is more than one _ decl in
+ the structured binding, just push and move it
+ away once. */
+ if (seen_name_independent_decl)
+ continue;
+ seen_name_independent_decl = true;
+ }
tree name = DECL_NAME (d);
names.safe_push (name);
bindings.safe_push (IDENTIFIER_BINDING (name));
--- gcc/testsuite/g++.dg/cpp26/name-independent-decl9.C.jj 2025-02-06
11:09:15.450816690 +0100
+++ gcc/testsuite/g++.dg/cpp26/name-independent-decl9.C 2025-02-06
11:19:01.704625049 +0100
@@ -0,0 +1,49 @@
+// PR c++/115586
+// { dg-do compile { target c++11 } }
+// { dg-options "-Wunused-variable -Wunused-but-set-variable
-Wunused-parameter -Wshadow" }
+
+struct S { int a, b, c; };
+
+void
+foo ()
+{
+ S s[4] = {};
+ for (auto [_, _, a] : s) // { dg-warning "name-independent declarations
only available with" "" { target c++23_down } }
+ ++a; // { dg-warning "structured bindings only
available with" "" { target c++14_down } .-1 }
+ for (auto _ : s)
+ ++_.b;
+ for (auto [a, _, b] : s) // { dg-warning "structured bindings only
available with" "" { target c++14_down } }
+ ++a;
+ for (auto [_, _, a] : s) // { dg-warning "name-independent declarations
only available with" "" { target c++23_down } }
+ int _ = ++a; // { dg-warning "structured bindings only
available with" "" { target c++14_down } .-1 }
+ for (auto _ : s)
+ {
+ int _ = 2; // { dg-warning "name-independent declarations
only available with" "" { target c++23_down } }
+ }
+ for (auto [a, _, b] : s) // { dg-warning "structured bindings only
available with" "" { target c++14_down } }
+ int _ = ++b; // { dg-warning "name-independent declarations
only available with" "" { target c++23_down } }
+}
+
+void
+bar ()
+{
+ S s[4] = {};
+ auto [_, c, _] = s[0]; // { dg-warning "name-independent declarations
only available with" "" { target c++23_down } }
+ ++c; // { dg-warning "structured bindings only
available with" "" { target c++14_down } .-1 }
+ for (auto [a, _, _] : s) // { dg-warning "name-independent declarations
only available with" "" { target c++23_down } }
+ ++a; // { dg-warning "structured bindings only
available with" "" { target c++14_down } .-1 }
+ for (auto _ : s)
+ ++_.c;
+ for (auto [a, b, _] : s) // { dg-warning "structured bindings only
available with" "" { target c++14_down } }
+ ++b;
+ for (auto [a, _, _] : s) // { dg-warning "name-independent declarations
only available with" "" { target c++23_down } }
+ { // { dg-warning "structured bindings only
available with" "" { target c++14_down } .-1 }
+ int _ = ++a;
+ }
+ for (auto _ : s)
+ int _ = 5; // { dg-warning "name-independent declarations
only available with" "" { target c++23_down } }
+ for (auto [a, b, _] : s) // { dg-warning "structured bindings only
available with" "" { target c++14_down } }
+ {
+ int _ = a + b; // { dg-warning "name-independent declarations
only available with" "" { target c++23_down } }
+ }
+}
--- gcc/testsuite/g++.dg/cpp26/name-independent-decl10.C.jj 2025-02-06
11:23:38.787751260 +0100
+++ gcc/testsuite/g++.dg/cpp26/name-independent-decl10.C 2025-02-06
11:29:34.043784569 +0100
@@ -0,0 +1,63 @@
+// PR c++/115586
+// { dg-do compile { target c++11 } }
+// { dg-options "" }
+
+struct S { int a, b, c; };
+
+void
+foo ()
+{
+ S s[4] = {};
+ for (auto [_, _, a] : s) // { dg-warning "name-independent declarations
only available with" "" { target c++23_down } }
+ ++_; // { dg-warning "structured bindings only
available with" "" { target c++14_down } .-1 }
+ // { dg-error "reference to '_' is ambiguous"
"" { target *-*-* } .-1 }
+ for (auto _ : s)
+ ++_.b;
+ for (auto [a, _, b] : s) // { dg-warning "structured bindings only
available with" "" { target c++14_down } }
+ ++_;
+ for (auto [_, _, a] : s) // { dg-warning "name-independent declarations
only available with" "" { target c++23_down } }
+ { // { dg-warning "structured bindings only
available with" "" { target c++14_down } .-1 }
+ ++_; // { dg-error "reference to '_' is ambiguous" }
+ }
+ for (auto _ : s)
+ {
+ ++_.b;
+ int _ = 2; // { dg-warning "name-independent declarations
only available with" "" { target c++23_down } }
+ ++_; // { dg-error "reference to '_' is ambiguous" }
+ }
+ for (auto [a, _, b] : s) // { dg-warning "structured bindings only
available with" "" { target c++14_down } }
+ {
+ ++_;
+ int _ = ++b; // { dg-warning "name-independent declarations
only available with" "" { target c++23_down } }
+ ++_; // { dg-error "reference to '_' is ambiguous" }
+ }
+}
+
+void
+bar ()
+{
+ S s[4] = {};
+ auto [_, c, _] = s[0]; // { dg-warning "name-independent declarations
only available with" "" { target c++23_down } }
+ ++_; // { dg-warning "structured bindings only
available with" "" { target c++14_down } .-1 }
+ // { dg-error "reference to '_' is ambiguous"
"" { target *-*-* } .-1 }
+ for (auto [a, _, _] : s) // { dg-warning "name-independent declarations
only available with" "" { target c++23_down } }
+ ++_; // { dg-warning "structured bindings only
available with" "" { target c++14_down } .-1 }
+ // { dg-error "reference to '_' is ambiguous"
"" { target *-*-* } .-1 }
+ for (auto _ : s)
+ ++_.c;
+ for (auto [a, b, _] : s) // { dg-warning "structured bindings only
available with" "" { target c++14_down } }
+ ++_;
+ for (auto [a, _, _] : s) // { dg-warning "name-independent declarations
only available with" "" { target c++23_down } }
+ { // { dg-warning "structured bindings only
available with" "" { target c++14_down } .-1 }
+ ++_; // { dg-error "reference to '_' is ambiguous" }
+ ++a;
+ }
+ for (auto _ : s)
+ int _ = 5; // { dg-warning "name-independent declarations
only available with" "" { target c++23_down } }
+ for (auto [a, b, _] : s) // { dg-warning "structured bindings only
available with" "" { target c++14_down } }
+ {
+ ++_;
+ int _ = a + b; // { dg-warning "name-independent declarations
only available with" "" { target c++23_down } }
+ ++_; // { dg-error "reference to '_' is ambiguous" }
+ }
+}
Jakub
