PR 93804 points out that issuing -Wredundant-tags for declarations
in C headers included in C++ isn't helpful because the tags cannot
be removed without breaking C programs that depend on the headers.
Attached is a patch that avoids the warning in these cases tested
on x86_64-linux. While strictly not a regression (and even though
I initially considered it a GCC 11 enhancement), since most C++
code includes some C headers, without the patch the warning would
likely cause too much noise to be widely useful.
Martin
PR c++/93804 - exempt extern C headers from -Wredundant-tags
gcc/cp/ChangeLog:
PR c++/93804
* parser.c (cp_parser_check_class_key): Avoid issuing -Wredundant-tags
in shared C/C++ code in headers.
gcc/testsuite/ChangeLog:
PR c++/93804
* g++.dg/warn/Wredundant-tags-4.C: New test.
* g++.dg/warn/Wredundant-tags-5.C: New test.
* g++.dg/warn/Wredundant-tags-5.h: New test.
diff --git a/gcc/cp/parser.c b/gcc/cp/parser.c
index e8a536ae22f..2c6f5522bf3 100644
--- a/gcc/cp/parser.c
+++ b/gcc/cp/parser.c
@@ -30999,15 +30999,32 @@ cp_parser_check_class_key (cp_parser *parser, location_t key_loc,
neither definitions of it nor declarations, and for which name
lookup returns just the type itself. */
bool key_redundant = !def_p && !decl_p && decl == type_decl;
+
+ if (key_redundant
+ && class_key != class_type
+ && current_lang_name != lang_name_cplusplus
+ && current_namespace == global_namespace)
+ {
+ /* Avoid issuing the diagnostic for apparently redundant struct
+ and union class-keys in shared C/C++ code in files (such as
+ headers) included in the main source file. */
+ const line_map_ordinary *map = NULL;
+ linemap_resolve_location (line_table, key_loc,
+ LRK_MACRO_DEFINITION_LOCATION,
+ &map);
+ if (!MAIN_FILE_P (map))
+ key_redundant = false;
+ }
+
if (key_redundant)
{
gcc_rich_location richloc (key_loc);
richloc.add_fixit_remove (key_loc);
warning_at (&richloc, OPT_Wredundant_tags,
- "redundant class-key %qs in reference to %q#T",
- class_key == union_type ? "union"
- : class_key == record_type ? "struct" : "class",
- type);
+ "redundant class-key %qs in reference to %q#T",
+ class_key == union_type ? "union"
+ : class_key == record_type ? "struct" : "class",
+ type);
}
if (seen_as_union || !warn_mismatched_tags)
diff --git a/gcc/testsuite/g++.dg/warn/Wredundant-tags-4.C b/gcc/testsuite/g++.dg/warn/Wredundant-tags-4.C
new file mode 100644
index 00000000000..1a5833e6994
--- /dev/null
+++ b/gcc/testsuite/g++.dg/warn/Wredundant-tags-4.C
@@ -0,0 +1,92 @@
+/* PR c++/93804 - exempt extern "C" headers from -Wredundant-tags
+ Verify that -Wredundant-tags is not issued for redundant class-key
+ in extern "C" references in a header file.
+ { dg-do compile }
+ { dg-options "-Wredundant-tags" } */
+
+# 1 "Wredundant-tags-4.C"
+# 1 "Wredundant-tags-4.h" 1
+extern "C" {
+
+class C1 { };
+struct S1 { };
+union U1 { };
+
+# line 16
+ /* The warning should be issued for the class-key class even in
+ an extern "C" block. */
+ void f0 (class C1); // { dg-warning "\\\[-Wredundant-tags" }
+ void f1 (struct S1); // { dg-bogus "\\\[-Wredundant-tags" }
+ void f2 (union U1); // { dg-bogus "\\\[-Wredundant-tags" }
+
+ inline int
+ finline1 (class C1) // { dg-warning "\\\[-Wredundant-tags" }
+ { return sizeof (class C1); } // { dg-warning "\\\[-Wredundant-tags" }
+
+ inline int
+ finline2 (struct S1) // { dg-bogus "\\\[-Wredundant-tags" }
+ { return sizeof (struct S1); }
+
+ inline int
+ finline3 (union U1) // { dg-bogus "\\\[-Wredundant-tags" }
+ { return sizeof (union U1); }
+
+ extern class C1 c1; // { dg-warning "\\\[-Wredundant-tags" }
+ extern struct S1 s1; // { dg-bogus "\\\[-Wredundant-tags" }
+ extern union U1 u1; // { dg-bogus "\\\[-Wredundant-tags" }
+
+ namespace N1 {
+ /* Verify that -Wredundant-tags is issued in a namespace enclosed
+ in an extern "C" block. (Such code cannot be shared with C.) */
+ extern class C1 n1c1; // { dg-warning "\\\[-Wredundant-tags" }
+ extern struct S1 n1s1; // { dg-warning "\\\[-Wredundant-tags" }
+ extern union U1 n1u1; // { dg-warning "\\\[-Wredundant-tags" }
+ }
+}
+
+
+extern "C++" {
+
+class C2 { };
+struct S2 { };
+union U2 { };
+
+ void f3 (class C2); // { dg-warning "\\\[-Wredundant-tags" }
+ void f4 (struct S2); // { dg-warning "\\\[-Wredundant-tags" }
+ void f5 (union U2); // { dg-warning "\\\[-Wredundant-tags" }
+
+ extern class C2 c2; // { dg-warning "\\\[-Wredundant-tags" }
+ extern struct S2 s2; // { dg-warning "\\\[-Wredundant-tags" }
+ extern union U2 u2; // { dg-warning "\\\[-Wredundant-tags" }
+}
+
+
+namespace N {
+
+class C3 { };
+struct S3 { };
+union U3 { };
+
+void f6 (class C3); // { dg-warning "\\\[-Wredundant-tags" }
+void f7 (struct S3); // { dg-warning "\\\[-Wredundant-tags" }
+void f8 (union U3); // { dg-warning "\\\[-Wredundant-tags" }
+
+extern class C3 c3; // { dg-warning "\\\[-Wredundant-tags" }
+extern struct S3 s3; // { dg-warning "\\\[-Wredundant-tags" }
+extern union U3 u3; // { dg-warning "\\\[-Wredundant-tags" }
+
+extern "C" {
+
+ /* Verify that -Wredundant-tags is issued in an extern "C" block
+ enclosed within a namespace. (Such code cannot be shared with
+ C.) */
+ class C4 { };
+ struct S4 { };
+ union U4 { };
+
+ extern class C4 c4; // { dg-warning "\\\[-Wredundant-tags" }
+ extern struct S4 s4; // { dg-warning "\\\[-Wredundant-tags" }
+ extern union U4 u4; // { dg-warning "\\\[-Wredundant-tags" }
+}
+
+} // namespace N
diff --git a/gcc/testsuite/g++.dg/warn/Wredundant-tags-5.C b/gcc/testsuite/g++.dg/warn/Wredundant-tags-5.C
new file mode 100644
index 00000000000..9bb5cc4e1b5
--- /dev/null
+++ b/gcc/testsuite/g++.dg/warn/Wredundant-tags-5.C
@@ -0,0 +1,49 @@
+// PR c++/93804 - exempt extern "C" headers from -Wredundant-tags
+// Verify that -Wredundant-tags is issued even for redundant class-key
+// in references in the main source file to extern "C" classes defined
+// in headers.
+// { dg-do compile }
+// { dg-options "-Wredundant-tags" }
+
+#include "Wredundant-tags-5.h"
+
+extern "C" {
+
+ void f0 (class C1) // { dg-warning "\\\[-Wredundant-tags" }
+ {
+ }
+
+ void f1 (struct S1) // { dg-warning "\\\[-Wredundant-tags" }
+ {
+ }
+
+ void f2 (union U1) // { dg-warning "\\\[-Wredundant-tags" }
+ {
+ }
+
+}
+
+void f3 (class C2) // { dg-warning "\\\[-Wredundant-tags" }
+{
+}
+
+void f4 (struct S2) // { dg-warning "\\\[-Wredundant-tags" }
+{
+}
+
+void f5 (union U2) // { dg-warning "\\\[-Wredundant-tags" }
+{
+}
+
+
+void f6 (class C3) // { dg-warning "\\\[-Wredundant-tags" }
+{
+}
+
+void f7 (struct S3) // { dg-warning "\\\[-Wredundant-tags" }
+{
+}
+
+void f8 (union U3) // { dg-warning "\\\[-Wredundant-tags" }
+{
+}
diff --git a/gcc/testsuite/g++.dg/warn/Wredundant-tags-5.h b/gcc/testsuite/g++.dg/warn/Wredundant-tags-5.h
new file mode 100644
index 00000000000..c9c2ec278c8
--- /dev/null
+++ b/gcc/testsuite/g++.dg/warn/Wredundant-tags-5.h
@@ -0,0 +1,58 @@
+#ifndef WREDUNDANT_TAGS_H
+#define WREDUNDANT_TAGS_H
+
+extern "C" {
+
+class C1 { };
+struct S1 { };
+union U1 { };
+
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wredundant-tags"
+ void f0 (class C1); // -Wredundant-tags
+#pragma GCC diagnostic pop
+
+ void f1 (struct S1);
+ void f2 (union U1);
+
+ void f0 (C1);
+ void f1 (S1);
+ void f2 (U1);
+}
+
+
+extern "C++" {
+
+class C2 { };
+struct S2 { };
+union U2 { };
+
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wredundant-tags"
+ void f3 (class C2); // -Wredundant-tags
+ void f4 (struct S2); // -Wredundant-tags
+ void f5 (union U2); // -Wredundant-tags
+#pragma GCC diagnostic pop
+
+ void f3 (C2);
+ void f4 (S2);
+ void f5 (U2);
+}
+
+
+class C3 { };
+struct S3 { };
+union U3 { };
+
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wredundant-tags"
+ void f6 (class C3); // -Wredundant-tags
+ void f7 (struct S3); // -Wredundant-tags
+ void f8 (union U3); // -Wredundant-tags
+#pragma GCC diagnostic pop
+
+ void f6 (C3);
+ void f7 (S3);
+ void f8 (U3);
+
+#endif // WREDUNDANT_TAGS_H
