The code for -Wmismatched-tags tests warn_mismatched_tags and when
it's non-zero assumes that calls to warning_at() necessarily succeed,
proceeding to call inform() to unconditionally issue informational
notes. This assumption is wrong when -Wmismatched-tags is enabled
(and warn_mismatched_tags is nonzero) but the instance of the warning
is for code in a system header and -Wsystem-headers is disabled. In
that case, the warning is suppressed but the notes are still printed.
The attached near-trivial change makes the calls to inform() conditional
on the result from warning_at().
I think a more robust solution than testing global variables like
warn_mismatched_tags is to introduce a functional API to query
the result of a warning_at() call without actually issuing a warning.
The patch doesn't do that but I have a follow-up enhancement to do
just that.
Martin
Avoid printing informational notes when -Wmismatched-tags is suppressed in system headers.
Related:
PR c++/96063 - mismatched-tags warnings in stdlib headers
gcc/cp/ChangeLog:
PR c++/96063
* parser.c (class_decl_loc_t::diag_mismatched_tags): Print notes only
if warning_at returns nonzero.
gcc/testsuite/ChangeLog:
PR c++/96063
* g++.dg/warn/Wmismatched-tags-7.C: New test.
* g++.dg/warn/Wmismatched-tags-8.C: New test.
diff --git a/gcc/cp/parser.c b/gcc/cp/parser.c
index 6e7637c6016..e58d8eb298c 100644
--- a/gcc/cp/parser.c
+++ b/gcc/cp/parser.c
@@ -31443,25 +31443,26 @@ class_decl_loc_t::diag_mismatched_tags (tree type_decl)
/* Issue a warning for the first mismatched declaration.
Avoid using "%#qT" since the class-key for the same type will
be the same regardless of which one was used in the declaraion. */
- warning_at (loc, OPT_Wmismatched_tags,
- "%qT declared with a mismatched class-key %qs",
- type_decl, xmatchkstr);
-
- /* Suggest how to avoid the warning for each instance since
- the guidance may be different depending on context. */
- inform (loc,
- (key_redundant_p
- ? G_("remove the class-key or replace it with %qs")
- : G_("replace the class-key with %qs")),
- xpectkstr);
-
- /* Also point to the first declaration or definition that guided
- the decision to issue the warning above. */
- inform (cdlguide->location (idxguide),
- (def_p
- ? G_("%qT defined as %qs here")
- : G_("%qT first declared as %qs here")),
- type_decl, xpectkstr);
+ if (warning_at (loc, OPT_Wmismatched_tags,
+ "%qT declared with a mismatched class-key %qs",
+ type_decl, xmatchkstr))
+ {
+ /* Suggest how to avoid the warning for each instance since
+ the guidance may be different depending on context. */
+ inform (loc,
+ (key_redundant_p
+ ? G_("remove the class-key or replace it with %qs")
+ : G_("replace the class-key with %qs")),
+ xpectkstr);
+
+ /* Also point to the first declaration or definition that guided
+ the decision to issue the warning above. */
+ inform (cdlguide->location (idxguide),
+ (def_p
+ ? G_("%qT defined as %qs here")
+ : G_("%qT first declared as %qs here")),
+ type_decl, xpectkstr);
+ }
/* Issue warnings for the remaining inconsistent declarations. */
for (unsigned i = idx + 1; i != ndecls; ++i)
@@ -31476,16 +31477,16 @@ class_decl_loc_t::diag_mismatched_tags (tree type_decl)
key_redundant_p = key_redundant (i);
/* Set the function declaration to print in diagnostic context. */
current_function_decl = function (i);
- warning_at (loc, OPT_Wmismatched_tags,
- "%qT declared with a mismatched class-key %qs",
- type_decl, xmatchkstr);
- /* Suggest how to avoid the warning for each instance since
- the guidance may be different depending on context. */
- inform (loc,
- (key_redundant_p
- ? G_("remove the class-key or replace it with %qs")
- : G_("replace the class-key with %qs")),
- xpectkstr);
+ if (warning_at (loc, OPT_Wmismatched_tags,
+ "%qT declared with a mismatched class-key %qs",
+ type_decl, xmatchkstr))
+ /* Suggest how to avoid the warning for each instance since
+ the guidance may be different depending on context. */
+ inform (loc,
+ (key_redundant_p
+ ? G_("remove the class-key or replace it with %qs")
+ : G_("replace the class-key with %qs")),
+ xpectkstr);
}
/* Restore the current function in case it was replaced above. */
diff --git a/gcc/testsuite/g++.dg/warn/Wmismatched-tags-7.C b/gcc/testsuite/g++.dg/warn/Wmismatched-tags-7.C
new file mode 100644
index 00000000000..3180c22c054
--- /dev/null
+++ b/gcc/testsuite/g++.dg/warn/Wmismatched-tags-7.C
@@ -0,0 +1,13 @@
+/* Verify that -Wmismatched-tags doesn't print stray notes for warnings
+ disabled in system headers.
+ { dg-do "compile" }
+ { dg-options "-Wmismatched-tags" } */
+
+# 6 "Wmismatched-tags-7.C" 1
+# 1 "system-header.h" 1 3 4
+# 9 "system-header.h" 3 4
+class A; // { dg-bogus "first declared" }
+struct A; // { dg-bogus "replace" }
+# 12 "Wmismatched-tags-7.C" 2
+class B; // { dg-message "first declared" }
+struct B; // { dg-warning "\\\[-Wmismatched-tags" }
diff --git a/gcc/testsuite/g++.dg/warn/Wmismatched-tags-8.C b/gcc/testsuite/g++.dg/warn/Wmismatched-tags-8.C
new file mode 100644
index 00000000000..0ebca3db90f
--- /dev/null
+++ b/gcc/testsuite/g++.dg/warn/Wmismatched-tags-8.C
@@ -0,0 +1,22 @@
+/* Verify that #pragma GCC diagnostic works for -Wmismatched-tags.
+ { dg-do "compile" }
+ { dg-options "-Wmismatched-tags" } */
+
+#pragma GCC diagnostic push
+#pragma GCC diagnostic error "-Wmismatched-tags"
+class A; // { dg-message "first declared"
+struct A; // { dg-error "\\\[-Werror=mismatched-tags" }
+
+#pragma GCC diagnostic ignored "-Wmismatched-tags"
+class B; // { dg-bogus "first declared" }
+struct B;
+
+#pragma GCC diagnostic warning "-Wmismatched-tags"
+class C; // { dg-message "first declared"
+struct C; // { dg-warning "\\\[-Wmismatched-tags" }
+#pragma GCC diagnostic pop
+
+class D; // { dg-message "first declared"
+struct D; // { dg-warning "\\\[-Wmismatched-tags" }
+
+// { dg-prune-output "some warnings being treated as errors" }
