diff options
author | Marek Polacek <polacek@redhat.com> | 2022-10-26 21:15:53 -0400 |
---|---|---|
committer | Marek Polacek <polacek@redhat.com> | 2022-10-28 13:40:41 -0400 |
commit | e583c86f49b9ef6991b25308a0ad60de9697f24a (patch) | |
tree | 30308ec5aaae1eea9944a8ad734a661c7ef209a3 | |
parent | 38a628f52cf0ff5db6708578248484d50a50b366 (diff) |
c++: -Wdangling-reference and system headers
I got this testcase:
auto f() -> std::optional<std::string>;
for (char c : f().value()) { }
which has a dangling reference: std::optional<T>::value returns
a reference to the contained value, but here it's the f() temporary.
We warn, which is great, but only with -Wsystem-headers, because
the function comes from a system header and warning_enabled_at used
in do_warn_dangling_reference checks diagnostic_report_warnings_p,
which in this case returned false so we didn't warn.
Fixed as below. I could also override dc_warn_system_headers so that
the warning is enabled in system headers always. With that, I found one
issue in libstdc++:
libstdc++-v3/include/bits/fs_path.h:1265:15: warning: possibly dangling reference to a temporary [-Wdangling-reference]
1265 | auto& __last = *--end();
| ^~~~~~
which looks like a true positive as well.
gcc/cp/ChangeLog:
* call.cc (maybe_warn_dangling_reference): Enable the warning in
system headers if the decl isn't in a system header.
gcc/testsuite/ChangeLog:
* g++.dg/warn/Wdangling-reference4.C: New test.
-rw-r--r-- | gcc/cp/call.cc | 7 | ||||
-rw-r--r-- | gcc/testsuite/g++.dg/warn/Wdangling-reference4.C | 14 |
2 files changed, 21 insertions, 0 deletions
diff --git a/gcc/cp/call.cc b/gcc/cp/call.cc index 951b9fd2a88..c7c7a122045 100644 --- a/gcc/cp/call.cc +++ b/gcc/cp/call.cc @@ -13539,6 +13539,13 @@ maybe_warn_dangling_reference (const_tree decl, tree init) return; if (!TYPE_REF_P (TREE_TYPE (decl))) return; + /* Don't suppress the diagnostic just because the call comes from + a system header. If the DECL is not in a system header, or if + -Wsystem-headers was provided, warn. */ + auto wsh + = make_temp_override (global_dc->dc_warn_system_headers, + (!in_system_header_at (DECL_SOURCE_LOCATION (decl)) + || global_dc->dc_warn_system_headers)); if (tree call = do_warn_dangling_reference (init)) { auto_diagnostic_group d; diff --git a/gcc/testsuite/g++.dg/warn/Wdangling-reference4.C b/gcc/testsuite/g++.dg/warn/Wdangling-reference4.C new file mode 100644 index 00000000000..aee7a29019b --- /dev/null +++ b/gcc/testsuite/g++.dg/warn/Wdangling-reference4.C @@ -0,0 +1,14 @@ +// { dg-do compile { target c++17 } } +// { dg-options "-Wdangling-reference" } +// Check that we warn here even without -Wsystem-headers. + +#include <optional> +#include <string> + +auto f() -> std::optional<std::string>; + +void +g () +{ + for (char c : f().value()) { (void) c; } // { dg-warning "dangling reference" } +} |