[Bug libstdc++/98605] New: clang-tidy error parsing <mutex> on libstdc++-v3

[Bug libstdc++/98605] New: clang-tidy error parsing <mutex> on libstdc++-v3

[mizvekov at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98605

            Bug ID: 98605
           Summary: clang-tidy error parsing <mutex> on libstdc++-v3
           Product: gcc
           Version: 10.2.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: mizvekov at gmail dot com
  Target Milestone: ---

clang-tidy errors parsing `#include <mutex>` when _GLIBCXX_HAVE_TLS is not
defined, with the following message:
```
include/c++/mutex:738:7: error: use of undeclared identifier '__once_callable';
did you mean '__callable'? [clang-diagnostic-error]
      __once_callable = nullptr;
      ^
include/c++/mutex:716:12: note: '__callable' declared here
      auto __callable = [&] {
           ^
include/c++/mutex:739:7: error: use of undeclared identifier '__once_call'
[clang-diagnostic-error]
      __once_call = nullptr;
      ^
```

This was caused by the following commit:

```
commit 018813c8994b7dceab1b7d999e9c09654a22ef50
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Fri Oct 13 12:56:07 2017 +0100

    PR libstdc++/82481 Suppress clang-tidy warnings

            PR libstdc++/82481
            * include/std/mutex (call_once): Suppress clang-tidy warnings about
            dangling references.

diff --git a/libstdc++-v3/include/std/mutex b/libstdc++-v3/include/std/mutex
index 8c692a88ffd..50420ee22d4 100644
--- a/libstdc++-v3/include/std/mutex
+++ b/libstdc++-v3/include/std/mutex
@@ -688,6 +688,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
         __set_once_functor_lock_ptr(0);
 #endif

+#ifdef __clang_analyzer__
+      // PR libstdc++/82481
+      __once_callable = nullptr;
+      __once_call = nullptr;
+#endif
+
       if (__e)
        __throw_system_error(__e);
     }
```

The problem is that __once_callable et al are only declared when
_GLIBCXX_HAVE_TLS is defined.

A simple patch like this would fix it:
```
--- a/libstdc++-v3/include/std/mutex
+++ b/libstdc++-v3/include/std/mutex
@@ -731,9 +731,7 @@
 #ifndef _GLIBCXX_HAVE_TLS
       if (__functor_lock)
         __set_once_functor_lock_ptr(0);
-#endif
-
-#ifdef __clang_analyzer__
+#elif defined(__clang_analyzer__)
       // PR libstdc++/82481
       __once_callable = nullptr;
       __once_call = nullptr;
```

[Bug libstdc++/98605] clang-tidy error parsing <mutex> on libstdc++-v3

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98605

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |ASSIGNED
           Assignee|unassigned at gcc dot gnu.org      |redi at gcc dot gnu.org
   Last reconfirmed|                            |2021-01-09
     Ever confirmed|0                           |1

[Bug libstdc++/98605] clang-tidy error parsing <mutex> on libstdc++-v3

[mizvekov at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98605

--- Comment #1 from Matheus Izvekov <mizvekov at gmail dot com> ---
By the way, FYII it is also possible to suppress clang-tidy specific
diagnostics on specific lines with a "comment pragma", like so (untested):

// NOLINT(bugprone-dangling-handle)
// NOLINTNEXTLINE(bugprone-dangling-handle)

This might be better than having the linter parse different code than the real
compiler, while avoiding these kinds of problems where its hard to test every
define combination.

[Bug libstdc++/98605] clang-tidy error parsing <mutex> on libstdc++-v3

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98605

--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Yes, that seems preferable, thanks.

[Bug libstdc++/98605] clang-tidy error parsing <mutex> on libstdc++-v3

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98605

--- Comment #3 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to Matheus Izvekov from comment #0)
> This was caused by the following commit:
> 
> ```
> commit 018813c8994b7dceab1b7d999e9c09654a22ef50

I can't identify that commit. The one in the GCC tree is:

Author:     Jonathan Wakely <jwakely@redhat.com>
AuthorDate: Fri Oct 13 13:39:24 2017

    PR libstdc++/82481 Suppress clang-tidy warnings

            PR libstdc++/82481
            * include/std/mutex (call_once): Suppress clang-tidy warnings about
            dangling references.

    From-SVN: r253724

[Bug libstdc++/98605] clang-tidy error parsing <mutex> on libstdc++-v3

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98605

--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Doh, I missed out the actual commit hash. It was:

commit d1e85aa999ab87009fa02a5261754fbaa69206f2

[Bug libstdc++/98605] [8/9/10 Regression] clang-tidy error parsing <mutex> on libstdc++-v3

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98605

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |8.5
      Known to work|                            |11.0, 7.2.0
      Known to fail|                            |10.2.0, 7.3.0, 8.4.0, 9.3.0
            Summary|clang-tidy error parsing    |[8/9/10 Regression]
                   |<mutex> on libstdc++-v3     |clang-tidy error parsing
                   |                            |<mutex> on libstdc++-v3

[Bug libstdc++/98605] [8/9/10 Regression] clang-tidy error parsing <mutex> on libstdc++-v3

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98605

--- Comment #5 from Jonathan Wakely <redi at gcc dot gnu.org> ---
I can't reproduce the original error reported in PR 82481 anyway. Maybe
clang-tidy got smarter (it doesn't show problems in system headers by default,
which helps).

Maybe we can just remove that code entirely.

[Bug libstdc++/98605] [8/9/10 Regression] clang-tidy error parsing <mutex> on libstdc++-v3

[mizvekov at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98605

--- Comment #6 from Matheus Izvekov <mizvekov at gmail dot com> ---
What clang-tidy version? From the date of the commit, it was probably no older
than 6, probably 4 or 5.
If that is too old and probably considered unsupported, I think that is fine.

But even if in the end it was a false positive, the warning seemed to me to be
of high quality, ie to some standard of coding practice, it would be advised to
document this somewhat subtle assumption. Not sure that applies to libstdc++
standards :)

But if you cannot reproduce the original warning anyway, then I guess it's
better to just remove it than make some change that can't even be tested.

[Bug libstdc++/98605] [8/9/10 Regression] clang-tidy error parsing <mutex> on libstdc++-v3

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98605

--- Comment #7 from Jonathan Wakely <redi at gcc dot gnu.org> ---
The original report said it was with 4.0.0

[Bug libstdc++/98605] [8/9/10 Regression] clang-tidy error parsing <mutex> on libstdc++-v3

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98605

--- Comment #8 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-10 branch has been updated by Jonathan Wakely
<redi@gcc.gnu.org>:

https://gcc.gnu.org/g:8d3636923a309074eb19240ebaa30c1a0801eaaf

commit r10-9267-g8d3636923a309074eb19240ebaa30c1a0801eaaf
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Wed Jan 13 11:03:58 2021 +0000

    libstdc++: Fix clang analyzer suppression [PR 98605]

    The fix for PR libstdc++/82481 should only have applied for targets
    where _GLIBCXX_HAVE_TLS is defined. Because it was also done for non-TLS
    targets, it isn't possible to use clang's analyzers on non-TLS targets
    if the code uses <mutex>. This fixes it by using a NOLINT comment on
    the relevant line instead of testing #ifdef __clang_analyzer__ and
    compiling different code when analyzing.

    I'm not actually able to reproduce the analyzer warning with the tools
    from Clang 10.0.1 so I'm not going to try to make the suppression more
    specific with NOLINTNEXTLINE(clang-analyzer-code.StackAddressEscape).

    libstdc++-v3/ChangeLog:

            PR libstdc++/98605
            * include/std/mutex (call_once): Use NOLINT to suppress clang
            analyzer warnings.

[Bug libstdc++/98605] [8/9/10 Regression] clang-tidy error parsing <mutex> on libstdc++-v3

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98605

--- Comment #9 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-9 branch has been updated by Jonathan Wakely
<redi@gcc.gnu.org>:

https://gcc.gnu.org/g:4aeae11db66c9bce0aadf447e6ff0776a97bfccf

commit r9-9180-g4aeae11db66c9bce0aadf447e6ff0776a97bfccf
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Wed Jan 13 11:03:58 2021 +0000

    libstdc++: Fix clang analyzer suppression [PR 98605]

    The fix for PR libstdc++/82481 should only have applied for targets
    where _GLIBCXX_HAVE_TLS is defined. Because it was also done for non-TLS
    targets, it isn't possible to use clang's analyzers on non-TLS targets
    if the code uses <mutex>. This fixes it by using a NOLINT comment on
    the relevant line instead of testing #ifdef __clang_analyzer__ and
    compiling different code when analyzing.

    I'm not actually able to reproduce the analyzer warning with the tools
    from Clang 10.0.1 so I'm not going to try to make the suppression more
    specific with NOLINTNEXTLINE(clang-analyzer-code.StackAddressEscape).

    libstdc++-v3/ChangeLog:

            PR libstdc++/98605
            * include/std/mutex (call_once): Use NOLINT to suppress clang
            analyzer warnings.

    (cherry picked from commit 8d3636923a309074eb19240ebaa30c1a0801eaaf)

[Bug libstdc++/98605] [8/9/10 Regression] clang-tidy error parsing <mutex> on libstdc++-v3

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98605

--- Comment #10 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-8 branch has been updated by Jonathan Wakely
<redi@gcc.gnu.org>:

https://gcc.gnu.org/g:283c218a4846075c549f0215d6883e577b26e845

commit r8-10726-g283c218a4846075c549f0215d6883e577b26e845
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Wed Jan 13 11:03:58 2021 +0000

    libstdc++: Fix clang analyzer suppression [PR 98605]

    The fix for PR libstdc++/82481 should only have applied for targets
    where _GLIBCXX_HAVE_TLS is defined. Because it was also done for non-TLS
    targets, it isn't possible to use clang's analyzers on non-TLS targets
    if the code uses <mutex>. This fixes it by using a NOLINT comment on
    the relevant line instead of testing #ifdef __clang_analyzer__ and
    compiling different code when analyzing.

    I'm not actually able to reproduce the analyzer warning with the tools
    from Clang 10.0.1 so I'm not going to try to make the suppression more
    specific with NOLINTNEXTLINE(clang-analyzer-code.StackAddressEscape).

    libstdc++-v3/ChangeLog:

            PR libstdc++/98605
            * include/std/mutex (call_once): Use NOLINT to suppress clang
            analyzer warnings.

    (cherry picked from commit 8d3636923a309074eb19240ebaa30c1a0801eaaf)

[Bug libstdc++/98605] [8/9/10 Regression] clang-tidy error parsing <mutex> on libstdc++-v3

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98605

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|---                         |FIXED

--- Comment #11 from Jonathan Wakely <redi at gcc dot gnu.org> ---
This should be fixed in all active branches now.

[Bug libstdc++/98605] [8/9/10 Regression] clang-tidy error parsing <mutex> on libstdc++-v3

[mizvekov at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98605

--- Comment #12 from Matheus Izvekov <mizvekov at gmail dot com> ---
Thank you!!!