Description

nohlson

opened on Jun 26, 2024

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Bug report

Bug description:

Due to the addition of -Wimplicit-fallthrough as a BASEFLAG new warnings are generated.

This should be reverted until tooling is created to track these new warnings per #112301

Warnings can be found in builds https://buildbot.python.org/all/#/builders/721/builds/1465/steps/3/logs/warnings__143_ from #121030

CPython versions tested on:

CPython main branch

Operating systems tested on:

Linux

Linked PRs

• gh-121040: Remove fallthrough warnings compiler option #121041
• gh-121040: Use __attribute__((fallthrough)) #121044

Activity

1. nohlson

   added

   type-bugAn unexpected behavior, bug, or errorAn unexpected behavior, bug, or error

   on Jun 26, 2024
2. corona10

   added a commit that references this issue on Jun 26, 2024

   gh-121040: Remove fallthrough warnings compiler option (gh-121041)

   ef28f6d
3. sobolevn commented on Jun 26, 2024

   

   sobolevn

   on Jun 26, 2024

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   A potential fix could look something like:

   #if __has_attribute(__fallthrough__)
   #  define _Py_FALLTHROUGH __attribute__((__fallthrough__))
   #else
   #  define _Py_FALLTHROUGH do { } while (0)
   #endif
4. vstinner

   added 2 commits that reference this issue on Jun 26, 2024

   pythongh-121040: Use __attribute__((fallthrough))

   89ca8fd

   pythongh-121040: Use __attribute__((fallthrough))

   bb2eb56
5. vstinner commented on Jun 26, 2024

   

   vstinner

   on Jun 26, 2024

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   Previous issues:

   • Add -Wimplicit-fallthrough=0 to Makefile ? #75106
   • gcc 7 fallthrough warnings #75200
6. vstinner commented on Jun 26, 2024

   

   vstinner

   on Jun 26, 2024

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   A potential fix could look something like: (...)

   I wrote PR gh-121044 to fix these compiler warnings; the PR adds a new _Py_FALLTHROUGH macro.
7. corona10 commented on Jun 26, 2024

   

   corona10

   on Jun 26, 2024

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   A potential fix could look something like:

   It can not be the ultimate solution.

   • Should check MSVC is accept this macro. (or do nothing if the compiler is MSVC)
   • Even if we added the macro for our codebase, vendored libraries like libexpat should follow the new compiler rule.
8. vstinner commented on Jun 26, 2024

   

   vstinner

   on Jun 26, 2024

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   Should check MSVC is accept this macro. (or do nothing if the compiler is MSVC)

   Does MSC implement a flag like -Wimplicit-fallthrough? If not, I don't think that we should care about MSC in _Py_FALLTHROUGH macro.

   Even if we added the macro for our codebase, vendored libraries like libexpat should follow the new compiler rule.

   If you want to use this compiler flag, you can use system libraries, instead of building embedded copies of libexpat and libmpdecimal.
9. corona10 commented on Jun 26, 2024

   

   corona10

   on Jun 26, 2024

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   If you want to use this compiler flag, you can use system libraries, instead of building embedded copies of libexpat and libmpdecimal.

   IIUC, the original intention was to adopt that compiler flag as default, not optional.
10. corona10 commented on Jun 26, 2024

    

    corona10

    on Jun 26, 2024

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    Does MSC implement a flag like -Wimplicit-fallthrough? If not, I don't think that we should care about MSC in _Py_FALLTHROUGH macro.

    But it emits the compiler warning so we should provide dummy macro for the MSVC
    see: https://github.com/python/cpython/pull/121044/files#r1654967484
11. vstinner commented on Jun 26, 2024

    

    vstinner

    on Jun 26, 2024

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    But it emits the compiler warning so we should provide dummy macro for the MSVC
    see: https://github.com/python/cpython/pull/121044/files#r1654967484

    You misunderstood the warning. It was only about __has_attribute(). I fixed this issue.
12. vstinner

    added a commit that references this issue on Jun 27, 2024

    gh-121040: Use __attribute__((fallthrough)) (#121044)

    12af8ec
13. vstinner commented on Jun 27, 2024

    

    vstinner

    on Jun 27, 2024

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    Warnings were fixed by 12af8ec. I close the issue.
14. vstinner

    closed this as completedon Jun 27, 2024
15. mrahtz

    added 2 commits that reference this issue on Jun 30, 2024

    pythongh-121040: Remove fallthrough warnings compiler option (pythong…

    c8152ac

    pythongh-121040: Use __attribute__((fallthrough)) (python#121044)

    638d523
16. estyxx

    added 2 commits that reference this issue on Jul 17, 2024

    pythongh-121040: Remove fallthrough warnings compiler option (pythong…

    73a8f4b

    pythongh-121040: Use __attribute__((fallthrough)) (python#121044)

    f1286b8

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