A result type of __builtin_choose_expr that returns a pointer to a function is not correctly inferred in clang mode

[mame]

Bug type: Language Service

Describe the bug

• OS and Version: Windows 11
• VS Code Version: 1.67.2
• C/C++ Extension Version: 1.9.8
• Other extensions you installed: Nothing
• If using SSH remote, specify OS of remote machine: Ubuntu on WSL
• When __builtin_choose_expr returns a pointer to a function, the result type seems not to be inferred correctly.

Steps to reproduce

1. Save the code sample as a file and open it in VSCode.
2. You will see an error expression preceding parentheses of apparent call must have (pointer-to-) function type

Expected behavior

No error is shown.

Code sample and logs

• Code sample

int foo(void) {
    puts("foo");
}

int bar(void) {
    puts("bar");
}

int main(void) {
    __builtin_choose_expr(1, foo, bar)();
}

Screenshots

NOTE: Screenshot is incorrect and missing an `_`.

Additional context

This idiom is heavily used in the source code of the programming language Ruby.

https://github.com/ruby/ruby/blob/2556e15d7520913119175c8166b1f9d17eb33415/include/ruby/internal/anyargs.h#L287

RBIMPL_ANYARGS_DISPATCH_rb_define_method((arity), (func)) returns a pointer to a function by using __builtin_choose_expr, and then the function is invoked.

[sean-mcmanus]

The bug doesn't repro when the missing _ is added -- are you still reproing this with __builtin_choose_expr? If so, can you give the exact compiler and cStandard setting that is being used for the repro and/or output of C/C++: Log Diagnostics?

[mame]

Thank you for your reply. Sorry, I seem to have lost the underscore when taking the screenshot. The issue still reproduces even with __builtin_choose_expr as follows.

The example project has no c_cpp_properties.json. I created the file as follows, and the issue is still reproduced.

{
    "configurations": [
        {
            "name": "Linux",
            "includePath": [
                "${workspaceFolder}/**"
            ],
            "defines": [],
            "compilerPath": "/usr/bin/clang",
            "cStandard": "c17",
            "cppStandard": "c++14",
            "intelliSenseMode": "linux-clang-x64"
        }
    ],
    "version": 4
}

Here is the output of C/C++: Log diagnostics

-------- Diagnostics - 6/1/2022, 11:15:36 AM
Version: 1.9.8
Current Configuration:
{
    "name": "Linux",
    "includePath": [
        "${workspaceFolder}/**"
    ],
    "defines": [],
    "compilerPath": "/usr/bin/clang",
    "cStandard": "c17",
    "cppStandard": "c++14",
    "intelliSenseMode": "linux-clang-x64",
    "compilerPathIsExplicit": true,
    "cStandardIsExplicit": true,
    "cppStandardIsExplicit": true,
    "intelliSenseModeIsExplicit": true,
    "compilerArgs": [],
    "mergeConfigurations": false,
    "browse": {
        "path": [
            "${workspaceFolder}/**"
        ],
        "limitSymbolsToIncludedHeaders": true
    }
}
Translation Unit Mappings:
[ /home/mame/work/ruby/t.c ]:
    /home/mame/work/ruby/t.c
Translation Unit Configurations:
[ /home/mame/work/ruby/t.c ]:
    Process ID: 417522
    Memory Usage: 11 MB
    Compiler Path: /usr/bin/clang
    Includes:
        /usr/lib/llvm-14/lib/clang/14.0.0/include
        /usr/local/include
        /usr/include/x86_64-linux-gnu
        /usr/include
    Standard Version: c17
    IntelliSense Mode: linux-clang-x64
    Other Flags:
        --clang
        --clang_version=140000
Total Memory Usage: 11 MB

------- Workspace parsing diagnostics -------
Number of files discovered (not excluded): 27641
Number of files parsed: 1

FYI: This is a screenshot of the issue with a working real-world application (Ruby)

https://github.com/ruby/ruby/blob/936e54063d4de0e44925e9139cb4d25cce27c187/array.c#L8746-L8779

rb_define_method is a macro, and the expanded code uses __builtin_choose_expr that returns a function pointer.

[sean-mcmanus]

This is the "same" issue as #8294, which got fixed for gcc mode but not clang mode.

[mame]

Thank you! I confirmed the errors dissapper if I change the compilerPath to "/usr/bin/gcc" in c_cpp_properties.json.

[sean-mcmanus]

This is fixed in 1.13.4 (pre-release): https://github.com/microsoft/vscode-cpptools/releases/tag/v1.13.4, although there's a related issue at #10168 that won't be fixed till 1.14.0.