[Clangd] C++20 modules support ignores CompileFlags.Add/Remove compiling a module preamble

[petr-polezhaev]

When used with compile_commands.json clangd seem to ignore flag modifications from .clangd when (and only when) compiling module information, leading to module search issues

Given compile_commands.json:

[
    {
      "directory": "/path/to/example",
      "command": "/usr/bin/clang++ -std=c++23 -ffoobar test.cppm",
      "file": "test.cppm",
      "output": "build/test.cppm.o"
    },
    {
        "directory": "/path/to/example",
        "command": "/usr/bin/clang++ -std=c++23 -ffoobar main.cpp",
        "file": "main.cpp",
        "output": "build/main.cpp.o"
    }
  ]

.clangd:

CompileFlags:
    CompilationDatabase: "."
    Remove:
    - "-ffoobar"

test.cppm:

export module test;

export void test() {}

main.cpp:

import test;

int main() { return 0; }

Results in:

E[02:40:54.668] Scanning modules dependencies for /home/test/clangd_modules_test/test.cppm failed: error: unknown argument: '-ffoobar'

I[02:40:54.668] Built prerequisite modules for file /home/test/clangd_modules_test/test.cppm in 0.00 seconds
E[02:40:54.668] Scanning modules dependencies for /home/test/clangd_modules_test/main.cpp failed: error: unknown argument: '-ffoobar'

I[02:40:54.668] Built prerequisite modules for file /home/test/clangd_modules_test/main.cpp in 0.00 seconds

If I remove -ffoobar from compile_commands.json it works correctly

This breaks support for compiling with gcc (that requires -fmodule-ts and other arguments clang does not understand) and using clangd, while generating compile_commands.json with cmake. Using .clangd to remove unsupported options (and add other options needed for clang) works for the rest of the functionality but not for modules

[llvmbot]

@llvm/issue-subscribers-clang-modules

Author: Petr Polezhaev (petr-polezhaev)

When used with `compile_commands.json` clangd seem to ignore flag modifications from `.clangd` when (and only when) compiling module information, leading to module search issues

Given compile_commands.json:

[
    {
      "directory": "/path/to/example",
      "command": "/usr/bin/clang++ -std=c++23 -ffoobar test.cppm",
      "file": "test.cppm",
      "output": "build/test.cppm.o"
    },
    {
        "directory": "/path/to/example",
        "command": "/usr/bin/clang++ -std=c++23 -ffoobar main.cpp",
        "file": "main.cpp",
        "output": "build/main.cpp.o"
    }
  ]

.clangd:

CompileFlags:
    CompilationDatabase: "."
    Remove:
    - "-ffoobar"

test.cppm:

export module test;

export void test() {}

main.cpp:

import test;

int main() { return 0; }

Results in:

E[02:40:54.668] Scanning modules dependencies for /home/test/clangd_modules_test/test.cppm failed: error: unknown argument: '-ffoobar'

I[02:40:54.668] Built prerequisite modules for file /home/test/clangd_modules_test/test.cppm in 0.00 seconds
E[02:40:54.668] Scanning modules dependencies for /home/test/clangd_modules_test/main.cpp failed: error: unknown argument: '-ffoobar'

I[02:40:54.668] Built prerequisite modules for file /home/test/clangd_modules_test/main.cpp in 0.00 seconds

If I remove -ffoobar from compile_commands.json it works correctly

This breaks support for compiling with gcc (that requires -fmodule-ts and other arguments clang does not understand) and using clangd, while generating compile_commands.json with cmake. Using .clangd to remove unsupported options (and add other options needed for clang) works for the rest of the functionality but not for modules

[llvmbot]

@llvm/issue-subscribers-clangd

Author: Petr Polezhaev (petr-polezhaev)

When used with `compile_commands.json` clangd seem to ignore flag modifications from `.clangd` when (and only when) compiling module information, leading to module search issues

Given compile_commands.json:

[
    {
      "directory": "/path/to/example",
      "command": "/usr/bin/clang++ -std=c++23 -ffoobar test.cppm",
      "file": "test.cppm",
      "output": "build/test.cppm.o"
    },
    {
        "directory": "/path/to/example",
        "command": "/usr/bin/clang++ -std=c++23 -ffoobar main.cpp",
        "file": "main.cpp",
        "output": "build/main.cpp.o"
    }
  ]

.clangd:

CompileFlags:
    CompilationDatabase: "."
    Remove:
    - "-ffoobar"

test.cppm:

export module test;

export void test() {}

main.cpp:

import test;

int main() { return 0; }

Results in:

E[02:40:54.668] Scanning modules dependencies for /home/test/clangd_modules_test/test.cppm failed: error: unknown argument: '-ffoobar'

I[02:40:54.668] Built prerequisite modules for file /home/test/clangd_modules_test/test.cppm in 0.00 seconds
E[02:40:54.668] Scanning modules dependencies for /home/test/clangd_modules_test/main.cpp failed: error: unknown argument: '-ffoobar'

I[02:40:54.668] Built prerequisite modules for file /home/test/clangd_modules_test/main.cpp in 0.00 seconds

If I remove -ffoobar from compile_commands.json it works correctly

This breaks support for compiling with gcc (that requires -fmodule-ts and other arguments clang does not understand) and using clangd, while generating compile_commands.json with cmake. Using .clangd to remove unsupported options (and add other options needed for clang) works for the rest of the functionality but not for modules