[PATCH] D155392: [clangd] add a config knob to disable modules

[Sam McCall via Phabricator via cfe-commits]

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We don't yet have any intentional modules support:
https://github.com/clangd/clangd/issues/1293

However if the user has modules-related flags in their CDB, modules will still
be enabled inside clang.

- for some configurations this works well enough, apparently. We should allow them to keep using this config if they wish, though unsupported.
- for other configurations this is crashy/buggy. We can't really control the behavior/stability, so long-term this should not be the default.
- there is no flag to disable modules if when using `-std=c++20`. Since clangd does not support modules, we should provide a mechanism.
- in future we're likely to explicitly add modules support. This will not be a simple passthrough of flags to clang, so we'll need another mode.

This patch adds a config option:

  CompileFlags:
    NaiveModules: false

For now, the default is true, and modules are internally enabled/disabled
according to compile flags. When set to false, we force Modules/CPlusPlusModules
lang opts off.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D155392

Files:
  clang-tools-extra/clangd/Compiler.cpp
  clang-tools-extra/clangd/Config.h
  clang-tools-extra/clangd/ConfigCompile.cpp
  clang-tools-extra/clangd/ConfigFragment.h
  clang-tools-extra/clangd/ConfigYAML.cpp
  clang-tools-extra/clangd/unittests/FindSymbolsTests.cpp
  clang-tools-extra/clangd/unittests/ModulesTests.cpp
  clang-tools-extra/clangd/unittests/SymbolCollectorTests.cpp

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