[all-commits] [llvm/llvm-project] b768a8: [clang][deps] Lazy dependency directives (#86347)

[Jan Svoboda via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: b768a8c1db85b9e84fd8b356570a3a8fbe37acf6
      https://github.com/llvm/llvm-project/commit/b768a8c1db85b9e84fd8b356570a3a8fbe37acf6
  Author: Jan Svoboda <jan_svoboda at apple.com>
  Date:   2024-03-22 (Fri, 22 Mar 2024)

  Changed paths:
    M clang/include/clang/Tooling/DependencyScanning/DependencyScanningFilesystem.h
    M clang/lib/Tooling/DependencyScanning/DependencyScanningFilesystem.cpp
    M clang/lib/Tooling/DependencyScanning/DependencyScanningWorker.cpp
    A clang/test/ClangScanDeps/modules-extension.c

  Log Message:
  -----------
  [clang][deps] Lazy dependency directives (#86347)

Since b4c83a13f664582015ea22924b9a0c6290d41f5b, `Preprocessor` and
`Lexer` are aware of the concept of scanning dependency directives. This
makes it possible to scan for them on-demand rather than eagerly on the
first filesystem operation (open, or even just stat).

This might improve performance, but is also necessary for the "PCH as
module" mode. Some precompiled header sources use the ".pch" file
extension, which means they were not getting scanned for dependency
directives. This was okay when the PCH was the main input file in a
separate scan step, because there we just lex the file in a
scanning-specific frontend action. But when such source gets treated as
a module implicitly loaded from a TU, it will get compiled as any other
module - with Sema - which will result in compilation errors. (See
attached test case.)

rdar://107663951



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