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[clang][deps] Prevent unintended modifications of the original TU command-line

Authored by jansvoboda11 on Jun 14 2021, 3:24 AM.

Description

[clang][deps] Prevent unintended modifications of the original TU command-line

One of the goals of the dependency scanner is to generate command-lines that can be used to explicitly build modular dependencies of a translation unit. The only modifications to these command-lines should be for the purposes of explicit modular build.

However, the current version of dependency scanner leaks its implementation details into the command-lines.

The first problem is that the clang-scan-deps tool adjusts the original textual command-line (adding -Eonly -M -MT <target> -sys-header-deps -Wno-error -o /dev/null , removing --serialize-diagnostics) in order to set up the DependencyScanning library. This has been addressed in D103461, D104012, D104030, D104031, D104033. With these patches, the DependencyScanning library receives the unmodified CompilerInvocation, sets it up and uses it for the implicit modular build.

Finally, to prevent leaking the implementation details to the resulting command-lines, this patch generates them from the original unmodified CompilerInvocation rather than from the one that drives the implicit build.

Reviewed By: dexonsmith

Differential Revision: https://reviews.llvm.org/D104036