[PATCH] D139168: [C++20] [Modules] [ClangScanDeps] Enable to print make-style dependency file within P1689 format (4/4)

[Tom Honermann via Phabricator via cfe-commits]

tahonermann added a comment.

> Header units have even more need to be involved in the build graph than named units. ODR violations and cache invalidation problems await anyone just winging it on header units (at least that's the understanding I've gotten from SG15 meetings).

I think that latter claim applies equally to all module units. The ODR violation and cache invalidation concerns sometimes associated with header units occur in implicit module build systems in which a header unit might be built multiple times with different sets of options that result in an ODR violation. The same problem can occur with other kinds of module units if they are built multiple times with different options and then imported by distinct TUs that are then linked together. The general rule is, given a set of TUs that will be linked together, all imported module units should be built exactly one time.


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  https://reviews.llvm.org/D139168/new/

https://reviews.llvm.org/D139168