[6.2 🍒][Dependency Scanning] Emit a detailed error diagnostic on Clang module variant discovery #81337
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…e variant discovery In expectation, this should never happen. Such a situation means that within the same scanning action, Clang Dependency Scanner has produced two different variants of the same module. This is not supposed to happen, but we are currently hunting down the rare cases where it does, seemingly due to differences in Clang Scanner direct by-name queries and transitive header lookup queries.
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We've seen multiple cases where builds complain about PCM being out of date. The root cause of these failures is mostly project configurations which take a lot of engineering time to track down. Having more detailed and explicit error messages like this helps us track down those issues more efficiently, thus I consider this to be a high value change to be cherry-picked. Additionally, this pure additive diagnostic logics are quite safe too.
| @@ -618,5 +618,15 @@ ERROR(ast_format_requires_dump_ast,none, | |||
| ERROR(unknown_dump_ast_format,none, | |||
| "unknown format '%0' requested with '-dump-ast-format'", (StringRef)) | |||
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| ERROR(dependency_scan_unexpected_variant, none, | |||
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Can we downgrade this from error to a warning? I suspect this would happen semi-frequently that a fatal error is probably an overkill.
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We should discuss more about the implication with @cyndyishida and other folks. Please hold off merging before that.
There is concern that this diagnostic may be breaking in some cases on its own.
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Thank you for downgrading to warning Artem! It's then safe enough to be merged for 6.2. |
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Cherry-pick of #81313
Explanation: In expectation, this should never happen. Such a situation means that within the same scanning action, Clang Dependency Scanner has produced two different variants of the same module. We are currently hunting down the rare cases where it does, seemingly due to differences in Clang Scanner direct by-name queries and transitive header lookup queries and potential other causes. The code-path that this change modifies is only possible to trigger in a case that would already guarantee a build failure down-the-line.
Scope: Rare cases where dependency scanning ends up in a situation where it "discovers" two variants of the same Clang module
Risk: Low, this change affects only a code-path that would lead to a downstream build failure.
Issue: rdar://149230376
Reviewed By: @beccadax
Original PR: [Dependency Scanning] Emit a detailed error diagnostic on Clang module variant discovery #81313