[clang] [clang][modules] Allow module maps with textual headers to be non-affecting (PR #89441)

[Sam McCall via cfe-commits]

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@@ -1574,6 +1574,7 @@ bool HeaderSearch::ShouldEnterIncludeFile(Preprocessor &PP,
     }
   }
 
+  FileInfo.IsLocallyIncluded = true;
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sam-mccall wrote:

I'd consider placing this at the end of HandleHeaderIncludeOrImport rather than here:

- it looks like there are cases where this function returns true and we don't enter the file textually (or at least, it's not *obvious* that there are no such cases)
- having a load-bearing side-effect of a "should we do X" query seems unexpected and liable to break during refactoring or in edge cases

Concretely I don't see a case where this doesn't work though, up to you.

https://github.com/llvm/llvm-project/pull/89441