This hash is also used for the dependency scanning hash. In both cases, PCH contents may differ based on whether a certain module they depend on is found in a system or non-system search path. In dependency scanning, systemness should cause a full change of scanning context requiring a from-scratch scan.
Resolves rdar://150334077
The headers this test is relying on have some macos-specific dependency behavior. Restrict the test for now, to unblock testing on other platforms.
Resolves rdar://146771469
Checking each module dependency info if it is up-to-date with respect to when the cache contents were serialized in a prior scan.
- Add a timestamp field to the serialization format for the dependency scanner cache
- Add a flag "-validate-prior-dependency-scan-cache" which, when combined with "-load-dependency-scan-cache" will have the scanner prune dependencies from the deserialized cache which have inputs that are newer than the prior scan itself
With the above in-place, the scan otherwise proceeds as-is, getting cache hits for entries still valid since the prior scan.
