Fix core file location in GetLinkable

[soulomoon]

Fix #4145
The error case is demonstrated in #4145 (comment)

1. Include ModLocation in the ModSummaryResult fingerprint.
2. Instead of getting the core file location from GetModSummary, get it from the result of GetModIface directly since that is the actual location the core file written to. While the GetModSummary contains the future core file location that would be written only if we would have made some change cause the rewrite. See Note [Avoiding bad interface files]

[wz1000]

Can you explain why the core file in the ModSummaryResult and HiFileResult are different? If one is getting updated and not the other then it seems like this is more of a dependency tracking/invalidation issue.

[soulomoon]

@wz1000, The cause of this different is that GetModSummary's fingerprint is irrelevant to the core file location. So some of its' reverse deps are being earlycutoff even core file location changed. Is this expected ?

It's not hard to change the fingerprint algorithm to reflect the core file location though.

haskell-language-server/ghcide/src/Development/IDE/Core/Compile.hs

Line 1017 in 3747ae5

computeFingerprint opts ModSummary{..} = do

[wz1000]

It's not hard to change the fingerprint algorithm to reflect the core file location though.

haskell-language-server/ghcide/src/Development/IDE/Core/Compile.hs

Line 1017 in 3747ae5

computeFingerprint opts ModSummary{..} = do

Yes I think the correct solution is to include the fingerprint of the entire ModLocation in computeFingerprint.

This patch is a good cleanup though, so perhaps you can apply it after testing that just changing computeFingerprint to take the ModLocation into account also fixes the bug.

[soulomoon]

Yes, local testing show that fingierprinting the ModLocation fix the .hi.core problem.