Generate FileTarget for all possible targetLocations

[fendor]

If a target file has multiple possible locations, then we
assume they are all separate file targets.
This happens with '.hs-boot' files if they are in the root directory of the project.
GHC reports options such as '-i. A' as 'TargetFile A.hs' instead of 'TargetModule A'.
In 'fromTargetId', we dutifully look for '.hs-boot' files and add them to the
targetLocations of the TargetDetails. Then we add everything to the 'knownTargetsVar'.
However, when we look for a 'Foo.hs-boot' file in 'FindImports.hs', we look for either

• TargetFile Foo.hs-boot
• TargetModule Foo

If we don't generate a TargetFile for each potential location, we will only have
'TargetFile Foo.hs' in the 'knownTargetsVar', thus not find 'TargetFile Foo.hs-boot'
and also not find 'TargetModule Foo'.

It took a while, but this fixes #3794

[michaelpj]

Not sure I entirely understand, but seems plausible!

[fendor]

Test failures seem genuine :(

[wz1000]

Patch seems fine to me. Did you check locally to see why tests are failing?

[fendor]

Not yet, but will look into it!

[fendor]

The existence check seems to be removing valid file targets. I.e., there are many file targets that don't exist on disk. Probably related to the VFS? I am confused why it works with Module Targets in that case, since we always filter those.

[wz1000]

The existence check seems to be removing valid file targets. I.e., there are many file targets that don't exist on disk. Probably related to the VFS? I am confused why it works with Module Targets in that case, since we always filter those.

Many files from the testsuite only exist in the VFS, and those files are always FileTargets. I guess we should also check for existence in the VFS.

[wz1000]

We could also ensure that explicit file targets aren't filtered out.

[fendor]

We could also ensure that explicit file targets aren't filtered out.

What are explicit file targets?
For now, I've just decided that all file target locations are valid FileTargets.

[wz1000]

For now, I've just decided that all file target locations are valid FileTargets.

This is incorrect. We might end up trying to typecheck non-existent hs-boot files, or files in the wrong include directory

What are explicit file targets?

The FilePath argument to TargetFile :: FilePath -> Target is the explicit target. The [FilePath] in the targetLocations still needs to be filtered. We just need to ensure that the explicit target is included in the final result:

case targetTarget of
  TargetFile f -> do
    found <- filterM (IO.doesFileExist . fromNormalizedFilePath) targetLocations
    return [(targetTarget, nubOrd (f:found))]

[fendor]

Ah, I see!
Ok, the code presented is still not correct with respect to files that only exist in the VFS, right?

[wz1000]

No, but the problematic situation will only be when a file is listed as a Target but not saved to disk, i.e. the user has edited the cabal file to include the module, but has not saved the module yet.

[fendor]

@wz1000 Looks good now?