record resolution for relative file name if file was found via absolu…

[vladima]

…te name. Fixes #2192.

The same file can be referenced using different relative names. For example:

 folder1
   |---folder2
   |      |---file1.ts
   |      |---folder3

if folder3 is current directory then file1.ts can be referenced as ../file1.ts or as ../../folder2/file1.ts. Both these names are correct however now we'll record resolutions for both relative and and absolute names only for the first requested file i.e. ../file1.ts. Subsequent request to find source file for ../../folder2/file1.ts will fail to find it for relative name but will succeed to do it for absolute name and this result will be returned without recording association 'relative name' -> 'resolved file'. This means that calling program.getSourceFile('../../folder2/file1.ts') will return undefined though clearly this file is in the program. Solution: when lookup fails for relative name but succeeds for absolute - record association for relative as well.

Also PR reduces nesting in findSourceFile and drops unnecessary calls to CompilerHost.getCannonicalFileName - FileMap will do this internally anyways so there is no need to do it several times

[DanielRosenwasser]

I recall we made some optimization to avoid recalculating dependencies. Could there be an issue in caching for language service scenarios? For instance, let's say you have files ./A.ts and ./B.ts. It doesn't really matter what's in B.ts, it just matters that A.ts incorrectly references it:

import "B";

Now you introduce node_modules/B.d.ts. Does the import of B suddenly work correctly?

[vladima]

@DanielRosenwasser no, it should be fine. We never directly interpret module name in import as file name. The whole process will look like:

• parse 'A.ts'
• try to resolve imports in 'A' to actual module files
• (assuming that current module target is CommonJS) "B" is not relative name so run node resolution process to find module named "B". If it cannot be found then resolution fails and internally we'll record this in internal map on the SourceFile. findSourceFile will be called only if resolution succeeded.

[mhegazy]

👍