Relative patterns in .fantomasignore don't match any files

[amongonz]

Ignore patterns relative to the directory of .fantomasignore, such as vendored/*.fs or src/Generated.fs, don't match any files (unless the ignore file is at the root directory). A simple repro is adding the latter pattern to .fantomasignore and testing in an F# script or FSI session:

#r "nuget:Fantomas.Extras"
// Prints "IsIgnored: false"
Fantomas.Extras.IgnoreFile.isIgnoredFile "src/Generated.fs" |> printfn "IsIgnored: %b"

This is because IsIgnored is being given an absolute path, but this API interprets paths as relative to the root of the patterns, which is meant to be directory of .fantomasignore.

A simple fix would be calling Path.GetRelativePath(ignoreFileDirFullPath, fileFullPath), but for that Fantomas.Extras would have to target netstandard2.1, which is a breaking change. Alternatively, a base directory could be prepended to these patterns so they match absolute paths. That would ideally be a feature of MAB.DotIgnore, but it can be done before adding relative patterns to IgnoreList. I can create a PR once it's clear which is the best fix.

[nojaf]

Hello Adrián, thank you for raising this issue.
Feels related to markashleybell/MAB.DotIgnore#9 (comment).
And I'm also considering switching to https://github.com/goelhardik/ignore in the next major, see markashleybell/MAB.DotIgnore#24.

Short term I would accept a PR that prepends the base directory to relative patterns if you think this is achievable.

[knocte]

It seems this issue can be closed after PR#1920 has been merged.