x/tools/gopls: directoryFilters are mishandled when descending the workspace root to find a go.mod file

[wtlangford]

What did you do?

Configured gopls in vscode as follows:

"gopls": {
  "build.directoryFilters": [
    "-some/dir",
    "+some/dir/moduleroot"
  ]
}

Where some/dir/moduleroot contains a go.mod.

What did you expect to see?

gopls detects the go.mod file in some/dir/moduleroot and uses it.

What did you see instead?

gopls did not detect the go.mod file and was unable to resolve any imports.

Build info

golang.org/x/tools/gopls v0.6.9
    golang.org/x/tools/gopls@v0.6.9 h1:LBBcE2y3Tb4bp79JVLWCQBbvYCFEs5ADGWsQDoSLk1Q=
    github.com/BurntSushi/toml@v0.3.1 h1:WXkYYl6Yr3qBf1K79EBnL4mak0OimBfB0XUf9Vl28OQ=
    github.com/google/go-cmp@v0.5.4 h1:L8R9j+yAqZuZjsqh/z+F1NCffTKKLShY6zXTItVIZ8M=
    github.com/sergi/go-diff@v1.1.0 h1:we8PVUC3FE2uYfodKH/nBHMSetSfHDR6scGdBi+erh0=
    golang.org/x/mod@v0.4.1 h1:Kvvh58BN8Y9/lBi7hTekvtMpm07eUZ0ck5pRHpsMWrY=
    golang.org/x/sync@v0.0.0-20201020160332-67f06af15bc9 h1:SQFwaSi55rU7vdNs9Yr0Z324VNlrF+0wMqRXT4St8ck=
    golang.org/x/sys@v0.0.0-20210124154548-22da62e12c0c h1:VwygUrnw9jn88c4u8GD3rZQbqrP/tgas88tPUbBxQrk=
    golang.org/x/tools@v0.1.1-0.20210319172145-bda8f5cee399 h1:O5bm8buX/OaamnfcBrkjn0SPUIU30jFmaS8lP+ikkxs=
    golang.org/x/xerrors@v0.0.0-20200804184101-5ec99f83aff1 h1:go1bK/D/BFZV2I8cIQd1NKEZ+0owSTG1fDTci4IqFcE=
    honnef.co/go/tools@v0.1.1 h1:EVDuO03OCZwpV2t/tLLxPmPiomagMoBOgfPt0FM+4IY=
    mvdan.cc/gofumpt@v0.1.0 h1:hsVv+Y9UsZ/mFZTxJZuHVI6shSQCtzZ11h1JEFPAZLw=
    mvdan.cc/xurls/v2@v2.2.0 h1:NSZPykBXJFCetGZykLAxaL6SIpvbVy/UFEniIfHAa8A=

[heschi]

I believe I made a stupid mistake in findModules: we don't recurse into a directory that is filtered out, which means that cases exactly like this one won't work. For now it'd probably be easier to recurse unconditionally, but that's unfortunate if the filter is (e.g.) node_modules.

[wtlangford]

You could also potentially look to see if there are any later + entries that have the - entry as a prefix and only recurse in that case.

[findleyr]

I believe at this point this is a dupe of #52970: modules can be excluded using go.work files, but we need to reconcile this with the directoryFilters setting.