internal/lsp/cache: always consider go.work files for ws expansion

If a go.work file is present, we activate the workspace mode regardless
of the experimentalWorkspaceModule setting.

Fixing this also revealed a long-standing bug in traversing parent
directories. Amazingly I have no recollection of this bug being
reported, but it is far more likely to be hit with go.work files, when
users regularly open nested subdirectories.

Fixes golang/go#51477

Change-Id: I310a11b14f3bbc18fdd604c5c0ec33d7ee8f1174
Reviewed-on: https://go-review.googlesource.com/c/tools/+/389300
Trust: Robert Findley <rfindley@google.com>
Run-TryBot: Robert Findley <rfindley@google.com>
Reviewed-by: Michael Matloob <matloob@golang.org>
gopls-CI: kokoro <noreply+kokoro@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

gopls/internal/regtest/workspace/workspace_test.go

@@ -865,6 +865,55 @@ module example.com/bar/baz
 	})
 }
 
+func TestExpandToGoWork(t *testing.T) {
+	testenv.NeedsGo1Point(t, 18)
+	const workspace = `
+-- moda/a/go.mod --
+module a.com
+
+require b.com v1.2.3
+-- moda/a/a.go --
+package a
+
+import (
+	"b.com/b"
+)
+
+func main() {
+	var x int
+	_ = b.Hello()
+}
+-- modb/go.mod --
+module b.com
+
+require example.com v1.2.3
+-- modb/b/b.go --
+package b
+
+func Hello() int {
+	var x int
+}
+-- go.work --
+go 1.17
+
+use (
+	./moda/a
+	./modb
+)
+`
+	WithOptions(
+		WorkspaceFolders("moda/a"),
+	).Run(t, workspace, func(t *testing.T, env *Env) {
+		env.OpenFile("moda/a/a.go")
+		env.Await(env.DoneWithOpen())
+		location, _ := env.GoToDefinition("moda/a/a.go", env.RegexpSearch("moda/a/a.go", "Hello"))
+		want := "modb/b/b.go"
+		if !strings.HasSuffix(location, want) {
+			t.Errorf("expected %s, got %v", want, location)
+		}
+	})
+}
+
 func TestNonWorkspaceFileCreation(t *testing.T) {
 	testenv.NeedsGo1Point(t, 13)
 

internal/lsp/cache/view.go

@@ -832,7 +832,7 @@ func go111moduleForVersion(go111module string, goversion int) go111module {
 // TODO (rFindley): move this to workspace.go
 // TODO (rFindley): simplify this once workspace modules are enabled by default.
 func findWorkspaceRoot(ctx context.Context, folder span.URI, fs source.FileSource, excludePath func(string) bool, experimental bool) (span.URI, error) {
-	patterns := []string{"go.mod"}
+	patterns := []string{"go.work", "go.mod"}
 	if experimental {
 		patterns = []string{"go.work", "gopls.mod", "go.mod"}
 	}
@@ -882,7 +882,8 @@ func findRootPattern(ctx context.Context, folder span.URI, basename string, fs s
 		if exists {
 			return span.URIFromPath(dir), nil
 		}
-		next, _ := filepath.Split(dir)
+		// Trailing separators must be trimmed, otherwise filepath.Split is a noop.
+		next, _ := filepath.Split(strings.TrimRight(dir, string(filepath.Separator)))
 		if next == dir {
 			break
 		}

internal/lsp/cache/view_test.go

@@ -55,6 +55,8 @@ func TestFindWorkspaceRoot(t *testing.T) {
 module a
 -- a/x/x.go
 package x
+-- a/x/y/y.go
+package x
 -- b/go.mod --
 module b
 -- b/c/go.mod --
@@ -79,6 +81,7 @@ module fg
 		{"", "", false}, // no module at root, and more than one nested module
 		{"a", "a", false},
 		{"a/x", "a", false},
+		{"a/x/y", "a", false},
 		{"b/c", "b/c", false},
 		{"d", "d/e", false},
 		{"d", "d", true},