go/packages: only list current module's directory in determineRootDirs

When determining the root directory of a module, the go list overlay
code would do a go list -m all to get the module information for all
modules. Stop doing that and only list the current module. This fixes
an issue when users had overlays and were using automatic vendoring
because go list -m all doesn't work with automatic vendoring.

It isn't clear if overlays outside of the main module were ever working
and overlays in the module cache don't make sense. There's a chance that
this might break users with overlays in replaced directories, but it's
not clear that that previously worked, and it wasn't tested. If this
change causes breakages, we can use bcmills' suggestion in
golang.org/issue/37629#issuecomment-594179751 point 3 to fix it.

Fixes golang/go#37629

Change-Id: I826a86bbe54311cac72cbcafb2de4863dc805c2d
Reviewed-on: https://go-review.googlesource.com/c/tools/+/227117
Run-TryBot: Michael Matloob <matloob@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Rebecca Stambler <rstambler@golang.org>

1 files changed, 41 insertions, 0 deletions

diff --git a/go/packages/packages_test.go b/go/packages/packages_test.go
index 95ce27124..259441bdf 100644
--- a/go/packages/packages_test.go
+++ b/go/packages/packages_test.go
@@ -2593,6 +2593,47 @@ func testForTestField(t *testing.T, exporter packagestest.Exporter) {
 	}
 }
 
+func TestIssue37529(t *testing.T) {
+	packagestest.TestAll(t, testIssue37529)
+}
+func testIssue37529(t *testing.T, exporter packagestest.Exporter) {
+	// Tests #37529. When automatic vendoring is triggered, and we try to determine
+	// the module root dir for a new overlay package, we previously would do a go list -m all,
+	// which is incompatible with automatic vendoring.
+
+	exported := packagestest.Export(t, exporter, []packagestest.Module{{
+		Name: "golang.org/fake",
+		Files: map[string]interface{}{
+			"c/c2.go":             `package c`,
+			"a/a.go":              `package a; import "b.com/b"; const A = b.B`,
+			"vendor/b.com/b/b.go": `package b; const B = 4`,
+		}}})
+	rootDir := filepath.Dir(filepath.Dir(exported.File("golang.org/fake", "a/a.go")))
+	exported.Config.Overlay = map[string][]byte{
+		filepath.Join(rootDir, "c/c.go"): []byte(`package c; import "golang.org/fake/a"; const C = a.A`),
+	}
+	exported.Config.Env = append(exported.Config.Env, "GOFLAGS=-mod=vendor")
+	exported.Config.Mode = packages.LoadAllSyntax
+
+	defer exported.Cleanup()
+
+	initial, err := packages.Load(exported.Config, "golang.org/fake/c")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// Check value of a.A.
+	a := initial[0]
+	aA := constant(a, "C")
+	if aA == nil {
+		t.Fatalf("a.A: got nil")
+	}
+	got := aA.Val().String()
+	if got != "4" {
+		t.Errorf("a.A: got %s, want %s", got, "4")
+	}
+}
+
 func errorMessages(errors []packages.Error) []string {
 	var msgs []string
 	for _, err := range errors {