go/packages: handle invalid files in overlays

This change handles a specific case where `go list` returns an error on
a file that lacks a package declaration. If only one package is returned
as a response, we should add that file to that package, since it may
have valid content in an overlay.

This change uses the internal/span package to correctly parse the error
message from `go list`.

Change-Id: I5909c4fd765746df1003685aa915b7c5f9cdcee5
Reviewed-on: https://go-review.googlesource.com/c/tools/+/201220
Run-TryBot: Rebecca Stambler <rstambler@golang.org>
Reviewed-by: Michael Matloob <matloob@golang.org>

1 files changed, 49 insertions, 0 deletions

diff --git a/go/packages/packages_test.go b/go/packages/packages_test.go
index 2a73156a3..e3c70080b 100644
--- a/go/packages/packages_test.go
+++ b/go/packages/packages_test.go
@@ -1079,6 +1079,51 @@ func testNewPackagesInOverlay(t *testing.T, exporter packagestest.Exporter) {
 	}
 }
 
+func TestContainsInOverlays(t *testing.T) { packagestest.TestAll(t, testcontainsInOverlays) }
+func testcontainsInOverlays(t *testing.T, exporter packagestest.Exporter) {
+	// This test checks a specific case where a file is empty on disk.
+	// In this case, `go list` will return the package golang.org/fake/c
+	// with only c.go as a GoFile, with an error message for c2.go.
+	// Since there is only one possible package for c2.go to be a part of,
+	// go/packages will parse the filename out of error and add it to GoFiles and CompiledGoFiles.
+	exported := packagestest.Export(t, exporter, []packagestest.Module{{
+		Name: "golang.org/fake",
+		Files: map[string]interface{}{
+			"c/c.go":  `package c; const C = "c"`,
+			"c/c2.go": ``,
+		}}})
+	defer exported.Cleanup()
+
+	dir := filepath.Dir(exported.File("golang.org/fake", "c/c.go"))
+
+	for _, test := range []struct {
+		overlay map[string][]byte
+		want    string
+	}{
+		{
+			overlay: map[string][]byte{filepath.Join(dir, "c2.go"): []byte(`nonsense`)},
+			want:    "golang.org/fake/c",
+		},
+	} {
+		exported.Config.Overlay = test.overlay
+		exported.Config.Mode = packages.LoadImports
+		exported.Config.Logf = t.Logf
+		for filename := range exported.Config.Overlay {
+			initial, err := packages.Load(exported.Config, "file="+filename)
+			if err != nil {
+				t.Fatal(err)
+			}
+			if len(initial) == 0 {
+				t.Fatalf("no packages for %s", filename)
+			}
+			pkg := initial[0]
+			if pkg.PkgPath != test.want {
+				t.Errorf("got %s, want %s", pkg.PkgPath, test.want)
+			}
+		}
+	}
+}
+
 func TestAdHocPackagesBadImport(t *testing.T) {
 	// TODO: Enable this test when github.com/golang/go/issues/33374 is resolved.
 	t.Skip()
@@ -2201,10 +2246,14 @@ func testAdHocContains(t *testing.T, exporter packagestest.Exporter) {
 	}()
 
 	exported.Config.Mode = packages.NeedImports | packages.NeedFiles
+	exported.Config.Logf = t.Logf
 	pkgs, err := packages.Load(exported.Config, "file="+filename)
 	if err != nil {
 		t.Fatal(err)
 	}
+	if len(pkgs) == 0 {
+		t.Fatalf("no packages for %s", filename)
+	}
 	if len(pkgs) != 1 && pkgs[0].PkgPath != "command-line-arguments" {
 		t.Fatalf("packages.Load: want [command-line-arguments], got %v", pkgs)
 	}