internal/postgres: ignore self-imports in imported-by counts

Do not count package A as importing package B if they
are in the same module.

Change-Id: Ic0f98af8d72b8fff29e105779c6eb619214335e9
Reviewed-on: https://team-review.git.corp.google.com/c/golang/discovery/+/596525
CI-Result: Cloud Build <devtools-proctor-result-processor@system.gserviceaccount.com>
Reviewed-by: Julie Qiu <julieqiu@google.com>

2 files changed, 26 insertions, 0 deletions

diff --git a/internal/stdlib/stdlib.go b/internal/stdlib/stdlib.go
index 8a081cfc..adf1cf49 100644
--- a/internal/stdlib/stdlib.go
+++ b/internal/stdlib/stdlib.go
@@ -357,6 +357,14 @@ func subTree(r *git.Repository, t *object.Tree, name string) (*object.Tree, erro
 	return nil, os.ErrNotExist
 }
 
+// Contains reports whether the given import path is part of the Go standard library.
+func Contains(path string) bool {
+	if i := strings.IndexByte(path, '/'); i != -1 {
+		path = path[:i]
+	}
+	return !strings.Contains(path, ".")
+}
+
 // References used for Versions during testing.
 var testRefs = []plumbing.ReferenceName{
 	"refs/changes/56/93156/13",
diff --git a/internal/stdlib/stdlib_test.go b/internal/stdlib/stdlib_test.go
index eca3760d..a0116100 100644
--- a/internal/stdlib/stdlib_test.go
+++ b/internal/stdlib/stdlib_test.go
@@ -189,3 +189,21 @@ func TestVersionForTag(t *testing.T) {
 		}
 	}
 }
+
+func TestContains(t *testing.T) {
+	for _, test := range []struct {
+		in   string
+		want bool
+	}{
+		{"fmt", true},
+		{"encoding/json", true},
+		{"something/with.dots", true},
+		{"example.com", false},
+		{"example.com/fmt", false},
+	} {
+		got := Contains(test.in)
+		if got != test.want {
+			t.Errorf("Contains(%q) = %t, want %t", test.in, got, test.want)
+		}
+	}
+}