identify context cancellation error in packages.loader.loadPackage

Author: mmirolim

go/packages/packages.go

@@ -324,6 +324,7 @@ const (
 ListError
 ParseError
 TypeError
+ContextCancelError
 )
 
 func (err Error) Error() string {
@@ -781,14 +782,23 @@ func (ld *loader) loadPackage(lpkg *loaderPackage) {
 
 default:
 // unexpected impoverished error from parser?
+errKind := UnknownError
+
+// check if err from context
+if ld.Context.Err() != nil {
+errKind = ContextCancelError
+}
+
 errs = append(errs, Error{
 Pos: "-",
 Msg: err.Error(),
-Kind: UnknownError,
+Kind: errKind,
 })
 
-// If you see this error message, please file a bug.
-log.Printf("internal error: error %q (%T) without position", err, err)
+if errKind == UnknownError {
+// If you see this error message, please file a bug.
+log.Printf("internal error: error %q (%T) without position", err, err)
+}
 }
 
 lpkg.Errors = append(lpkg.Errors, errs...)

go/packages/packages_test.go

@@ -2121,6 +2121,59 @@ func testReturnErrorForUnexpectedDirectoryLayout(t *testing.T, exporter packages
 }
 }
 
+func TestReturnErrorForContextCanceled(t *testing.T) {
+packagestest.TestAll(t, testReturnErrorForContextCanceled)
+}
+
+type slowContext struct {
+context.Context
+delay time.Duration
+}
+
+func (ctx slowContext) Err() error {
+time.Sleep(ctx.delay)
+return ctx.Context.Err()
+}
+
+func testReturnErrorForContextCanceled(t *testing.T, exporter packagestest.Exporter) {
+exported := packagestest.Export(t, exporter, []packagestest.Module{{
+Name: "golang.org/fake",
+Files: map[string]interface{}{
+"a/a.go": `package a; const A = "a" `,
+}}})
+defer exported.Cleanup()
+
+ctx, cancel := context.WithCancel(context.Background())
+// we need to slow a Load function to be able to test ctx cancellation
+// in the middle of loading packages
+slowCtx := slowContext{ctx, 10 * time.Millisecond}
+
+go func() {
+// should have delay before canceling
+// otherwise returns early with 'signal killed'
+time.Sleep(8 * time.Millisecond)
+cancel()
+}()
+
+exported.Config.Mode = packages.LoadAllSyntax
+exported.Config.Context = slowCtx
+pkgs, err := packages.Load(exported.Config, "golang.org/fake/a")
+if err != nil {
+t.Fatal(err)
+}
+// flaky test, because of timings
+// sometimes Load returns early with err "signal: killed" when tested under Module
+want := packages.ContextCancelError
+if len(pkgs) > 0 {
+errKind := pkgs[0].Errors[0].Kind
+if want != errKind {
+t.Fatalf("want error kind: %v, got: %v", want, errKind)
+}
+} else {
+t.Fatal("unexpected no packages returned")
+}
+}
+
 func TestMissingDependency(t *testing.T) { packagestest.TestAll(t, testMissingDependency) }
 func testMissingDependency(t *testing.T, exporter packagestest.Exporter) {
 exported := packagestest.Export(t, exporter, []packagestest.Module{{