cmd/cgo: avoid worklist nondeterminism.

+ Regression test.

Fixes issue 9026.

LGTM=rsc
R=rsc
CC=golang-codereviews
https://codereview.appspot.com/162490043

2 files changed, 34 insertions, 0 deletions

diff --git a/misc/cgo/test/cgo_test.go b/misc/cgo/test/cgo_test.go
index 3b289ba7b..fbdfac87a 100644
--- a/misc/cgo/test/cgo_test.go
+++ b/misc/cgo/test/cgo_test.go
@@ -62,5 +62,6 @@ func Test8517(t *testing.T)                  { test8517(t) }
 func Test8811(t *testing.T)                  { test8811(t) }
 func TestReturnAfterGrow(t *testing.T)       { testReturnAfterGrow(t) }
 func TestReturnAfterGrowFromGo(t *testing.T) { testReturnAfterGrowFromGo(t) }
+func Test9026(t *testing.T)                  { test9026(t) }
 
 func BenchmarkCgoCall(b *testing.B) { benchCgoCall(b) }
diff --git a/misc/cgo/test/issue9026.go b/misc/cgo/test/issue9026.go
new file mode 100644
index 000000000..b17440452
--- /dev/null
+++ b/misc/cgo/test/issue9026.go
@@ -0,0 +1,33 @@
+package cgotest
+
+/*
+typedef struct {} git_merge_file_input;
+
+typedef struct {} git_merge_file_options;
+
+int git_merge_file(
+        git_merge_file_input *in,
+        git_merge_file_options *opts) {}
+*/
+import "C"
+import (
+	"fmt"
+	"testing"
+)
+
+func test9026(t *testing.T) {
+	var in C.git_merge_file_input
+	var opts *C.git_merge_file_options
+	C.git_merge_file(&in, opts)
+
+	// Test that the generated type names are deterministic.
+	// (Previously this would fail about 10% of the time.)
+	//
+	// Brittle: the assertion may fail spuriously when the algorithm
+	// changes, but should remain stable otherwise.
+	got := fmt.Sprintf("%T %T", in, opts)
+	want := "cgotest._Ctype_struct___12 *cgotest._Ctype_struct___13"
+	if got != want {
+		t.Errorf("Non-deterministic type names: got %s, want %s", got, want)
+	}
+}