compiler/natives/src/strings: Skip optional pointer manipulation.

dmitshur · dmitshur · commit 446447afae62 · 2018-02-16T18:04:23.000-05:00
It's being done upstream to trick the escape analysis and prevent
allocations. We can't rely on it here.

Fixes:

	=== RUN   TestBuilder
	--- FAIL: TestBuilder (0.01s)

	TypeError: Cannot create property '$proxies' on number '0'
diff --git a/compiler/natives/src/strings/strings.go b/compiler/natives/src/strings/strings.go
@@ -55,3 +55,13 @@ func (b *Builder) String() string {
 	//       and there are benchmarks available (see https://github.com/golang/go/issues/18990#issuecomment-352068533).
 	return string(b.buf)
 }
+
+func (b *Builder) copyCheck() {
+	if b.addr == nil {
+		// Upstream copyCheck uses noescape, which performs unsafe.Pointer manipulation.
+		// We can't do that, so skip it. See https://github.com/golang/go/commit/484586c81a0196e42ac52f651bc56017ca454280.
+		b.addr = b
+	} else if b.addr != b {
+		panic("strings: illegal use of non-zero Builder copied by value")
+	}
+}
diff --git a/compiler/natives/src/strings/strings_test.go b/compiler/natives/src/strings/strings_test.go
@@ -0,0 +1,9 @@
+// +build js
+
+package strings_test
+
+import "testing"
+
+func TestBuilderAllocs(t *testing.T) {
+	t.Skip("runtime.ReadMemStats, testing.AllocsPerRun not supported in GopherJS")
+}
