Adding unsafe.SliceData

grantnelson-wf · grantnelson-wf · commit a1a5345f2008 · 2024-05-08T13:08:38.000-06:00
diff --git a/compiler/expressions.go b/compiler/expressions.go
@@ -1059,11 +1059,8 @@ func (fc *funcContext) translateBuiltin(name string, sig *types.Signature, args
 		sel, _ := fc.selectionOf(astutil.RemoveParens(args[0]).(*ast.SelectorExpr))
 		return fc.formatExpr("%d", typesutil.OffsetOf(sizes32, sel))
 	case "SliceData":
-		// SliceData returns nil if the slice is nil, otherwise returns a pointer to the first index of the array, &s[0].
-		// If the slice is empty (cap == 0), it returns an "unspecified memory address" or in our case, a pointer to the empty array.
 		t := fc.typeOf(args[0]).Underlying().(*types.Slice)
-		elemPtrType := types.NewPointer(t.Elem())
-		return fc.formatExpr("(%1e === %2s.nil) ? %3s.nil : $indexPtr(%1e.$array, %1e.$offset, %3s)", args[0], fc.typeName(t), fc.typeName(elemPtrType))
+		return fc.formatExpr(`$sliceData(%e, %s)`, args[0], fc.typeName(t))
 	default:
 		panic(fmt.Sprintf("Unhandled builtin: %s\n", name))
 	}
diff --git a/compiler/prelude/prelude.js b/compiler/prelude/prelude.js
@@ -569,3 +569,10 @@ var $instanceOf = (x, y) => {
 var $typeOf = x => {
     return typeof (x);
 };
+
+var $sliceData = (slice, typ) => {
+    if (slice === typ.nil) {
+        return $ptrType(typ.elem).nil;
+    }
+    return $indexPtr(slice.$array, slice.$offset, typ.elem);
+};
diff --git a/tests/js_test.go b/tests/js_test.go
@@ -9,6 +9,7 @@ import (
 	"strings"
 	"testing"
 	"time"
+	"unsafe"
 
 	"github.com/google/go-cmp/cmp"
 	"github.com/gopherjs/gopherjs/js"
@@ -936,3 +937,41 @@ func TestStructWithNonIdentifierJSTag(t *testing.T) {
 		t.Errorf("value via js.Object.Get gave %q, want %q", got, want)
 	}
 }
+
+func TestSliceData(t *testing.T) {
+	var (
+		s0 = []int(nil)
+		s1 = []int{}
+		s2 = []int{1, 2, 3}
+		s3 = s2[1:]
+		s4 = []int{4, 5, 6}
+
+		sd0 = unsafe.SliceData(s0)
+		sd1 = unsafe.SliceData(s1)
+		sd2 = unsafe.SliceData(s2)
+		sd3 = unsafe.SliceData(s3)
+		sd4 = unsafe.SliceData(s4)
+	)
+
+	if sd0 != nil {
+		t.Errorf("slice data for nil slice was not nil")
+	}
+	if sd1 == nil {
+		t.Errorf("slice data for empty slice was nil")
+	}
+	if sd2 == nil {
+		t.Errorf("slice data for non-empty slice was nil")
+	}
+	if sd3 == nil {
+		t.Errorf("slice data for sub-slice was nil")
+	}
+	if sd1 != sd2 {
+		t.Errorf("slice data for empty and non-empty slices were the same")
+	}
+	if sd2 == sd3 {
+		t.Errorf("slice data for slice and sub-slice were the same")
+	}
+	if sd2 == sd4 {
+		t.Errorf("slice data for different slices were the same")
+	}
+}
