cb.emitTypeAssert: Go does not fully implement chained call safety

Author: xushiwei

codebuild.go

@@ -1302,7 +1302,7 @@ func (p *CodeBuilder) Index(nidx int, lhs int, src ...ast.Node) *CodeBuilder {
 	}
 	argVal := args[0].Val
 	if ivKind == ivMapStringAny {
-		argVal = &ast.TypeAssertExpr{X: argVal, Type: toMapType(p.pkg, tyMapStringAny)}
+		argVal = p.emitTypeAssert(argVal)
 	}
 	elem := &internal.Elem{
 		Val: &ast.IndexExpr{X: argVal, Index: args[1].Val}, Type: tyRet, Src: srcExpr,
@@ -1785,10 +1785,8 @@ retry:
 		o.Complete()
 
 		if o.Empty() { // empty interface (https://github.com/goplus/xgo/issues/2571)
-			tyMap := tyMapStringAny
-			p.TypeAssert(tyMap, 0)
-			arg = p.stk.Get(-1)
-			return p.mapIndexExpr(tyMap, name, lhs, arg.Val, srcExpr)
+			argVal := p.emitTypeAssert(arg.Val)
+			return p.mapIndexExpr(tyMapStringAny, name, lhs, argVal, srcExpr)
 		}
 
 		if kind := p.method(o, name, aliasName, flag, arg, srcExpr); kind != MemberInvalid {
@@ -1828,6 +1826,20 @@ retry:
 	return MemberInvalid
 }
 
+// See https://github.com/goplus/xgo/issues/2572#issuecomment-3807206716
+func (p *CodeBuilder) emitTypeAssert(argVal ast.Expr) ast.Expr {
+	pkg := p.pkg
+	e := &ast.TypeAssertExpr{X: argVal, Type: toMapType(pkg, tyMapStringAny)}
+	ret := ast.NewIdent(pkg.autoName())
+	stmt := &ast.AssignStmt{
+		Lhs: []ast.Expr{ret, underscore},
+		Tok: token.DEFINE,
+		Rhs: []ast.Expr{e},
+	}
+	p.emitStmt(stmt)
+	return ret
+}
+
 func (p *CodeBuilder) mapIndexExpr(o *types.Map, name string, lhs int, argVal ast.Expr, src ast.Node) MemberKind {
 	tyRet := o.Elem()
 	if lhs == 2 { // two-value assignment

package_test.go

@@ -3407,11 +3407,14 @@ func TestIndex(t *testing.T) {
 
 func foo(x []int, y map[string]int, z interface{}) int {
 	v, ok := y["a"]
-	v1, ok := z.(map[string]any)["a"]
+	_autoGo_1, _ := z.(map[string]any)
+	v1, ok := _autoGo_1["a"]
 	v2 := y["a"]
 	v3, ok := y["b"]
-	v4, ok := z.(map[string]any)["c"]
-	v5 := z.(map[string]any)["d"]
+	_autoGo_2, _ := z.(map[string]any)
+	v4, ok := _autoGo_2["c"]
+	_autoGo_3, _ := z.(map[string]any)
+	v5 := _autoGo_3["d"]
 	return x[0]
 }
 func main() {