compiler: create new locals for range loops when needed, fix #2855

pkg/compiler/codegen.go

@@ -1313,7 +1313,11 @@ func (c *codegen) Visit(node ast.Node) ast.Visitor {
 			} else {
 				emit.Opcodes(c.prog.BinWriter, opcode.DUP)
 			}
-			c.emitStoreVar("", n.Key.(*ast.Ident).Name)
+			keyIdent := n.Key.(*ast.Ident)
+			if n.Tok == token.DEFINE {
+				c.scope.newLocal(keyIdent.Name)
+			}
+			c.emitStoreVar("", keyIdent.Name)
 		}
 		if needValue {
 			if !isMap || !keyLoaded {
@@ -1327,7 +1331,11 @@ func (c *codegen) Visit(node ast.Node) ast.Visitor {
 					opcode.SWAP, // key should be on top
 					opcode.PICKITEM)
 			}
-			c.emitStoreVar("", n.Value.(*ast.Ident).Name)
+			valIdent := n.Value.(*ast.Ident)
+			if n.Tok == token.DEFINE {
+				c.scope.newLocal(valIdent.Name)
+			}
+			c.emitStoreVar("", valIdent.Name)
 		}
 
 		ast.Walk(c, n.Body)

pkg/compiler/for_test.go

@@ -714,6 +714,32 @@ var forLoopTestCases = []testCase{
 		`,
 		big.NewInt(6),
 	},
+	{
+		"shadow range key",
+		`func F%d() int {
+			i := 10
+			ints := []int{1, 2, 3, 4, 5}
+			for i := range ints {
+				_ = i
+			}
+			return i
+		}
+		`,
+		big.NewInt(10),
+	},
+	{
+		"shadow range value",
+		`func F%d() int {
+			i := 10
+			ints := []int{1, 2, 3, 4, 5}
+			for _, i := range ints {
+				_ = i
+			}
+			return i
+		}
+		`,
+		big.NewInt(10),
+	},
 }
 
 func TestForLoop(t *testing.T) {