go/types: fix assertion failure when range over int is not permitted

Fixes an assertion failure in Checker.rangeStmt that range over int
only has a key type and no value type. When allowVersion failed,
rangeKeyVal returns Typ[Invalid] for the value instead of nil. When
Config.Error != nil, rangeStmt proceeded. The check for rhs[1]==nil
was not enough to catch this case. It must also check rhs[1]==

Updates #68334

Change-Id: Iffa1b2f7b6a94570ec50b8c6603e727a45ba3357
Reviewed-on: https://go-review.googlesource.com/c/go/+/597356
Reviewed-by: Robert Findley <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>

Author: timothy-king

src/cmd/compile/internal/types2/issues_test.go

@@ -1092,3 +1092,32 @@ func _() {
 	conf := Config{GoVersion: "go1.17"}
 	mustTypecheck(src, &conf, nil)
 }
+
+func TestIssue68334(t *testing.T) {
+	const src = `
+package p
+
+func f(x int) {
+	for i, j := range x {
+		_, _ = i, j
+	}
+	var a, b int
+	for a, b = range x {
+		_, _ = a, b
+	}
+}
+`
+
+	got := ""
+	conf := Config{
+		GoVersion: "go1.21",                                      // #68334 requires GoVersion <= 1.21
+		Error:     func(err error) { got += err.Error() + "\n" }, // #68334 requires Error != nil
+	}
+	typecheck(src, &conf, nil) // do not crash
+
+	want := "p:5:20: cannot range over x (variable of type int): requires go1.22 or later\n" +
+		"p:9:19: cannot range over x (variable of type int): requires go1.22 or later\n"
+	if got != want {
+		t.Errorf("got: %s want: %s", got, want)
+	}
+}

src/cmd/compile/internal/types2/stmt.go

@@ -920,14 +920,15 @@ func (check *Checker) rangeStmt(inner stmtContext, s *syntax.ForStmt, rclause *s
 
 			// initialize lhs iteration variable, if any
 			typ := rhs[i]
-			if typ == nil {
+			if typ == nil || typ == Typ[Invalid] {
+				// typ == Typ[Invalid] can happen if allowVersion fails.
 				obj.typ = Typ[Invalid]
 				obj.used = true // don't complain about unused variable
 				continue
 			}
 
 			if rangeOverInt {
-				assert(i == 0) // at most one iteration variable (rhs[1] == nil for rangeOverInt)
+				assert(i == 0) // at most one iteration variable (rhs[1] == nil or Typ[Invalid] for rangeOverInt)
 				check.initVar(obj, &x, "range clause")
 			} else {
 				var y operand
@@ -957,12 +958,12 @@ func (check *Checker) rangeStmt(inner stmtContext, s *syntax.ForStmt, rclause *s
 
 			// assign to lhs iteration variable, if any
 			typ := rhs[i]
-			if typ == nil {
+			if typ == nil || typ == Typ[Invalid] {
 				continue
 			}
 
 			if rangeOverInt {
-				assert(i == 0) // at most one iteration variable (rhs[1] == nil for rangeOverInt)
+				assert(i == 0) // at most one iteration variable (rhs[1] == nil or Typ[Invalid] for rangeOverInt)
 				check.assignVar(lhs, nil, &x, "range clause")
 				// If the assignment succeeded, if x was untyped before, it now
 				// has a type inferred via the assignment. It must be an integer.

src/go/types/issues_test.go

@@ -1102,3 +1102,32 @@ func _() {
 	conf := Config{GoVersion: "go1.17"}
 	mustTypecheck(src, &conf, nil)
 }
+
+func TestIssue68334(t *testing.T) {
+	const src = `
+package p
+
+func f(x int) {
+	for i, j := range x {
+		_, _ = i, j
+	}
+	var a, b int
+	for a, b = range x {
+		_, _ = a, b
+	}
+}
+`
+
+	got := ""
+	conf := Config{
+		GoVersion: "go1.21",                                      // #68334 requires GoVersion <= 1.21
+		Error:     func(err error) { got += err.Error() + "\n" }, // #68334 requires Error != nil
+	}
+	typecheck(src, &conf, nil) // do not crash
+
+	want := "p:5:20: cannot range over x (variable of type int): requires go1.22 or later\n" +
+		"p:9:19: cannot range over x (variable of type int): requires go1.22 or later\n"
+	if got != want {
+		t.Errorf("got: %s want: %s", got, want)
+	}
+}

src/go/types/stmt.go

@@ -922,14 +922,15 @@ func (check *Checker) rangeStmt(inner stmtContext, s *ast.RangeStmt) {
 
 			// initialize lhs iteration variable, if any
 			typ := rhs[i]
-			if typ == nil {
+			if typ == nil || typ == Typ[Invalid] {
+				// typ == Typ[Invalid] can happen if allowVersion fails.
 				obj.typ = Typ[Invalid]
 				obj.used = true // don't complain about unused variable
 				continue
 			}
 
 			if rangeOverInt {
-				assert(i == 0) // at most one iteration variable (rhs[1] == nil for rangeOverInt)
+				assert(i == 0) // at most one iteration variable (rhs[1] == nil or Typ[Invalid] for rangeOverInt)
 				check.initVar(obj, &x, "range clause")
 			} else {
 				var y operand
@@ -959,12 +960,12 @@ func (check *Checker) rangeStmt(inner stmtContext, s *ast.RangeStmt) {
 
 			// assign to lhs iteration variable, if any
 			typ := rhs[i]
-			if typ == nil {
+			if typ == nil || typ == Typ[Invalid] {
 				continue
 			}
 
 			if rangeOverInt {
-				assert(i == 0) // at most one iteration variable (rhs[1] == nil for rangeOverInt)
+				assert(i == 0) // at most one iteration variable (rhs[1] == nil or Typ[Invalid] for rangeOverInt)
 				check.assignVar(lhs, nil, &x, "range clause")
 				// If the assignment succeeded, if x was untyped before, it now
 				// has a type inferred via the assignment. It must be an integer.