1 files changed, 41 insertions, 18 deletions

diff --git a/src/cmd/compile/internal/types2/stmt.go b/src/cmd/compile/internal/types2/stmt.go
index 7fd7009e13..655d072171 100644
--- a/src/cmd/compile/internal/types2/stmt.go
+++ b/src/cmd/compile/internal/types2/stmt.go
@@ -898,7 +898,7 @@ func (check *Checker) rangeStmt(inner stmtContext, s *syntax.ForStmt, rclause *s
 	lhs := [2]Expr{sKey, sValue} // sKey, sValue may be nil
 	rhs := [2]Type{key, val}     // key, val may be nil
 
-	constIntRange := x.mode == constant_ && isInteger(x.typ)
+	rangeOverInt := isInteger(x.typ)
 
 	if isDef {
 		// short variable declaration
@@ -923,19 +923,27 @@ func (check *Checker) rangeStmt(inner stmtContext, s *syntax.ForStmt, rclause *s
 				check.errorf(lhs, InvalidSyntaxTree, "cannot declare %s", lhs)
 				obj = NewVar(lhs.Pos(), check.pkg, "_", nil) // dummy variable
 			}
+			assert(obj.typ == nil)
 
-			// initialize lhs variable
-			if constIntRange {
-				check.initVar(obj, &x, "range clause")
-			} else if typ := rhs[i]; typ != nil {
-				x.mode = value
-				x.expr = lhs // we don't have a better rhs expression to use here
-				x.typ = typ
-				check.initVar(obj, &x, "assignment") // error is on variable, use "assignment" not "range clause"
-			} else {
+			// initialize lhs iteration variable, if any
+			typ := rhs[i]
+			if typ == nil {
 				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)
+				check.initVar(obj, &x, "range clause")
+			} else {
+				var y operand
+				y.mode = value
+				y.expr = lhs // we don't have a better rhs expression to use here
+				y.typ = typ
+				check.initVar(obj, &y, "assignment") // error is on variable, use "assignment" not "range clause"
 			}
+			assert(obj.typ != nil)
 		}
 
 		// declare variables
@@ -954,21 +962,36 @@ func (check *Checker) rangeStmt(inner stmtContext, s *syntax.ForStmt, rclause *s
 				continue
 			}
 
-			if constIntRange {
+			// assign to lhs iteration variable, if any
+			typ := rhs[i]
+			if typ == nil {
+				continue
+			}
+
+			if rangeOverInt {
+				assert(i == 0) // at most one iteration variable (rhs[1] == nil for rangeOverInt)
 				check.assignVar(lhs, nil, &x, "range clause")
-			} else if typ := rhs[i]; typ != nil {
-				x.mode = value
-				x.expr = lhs // we don't have a better rhs expression to use here
-				x.typ = typ
-				check.assignVar(lhs, nil, &x, "assignment") // error is on variable, use "assignment" not "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.
+				// (go.dev/issues/67027)
+				if x.mode != invalid && !isInteger(x.typ) {
+					check.softErrorf(lhs, InvalidRangeExpr, "cannot use iteration variable of type %s", x.typ)
+				}
+			} else {
+				var y operand
+				y.mode = value
+				y.expr = lhs // we don't have a better rhs expression to use here
+				y.typ = typ
+				check.assignVar(lhs, nil, &y, "assignment") // error is on variable, use "assignment" not "range clause"
 			}
 		}
-	} else if constIntRange {
+	} else if rangeOverInt {
 		// If we don't have any iteration variables, we still need to
 		// check that a (possibly untyped) integer range expression x
 		// is valid.
 		// We do this by checking the assignment _ = x. This ensures
-		// that an untyped x can be converted to a value of type int.
+		// that an untyped x can be converted to a value of its default
+		// type (rune or int).
 		check.assignment(&x, nil, "range clause")
 	}