checker: disallow using a preexisting const name in a for loop, as either a key or value ident (#22108)

vlib/math/poly.v

@@ -8,8 +8,8 @@ fn poly_n_eval(c []f64, n int, x f64) f64 {
 	}
 	len := int(min(c.len, n))
 	mut ans := c[len - 1]
-	for e in c[..len - 1] {
-		ans = e + x * ans
+	for e_ in c[..len - 1] {
+		ans = e_ + x * ans
 	}
 	return ans
 }
@@ -20,8 +20,8 @@ fn poly_n_1_eval(c []f64, n int, x f64) f64 {
 	}
 	len := int(min(c.len, n)) - 1
 	mut ans := c[len - 1]
-	for e in c[..len - 1] {
-		ans = e + x * ans
+	for e_ in c[..len - 1] {
+		ans = e_ + x * ans
 	}
 	return ans
 }

vlib/v/ast/ast.v

@@ -1277,6 +1277,7 @@ pub:
 	is_range   bool
 	pos        token.Pos
 	kv_pos     token.Pos
+	vv_pos     token.Pos
 	comments   []Comment
 	val_is_mut bool // `for mut val in vals {` means that modifying `val` will modify the array
 	// and the array cannot be indexed inside the loop

vlib/v/checker/for.v

@@ -44,6 +44,14 @@ fn (mut c Checker) for_in_stmt(mut node ast.ForInStmt) {
 			c.error('invalid use of reserved type `${node.val_var}` as value name', node.pos)
 		}
 	}
+	if _ := c.file.global_scope.find_const('${c.mod}.${node.key_var}') {
+		c.error('duplicate of a const name `${c.mod}.${node.key_var}`', node.kv_pos)
+	}
+
+	if _ := c.file.global_scope.find_const('${c.mod}.${node.val_var}') {
+		c.error('duplicate of a const name `${c.mod}.${node.val_var}`', node.vv_pos)
+	}
+
 	if node.is_range {
 		typ_idx := typ.idx()
 		high_type := c.expr(mut node.high)

vlib/v/checker/tests/const_name_for_loop_duplicate_name_err.out

@@ -0,0 +1,14 @@
+vlib/v/checker/tests/const_name_for_loop_duplicate_name_err.vv:5:6: error: duplicate of a const name `item`
+    3 | 
+    4 | fn main() {
+    5 |     for item, i in ['abc', 'def'] {
+      |         ~~~~
+    6 |         println(item)
+    7 |         println(i)
+vlib/v/checker/tests/const_name_for_loop_duplicate_name_err.vv:5:12: error: duplicate of a const name `i`
+    3 | 
+    4 | fn main() {
+    5 |     for item, i in ['abc', 'def'] {
+      |               ^
+    6 |         println(item)
+    7 |         println(i)

vlib/v/checker/tests/const_name_for_loop_duplicate_name_err.vv

@@ -0,0 +1,9 @@
+const item = 24
+const i = 23
+
+fn main() {
+	for item, i in ['abc', 'def'] {
+		println(item)
+		println(i)
+	}
+}

vlib/v/parser/for.v

@@ -205,6 +205,7 @@ fn (mut p Parser) for_stmt() ast.Stmt {
 			is_range:   is_range
 			pos:        pos
 			kv_pos:     key_var_pos
+			vv_pos:     val_var_pos
 			comments:   comments
 			val_is_mut: val_is_mut
 			scope:      p.scope