checker, cgen: check comptime selector that has no field name (#14282)

vlib/v/checker/checker.v

@@ -2661,7 +2661,7 @@ pub fn (mut c Checker) expr(node_ ast.Expr) ast.Type {
 			return c.comptime_call(mut node)
 		}
 		ast.ComptimeSelector {
-			node.left_type = c.unwrap_generic(c.expr(node.left))
+			node.left_type = c.expr(node.left)
 			expr_type := c.unwrap_generic(c.expr(node.field_expr))
 			expr_sym := c.table.sym(expr_type)
 			if expr_type != ast.string_type {

vlib/v/checker/tests/comptime_selector_expr_type_err.out

@@ -0,0 +1,7 @@
+vlib/v/checker/tests/comptime_selector_expr_type_err.vv:12:27: cgen error: `a` has no field named `value`
+   10 |     for i in a {
+   11 |         $for field in Row.fields {
+   12 |             println('field $i: ' + a.$(field.name).str() )
+      |                                    ^
+   13 |         }
+   14 |     }

vlib/v/checker/tests/comptime_selector_expr_type_err.vv

@@ -0,0 +1,15 @@
+module main
+
+pub struct Row {
+pub mut:
+	value string
+}
+
+fn main() {
+	a := []Row{}
+	for i in a {
+		$for field in Row.fields {
+			println('field $i: ' + a.$(field.name).str() )
+		}
+	}
+}

vlib/v/gen/c/comptime.v

@@ -20,7 +20,12 @@ fn (mut g Gen) comptime_selector(node ast.ComptimeSelector) {
 		if node.field_expr.expr is ast.Ident {
 			if node.field_expr.expr.name == g.comptime_for_field_var
 				&& node.field_expr.field_name == 'name' {
-				g.write(c_name(g.comptime_for_field_value.name))
+				field_name := g.comptime_for_field_value.name
+				left_sym := g.table.sym(g.unwrap_generic(node.left_type))
+				_ := g.table.find_field_with_embeds(left_sym, field_name) or {
+					g.error('`$node.left` has no field named `$field_name`', node.left.pos())
+				}
+				g.write(c_name(field_name))
 				return
 			}
 		}