From 2e23f2a18b02ebfc805f2dc038f75acbdc72af3a Mon Sep 17 00:00:00 2001
From: kbkpbot <kbkpbot@sina.com>
Date: Thu, 21 Aug 2025 15:27:30 +0800
Subject: [PATCH] checker: ensure the defer behavior matches that of cgen (fix
 #25148) (#25146)

---
 vlib/v/checker/fn.v                         | 10 +++++++++
 vlib/v/checker/return.v                     |  9 ++++++++
 vlib/v/checker/tests/comptime_defer_err.out | 21 +++++++++++++++++++
 vlib/v/checker/tests/comptime_defer_err.vv  | 23 +++++++++++++++++++++
 vlib/v/checker/tests/defer_in_for.out       |  7 +++++++
 5 files changed, 70 insertions(+)
 create mode 100644 vlib/v/checker/tests/comptime_defer_err.out
 create mode 100644 vlib/v/checker/tests/comptime_defer_err.vv

diff --git a/vlib/v/checker/fn.v b/vlib/v/checker/fn.v
index ef32676db..73f27910a 100644
--- a/vlib/v/checker/fn.v
+++ b/vlib/v/checker/fn.v
@@ -558,6 +558,16 @@ fn (mut c Checker) fn_decl(mut node ast.FnDecl) {
 			c.error('missing return at end of function `${node.name}`', node.pos)
 		}
 	}
+	if !node.has_return {
+		// for `node.has_return`, checking in `return.v` `return_stmt`
+		old_inside_defer := c.inside_defer
+		c.inside_defer = true
+		for i := c.table.cur_fn.defer_stmts.len - 1; i >= 0; i-- {
+			c.stmts(mut c.table.cur_fn.defer_stmts[i].stmts)
+		}
+		c.inside_defer = old_inside_defer
+	}
+
 	node.source_file = c.file
 
 	if node.name in c.table.fns {
diff --git a/vlib/v/checker/return.v b/vlib/v/checker/return.v
index 883fa31da..966fddb47 100644
--- a/vlib/v/checker/return.v
+++ b/vlib/v/checker/return.v
@@ -33,6 +33,15 @@ fn (mut c Checker) return_stmt(mut node ast.Return) {
 	defer {
 		c.inside_return = prev_inside_return
 	}
+
+	// check `defer_stmts` in return, to ensure the same behavior with `cgen`
+	old_inside_defer := c.inside_defer
+	c.inside_defer = true
+	for i := c.table.cur_fn.defer_stmts.len - 1; i >= 0; i-- {
+		c.stmts(mut c.table.cur_fn.defer_stmts[i].stmts)
+	}
+	c.inside_defer = old_inside_defer
+
 	c.expected_type = c.table.cur_fn.return_type
 	mut expected_type := c.unwrap_generic(c.expected_type)
 	if expected_type != 0 && c.table.sym(expected_type).kind == .alias {
diff --git a/vlib/v/checker/tests/comptime_defer_err.out b/vlib/v/checker/tests/comptime_defer_err.out
new file mode 100644
index 000000000..46f3a0469
--- /dev/null
+++ b/vlib/v/checker/tests/comptime_defer_err.out
@@ -0,0 +1,21 @@
+vlib/v/checker/tests/comptime_defer_err.vv:17:14: error: compile time field access can only be used when iterating over `T.fields`
+   15 |         $if field.typ is string {
+   16 |             defer {
+   17 |                 if tst.$(field.name) == 'tst-s' {
+      |                          ~~~~~
+   18 |                     println('found tst-s')
+   19 |                 }
+vlib/v/checker/tests/comptime_defer_err.vv:17:14: error: unknown `$for` variable `field`
+   15 |         $if field.typ is string {
+   16 |             defer {
+   17 |                 if tst.$(field.name) == 'tst-s' {
+      |                          ~~~~~
+   18 |                     println('found tst-s')
+   19 |                 }
+vlib/v/checker/tests/comptime_defer_err.vv:17:12: error: non-bool type `void` used as if condition
+   15 |         $if field.typ is string {
+   16 |             defer {
+   17 |                 if tst.$(field.name) == 'tst-s' {
+      |                        ~~~~~~~~~~~~~~~~~~~~~~~~
+   18 |                     println('found tst-s')
+   19 |                 }
diff --git a/vlib/v/checker/tests/comptime_defer_err.vv b/vlib/v/checker/tests/comptime_defer_err.vv
new file mode 100644
index 000000000..162b4402b
--- /dev/null
+++ b/vlib/v/checker/tests/comptime_defer_err.vv
@@ -0,0 +1,23 @@
+module main
+
+struct Struct {
+	s string
+	i int
+}
+
+fn main() {
+	tst := Struct{
+		s: 'tst-s'
+		i: 42
+	}
+
+	$for field in Struct.fields {
+		$if field.typ is string {
+			defer {
+				if tst.$(field.name) == 'tst-s' {
+					println('found tst-s')
+				}
+			}
+		}
+	}
+}
diff --git a/vlib/v/checker/tests/defer_in_for.out b/vlib/v/checker/tests/defer_in_for.out
index 56c7b9190..96f13146a 100644
--- a/vlib/v/checker/tests/defer_in_for.out
+++ b/vlib/v/checker/tests/defer_in_for.out
@@ -5,3 +5,10 @@ vlib/v/checker/tests/defer_in_for.vv:4:4: error: `break` is not allowed in defer
       |             ~~~~~
     5 |         }
     6 |     }
+vlib/v/checker/tests/defer_in_for.vv:4:4: error: break statement not within a loop
+    2 |     for true {
+    3 |         defer {
+    4 |             break
+      |             ~~~~~
+    5 |         }
+    6 |     }
-- 
2.39.5