From 5ead7bcc102294541c06b128edff601d26413cee Mon Sep 17 00:00:00 2001
From: JMD <56417208+StunxFS@users.noreply.github.com>
Date: Wed, 15 Oct 2025 04:42:46 -0400
Subject: [PATCH] checker: disallow multiple left variables in if guards, that
 do not receive multireturn values (fix #24930) (#25507)

---
 vlib/v/checker/if.v                           |  5 +++
 .../checker/tests/if_guard_variables_err.out  | 43 +++++++++++--------
 .../v/checker/tests/if_guard_variables_err.vv |  9 ++++
 3 files changed, 39 insertions(+), 18 deletions(-)

diff --git a/vlib/v/checker/if.v b/vlib/v/checker/if.v
index 720a6ded1..5a2d72204 100644
--- a/vlib/v/checker/if.v
+++ b/vlib/v/checker/if.v
@@ -201,6 +201,11 @@ fn (mut c Checker) if_expr(mut node ast.IfExpr) ast.Type {
 					}
 				}
 			} else {
+				if branch.cond.vars.len != 1 {
+					c.error('if guard expects a single variable, but got ${branch.cond.vars.len}',
+						branch.pos)
+					continue
+				}
 				for _, var in branch.cond.vars {
 					if var.name == '_' {
 						continue
diff --git a/vlib/v/checker/tests/if_guard_variables_err.out b/vlib/v/checker/tests/if_guard_variables_err.out
index e30acdcca..df37f4ac5 100644
--- a/vlib/v/checker/tests/if_guard_variables_err.out
+++ b/vlib/v/checker/tests/if_guard_variables_err.out
@@ -1,21 +1,28 @@
-vlib/v/checker/tests/if_guard_variables_err.vv:10:2: error: if guard expects 3 variables, but got 1
-    8 | 
-    9 | fn main() {
-   10 |     if r1 := create() {
+vlib/v/checker/tests/if_guard_variables_err.vv:14:2: error: if guard expects 3 variables, but got 1
+   12 | 
+   13 | fn main() {
+   14 |     if r1 := create() {
       |     ~~~~~~~~~~~~~~~~~
-   11 |         println(r1)
-   12 |     }
-vlib/v/checker/tests/if_guard_variables_err.vv:14:2: error: if guard expects 3 variables, but got 4
-   12 |     }
-   13 | 
-   14 |     if r1, r2, r3, r4 := create() {
-      |     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    15 |         println(r1)
-   16 |         println(r2)
-vlib/v/checker/tests/if_guard_variables_err.vv:21:2: error: if guard expects 2 variables, but got 1
-   19 |     }
-   20 | 
-   21 |     if x := maybe() {
-      |     ~~~~~~~~~~~~~~~
-   22 |         println('${x}')
+   16 |     }
+vlib/v/checker/tests/if_guard_variables_err.vv:18:2: error: if guard expects 3 variables, but got 4
+   16 |     }
+   17 | 
+   18 |     if r1, r2, r3, r4 := create() {
+      |     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+   19 |         println(r1)
+   20 |         println(r2)
+vlib/v/checker/tests/if_guard_variables_err.vv:25:2: error: if guard expects 2 variables, but got 1
    23 |     }
+   24 | 
+   25 |     if x := maybe() {
+      |     ~~~~~~~~~~~~~~~
+   26 |         println('${x}')
+   27 |     }
+vlib/v/checker/tests/if_guard_variables_err.vv:29:2: error: if guard expects a single variable, but got 2
+   27 |     }
+   28 | 
+   29 |     if a, b := simple() {
+      |     ~~~~~~~~~~~~~~~~~~~
+   30 |         println(a)
+   31 |         println(b)
diff --git a/vlib/v/checker/tests/if_guard_variables_err.vv b/vlib/v/checker/tests/if_guard_variables_err.vv
index 3a63eb815..1d783d4e4 100644
--- a/vlib/v/checker/tests/if_guard_variables_err.vv
+++ b/vlib/v/checker/tests/if_guard_variables_err.vv
@@ -6,6 +6,10 @@ fn maybe() ?(int, int) {
 	return 1, 2
 }
 
+fn simple() ?int {
+	return 1
+}
+
 fn main() {
 	if r1 := create() {
 		println(r1)
@@ -21,4 +25,9 @@ fn main() {
 	if x := maybe() {
 		println('${x}')
 	}
+
+	if a, b := simple() {
+		println(a)
+		println(b)
+	}
 }
-- 
2.39.5