From 87511babb561315b2e650909ec782ce4704a4c1b Mon Sep 17 00:00:00 2001
From: ringabout <43030857+ringabout@users.noreply.github.com>
Date: Tue, 8 Sep 2026 04:23:43 +0800
Subject: [PATCH] =?UTF-8?q?fixes=20#26176;=20nim=20js:=20explicit=20{.clos?=
 =?UTF-8?q?ure.}=20on=20a=20lambda=20with=20parameter=E2=80=A6=20(#26179)?=
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…s crashes codegen

fixes #26176

It follows the same method of the C backend. Don't insert "this" in
JavaScript backend If no variables are captured by closure functions.
---
 compiler/jsgen.nim     | 2 +-
 tests/js/tclosures.nim | 5 +++++
 2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/compiler/jsgen.nim b/compiler/jsgen.nim
index a0134acbe9..3d32e7d60f 100644
--- a/compiler/jsgen.nim
+++ b/compiler/jsgen.nim
@@ -1220,7 +1220,7 @@ proc generateHeader(p: PProc, prc: PSym): Rope =
   result = ""
   let typ = prc.typ
   if jsNoLambdaLifting notin p.config.legacyFeatures:
-    if typ.callConv == ccClosure:
+    if typ.callConv == ccClosure and tfCapturesEnv in typ.flags:
       # we treat Env as the `this` parameter of the function
       # to keep it simple
       let env = prc.ast[paramsPos].lastSon
diff --git a/tests/js/tclosures.nim b/tests/js/tclosures.nim
index 4f1c28de3f..ee3a35cb61 100644
--- a/tests/js/tclosures.nim
+++ b/tests/js/tclosures.nim
@@ -50,6 +50,11 @@ let results = runCallbacks()
 
 doAssert(expected == $results)
 
+block issue26176:
+  let g = proc(x: int): int {.closure.} =
+    result = x + 1
+  doAssert g(1) == 2
+
 block issue7048:
   block:
     proc foo(x: seq[int]): auto =