From 66e2352bf983126150d6885d3b6834ed8b85203b Mon Sep 17 00:00:00 2001
From: ringabout <43030857+ringabout@users.noreply.github.com>
Date: Thu, 27 Feb 2025 23:48:15 +0800
Subject: [PATCH] fixes #24339; underscores used with `fields` and `fieldPairs`
 (#24341)

fixes #24339

(cherry picked from commit 7ecb35115b4b01b15aa8316f23ba13b763cb7e50)
---
 compiler/semfields.nim         | 6 ++++--
 tests/stmt/tmiscunderscore.nim | 5 +++++
 2 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/compiler/semfields.nim b/compiler/semfields.nim
index 7e2f5d6fdd..5bace728f3 100644
--- a/compiler/semfields.nim
+++ b/compiler/semfields.nim
@@ -36,7 +36,8 @@ proc instFieldLoopBody(c: TFieldInstCtx, n: PNode, forLoop: PNode): PNode =
   of nkIdent, nkSym:
     result = n
     let ident = considerQuotedIdent(c.c, n)
-    if c.replaceByFieldName:
+    if c.replaceByFieldName and
+        ident.id != ord(wUnderscore):
       if ident.id == considerQuotedIdent(c.c, forLoop[0]).id:
         let fieldName = if c.tupleType.isNil: c.field.name.s
                         elif c.tupleType.n.isNil: "Field" & $c.tupleIndex
@@ -45,7 +46,8 @@ proc instFieldLoopBody(c: TFieldInstCtx, n: PNode, forLoop: PNode): PNode =
         return
     # other fields:
     for i in ord(c.replaceByFieldName)..<forLoop.len-2:
-      if ident.id == considerQuotedIdent(c.c, forLoop[i]).id:
+      if ident.id == considerQuotedIdent(c.c, forLoop[i]).id and
+            ident.id != ord(wUnderscore):
         var call = forLoop[^2]
         var tupl = call[i+1-ord(c.replaceByFieldName)]
         if c.field.isNil:
diff --git a/tests/stmt/tmiscunderscore.nim b/tests/stmt/tmiscunderscore.nim
index c4bae1c3d8..01db9b573d 100644
--- a/tests/stmt/tmiscunderscore.nim
+++ b/tests/stmt/tmiscunderscore.nim
@@ -13,3 +13,8 @@ block:
   type _ = float
   doAssert not (compiles do:
     let x: _ = 3)
+
+block: # bug #24339
+  const r = (0, 0)
+  for _ in r.fields:
+    let _ = 0