From 9bb7e53e7f56fe3ddaa69849ff663ad18858e038 Mon Sep 17 00:00:00 2001
From: ringabout <43030857+ringabout@users.noreply.github.com>
Date: Thu, 12 Dec 2024 04:02:24 +0800
Subject: [PATCH] fixes #22153; UB calling allocCStringArray([""]) with
 --mm:refc (#24529)

fixes #22153

It's a problem for refc because you cannot index a nil string: i.e.
`[""]` is `{((NimStringDesc*) NIM_NIL)}` which cannot be indexed
---
 lib/system.nim           | 2 +-
 tests/objects/t20972.nim | 8 ++++++++
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/lib/system.nim b/lib/system.nim
index b2cf92ffb7..abfd1bcd41 100644
--- a/lib/system.nim
+++ b/lib/system.nim
@@ -2143,7 +2143,7 @@ when not defined(js) and declared(alloc0) and declared(dealloc):
     let x = cast[ptr UncheckedArray[string]](a)
     for i in 0 .. a.high:
       result[i] = cast[cstring](alloc0(x[i].len+1))
-      copyMem(result[i], addr(x[i][0]), x[i].len)
+      copyMem(result[i], x[i].cstring, x[i].len)
 
   proc deallocCStringArray*(a: cstringArray) =
     ## Frees a NULL terminated cstringArray.
diff --git a/tests/objects/t20972.nim b/tests/objects/t20972.nim
index 6383dc9b11..627357bc56 100644
--- a/tests/objects/t20972.nim
+++ b/tests/objects/t20972.nim
@@ -13,3 +13,11 @@ var info = ForkedEpochInfo(kind: true)
 doAssert info.kind
 info.kind = false
 doAssert not info.kind
+
+block: # bug #22153
+  discard allocCStringArray([""])
+  discard allocCStringArray(["1234"])
+
+  var s = "1245"
+  s.add "1"
+  discard allocCStringArray([s])