From 4c5b0e3a5d8b2ae3055e84038c3aa04ed2a56511 Mon Sep 17 00:00:00 2001
From: Randy Eckenrode <randy@largeandhighquality.com>
Date: Mon, 19 Jan 2026 19:38:26 -0500
Subject: [PATCH] darwin.ICU: avoid conflicts with the system libicucore

The ICU C++ ABI is not stable and can change from version to version. If
the system `libicucore.A.dylib` is pulled into a process at the same time as
`libicucore.A.dylib` from Nixpkgs, it can result in a crash when those
two dylibs are from different ICU versions.

For example, macOS 26.4 appears to have updated ICU to ICU 78, but the
source release packages is still ICU 76. This causes `dotnet --info` to
crash when it tries to load `libicucore.dylib`, gets both, and the
symbols get mixed up.

This patch avoids the issue by adding a version suffix to the C++
symbols. When `dotnet` loads `libicucore.dylib`, the symbols are
resolved correctly, and it no longer crashes. Note that the C symbols
are note versioned because they are exported as the stable ABI.
---
 pkgs/os-specific/darwin/by-name/ic/ICU/package.nix | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/pkgs/os-specific/darwin/by-name/ic/ICU/package.nix b/pkgs/os-specific/darwin/by-name/ic/ICU/package.nix
index 27d7af4b0b95..f742f4743807 100644
--- a/pkgs/os-specific/darwin/by-name/ic/ICU/package.nix
+++ b/pkgs/os-specific/darwin/by-name/ic/ICU/package.nix
@@ -133,6 +133,16 @@ let
           --replace-fail '$(top_srcdir)/../LICENSE' "$NIX_BUILD_TOP/source/icu/LICENSE"
         substituteInPlace config/dist-data.sh \
           --replace-fail "\''${top_srcdir}/../LICENSE" "$NIX_BUILD_TOP/source/icu/LICENSE"
+
+        # Make sure this ICU build puts C++ symbols in a distinct namespace to avoid symbol clashes with other ICU
+        # implementations (including both the system ICU and builds of the upstream ICU).
+        # This breaks binary compatibility for the C++ API, but it’s not ABI stable anyway. Without doing this,
+        # `dotnet` crashes on macOS 26.4 when linked against `libicucore.A.dylib` from Nixpkgs.
+        substituteInPlace common/unicode/uvernum.h \
+          --replace-fail 'U_ICU_VERSION_SUFFIX ' 'U_ICU_VERSION_SUFFIX _nix'
+        # Only enable symbol renaming for C++ symbols. C symbols need to remain unversioned for compatibility.
+        substituteInPlace common/unicode/uversion.h \
+          --replace-fail U_DISABLE_RENAMING 0
       '';
 
     # remove dependency on bootstrap-tools in early stdenv build