From e0c5e8b7a48033fb82e18dbe74b75c9b8d1d641d Mon Sep 17 00:00:00 2001
From: Rongsong Shen <rshen@shenrs.eu>
Date: Fri, 24 Jul 2026 08:25:38 +0000
Subject: [PATCH] fix(nix): pin capnpc source to immutable commit, not mutable
 main ref

xbuild's capnpc package pinned src to shen390s/c-capnproto's `main`
branch with a hardcoded sha256, so every upstream push broke `nix
develop` with a fixed-output-derivation hash mismatch (bug-918,
recurred 4x in this worktree). Override capnpc's src to a
fetchFromGitHub pinned at an immutable commit instead.
---
 src/nixSupport/xce.nix | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/src/nixSupport/xce.nix b/src/nixSupport/xce.nix
index 65c47ede..63a4902a 100644
--- a/src/nixSupport/xce.nix
+++ b/src/nixSupport/xce.nix
@@ -35,6 +35,17 @@ stdenv.mkDerivation {
     struct2json
     (capnpc.overrideAttrs (oldAttrs: {
       separateDebugInfo = true;
+      # bug-918: upstream xbuild's capnpc package.nix pins src to the
+      # MUTABLE `main` ref of shen390s/c-capnproto with a hardcoded sha256,
+      # so it hard-breaks (fixed-output hash mismatch) every time that
+      # branch moves. Pin to an immutable commit here instead so this repo
+      # stops depending on upstream's moving target.
+      src = pkgs.fetchFromGitHub {
+        owner = "shen390s";
+        repo = "c-capnproto";
+        rev = "e45ff682c4756ac5067cbac6d0f282a8ea5f0155";
+        sha256 = "sha256-9rTlcTia+s9ARGeTi+8auGvM0RkS+wZK7aIkzecaeSk=";
+      };
     }))
     which
     findutils