From 436f2e2b15c3eac5d2c33940238b48a1cfa144af Mon Sep 17 00:00:00 2001
From: jmorganca <jmorganca@gmail.com>
Date: Sat, 18 Apr 2026 23:34:54 -0700
Subject: [PATCH] llama/compat: make patch-apply idempotent
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

FetchContent's PATCH_COMMAND runs after each update step — including on
incremental rebuilds. `git apply` fails when the patch is already applied,
which bricks the build until the dev wipes build/ entirely.

Fix by routing the apply through a small apply-patch.cmake helper that
checks `git apply --reverse --check` first. If the patch cleanly reverses,
it's already applied and we skip. Otherwise apply forward. Both branches
surface real errors (drift against upstream, missing patch file, etc.).

Verified: fresh configure+build applies the patch once; re-running the
same commands is a no-op with no errors.
---
 llama/compat/apply-patch.cmake | 44 ++++++++++++++++++++++++++++++++++
 llama/compat/compat.cmake      | 11 +++++----
 2 files changed, 50 insertions(+), 5 deletions(-)
 create mode 100644 llama/compat/apply-patch.cmake

diff --git a/llama/compat/apply-patch.cmake b/llama/compat/apply-patch.cmake
new file mode 100644
index 000000000..708be4332
--- /dev/null
+++ b/llama/compat/apply-patch.cmake
@@ -0,0 +1,44 @@
+# Idempotent patch applier used by compat.cmake.
+#
+# Invocation (from a CMake PATCH_COMMAND):
+#   cmake -DPATCH_FILE=<abs path> -P apply-patch.cmake
+#
+# The patch is applied in the current working directory (which ExternalProject
+# / FetchContent sets to the fetched source's SOURCE_DIR). If the patch is
+# already applied — detected via `git apply --reverse --check` — this script
+# is a no-op. This makes re-configuring and re-building the project safe.
+
+if(NOT DEFINED PATCH_FILE)
+    message(FATAL_ERROR "apply-patch.cmake: PATCH_FILE not set")
+endif()
+if(NOT EXISTS "${PATCH_FILE}")
+    message(FATAL_ERROR "apply-patch.cmake: PATCH_FILE does not exist: ${PATCH_FILE}")
+endif()
+
+find_package(Git QUIET REQUIRED)
+
+# If the patch can be REVERSED cleanly, it's already applied. Skip.
+execute_process(
+    COMMAND ${GIT_EXECUTABLE} apply --reverse --check "${PATCH_FILE}"
+    RESULT_VARIABLE _reverse_check
+    OUTPUT_QUIET ERROR_QUIET
+)
+if(_reverse_check EQUAL 0)
+    message(STATUS "llama/compat: patch already applied, skipping")
+    return()
+endif()
+
+# Otherwise, apply forward.
+execute_process(
+    COMMAND ${GIT_EXECUTABLE} apply --whitespace=nowarn "${PATCH_FILE}"
+    RESULT_VARIABLE _apply_result
+)
+if(NOT _apply_result EQUAL 0)
+    message(FATAL_ERROR
+        "llama/compat: failed to apply ${PATCH_FILE}\n"
+        "This usually means upstream llama.cpp has drifted. "
+        "Regenerate the patch (see llama/compat/README.md) against the "
+        "pinned LLAMA_CPP_VERSION and retry.")
+endif()
+
+message(STATUS "llama/compat: applied patch")
diff --git a/llama/compat/compat.cmake b/llama/compat/compat.cmake
index db6d429fb..ef8fc9dfe 100644
--- a/llama/compat/compat.cmake
+++ b/llama/compat/compat.cmake
@@ -24,9 +24,9 @@
 set(_compat_dir ${CMAKE_CURRENT_LIST_DIR})
 
 # Expose a single variable the main CMakeLists passes into FetchContent's
-# PATCH_COMMAND. Uses CMake's own `-E copy` so it's cross-platform; uses
-# `git apply` because the patch is in unified git-diff format (same as what
-# `git diff` produces — regeneration is one command, see README).
+# PATCH_COMMAND. Uses CMake's own `-E copy` for cross-platform file copy.
+# The patch itself is applied via a small CMake script so the step is
+# idempotent — re-configuring or rebuilding won't fail with "already applied".
 set(OLLAMA_LLAMA_CPP_COMPAT_PATCH_COMMAND
     ${CMAKE_COMMAND} -E copy
         "${_compat_dir}/llama-ollama-compat.h"
@@ -34,8 +34,9 @@ set(OLLAMA_LLAMA_CPP_COMPAT_PATCH_COMMAND
     COMMAND ${CMAKE_COMMAND} -E copy
         "${_compat_dir}/llama-ollama-compat.cpp"
         "src/llama-ollama-compat.cpp"
-    COMMAND git apply --whitespace=nowarn
-        "${_compat_dir}/upstream-edits.patch"
+    COMMAND ${CMAKE_COMMAND}
+        -DPATCH_FILE=${_compat_dir}/upstream-edits.patch
+        -P ${_compat_dir}/apply-patch.cmake
     CACHE INTERNAL "llama.cpp compat patch command for FetchContent")
 
 # Also export the individual paths in case callers want to do something