This series improves macOS build reliability and distribution support when
Rust is enabled in the Git build system. It addresses two distinct
challenges: a parallel build race condition in git-credential-osxkeychain
and support for macOS Universal Binaries (multi-architecture distribution).

Why This Series is Needed
=========================

 1. Parallel Build Race Condition ("make -j"): While commit 522ea8ef7d
    ("osxkeychain: fix build with Rust") updated the link command for
    git-credential-osxkeychain to pass $(LIBS), it omitted $(RUST_LIB) from
    the target prerequisite list. When running a parallel build ("make -j")
    from a clean working tree, Make can attempt to link
    git-credential-osxkeychain before Cargo has finished compiling
    libgitcore.a, causing linker failures.

 2. macOS Universal Binary (lipo) Support: On macOS, Universal Binaries
    bundle native executable code for multiple architectures (Intel x86_64
    and Apple Silicon arm64) into a single file. This is standard practice
    for macOS distribution and CI packaging (such as Burrito, Homebrew, and
    Git's macOS CI runners), allowing a single artifact to run natively
    across all Macs without Rosetta translation.

While Apple's C compiler (clang) natively supports universal builds by
passing "-arch x86_64 -arch arm64" in CFLAGS and LDFLAGS, Cargo and rustc do
not support multiple "-arch" flags in a single invocation. Instead, Cargo
must be invoked separately for each target triple ("--target
x86_64-apple-darwin" and "--target aarch64-apple-darwin"). This series
bridges that gap.

Overview of Patches
===================

 * Patch 1: Makefile: add $(RUST_LIB) prerequisite to osxkeychain Adds
   $(RUST_LIB) as a prerequisite dependency to the osxkeychain target,
   eliminating the parallel build race condition. Additionally, wraps the
   definitions of $(RUST_LIB) and the "rust" build target in "ifndef
   NO_RUST" so that disabling Rust cleanly makes the dependency a no-op.

 * Patch 2: Makefile: support universal macOS builds via RUST_TARGETS Allows
   users to specify space-separated target triples in RUST_TARGETS.
   Introduces declarative pattern rules (target/%/...) to compile each
   target slice via Cargo, and uses "lipo" (part of the mandatory Xcode
   Command Line Tools) to combine the resulting static archives into a
   universal library at target/release/libgitcore.a. Uses
   mkdir_p_parent_template to guarantee directory creation before lipo.

Changes since v2:

 * Split the original combined commit into a two-patch series to separate
   prerequisite bug fixes from Universal Binary features.
 * Added $(call mkdir_p_parent_template) prior to invoking lipo to guarantee
   that parent target directories exist.
 *

Shardul Natu (2):
  Makefile: add $(RUST_LIB) prerequisite to osxkeychain
  Makefile: support universal macOS builds via RUST_TARGETS

 Makefile | 46 +++++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 41 insertions(+), 5 deletions(-)

base-commit: 602f6c329a7d99df269d382df353b4e1bbbbd8aa

Submitted-As: https://lore.kernel.org/git/pull.2288.v4.git.git.1783188355.gitgitgadget@gmail.com
In-Reply-To: https://lore.kernel.org/git/pull.2288.git.git.1778001976709.gitgitgadget@gmail.com
In-Reply-To: https://lore.kernel.org/git/pull.2288.v2.git.git.1782943303219.gitgitgadget@gmail.com
In-Reply-To: https://lore.kernel.org/git/pull.2288.v3.git.git.1783030971.gitgitgadget@gmail.com