[PATCH v5 0/2] Makefile: link osxkeychain helper against Rust

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 v4:

 * Changed the osxkeychain prerequisite dependency from $(LIB_FILE)
   $(RUST_LIB) to $(GITLIBS) to match the canonical prerequisite pattern
   used by all other core Git targets linking $(LIBS).

Changes since v3:

 * Removed leading @ from $(call mkdir_p_parent_template) so it relies on
   the built-in $(QUIET_MKDIR_P_PARENT) behavior, matching existing Makefile
   conventions.
 * Replaced if [ with if test in Bourne shell recipe snippets to strictly
   adhere to the project's CodingGuidelines.

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 $(GITLIBS) prerequisite to osxkeychain
  Makefile: support universal macOS builds via RUST_TARGETS

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

base-commit: 602f6c329a7d99df269d382df353b4e1bbbbd8aa
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-2288%2Fkiranani%2Fnext-v5
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-2288/kiranani/next-v5
Pull-Request: https://github.com/git/git/pull/2288

Range-diff vs v4:

 1:  41de7d391a ! 1:  e0bb18ff01 Makefile: add $(RUST_LIB) prerequisite to osxkeychain
     @@ Metadata
      Author: Shardul Natu <snatu@google.com>
      
       ## Commit message ##
     -    Makefile: add $(RUST_LIB) prerequisite to osxkeychain
     +    Makefile: add $(GITLIBS) prerequisite to osxkeychain
      
          When Rust is enabled, the git-credential-osxkeychain helper depends on
          Rust symbols compiled into $(RUST_LIB). While commit 522ea8ef7d
     @@ Commit message
          clean working tree can fail because Make does not know to invoke Cargo
          to build libgitcore.a before linking git-credential-osxkeychain.
      
     -    Add $(RUST_LIB) as a prerequisite dependency to the
     -    git-credential-osxkeychain target.
     +    All other core Git targets that link $(LIBS) already depend on
     +    $(GITLIBS), which bundles common-main.o, $(LIB_FILE), and $(RUST_LIB)
     +    when Rust is enabled. Add $(GITLIBS) as a prerequisite dependency to the
     +    git-credential-osxkeychain target to make it consistent with the rest of
     +    the codebase.
      
          Additionally, wrap the definitions of $(RUST_LIB) and the "rust" build
          target in "ifndef NO_RUST". This ensures that when NO_RUST=1 is
     @@ Makefile: $(LIBGIT_HIDDEN_EXPORT): $(LIBGIT_PARTIAL_EXPORT)
       
      -contrib/credential/osxkeychain/git-credential-osxkeychain: contrib/credential/osxkeychain/git-credential-osxkeychain.o $(LIB_FILE) GIT-LDFLAGS
      +# When Rust is enabled, git-credential-osxkeychain depends on Rust symbols in $(RUST_LIB)
     -+contrib/credential/osxkeychain/git-credential-osxkeychain: contrib/credential/osxkeychain/git-credential-osxkeychain.o $(LIB_FILE) $(RUST_LIB) GIT-LDFLAGS
     ++contrib/credential/osxkeychain/git-credential-osxkeychain: contrib/credential/osxkeychain/git-credential-osxkeychain.o $(GITLIBS) GIT-LDFLAGS
       	$(QUIET_LINK)$(CC) $(ALL_CFLAGS) -o $@ $(ALL_LDFLAGS) \
       		$(filter %.o,$^) $(LIBS) -framework Security -framework CoreFoundation
       
 2:  88fc2e0bd8 ! 2:  66f71fb0d7 Makefile: support universal macOS builds via RUST_TARGETS
     @@ Commit message
            3. On macOS, if multiple targets are specified, use "lipo" (part of
               the mandatory Xcode Command Line Tools) to combine the resulting
               static libraries into target/release/libgitcore.a.
     -      4. Ensure target directory creation before invoking lipo via
     -         mkdir_p_parent_template.
      
          Once $(RUST_LIB) is compiled into a universal static archive, the
          standard C linker seamlessly links it with the C object files to
     @@ Makefile: include shared.mak
       # Building Rust code requires Cargo.
       #
      +# Define RUST_TARGETS if you want to cross-compile. If left unspecified, it uses
     -+# the default rust target on the system.
     ++# the default Rust target on the system.
      +#
      +# On macOS, this supports specifying multiple targets, separated by a space.
      +# This will produce a Universal static library using `lipo`.