Re: [PATCH v2] Makefile: link osxkeychain & support universal Rust

[Junio C Hamano <gitster@pobox.com>]

"Shardul Natu via GitGitGadget" <gitgitgadget@gmail.com> writes:

> From: Shnatu <snatu@google.com>
> Signed-off-by: Shardul Natu <snatu@google.com>

You'd want to make sure these two match.

> To implement this cleanly without complex shell scripting in recipes:
>   1. We introduce a declarative Make pattern rule (target/%/...) to
>      compile each target-specific library slice (e.g.,
>      target/aarch64-apple-darwin/...).
>   2. We update the $(RUST_LIB) recipe to depend on the list of
>      compiled target-specific member libraries ($(RUST_MEMBER_LIBS)).
>   3. On macOS, if multiple targets are specified, we use lipo to
>      combine them into a single Universal static library at
>      target/release/libgitcore.a.
>   4. If only one target is specified, we copy it to the standard
>      path.
>   5. We enforce that building for multiple targets requires macOS
>      (as lipo is only available there), raising a clear make error
>      on other platforms.
>
> This is a highly elegant and native Makefile solution that avoids
> complex shell scripting in recipes and fully supports macOS Universal
> Binaries.

You're the second person on this list I saw who calls their own
creation "elegant" ;-).

> +$(RUST_LIB): $(RUST_MEMBER_LIBS)
> +	$(QUIET_GEN)\
> +	if [ $(words $(RUST_TARGETS)) -gt 1 ]; then \
> +		lipo -create $^ -output $@; \
> +	else \
> +		cp $< $@; \
> +	fi
> +endif

Do we know that leading directories to $(RUST_LIB) target has
already been created at this point?  If not, we may want to have

    $(RUST_LIB): $(RUST_MEMBER_LIBS)
   +        $(call mkdir_p_parent_template)
            $(QUIET_GEN)\
            if [ $(words $(RUST_TARGETS)) -gt 1 ]; then \
                    lipo -create $^ -output $@; \

on top.

Thanks for making the build procedure better.