"Shardul Natu via GitGitGadget" [off-list ref] writes:

From: Shnatu <redacted>
Signed-off-by: Shardul Natu <redacted>

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.