Bug 1808184 - Avoid rebuilding RUST_LIBRARY_FILE based on dependencie…

…s r=sylvestre

This generalizes Bug 1806618 to library files, avoiding a few extra calls
to rustc.

Differential Revision: https://phabricator.services.mozilla.com/D165808

config/makefiles/rust.mk

@@ -428,6 +428,7 @@ ifeq (WASI,$(OS_ARCH))
 force-cargo-library-build: CARGO_RUSTCFLAGS += -C target-feature=-crt-static
 endif
 
+
 # Assume any system libraries rustc links against are already in the target's LIBS.
 #
 # We need to run cargo unconditionally, because cargo is the only thing that
@@ -437,7 +438,34 @@ force-cargo-library-build:
 	$(REPORT_BUILD)
 	$(call CARGO_BUILD) --lib $(cargo_target_flag) $(rust_features_flag) -- $(cargo_rustc_flags)
 
-$(RUST_LIBRARY_FILE): force-cargo-library-build
+# RUST_OBJ_DEPENDENCIES(RUST_OBJ,REBUILD_RULE)
+# Generates a rule suitable to rebuild RUST_OBJ with REBUILD_RULE only if its
+# dependencies are obsolete.
+#
+# It relies on the fact that upon build, cargo generates a dependency file named
+# `$(RUST_OBJ).d'. Unfortunately the lhs of the rule has an absolute path,
+# so we extract it under the name $(RUST_OBJ)_deps below.
+#
+# If the dependencies are empty, the file was not created so we force a rebuild.
+# Otherwise we add it to the dependency list.
+#
+# $(patsubst %.a,%,$(1)).d is used to extract the dependency name, the pattern
+# used by rust is:
+# 	- program_name -> program_name.d
+# 	- library_name.a -> library_name.d
+#
+# The actual rule is a bit tricky. The `+' prefix allow for recursive parallel
+# make, and it's skipped (`:') if we already triggered a rebuild as part of the
+# dependency chain.
+#
+define RUST_OBJ_DEPENDENCIES
+$(1)_deps := $(wordlist 2, 10000000, $(file < $(patsubst %.a,%,$(1)).d))
+$(1): $(CARGO_FILE) $(call resfile,module) $(if $$($(1)_deps),$$($(1)_deps),$(2))
+	$(if $$($(1)_deps),+$(MAKE) $(2),:)
+endef
+
+$(eval $(call RUST_OBJ_DEPENDENCIES,$(RUST_LIBRARY_FILE),force-cargo-library-build))
+
 # When we are building in --enable-release mode; we add an additional check to confirm
 # that we are not importing any networking-related functions in rust code. This reduces
 # the chance of proxy bypasses originating from rust code.
@@ -518,27 +546,7 @@ force-cargo-program-build: $(call resfile,module)
 	$(REPORT_BUILD)
 	$(call CARGO_BUILD) $(addprefix --bin ,$(RUST_CARGO_PROGRAMS)) $(cargo_target_flag) -- $(addprefix -C link-arg=$(CURDIR)/,$(call resfile,module)) $(CARGO_RUSTCFLAGS)
 
-# RUST_PROGRAM_DEPENDENCIES(RUST_PROGRAM)
-# Generates a rule suitable to rebuild RUST_PROGRAM only if its dependencies are
-# obsolete.
-# It relies on the fact that upon build, cargo generates a dependency file named
-# `$(RUST_PROGRAM).d'. Unfortunately the lhs of the rule has an absolute path,
-# so we extract it under the name $(RUST_PROGRAM)_deps below.
-#
-# If the dependencies are empty, the file was not created so we force a rebuild.
-# Otherwise we add it to the dependency list.
-#
-# The actual rule is a bit tricky. The `+' prefix allow for recursive parallel
-# make, and it's skipped (`:') if we already triggered a rebuild as part of the
-# dependency chain.
-#
-define RUST_PROGRAM_DEPENDENCIES
-$(1)_deps := $(wordlist 2, 10000000, $(file < $(1).d))
-$(1): $(CARGO_FILE) $(call resfile,module) $(if $$($(1)_deps),$$($(1)_deps),force-cargo-program-build)
-	$(if $$($(1)_deps),+$(MAKE) force-cargo-program-build,:)
-endef
-
-$(foreach RUST_PROGRAM,$(RUST_PROGRAMS), $(eval $(call RUST_PROGRAM_DEPENDENCIES,$(RUST_PROGRAM))))
+$(foreach RUST_PROGRAM,$(RUST_PROGRAMS), $(eval $(call RUST_PROGRAM_DEPENDENCIES,$(RUST_PROGRAM),force-cargo-program-build)))
 
 ifndef CARGO_NO_AUTO_ARG
 force-cargo-program-%: