Makefile: Use pattern rules to build Go binaries

We're using a phony `GITALY_EXECUTABLES` target to rebuild Gitaly
executables. This usage pattern is quite hard to read given that this
single target builds all binaries while not using any patterns at all.

Convert the target to instead use pattern rules, which are easier to
understand. Furthermore, instead of making these rules phony, let's
instead use a `.FORCE` dependency to force rebuilding them every time.

1 files changed, 12 insertions, 10 deletions

diff --git a/Makefile b/Makefile
index 9ae657240..453234731 100644
--- a/Makefile
+++ b/Makefile
@@ -218,7 +218,7 @@ TEST_REPO_GIT    := ${TEST_REPO_DIR}/gitlab-git-test.git
 BENCHMARK_REPO   := ${TEST_REPO_DIR}/benchmark.git
 
 # All executables provided by Gitaly
-GITALY_EXECUTABLES    = $(notdir $(shell find ${SOURCE_DIR}/cmd -mindepth 1 -maxdepth 1 -type d -print))
+GITALY_EXECUTABLES    = $(addprefix ${BUILD_DIR}/bin/,$(notdir $(shell find ${SOURCE_DIR}/cmd -mindepth 1 -maxdepth 1 -type d -print)))
 # Find all Go source files.
 find_go_sources       = $(shell find ${SOURCE_DIR} -type d \( -name ruby -o -name vendor -o -name testdata -o -name '_*' -o -path '*/proto/go/gitalypb' \) -prune -o -type f -name '*.go' -not -name '*.pb.go' -print | sort -u)
 
@@ -251,6 +251,9 @@ export CGO_LDFLAGS_ALLOW          = -D_THREAD_SAFE
 ## Default target which builds Gitaly.
 all: build
 
+.PHONY: .FORCE
+.FORCE:
+
 ## Print help about available targets and variables.
 help:
 	@echo "usage: make [<target>...] [<variable>=<value>...]"
@@ -276,23 +279,22 @@ help:
 ## Build Go binaries and install required Ruby Gems.
 build: ${SOURCE_DIR}/.ruby-bundle ${GITALY_EXECUTABLES}
 
-gitaly:            GO_BUILD_TAGS = ${SERVER_BUILD_TAGS}
-praefect:          GO_BUILD_TAGS = ${SERVER_BUILD_TAGS}
-gitaly-git2go-v14: GO_BUILD_TAGS = ${GIT2GO_BUILD_TAGS}
-gitaly-git2go-v14: libgit2
+${BUILD_DIR}/bin/gitaly:            GO_BUILD_TAGS = ${SERVER_BUILD_TAGS}
+${BUILD_DIR}/bin/praefect:          GO_BUILD_TAGS = ${SERVER_BUILD_TAGS}
+${BUILD_DIR}/bin/gitaly-git2go-v14: GO_BUILD_TAGS = ${GIT2GO_BUILD_TAGS}
+${BUILD_DIR}/bin/gitaly-git2go-v14: libgit2
 
-.PHONY: ${GITALY_EXECUTABLES}
-${GITALY_EXECUTABLES}:
-	${Q}go install -ldflags '${GO_LDFLAGS}' -tags "${GO_BUILD_TAGS}" $(addprefix ${GITALY_PACKAGE}/cmd/, $@)
+${BUILD_DIR}/bin/%: .FORCE
+	${Q}go install -ldflags '${GO_LDFLAGS}' -tags "${GO_BUILD_TAGS}" $(addprefix ${SOURCE_DIR}/cmd/,$(@F))
 	@ # To compute a unique and deterministic value for GNU build-id, we build the Go binary a second time.
 	@ # From the first build, we extract its unique and deterministic Go build-id, and use that to derive
 	@ # comparably unique and deterministic GNU build-id to inject into the final binary.
 	@ # If we cannot extract a Go build-id, we punt and fallback to using a random 32-byte hex string.
 	@ # This fallback is unique but non-deterministic, making it sufficient to avoid generating the
 	@ # GNU build-id from the empty string and causing guaranteed collisions.
-	${Q}GO_BUILD_ID=$$( go tool buildid $(addprefix ${BUILD_DIR}/bin/, $@) || openssl rand -hex 32 ) && \
+	${Q}GO_BUILD_ID=$$( go tool buildid "$@" || openssl rand -hex 32 ) && \
 	GNU_BUILD_ID=$$( echo $$GO_BUILD_ID | sha1sum | cut -d' ' -f1 ) && \
-	go install -ldflags '${GO_LDFLAGS}'" -B 0x$$GNU_BUILD_ID" -tags "${GO_BUILD_TAGS}" $(addprefix ${GITALY_PACKAGE}/cmd/, $@)
+	go install -ldflags '${GO_LDFLAGS}'" -B 0x$$GNU_BUILD_ID" -tags "${GO_BUILD_TAGS}" $(addprefix ${SOURCE_DIR}/cmd/,$(@F))
 
 .PHONY: install
 ## Install Gitaly binaries. The target directory can be modified by setting PREFIX and DESTDIR.