add TAGS variable prereq on make targets that use it (#10219)

Write out TAGS to .make_evidence/tags and compare it to the previous
invocation. If they differ, insert the evidence file into the prereqs
of targets that use TAGS. I made it .PHONY so it always builds.

I did not include the prereq on release tasks, asssuming the will always
do a clean build.

Fixes: https://github.com/go-gitea/gitea/issues/10196

Co-authored-by: techknowlogick <matti@mdranta.net>
Co-authored-by: Antoine GIRARD <sapk@users.noreply.github.com>

Makefile

@@ -70,6 +70,7 @@ FOMANTIC_DEST_DIR := public/fomantic
 FOMANTIC_EVIDENCE := $(MAKE_EVIDENCE_DIR)/fomantic
 
 TAGS ?=
+TAGS_EVIDENCE := $(MAKE_EVIDENCE_DIR)/tags
 
 TMPDIR := $(shell mktemp -d 2>/dev/null || mktemp -d -t 'gitea-temp')
 
@@ -168,8 +169,17 @@ fmt:
 vet:
 	$(GO) vet $(PACKAGES)
 
+.PHONY: $(TAGS_EVIDENCE)
+$(TAGS_EVIDENCE):
+	@mkdir -p $(MAKE_EVIDENCE_DIR)
+	@echo "$(TAGS)" > $(TAGS_EVIDENCE)
+
+ifneq "$(TAGS)" "$(shell cat $(TAGS_EVIDENCE) 2>/dev/null)"
+TAGS_PREREQ := $(TAGS_EVIDENCE)
+endif
+
 .PHONY: generate
-generate: fomantic webpack
+generate: fomantic webpack $(TAGS_PREREQ)
 	GO111MODULE=on $(GO) generate -mod=vendor -tags '$(TAGS)' $(PACKAGES)
 
 .PHONY: generate-swagger
@@ -425,14 +435,14 @@ migrations.sqlite.test: $(GO_SOURCES)
 .PHONY: check
 check: test
 
-.PHONY: install
+.PHONY: install $(TAGS_PREREQ)
 install: $(wildcard *.go)
 	$(GO) install -v -tags '$(TAGS)' -ldflags '-s -w $(LDFLAGS)'
 
 .PHONY: build
 build: go-check generate $(EXECUTABLE)
 
-$(EXECUTABLE): $(GO_SOURCES)
+$(EXECUTABLE): $(GO_SOURCES) $(TAGS_PREREQ)
 	GO111MODULE=on $(GO) build -mod=vendor $(GOFLAGS) $(EXTRA_GOFLAGS) -tags '$(TAGS)' -ldflags '-s -w $(LDFLAGS)' -o $@
 
 .PHONY: release