mk: deprecate BSD make in favor of GNU make

Being portable between BSD and GNU make is a nightmare. It restricts
features to a very minimal surface and in turn requires a lot of code
duplication and manual updating of file lists.

Worse, aerc's makefile relies on the shell assignment operator (!=)
which has been supported by BSD make 2.2 since 1997 but GNU make 4.0
since 2013. Unfortunately, MacOS runs GNU make 3.8 which does not have
that feature. Reducing the feature set even more.

Stop that nonsense and remove BSD make compatibility. The majority of
aerc's users either run a GNU Linux distribution or MacOS. For those who
run any *BSD variant, it is easy for them to install GNU make (gmake) if
they don't have it installed already.

Use GNU make constructs to generate build and install rules dynamically
based on source files discovery.

GNU make will use "GNUmakefile" in priority over "Makefile" if possible.
Leverage this to display an explicit message when other flavours of make
are used. Leave a "Makefile" with a .DEFAULT: target and rename the
actual file to "GNUmakefile".

Signed-off-by: Robin Jarry <robin@jarry.cc>

5 files changed, 222 insertions, 223 deletions

diff --git a/.builds/openbsd.yml b/.builds/openbsd.yml
index 811fbf7a..5ef3d463 100644
--- a/.builds/openbsd.yml
+++ b/.builds/openbsd.yml
@@ -4,6 +4,8 @@ packages:
   - go
   - gnupg
   - scdoc
+  - base64
+  - gmake
 sources:
   - "https://git.sr.ht/~rjarry/aerc"
 environment:
@@ -11,8 +13,8 @@ environment:
 tasks:
   - build: |
       cd aerc
-      make
+      gmake
   - install: |
       cd aerc
-      make install
-      make checkinstall
+      gmake install
+      gmake checkinstall
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 29fba540..e4d63bd4 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -43,6 +43,11 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 - `:export-mbox` only exports marked messages, if any. Otherwise it exports
   everything, as usual.
 
+### Deprecated
+
+- Aerc can no longer be compiled and installed with BSD make. GNU make must be
+  used instead.
+
 ## [0.15.2](https://git.sr.ht/~rjarry/aerc/refs/0.15.2) - 2023-05-11
 
 ### Fixed
diff --git a/GNUmakefile b/GNUmakefile
new file mode 100644
index 00000000..e8ac67fe
--- /dev/null
+++ b/GNUmakefile
@@ -0,0 +1,204 @@
+# variables that can be changed by users
+#
+VERSION ?= `git describe --long --abbrev=12 --tags --dirty 2>/dev/null || echo 0.15.2`
+PREFIX ?= /usr/local
+BINDIR ?= $(PREFIX)/bin
+SHAREDIR ?= $(PREFIX)/share/aerc
+LIBEXECDIR ?= $(PREFIX)/libexec/aerc
+MANDIR ?= $(PREFIX)/share/man
+GO ?= go
+GOFLAGS ?= `contrib/goflags.sh`
+BUILD_OPTS ?= -trimpath
+GO_LDFLAGS :=
+GO_LDFLAGS += -X main.Version=$(VERSION)
+GO_LDFLAGS += -X main.Flags=$$(echo -- $(GOFLAGS) | base64 | tr -d '\r\n')
+GO_LDFLAGS += -X git.sr.ht/~rjarry/aerc/config.shareDir=$(SHAREDIR)
+GO_LDFLAGS += -X git.sr.ht/~rjarry/aerc/config.libexecDir=$(LIBEXECDIR)
+GO_LDFLAGS += $(GO_EXTRA_LDFLAGS)
+CC ?= cc
+CFLAGS ?= -O2 -g
+
+# internal variables used for automatic rules generation with macros
+gosrc = $(shell find * -type f -name '*.go') go.mod go.sum
+man1 = $(subst .scd,,$(notdir $(wildcard doc/*.1.scd)))
+man5 = $(subst .scd,,$(notdir $(wildcard doc/*.5.scd)))
+man7 = $(subst .scd,,$(notdir $(wildcard doc/*.7.scd)))
+docs = $(man1) $(man5) $(man7)
+cfilters = $(subst .c,,$(notdir $(wildcard filters/*.c)))
+filters = $(filter-out filters/vectors filters/test.sh filters/%.c,$(wildcard filters/*))
+gofumpt_tag = v0.5.0
+
+# Dependencies are added dynamically to the "all" rule with macros
+.PHONY: all
+all: aerc
+	@:
+
+aerc: $(gosrc)
+	$(GO) build $(BUILD_OPTS) $(GOFLAGS) -ldflags "$(GO_LDFLAGS)" -o aerc
+
+.PHONY: dev
+dev:
+	$(RM) aerc
+	$(MAKE) --no-print-directory aerc BUILD_OPTS="-trimpath -race"
+	GORACE="log_path=race.log strip_path_prefix=git.sr.ht/~rjarry/aerc/" ./aerc
+
+.PHONY: fmt
+fmt:
+	$(GO) run mvdan.cc/gofumpt@$(gofumpt_tag) -w .
+
+linters.so: contrib/linters.go
+	$(GO) build -buildmode=plugin -o linters.so contrib/linters.go
+
+.PHONY: lint
+lint: linters.so
+	@contrib/check-whitespace `git ls-files ':!:filters/vectors'` && \
+		echo white space ok.
+	@$(GO) run mvdan.cc/gofumpt@$(gofumpt_tag) -d . | grep ^ \
+		&& echo The above files need to be formatted, please run make fmt && exit 1 \
+		|| echo all files formatted.
+	$(GO) run github.com/golangci/golangci-lint/cmd/golangci-lint@v1.51.2 run \
+		$$(echo $(GOFLAGS) | sed s/-tags=/--build-tags=/)
+
+.PHONY: vulncheck
+vulncheck:
+	$(GO) run golang.org/x/vuln/cmd/govulncheck@latest ./...
+
+.PHONY: tests
+tests: $(cfilters)
+	$(GO) test $(GOFLAGS) ./...
+	filters/test.sh
+
+.PHONY: debug
+debug: aerc.debug
+	@echo 'Run `./aerc.debug` and use this command in another terminal to attach a debugger:'
+	@echo '    dlv attach $$(pidof aerc.debug)'
+
+aerc.debug: $(gosrc)
+	$(GO) build $(GOFLAGS) -gcflags=*=-N -gcflags=*=-l -ldflags="$(GO_LDFLAGS)" -o aerc.debug
+
+.PHONY: doc
+doc: $(docs)
+	@:
+
+.PHONY: clean
+clean:
+	$(RM) $(docs) aerc $(cfilters)
+
+# Dependencies are added dynamically to the "install" rule with macros
+.PHONY: install
+install:
+	@:
+
+.PHONY: checkinstall
+checkinstall:
+	$(DESTDIR)$(BINDIR)/aerc -v
+	for m in $(man1); do test -e $(DESTDIR)$(MANDIR)/man1/$$m || exit; done
+	for m in $(man5); do test -e $(DESTDIR)$(MANDIR)/man5/$$m || exit; done
+	for m in $(man7); do test -e $(DESTDIR)$(MANDIR)/man7/$$m || exit; done
+
+RMDIR_IF_EMPTY:=sh -c '! [ -d $$0 ] || ls -1qA $$0 | grep -q . || rmdir $$0'
+
+.PHONY: uninstall
+uninstall:
+	$(RM) $(DESTDIR)$(BINDIR)/aerc
+	$(RM) $(DESTDIR)$(BINDIR)/carddav-query
+	for m in $(man1); do $(RM) $(DESTDIR)$(MANDIR)/man1/$$m; done
+	for m in $(man5); do $(RM) $(DESTDIR)$(MANDIR)/man5/$$m; done
+	for m in $(man7); do $(RM) $(DESTDIR)$(MANDIR)/man7/$$m; done
+	$(RM) -r $(DESTDIR)$(SHAREDIR)
+	$(RM) -r $(DESTDIR)$(LIBEXECDIR)
+	${RMDIR_IF_EMPTY} $(DESTDIR)$(BINDIR)
+	$(RMDIR_IF_EMPTY) $(DESTDIR)$(MANDIR)/man1
+	$(RMDIR_IF_EMPTY) $(DESTDIR)$(MANDIR)/man5
+	$(RMDIR_IF_EMPTY) $(DESTDIR)$(MANDIR)/man7
+	$(RMDIR_IF_EMPTY) $(DESTDIR)$(MANDIR)
+	$(RM) $(DESTDIR)$(PREFIX)/share/applications/aerc.desktop
+	$(RMDIR_IF_EMPTY) $(DESTDIR)$(PREFIX)/share/applications
+
+.PHONY: gitconfig
+gitconfig:
+	git config format.subjectPrefix "PATCH aerc"
+	git config sendemail.to "~rjarry/aerc-devel@lists.sr.ht"
+	@mkdir -p .git/hooks
+	@rm -f .git/hooks/sendemail-validate*
+	@if grep -q GIT_SENDEMAIL_FILE_COUNTER `git --exec-path`/git-send-email 2>/dev/null; then \
+		ln -svf ../../contrib/sendemail-validate .git/hooks/sendemail-validate && \
+		git config sendemail.validate true; \
+	fi
+
+.PHONY: check-patches
+check-patches:
+	@contrib/check-patches origin/master..
+
+# Generate build and install rules for one man page
+#
+# $1: man page name (e.g: aerc.1)
+#
+define install_man
+$1: doc/$1.scd
+	scdoc < $$< > $$@
+
+$1_section = $$(subst .,,$$(suffix $1))
+$1_install_dir = $$(DESTDIR)$$(MANDIR)/man$$($1_section)
+dirs += $$($1_install_dir)
+
+$$($1_install_dir)/$1: $1 | $$($1_install_dir)
+	install -m644 $$< $$@
+
+all: $1
+install: $$($1_install_dir)/$1
+endef
+
+# Generate build and install rules for one filter
+#
+# $1: filter source path or name
+#
+define install_filter
+ifneq ($(wildcard filters/$1.c),)
+$1: filters/$1.c
+	$$(CC) $$(CFLAGS) $$(LDFLAGS) -o $$@ $$<
+
+all: $1
+endif
+
+$1_install_dir = $$(DESTDIR)$$(LIBEXECDIR)/filters
+dirs += $$($1_install_dir)
+
+$$($1_install_dir)/$$(notdir $1): $1 | $$($1_install_dir)
+	install -m755 $$< $$@
+
+install: $$($1_install_dir)/$$(notdir $1)
+endef
+
+# Generate install rules for any file
+#
+# $1: source file
+# $2: mode
+# $3: target dir
+#
+define install_file
+dirs += $3
+
+$3/$$(notdir $1): $1 | $3
+	install -m$2 $$< $$@
+
+install: $3/$$(notdir $1)
+endef
+
+# Call macros to generate build and install rules
+$(foreach m,$(docs),\
+	$(eval $(call install_man,$m)))
+$(foreach f,$(filters) $(cfilters),\
+	$(eval $(call install_filter,$f)))
+$(foreach f,$(wildcard config/*.conf),\
+	$(eval $(call install_file,$f,644,$(DESTDIR)$(SHAREDIR))))
+$(foreach s,$(wildcard stylesets/*),\
+	$(eval $(call install_file,$s,644,$(DESTDIR)$(SHAREDIR)/stylesets)))
+$(foreach t,$(wildcard templates/*),\
+	$(eval $(call install_file,$t,644,$(DESTDIR)$(SHAREDIR)/templates)))
+$(eval $(call install_file,contrib/aerc.desktop,644,$(DESTDIR)$(PREFIX)/share/applications))
+$(eval $(call install_file,aerc,755,$(DESTDIR)$(BINDIR)))
+$(eval $(call install_file,contrib/carddav-query,755,$(DESTDIR)$(BINDIR)))
+
+$(sort $(dirs)):
+	mkdir -p $@
diff --git a/Makefile b/Makefile
index acd8a728..ebbfb428 100644
--- a/Makefile
+++ b/Makefile
@@ -1,220 +1,7 @@
-.POSIX:
-.SUFFIXES:
-.SUFFIXES: .1 .5 .7 .1.scd .5.scd .7.scd
-
-VERSION?=`git describe --long --abbrev=12 --tags --dirty 2>/dev/null || echo 0.15.2`
-VPATH=doc
-PREFIX?=/usr/local
-BINDIR?=$(PREFIX)/bin
-SHAREDIR?=$(PREFIX)/share/aerc
-LIBEXECDIR?=$(PREFIX)/libexec/aerc
-MANDIR?=$(PREFIX)/share/man
-GO?=go
-GOFLAGS?=`contrib/goflags.sh`
-BUILD_OPTS?=-trimpath
-# ignore environment variable
-GO_LDFLAGS:=
-GO_LDFLAGS+=-X main.Version=$(VERSION)
-GO_LDFLAGS+=-X main.Flags=$$(echo -- $(GOFLAGS) | base64 | tr -d '\r\n')
-GO_LDFLAGS+=-X git.sr.ht/~rjarry/aerc/config.shareDir=$(SHAREDIR)
-GO_LDFLAGS+=-X git.sr.ht/~rjarry/aerc/config.libexecDir=$(LIBEXECDIR)
-GO_LDFLAGS+=$(GO_EXTRA_LDFLAGS)
-
-GOSRC!=find * -type f -name '*.go'
-GOSRC+=go.mod go.sum
-
-DOCS := \
-	aerc.1 \
-	aerc-search.1 \
-	aerc-accounts.5 \
-	aerc-binds.5 \
-	aerc-config.5 \
-	aerc-imap.5 \
-	aerc-jmap.5 \
-	aerc-maildir.5 \
-	aerc-sendmail.5 \
-	aerc-notmuch.5 \
-	aerc-smtp.5 \
-	aerc-tutorial.7 \
-	aerc-templates.7 \
-	aerc-stylesets.7 \
-	carddav-query.1
-
-all: aerc wrap colorize $(DOCS)
-
-aerc: $(GOSRC)
-	$(GO) build $(BUILD_OPTS) $(GOFLAGS) -ldflags "$(GO_LDFLAGS)" -o aerc
-
-CC?=cc
-CFLAGS?=-O2 -g
-
-wrap: filters/wrap.c
-	$(CC) $(CFLAGS) $(LDFLAGS) -o wrap filters/wrap.c
-
-colorize: filters/colorize.c
-	$(CC) $(CFLAGS) $(LDFLAGS) -o colorize filters/colorize.c
-
-.PHONY: dev
-dev:
-	$(MAKE) aerc BUILD_OPTS="-trimpath -race"
-	GORACE="log_path=race.log strip_path_prefix=git.sr.ht/~rjarry/aerc/" ./aerc
-
-gofumpt_tag = v0.5.0
-
-.PHONY: fmt
-fmt:
-	$(GO) run mvdan.cc/gofumpt@$(gofumpt_tag) -w .
-
-linters.so: contrib/linters.go
-	$(GO) build -buildmode=plugin -o linters.so contrib/linters.go
-
-.PHONY: lint
-lint: linters.so
-	@contrib/check-whitespace `git ls-files ':!:filters/vectors'` && \
-		echo white space ok.
-	@$(GO) run mvdan.cc/gofumpt@$(gofumpt_tag) -d . | grep ^ \
-		&& echo The above files need to be formatted, please run make fmt && exit 1 \
-		|| echo all files formatted.
-	$(GO) run github.com/golangci/golangci-lint/cmd/golangci-lint@v1.51.2 run \
-		$$(echo $(GOFLAGS) | sed s/-tags=/--build-tags=/)
-
-.PHONY: vulncheck
-vulncheck:
-	$(GO) run golang.org/x/vuln/cmd/govulncheck@latest ./...
-
-.PHONY: tests
-tests: wrap colorize
-	$(GO) test $(GOFLAGS) ./...
-	filters/test.sh
-
-.PHONY: debug
-debug: aerc.debug
-	@echo 'Run `./aerc.debug` and use this command in another terminal to attach a debugger:'
-	@echo '    dlv attach $$(pidof aerc.debug)'
-
-aerc.debug: $(GOSRC)
-	$(GO) build $(GOFLAGS) -gcflags=*=-N -gcflags=*=-l -ldflags="$(GO_LDFLAGS)" -o aerc.debug
-
-.1.scd.1:
-	scdoc < $< > $@
-
-.5.scd.5:
-	scdoc < $< > $@
-
-.7.scd.7:
-	scdoc < $< > $@
-
-doc: $(DOCS)
-
-# Exists in GNUMake but not in NetBSD make and others.
-RM?=rm -f
-
-clean:
-	$(RM) $(DOCS) aerc wrap colorize
-
-install: $(DOCS) aerc wrap colorize
-	@# `install -D` is not supported on all platforms (macos install(1)
-	@# dates back to the middle ages and does not have this flag).
-	@# The folders must be created manually first.
-	mkdir -m755 -p $(DESTDIR)$(BINDIR) $(DESTDIR)$(MANDIR)/man1 $(DESTDIR)$(MANDIR)/man5 $(DESTDIR)$(MANDIR)/man7 \
-		$(DESTDIR)$(SHAREDIR)/templates $(DESTDIR)$(SHAREDIR)/stylesets \
-		$(DESTDIR)$(PREFIX)/share/applications $(DESTDIR)$(LIBEXECDIR)/filters
-	install -m755 aerc $(DESTDIR)$(BINDIR)/aerc
-	install -m755 contrib/carddav-query $(DESTDIR)$(BINDIR)/carddav-query
-	install -m644 aerc.1 $(DESTDIR)$(MANDIR)/man1/aerc.1
-	install -m644 carddav-query.1 $(DESTDIR)$(MANDIR)/man1/carddav-query.1
-	install -m644 aerc-search.1 $(DESTDIR)$(MANDIR)/man1/aerc-search.1
-	install -m644 aerc-accounts.5 $(DESTDIR)$(MANDIR)/man5/aerc-accounts.5
-	install -m644 aerc-binds.5 $(DESTDIR)$(MANDIR)/man5/aerc-binds.5
-	install -m644 aerc-config.5 $(DESTDIR)$(MANDIR)/man5/aerc-config.5
-	install -m644 aerc-imap.5 $(DESTDIR)$(MANDIR)/man5/aerc-imap.5
-	install -m644 aerc-jmap.5 $(DESTDIR)$(MANDIR)/man5/aerc-jmap.5
-	install -m644 aerc-maildir.5 $(DESTDIR)$(MANDIR)/man5/aerc-maildir.5
-	install -m644 aerc-sendmail.5 $(DESTDIR)$(MANDIR)/man5/aerc-sendmail.5
-	install -m644 aerc-notmuch.5 $(DESTDIR)$(MANDIR)/man5/aerc-notmuch.5
-	install -m644 aerc-smtp.5 $(DESTDIR)$(MANDIR)/man5/aerc-smtp.5
-	install -m644 aerc-tutorial.7 $(DESTDIR)$(MANDIR)/man7/aerc-tutorial.7
-	install -m644 aerc-templates.7 $(DESTDIR)$(MANDIR)/man7/aerc-templates.7
-	install -m644 aerc-stylesets.7 $(DESTDIR)$(MANDIR)/man7/aerc-stylesets.7
-	install -m644 config/accounts.conf $(DESTDIR)$(SHAREDIR)/accounts.conf
-	install -m644 config/aerc.conf $(DESTDIR)$(SHAREDIR)/aerc.conf
-	install -m644 config/binds.conf $(DESTDIR)$(SHAREDIR)/binds.conf
-	install -m755 filters/calendar $(DESTDIR)$(LIBEXECDIR)/filters/calendar
-	install -m755 filters/hldiff $(DESTDIR)$(LIBEXECDIR)/filters/hldiff
-	install -m755 filters/html $(DESTDIR)$(LIBEXECDIR)/filters/html
-	install -m755 filters/html-unsafe $(DESTDIR)$(LIBEXECDIR)/filters/html-unsafe
-	install -m755 filters/plaintext $(DESTDIR)$(LIBEXECDIR)/filters/plaintext
-	install -m755 filters/show-ics-details.py $(DESTDIR)$(LIBEXECDIR)/filters/show-ics-details.py
-	install -m755 colorize $(DESTDIR)$(LIBEXECDIR)/filters/colorize
-	install -m755 wrap $(DESTDIR)$(LIBEXECDIR)/filters/wrap
-	install -m644 templates/new_message $(DESTDIR)$(SHAREDIR)/templates/new_message
-	install -m644 templates/quoted_reply $(DESTDIR)$(SHAREDIR)/templates/quoted_reply
-	install -m644 templates/forward_as_body $(DESTDIR)$(SHAREDIR)/templates/forward_as_body
-	install -m644 stylesets/default $(DESTDIR)$(SHAREDIR)/stylesets/default
-	install -m644 stylesets/dracula $(DESTDIR)$(SHAREDIR)/stylesets/dracula
-	install -m644 stylesets/nord $(DESTDIR)$(SHAREDIR)/stylesets/nord
-	install -m644 stylesets/pink $(DESTDIR)$(SHAREDIR)/stylesets/pink
-	install -m644 stylesets/blue $(DESTDIR)$(SHAREDIR)/stylesets/blue
-	install -m644 stylesets/solarized $(DESTDIR)$(SHAREDIR)/stylesets/solarized
-	install -m644 contrib/aerc.desktop $(DESTDIR)$(PREFIX)/share/applications/aerc.desktop
-
-.PHONY: checkinstall
-checkinstall:
-	$(DESTDIR)$(BINDIR)/aerc -v
-	test -e $(DESTDIR)$(MANDIR)/man1/aerc.1
-	test -e $(DESTDIR)$(MANDIR)/man5/aerc-accounts.5
-	test -e $(DESTDIR)$(MANDIR)/man5/aerc-binds.5
-	test -e $(DESTDIR)$(MANDIR)/man5/aerc-config.5
-	test -e $(DESTDIR)$(MANDIR)/man5/aerc-imap.5
-	test -e $(DESTDIR)$(MANDIR)/man5/aerc-jmap.5
-	test -e $(DESTDIR)$(MANDIR)/man5/aerc-notmuch.5
-	test -e $(DESTDIR)$(MANDIR)/man5/aerc-sendmail.5
-	test -e $(DESTDIR)$(MANDIR)/man5/aerc-smtp.5
-	test -e $(DESTDIR)$(MANDIR)/man7/aerc-tutorial.7
-	test -e $(DESTDIR)$(MANDIR)/man7/aerc-templates.7
-
-RMDIR_IF_EMPTY:=sh -c '! [ -d $$0 ] || ls -1qA $$0 | grep -q . || rmdir $$0'
-
-uninstall:
-	$(RM) $(DESTDIR)$(BINDIR)/aerc
-	$(RM) $(DESTDIR)$(BINDIR)/carddav-query
-	$(RM) $(DESTDIR)$(MANDIR)/man1/aerc.1
-	$(RM) $(DESTDIR)$(MANDIR)/man1/aerc-search.1
-	$(RM) $(DESTDIR)$(MANDIR)/man5/aerc-accounts.5
-	$(RM) $(DESTDIR)$(MANDIR)/man5/aerc-binds.5
-	$(RM) $(DESTDIR)$(MANDIR)/man5/aerc-config.5
-	$(RM) $(DESTDIR)$(MANDIR)/man5/aerc-imap.5
-	$(RM) $(DESTDIR)$(MANDIR)/man5/aerc-jmap.5
-	$(RM) $(DESTDIR)$(MANDIR)/man5/aerc-maildir.5
-	$(RM) $(DESTDIR)$(MANDIR)/man5/aerc-sendmail.5
-	$(RM) $(DESTDIR)$(MANDIR)/man5/aerc-notmuch.5
-	$(RM) $(DESTDIR)$(MANDIR)/man5/aerc-smtp.5
-	$(RM) $(DESTDIR)$(MANDIR)/man7/aerc-tutorial.7
-	$(RM) $(DESTDIR)$(MANDIR)/man7/aerc-templates.7
-	$(RM) $(DESTDIR)$(MANDIR)/man7/aerc-stylesets.7
-	$(RM) -r $(DESTDIR)$(SHAREDIR)
-	$(RM) -r $(DESTDIR)$(LIBEXECDIR)
-	${RMDIR_IF_EMPTY} $(DESTDIR)$(BINDIR)
-	$(RMDIR_IF_EMPTY) $(DESTDIR)$(MANDIR)/man1
-	$(RMDIR_IF_EMPTY) $(DESTDIR)$(MANDIR)/man5
-	$(RMDIR_IF_EMPTY) $(DESTDIR)$(MANDIR)/man7
-	$(RMDIR_IF_EMPTY) $(DESTDIR)$(MANDIR)
-	$(RM) $(DESTDIR)$(PREFIX)/share/applications/aerc.desktop
-	$(RMDIR_IF_EMPTY) $(DESTDIR)$(PREFIX)/share/applications
-
-.PHONY: gitconfig
-gitconfig:
-	git config format.subjectPrefix "PATCH aerc"
-	git config sendemail.to "~rjarry/aerc-devel@lists.sr.ht"
-	@mkdir -p .git/hooks
-	@rm -f .git/hooks/sendemail-validate*
-	@if grep -q GIT_SENDEMAIL_FILE_COUNTER `git --exec-path`/git-send-email 2>/dev/null; then \
-		ln -svf ../../contrib/sendemail-validate .git/hooks/sendemail-validate && \
-		git config sendemail.validate true; \
-	fi
-
-.PHONY: check-patches
-check-patches:
-	@contrib/check-patches origin/master..
-
-.PHONY: all doc clean install uninstall debug
+# This file is only left here for explicit error about GNU make requirement
+# when building with other make flavours.
+#
+# Do not edit this file. Edit GNUmakefile instead.
+.PHONY: all
+all .DEFAULT:
+	@echo "Please build and install using GNU make (gmake)"; exit 1
diff --git a/README.md b/README.md
index 242fb99d..727e8eae 100644
--- a/README.md
+++ b/README.md
@@ -72,6 +72,7 @@ Install the dependencies:
   older versions may be dropped at any time due to incompatibilities or newer
   required language features.)*
 - [scdoc](https://git.sr.ht/~sircmpwn/scdoc)
+- GNU make (on \*BSD, `make` commands must be replaced by `gmake`).
 
 Then compile aerc: