add new build environment for cross compile

.dockerignore

@@ -0,0 +1 @@
+*

Dockerfile

@@ -0,0 +1,24 @@
+# Dockerfile for cross-platform Pomo builds
+FROM golang:1.12-stretch
+
+ENV OSXCROSS_REPO="https://github.com/tpoechtrager/osxcross.git"
+ENV OSX_SDK_TARBALL="https://s3.dockerproject.org/darwin/v2/MacOSX10.11.sdk.tar.xz"
+
+RUN \
+    apt-get update -yyq \
+    && apt-get install -yyq \
+        clang \
+        libxml2 \
+        patch \
+        xz-utils
+
+RUN \
+    mkdir /build \
+    && cd /build \
+    && git clone --depth=1 "$OSXCROSS_REPO" \
+    && cd osxcross/tarballs \
+    && wget "$OSX_SDK_TARBALL" \
+    && cd .. \
+    && UNATTENDED=1 ./build.sh
+
+ENV PATH="$PATH:/build/osxcross/target/bin"

Makefile

@@ -1,25 +1,22 @@
+DOCKER_CMD=docker run --rm -ti --user 1000 -w /build/pomo -v $$PWD:/build/pomo
+DOCKER_IMAGE=pomo-build
 VERSION ?= $(shell git describe --tags 2>/dev/null)
 ifeq "$(VERSION)" ""
 	VERSION := UNKNOWN
 endif
 
 .PHONY: \
-	all \
 	test \
 	docs \
+	pomo-build \
 	readme \
 	release \
 	release-linux \
 	release-darwin
 
-all: bin/pomo
-
 bin/pomo: test
 	go build -o $@
 
-clean:
-	-rm -rfv bin/* docs/*
-
 bindata.go: tomato-icon.png
 	go-bindata -pkg main -o $@ $^
 
@@ -27,16 +24,23 @@ test:
 	go test ./...
 	go vet ./...
 
+pomo-build:
+	docker build -t $(DOCKER_IMAGE) .
+
+bin/pomo-linux: bin/pomo-$(VERSION)-linux-amd64
+
+bin/pomo-darwin: bin/pomo-$(VERSION)-darwin-amd64
+
 bin/pomo-$(VERSION)-linux-amd64: bin bindata.go
-	go build -ldflags "-X main.Version=$(VERSION)" -o $@
+	$(DOCKER_CMD) --env GOOS=linux --env GOARCH=amd64 $(DOCKER_IMAGE) go build -ldflags "-X main.Version=$(VERSION)" -o $@
 
 bin/pomo-$(VERSION)-linux-amd64.md5:
 	md5sum bin/pomo-$(VERSION)-linux-amd64 | sed -e 's/bin\///' > $@
 
 bin/pomo-$(VERSION)-darwin-amd64: bin bindata.go
-	# This is used to cross-compile a Darwin compatible Mach-O executable 
+	# This is used to cross-compile a Darwin compatible Mach-O executable
 	# on Linux for OSX, you need to install https://github.com/tpoechtrager/osxcross
-	PATH="$$PATH:/usr/local/osx-ndk-x86/bin" GOOS=darwin GOARCH=amd64 CC=/usr/local/osx-ndk-x86/bin/x86_64-apple-darwin15-cc CGO_ENABLED=1 go build $(FLAGS) -o $@
+	$(DOCKER_CMD) --env GOOS=darwin --env GOARCH=amd64 --env CC=x86_64-apple-darwin15-cc --env CGO_ENABLED=1 $(DOCKER_IMAGE) go build -ldflags "-X main.Version=$(VERSION)" -o $@
 
 
 bin/pomo-$(VERSION)-darwin-amd64.md5: