Add basic infrastructure for doing 32 and 64-bit GCC builds on macOS

Using make to do the platform selection is admittedly abusing the
hammer beyond any sort of sanity, but was a fun exercise ;)

.dockerignore

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

Dockerfile.linux-gcc

@@ -0,0 +1,12 @@
+FROM ubuntu:16.04
+
+ARG arch
+
+RUN dpkg --add-architecture $arch && \
+	apt-get update && \
+	apt-get install -y \
+		build-essential \
+		g++-multilib \
+		pkg-config:$arch \
+		libfuse-dev:$arch \
+		fuse:$arch

Makefile

@@ -1,7 +1,123 @@
+#
+#  Usage: make [target] [platform|alias|all], e.g.:
+#
+#   $ make clean all - cleans all available platforms
+#   $ make gcc - builds on all available GCC platforms
+#
+#  Copyright (c) 2018 Tor Arne Vestbø
+#
+#  Permission is hereby granted, free of charge, to any person obtaining a copy
+#  of this software and associated documentation files (the "Software"), to deal
+#  in the Software without restriction, including without limitation the rights
+#  to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+#  copies of the Software, and to permit persons to whom the Software is
+#  furnished to do so, subject to the following conditions:
+#
+#  The above copyright notice and this permission notice shall be included in all
+#  copies or substantial portions of the Software.
+#
+#  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+#  EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+#  MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
+#  IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
+#  DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
+#  OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE
+#  OR OTHER DEALINGS IN THE SOFTWARE.
+#
+# ------------ Platform selection ------------
+
+AVAILABLE_PLATFORMS := macos-clang-64 linux-gcc-32 linux-gcc-64
+
+OS := $(shell uname -s)
+ARCH ?= $(shell uname -m)
+
+ifeq ($(OS),Darwin)
+    NATIVE_PLATFORM=macos-clang-64
+else ifeq ($(OS),Linux)
+  ifeq ($(ARCH),x86_64)
+	NATIVE_PLATFORM=linux-gcc-64
+else
+	NATIVE_PLATFORM=linux-gcc-32
+  endif
+endif
+
+ACTUAL_GOALS := $(MAKECMDGOALS)
+ifneq ($(filter all,$(MAKECMDGOALS)),)
+    PLATFORMS := $(AVAILABLE_PLATFORMS)
+    ACTUAL_GOALS := $(filter-out all,$(ACTUAL_GOALS))
+    all: ; @:
+endif
+
+define expand_platform_alias
+  ifneq ($(filter $(alias),$(MAKECMDGOALS)),)
+    PLATFORMS += $(platform)
+    ACTUAL_GOALS := $(filter-out $(alias),$(ACTUAL_GOALS))
+    $(alias):: $$(PLATFORMS) ; @:
+  endif
+endef
+
+define detect_platform
+  ifneq ($(filter $(platform),$(MAKECMDGOALS)),)
+    PLATFORMS += $(platform)
+    ACTUAL_GOALS := $(filter-out $(platform),$(ACTUAL_GOALS))
+  endif
+  $(foreach alias,$(subst -, ,$(platform)), $(eval $(expand_platform_alias)))
+endef
+
+$(foreach platform,$(AVAILABLE_PLATFORMS), $(eval $(detect_platform)))
+PLATFORMS := $(strip $(sort $(subst $(COMMA), ,$(PLATFORMS))))
+ifeq ($(PLATFORMS),)
+    PLATFORMS := $(NATIVE_PLATFORM)
+endif
+
+COMMA := ,
+MFLAGS := $(filter-out --jobserver-fds%,$(MFLAGS))
+make_noop = $(eval $$($1): % : ; @:)
+ensure_binary = $(if $(shell which $1),,\
+	$(error Could not find '$(strip $1)' binary))
+
+# ------------ Multiple platforms ------------
+
+ifeq ($(shell expr $(words $(PLATFORMS)) \> 1), 1)
+
+%:: $(PLATFORMS) ;
+$(PLATFORMS):
+	@$(MAKE) -f $(MAKEFILE_LIST) $(MFLAGS) \
+		$(filter-out $(NATIVE_PLATFORM),$@) $(ACTUAL_GOALS)
+
+$(call make_noop,ACTUAL_GOALS)
+
+# ------------ Single non-native platform ------------
+
+else ifneq ($(NATIVE_PLATFORM),$(PLATFORMS))
+
+linux-gcc-%: docker ;
+docker:
+	$(call ensure_binary,docker-compose)
+	@docker-compose run --rm $(PLATFORMS) $(MFLAGS) $(ACTUAL_GOALS)
+	@stty sane # Work around docker-compose messing up the terminal
+
+$(call make_noop,ACTUAL_GOALS)
+
+%::
+	$(error "No way to build for $(PLATFORMS) on $(NATIVE_PLATFORM))
+
+# ------------ Native platform ------------
+
+else
+
 TARGET = sparsebundlefs
+.DEFAULT_GOAL := $(TARGET)
+
+$(call make_noop,NATIVE_PLATFORM)
+
+ifeq ($(strip $(ACTUAL_GOALS)),)
+    ACTUAL_GOALS := $(.DEFAULT_GOAL)
+    $(NATIVE_PLATFORM): $(ACTUAL_GOALS)
+endif
 
 # Note: Doesn't work for paths with spaces in them
-SRC_DIR=$(dir $(abspath $(lastword $(MAKEFILE_LIST))))
+SRC_DIR=$(patsubst %/,%,$(dir $(abspath $(lastword $(MAKEFILE_LIST)))))
 vpath %.cpp $(SRC_DIR)
 
 PKG_CONFIG = pkg-config
@@ -14,10 +130,10 @@ endif
 
 DEFINES = -DFUSE_USE_VERSION=26
 
-ifeq ($(shell uname), Darwin)
+ifeq ($(OS),Darwin)
     # Pick up OSXFUSE, even with pkg-config from MacPorts
     PKG_CONFIG := PKG_CONFIG_PATH=/usr/local/lib/pkgconfig $(PKG_CONFIG)
-else ifeq ($(shell uname), Linux)
+else ifeq ($(OS),Linux)
     LFLAGS += -Wl,-rpath=$(shell $(PKG_CONFIG) fuse --variable=libdir)
 endif
 
@@ -26,8 +142,8 @@ FUSE_FLAGS := $(shell $(PKG_CONFIG) fuse --cflags --libs)
 $(TARGET): sparsebundlefs.cpp
 	$(CXX) $< -o $@ $(CFLAGS) $(FUSE_FLAGS) $(LFLAGS) $(DEFINES)
 
-all: $(TARGET)
-
 clean:
 	rm -f $(TARGET)
 	rm -Rf $(TARGET).dSYM
+
+endif

docker-compose.yaml

@@ -0,0 +1,43 @@
+version: '3.7'
+
+x-base-service: &base-service
+  build: &base-build
+    context: .
+    dockerfile: Dockerfile.linux-gcc
+  volumes:
+    - &src-volume .:/src
+  working_dir: /build
+  entrypoint:
+    - make
+    - -f
+    - /src/Makefile
+  network_mode: none
+
+services:
+  linux-gcc-32:
+    <<: *base-service
+    build:
+      <<: *base-build
+      args:
+        - arch=i386
+    volumes:
+      - *src-volume
+      - linux-gcc-32:/build
+    environment:
+      - CFLAGS=-m32
+      - ARCH=i386
+
+  linux-gcc-64:
+    <<: *base-service
+    build:
+      <<: *base-build
+      args:
+        - arch=amd64
+    volumes:
+      - *src-volume
+      - linux-gcc-64:/build
+
+volumes:
+  linux-gcc-32:
+  linux-gcc-64:
+