Add amalgamation script

Sources are #included instead of inlined by default.

Makefile

@@ -172,9 +172,27 @@ ifneq (Cygwin,$(UNAME))
 endif
 endif
 
+AMALGAM ?= 0
+AMALGAM_INLINE ?= 0
+AMALGAM_SOURCE_INCLUDE := build/libsass-amalgam-include.cpp
+AMALGAM_SOURCE_INLINE := build/libsass-amalgam-inline.cpp
+
+ifeq (1,$(AMALGAM_INLINE))
+AMALGAM_SOURCE := $(AMALGAM_SOURCE_INLINE)
+else
+AMALGAM_SOURCE := $(AMALGAM_SOURCE_INCLUDE)
+endif
+
+AMALGAM_SOURCE_DIR := $(abspath $(dir $(AMALGAM_SOURCE)))
+
 include Makefile.conf
-OBJECTS = $(addprefix src/,$(SOURCES:.cpp=.o))
-COBJECTS = $(addprefix src/,$(CSOURCES:.c=.o))
+ifeq (1,$(AMALGAM))
+	OBJECTS = $(AMALGAM_SOURCE:.cpp=.o)
+	COBJECTS =
+else
+	OBJECTS = $(addprefix src/,$(SOURCES:.cpp=.o))
+	COBJECTS = $(addprefix src/,$(CSOURCES:.c=.o))
+endif
 RCOBJECTS = $(RESOURCES:.rc=.o)
 
 DEBUG_LVL ?= NONE
@@ -184,6 +202,7 @@ CLEANUPS += $(RCOBJECTS)
 CLEANUPS += $(COBJECTS)
 CLEANUPS += $(OBJECTS)
 CLEANUPS += $(LIBSASS_LIB)
+CLEANUPS += $(AMALGAM_SOURCE_INCLUDE) $(AMALGAM_SOURCE_INLINE)
 
 all: $(BUILD)
 
@@ -199,6 +218,28 @@ debug-shared: CFLAGS := -g -DDEBUG -DDEBUG_LVL="$(DEBUG_LVL)" $(filter-out -O2,$
 debug-shared: CXXFLAGS := -g -DDEBUG -DDEBUG_LVL="$(DEBUG_LVL)" $(filter-out -O2,$(CXXFLAGS))
 debug-shared: shared
 
+AMALGAMATE_BIN := script/amalgamate/build/amalgamate
+
+$(AMALGAMATE_BIN): script/amalgamate/amalgamate.cpp
+	$(MAKE) -C script/amalgamate build/amalgamate
+
+$(AMALGAM_SOURCE_DIR):
+	$(MKDIR) $(AMALGAM_SOURCE_DIR)
+
+ifeq (1,$(AMALGAM_INLINE))
+AMALGAM_INLINE_FLAG := true
+else
+AMALGAM_INLINE_FLAG := false
+endif
+
+$(AMALGAM_SOURCE): $(AMALGAMATE_BIN) $(addprefix src/,$(SOURCES)) $(addprefix src/,$(CSOURCES)) | $(AMALGAM_SOURCE_DIR)
+	$(AMALGAMATE_BIN) --out=$(AMALGAM_SOURCE) --inline=$(AMALGAM_INLINE_FLAG)
+
+ifneq (1,$(AMALGAM_INLINE))
+$(AMALGAM_SOURCE:.cpp=.o): $(AMALGAM_SOURCE)
+	$(CXX) $(CXXFLAGS) -I src -c -o $@ $<
+endif
+
 lib:
 	$(MKDIR) lib
 

script/amalgamate/.clang-format

@@ -0,0 +1 @@
+BasedOnStyle: Google

script/amalgamate/Makefile

@@ -0,0 +1,17 @@
+CXX ?= c++
+
+CXXFLAGS := -std=c++11
+CXXFLAGS_OPT := $(CXXFLAGS) -O2 -s
+CXXFLAGS_DBG := $(CXXFLAGS) -fsanitize=address -g -O1 -fno-omit-frame-pointer
+CXXFLAGS_FASTBUILD := $(CXXFLAGS) -O0 -s
+
+build/amalgamate: amalgamate.cpp | build
+	$(CXX) $(CXXFLAGS_FASTBUILD) -o build/amalgamate amalgamate.cpp
+
+build:
+	@mkdir build
+
+clean: | build
+	rm -rf build
+
+.PHONY: amalgamate clean

script/amalgamate/README.md

@@ -0,0 +1,44 @@
+# LibSass amalgamation script
+
+This script concatenates LibSass sources into a single file.
+
+This reduces single-core compilation time by 50% and the output shared library size by 10%.
+
+SQLite has a great writeup on amalgamation here:
+<https://www.sqlite.org/amalgamation.html>.
+
+## Options
+
+* `--inline`. Default: `false`\
+  When `true`, all sources are inlined into the amalgam file (including headers.\
+  When `false`, the amalgam file instead contains `#include` statements for each `.c,.cpp` file.
+* `--root`. Default: `$PWD`.\
+  The root directory.
+  By default, the `src/` subdirectory of root is searched and includes are
+  resolved relative to it.
+* `--out`. Default: `/dev/stdout`.\
+  Path to the amalgamated source output.
+
+## Benchmarks
+
+With amalgamation:
+
+~~~bash
+rm -f script/amalgamate/build/amalgamate && make clean AMALGAM=1 && \
+  time make lib/libsass.so AMALGAM=1 && du -sh lib/libsass.so
+~~~
+
+Compilation time (1 core): 30s
+`lib/libsass.so` size: 3.0M
+
+These numbers are the same affected for both inline and include-style amalgamation.
+
+Without amalgamation:
+
+~~~bash
+make clean AMALGAM=0 && time make -j`nproc` lib/libsass.so AMALGAM=0 && du -sh lib/libsass.so
+~~~
+
+Compilation time (1 core): 60s
+Compilation time (8 cores): 16s
+`lib/libsass.so` size: 3.3M