Implement a non-recursive make.

The idea here is that every Makefile at each lower level will be an
identical, tiny file that simply defers to a top-level make.

Meanwhile, the Makefile.local file at each level is a Makefile snippet
to be included at the top-level into a large, flat Makefile. As such,
it needs to define its rules with the entire relative directory to
each file, (typically in $(dir)). The local files can also append to
variables such as SRCS and CLEAN for files to be analyzed for
dependencies and to be cleaned.

Makefile

@@ -1,5 +1,3 @@
-PROGS=notmuch
-
 WARN_FLAGS=-Wall -Wextra -Wmissing-declarations -Wwrite-strings -Wswitch-enum
 
 NOTMUCH_DEPENDS_FLAGS=-I./lib `pkg-config --cflags glib-2.0 gmime-2.4 talloc`
@@ -11,22 +9,9 @@ NOTMUCH_CXXFLAGS=$(WARN_FLAGS) -O0 -g $(NOTMUCH_CXX_DEPENDS_FLAGS)
 NOTMUCH_LDFLAGS=`pkg-config --libs glib-2.0 gmime-2.4 talloc` \
 		`xapian-config --libs`
 
-LIBRARY=			\
-	lib/database.o		\
-	lib/index.o		\
-	lib/libsha1.o		\
-	lib/message.o		\
-	lib/message-file.o	\
-	lib/query.o		\
-	lib/sha1.o		\
-	lib/tags.o		\
-	lib/thread.o		\
-	lib/xutil.o
-
-MAIN=			\
-	notmuch.o
-
-all: $(PROGS)
+# Include our local Makfile.local first so that its first target is default
+include Makefile.local
+include lib/Makefile.local
 
 %.o: %.cc
 	$(CXX) -c $(CFLAGS) $(CXXFLAGS) $(NOTMUCH_CXXFLAGS) $< -o $@
@@ -34,22 +19,14 @@ all: $(PROGS)
 %.o: %.c
 	$(CC) -c $(CFLAGS) $(NOTMUCH_CFLAGS) $< -o $@
 
-notmuch: $(MAIN) $(LIBRARY)
-	$(CC) $(NOTMUCH_LDFLAGS) $^ -o $@
-
-.depends: *.c lib/*.c lib/*.cc
+.depends: $(SRCS)
 	$(CXX) -M $(CPPFLAGS) $(NOTMUCH_DEPENDS_FLAGS) \
 	$(NOTMUCH_CXX_DEPENDS_FLAGS) $^ > $@
 -include .depends
 
-notmuch.1.gz:
-	gzip --stdout notmuch.1 > notmuch.1.gz
-
-install: all notmuch.1.gz
-	install -C -D notmuch $(DESTDIR)/usr/bin/notmuch
-	install -C -D notmuch.1.gz $(DESTDIR)/usr/share/man/man1
-	install -C -D notmuch-completion.bash \
-		$(DESTDIR)/etc/bash_completion.d/notmuch
+CLEAN := $(CLEAN) .depends
 
 clean:
-	rm -f $(PROGS) lib/*.o *.o .depends
+	rm -f $(CLEAN)
+
+

Makefile.local

@@ -0,0 +1,16 @@
+all: notmuch
+
+notmuch: notmuch.o lib/notmuch.a
+	$(CC) $(NOTMUCH_LDFLAGS) $^ -o $@
+
+notmuch.1.gz:
+	gzip --stdout notmuch.1 > notmuch.1.gz
+
+install: all notmuch.1.gz
+	install -C -D notmuch $(DESTDIR)/usr/bin/notmuch
+	install -C -D notmuch.1.gz $(DESTDIR)/usr/share/man/man1
+	install -C -D notmuch-completion.bash \
+		$(DESTDIR)/etc/bash_completion.d/notmuch
+
+SRCS  := $(SRCS) notmuch.c
+CLEAN := $(CLEAN) notmuch *.o

lib/Makefile

@@ -0,0 +1,5 @@
+all:
+	make -C .. all
+
+clean:
+	make -C .. clean

lib/Makefile.local

@@ -0,0 +1,19 @@
+dir=lib
+
+lib_notmuch_modules =		\
+	$(dir)/database.o	\
+	$(dir)/index.o		\
+	$(dir)/$(dir)sha1.o	\
+	$(dir)/message.o	\
+	$(dir)/message-file.o	\
+	$(dir)/query.o		\
+	$(dir)/sha1.o		\
+	$(dir)/tags.o		\
+	$(dir)/thread.o		\
+	$(dir)/xutil.o
+
+$(dir)/notmuch.a: $(lib_notmuch_modules)
+	$(AR) rcs $@ $^
+
+SRCS  := $(SRCS) lib/*.c lib/*.cc
+CLEAN := $(CLEAN) $(dir)/*.o $(dir)/notmuch.a