You can define other per-directory recursive targets too: simply
mention (usually, by setting) the variable &TARGETS_zonk, or whatever.
-This will create a src/zonk target.
+This will create a src/zonk target (for appropriate value of src/).
Unlike `all', these other targets only exist in areas of the project
where at least something mentions them. So for example, if
&TARGETS_zonk is mentioned in src but not lib, `make zonk' in
Perdir.sd.mk, inclusion
-----------------------
-The file Perdir.sd.mk in the toplevel of fthe source is automatically
+The file Perdir.sd.mk in the toplevel of the source is automatically
processed after each individual directory's Subdir.sd.mk, and the
&-substituted contents therefore appear once for each subdirectory.
automatic regeneration for all of this template substitution, and for
config.status etc. is done for you.
+Summary of recommended directory reference syntaxes
+---------------------------------------------------
+
+Path construction &-expansions, meanings summary:
+
+ In build tree In source tree
+ This directory just & &,
+ Top level &. implies absolute &;
+
+Adding `@' means "absolute path". This is not needed with &. because
+there is never any need to use &. since it would expand to nothing.
+`/' terminates the escape (needed if the next thing is not a lowercase
+character, or space). `=' means "just the value, no /". Space starts
+multi-word processing.
+
+ Recommended In build tree In source tree
+ when Relative Absolute Relative Absolute
+
+ This lc &file &@file &,file &@,file
+ directory any &/file &@/file &,/file &@,/file
+ several & f g h &@ f g h &, f g h &@, f g h
+
+ Top lc &.file &;file &@;file
+ level any file &./file &;/file &@;/file
+ several f g h &. f g h &; f g h &@; f g h
+ .mk.in file $(abs)/file $(src)/file $(abs_src)/file
+
Substitution syntax
-------------------
&^ => $(top_srcdir)/sub/dir or $(top_srcdir)
&~ => $(abs_top_srcdir)/sub/dir or $(abs_top_srcdir)
+In general:
+ ^ filenames in source tree rather than build tree
+ ~ filenames are absolute rather than relative
+ @ filenames do not contain subdir (useful with the above)
+
&& => && for convenience in shell runes
\& => & general escaping mechanism
&!<lwsp> disables & until EOL (and then disappears)
&# delete everything to end of line
- (useful if the RHS contains unrecognise & constructions)
+ (useful if the RHS contains unrecognised & constructions)
&!STUFF
changes the escape sequence from & to literally STUFF
&:include subdirmk/cdeps.sd.mk
&:include subdirmk/clean.sd.mk
+Hints
+-----
+
+You can convert your project incrementally. Start with the top-level
+Makefile.in and rename it to Subdir.sd.mk, and add the appropriate
+stuff to configure.ac, and fix everything up. Leave the existing
+$(MAKE) -C for your existing subdirectories alone. Then you can
+convert individual subdirectories, or classes of subdirectories, at
+your leisure. (You must be /sure/ that each subdirectory will be
+entered only once at a time, but your existing recursive make descent
+system should already do that or you already have concurrency bugs.)
+
+Aside from this, be very wary of any invocation of $(MAKE) anywhere.
+This is a frequent source of concurrency bugs in recursive make build
+systems. When combined with nonrecursive make it's all in the same
+directory and there is nothing stopping the different invocations
+ending up trying to make the same targets at the same time. That
+causes hideous racy lossage. There are ways to get this to work
+reliably but it is advanced stuff.
+
+If you make syntax errors, or certain kinds of other errors, in your
+makefiles, you may find that just `make' is broken now and cannot get
+far enough to regenerate a working set of makefiles. If this happens
+just rerun ./config.status by hand.
+
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