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:
+
+ Recommended In build tree In source tree
+ when Relative Absolute Relative Absolute
+
+ This directory & &@ &, &@,
+ Top level . &@. &; &@;
+
+Adding `@' means "absolute path". (`&.' is not allowed without @
+because just `&./' is a silly way of writing `.'.) `/' 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.
+
+In more detail, with the various options for what comes next:
+
+ 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
-------------------
variables usually uppercase. Otherwise, use another syntax:
&_ => sub_dir_ or TOP_
-&/ => sub/dir/ or nothing
&=_ => sub_dir or TOP
+
+&/ => sub/dir/ or nothing
&=/ => sub/dir or .
-&^ => $(top_srcdir)/sub/dir or $(top_srcdir)
-&~ => $(abs_top_srcdir)/sub/dir or $(abs_top_srcdir)
+
+&,lc => $(top_srcdir)/sub/dir/lc &,/ => $(top_srcdir)/sub/dir/
+&;lc => $(top_srcdir)/lc &;/ => $(top_srcdir)/
+
+&@lc => $(PWD)/sub/dir/lc &@/ => $(PWD)/sub/dir/
+&@.lc => $(PWD)/lc &@./ => $(PWD)/
+&@,lc => $(abs_top_srcdir)/sub/dir/lc &@,/ => $(abs_top_srcdir)/sub/dir/
+&@;lc => $(abs_top_srcdir)/lc &@;/ => $(abs_top_srcdir)/
+
+In general:
+ = return subdir without delimiter (not allowed with `,' `;' `@')
+ , pathname of this subdirectory in source tree
+ ; pathname of top level of source tree
+ . pathname of this directory in build tree, `@' must be specified
+ @ absolute pathnames
+
+So pathname syntax is a subset of:
+ '&' [ '@' ] [ ',' | ';' | '.' ] [ lc | '/' ]
+
+ To avoid incomprehensible .sd.mk files, some combinations are not
+ allowed. For example `&=./' would mean `.' and `&./' would be the
+ empty string. Variations with `=' and one of `@' `,' `;' are
+ uncommon and must be written using make variables instead.
&& => && for convenience in shell runes
\& => & general escaping mechanism
-& thing thing... &
-& ^ thing thing... &
-& ~ thing thing... &
+& thing thing... & &@ thing thing... &
+ &. thing thing... &
+&, thing thing... & &@, thing thing... &
+&; thing thing... & &@; thing thing... &
Convenience syntax for prefixing multiple filenames.
- Introduced by & followed by lwsp (space or tab).
- Each lwsp-separated non-ws word is prefixed by &/ &^/ &~/
- respectively. No other & escapes are recognised.
+ Introduced by & followed by lwsp where lc could go.
+ Each lwsp-separated non-ws word is prefixed by &/ etc.
+ etc. respectively. No other & escapes are recognised.
This processing continues until & preceded by lwsp,
or until EOL (the end of the line), or \ then EOL.
&:include subdirmk/cdeps.sd.mk
&:include subdirmk/clean.sd.mk
+Hints
+-----
+
+You can convert your project incrementally. Start with the top-level
+Makefile.in and rename it to Subdir.sd.mk, and add the appropriate
+stuff to configure.ac, and fix everything up. Leave the existing
+$(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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