X-Git-Url: https://www.chiark.greenend.org.uk/ucgi/~ian/git?p=subdirmk.git;a=blobdiff_plain;f=README;h=7fdeef52438817155503ce55cf72122e9e2b2050;hp=0ab3b50057b5ed23172f7fa60b911fd8c9d47e23;hb=08e0edf690f2ae65a6d2e82609da7562f55093ac;hpb=172580f2d7fb712f40e036c1417718b443e4adb9

diff --git a/README b/README
index 0ab3b50..7fdeef5 100644
--- a/README
+++ b/README
@@ -138,6 +138,33 @@ If you `include subdirmk/regen.mk', dependency management and
 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
 -------------------
 
@@ -163,22 +190,45 @@ empty string).
 	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		  &@;/	=> $(abs_top_srcdir)/
+
+In general:
+    =	return subdir without delimiter (not allowed with `,' `;' `@')
+    ,   pathname of this subdirectory in source tree
+    ;   pathname of top level of source tree
+    .   pathname of this directory in build tree, implies absolute pathnames
+    @   absolute pathnames (forbidden with `.', must come first)
+
+So pathname syntax is a subset of:
+    '&' [ '@' ] [ ',' | ';' | '.' ] [ lc | '/' ]
+
+    To avoid incomprehensible .sd.mk files, some combinations are not
+    allowed.  For example `&@=./' would mean `$(PWD)/sub/dir' but can
+    be spelled `$(PWD)/&=/', but more normally the trailing / can be
+    tolerated, so use `&@/'.
 
 &&		=>	&&		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.
 
@@ -282,15 +332,18 @@ 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.
+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 there is no
-separate-directory barrier stopping the different invocations ending
-up trying to make the same targets at the same time, which causes
-hideous racy lossage.  There are ways to get this to work reliably but
-it is advanced stuff.
+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