docs: Change . to require rather than imply @

[subdirmk.git] / README

diff --git a/README b/README
index e5ef4b4f5c28a1291e1d4b9c4e981d1ffb4f4eb7..0ade775ed3d954378b7268c1e2487db91a9309c8 100644 (file)
--- a/README
+++ b/README
@@ -138,6 +138,37 @@ 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.
 
 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
 -------------------
 
 Substitution syntax
 -------------------
 


@@ -163,22 +194,45 @@ empty string).
        variables usually uppercase.  Otherwise, use another syntax:
 
 &_             =>      sub_dir_                        or TOP_
        variables usually uppercase.  Otherwise, use another syntax:
 
 &_             =>      sub_dir_                        or TOP_

-&/             =>      sub/dir/                        or nothing

 &=_            =>      sub_dir                         or TOP
 &=_            =>      sub_dir                         or TOP

+
+&/             =>      sub/dir/                        or nothing

 &=/            =>      sub/dir                         or .
 &=/            =>      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
 
 
 &&             =>      &&              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.
        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.
 
        This processing continues until & preceded by lwsp,
        or until EOL (the end of the line), or \ then EOL.
 


@@ -275,6 +329,31 @@ have:
   &:include subdirmk/cdeps.sd.mk
   &:include subdirmk/clean.sd.mk
 
   &: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.
+

 
 Legal information
 -----------------
 
 Legal information
 -----------------