docs: Abolish all absolute pathname syntaxes

These are rare and make things much more confusing.

Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>

diff --git a/README b/README
index ef839d56d9e7669abf3143e172ab0efbcb334f3a..c9e4c0f9234f2fe42bac8187dd98c88784bb417a 100644 (file)
--- a/README
+++ b/README
@@ -152,30 +152,34 @@ locations:
  (ii) In (or relative to) the subdirectory to which this Subdir.sd.mk
      relates, or relative to the project's top level ?
 
- (iii) Absolute or relative pathname ?
-     (Usually relative pathnames suffice.)
+ (iii) Absolute or relative pathname ?  Usually relative pathnames
+     suffice.  Where an absolute pathname is needed, it can be built
+     out of &/ and an appropriate make variable such as $(PWD).
 
 Path construction &-expansions are built from the following:
 
-                      Relative paths in...   Absolute paths in...
-                      build     source       build           source
+                      Relative paths in...
+                      build     source
                                                        
-  This directory      &         &,           &@              &@,
-  Top level           .         &;           &@.             &@;
+  This directory      &         &,
+  Top level           .         &;
 
-In more detail, with the various options for what comes next:
+In more detail, with all the various options laid out:
 
       Recommended     Relative paths in...   Absolute paths in...
-             for      build     source       build           source
+             for      build     source       build         source
                                                        
-  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
+  This       lc       &file     &,file       $(PWD)/&file  $(abs_src)/&file
+  directory  any      &/file    &,/file      $(PWD)&/file  $(abs_src)/&/file
+             several  & f g h   &, f g h     $(addprefix...)
                                              
-  Top        lc       file      &;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      $(src)/file  $(abs)/file     $(abs_src)/file
+  Top        lc       file      &;file
+  level      any      file      &;/file      $(PWD)/file   $(abs_src)/file
+             .mk.in   file      $(src)/file  $(PWD)/file   $(abs_src)/file
+             several  f g h     &; f g h     $(addprefix...)
+
+(This assumes you have appropriate make variables src, PWD and
+abs_src.)
 
 Substitution syntax
 -------------------
@@ -207,38 +211,28 @@ empty string).
 &/             =>      sub/dir/                        or nothing
 &=/            =>      sub/dir                         or .
 
-&,lc   => $(top_srcdir)/sub/dir/lc       &,/   => $(top_srcdir)/sub/dir/
-&;lc   => $(top_srcdir)/lc               &;/   => $(top_srcdir)/
+&,lc           =>      $(top_srcdir)/sub/dir/lc
+&,/            =>      $(top_srcdir)/sub/dir/
 
-&@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)/
+&;lc           =>      $(top_srcdir)/lc
+&;/            =>      $(top_srcdir)/
 
 In general:
-    =  return subdir without delimiter (not allowed with `,' `;' `@')
+    =  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
     /  terminates the escape (needed if next is not lwsp or space)
   lwsp  starts multi-word processing (see below)
 
 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.
+    '&' [ ',' | ';' ] [ lc | '/' ]
 
 &&             =>      &&              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 where lc could go.
        Each lwsp-separated non-ws word is prefixed by &/ etc.