X-Git-Url: https://www.chiark.greenend.org.uk/ucgi/~ian/git?p=subdirmk.git;a=blobdiff_plain;f=README;h=3059d9a105cfb57a9071a4da0f50e9cc19783a62;hp=cc309f6ae1ec796febb92b7b4fad8083f2d9669d;hb=b64a2a9a093d13eda806ccf67ffb8bb4ba2a2cab;hpb=25a516a59e7811b8626b5fe40b49c5ef942db697

diff --git a/README b/README
index cc309f6..3059d9a 100644
--- a/README
+++ b/README
@@ -83,7 +83,7 @@ individual targets (as specified according to their dependencies).
 
 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
@@ -93,7 +93,7 @@ mention its name in Perdir.sd.mk (see below).
 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.
 
@@ -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
 -------------------
 
@@ -169,6 +196,11 @@ empty string).
 &^		=>	$(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
 
@@ -193,7 +225,7 @@ empty string).
 &!<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
@@ -275,6 +307,31 @@ have:
   &: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
 -----------------