docs

[subdirmk.git] / subdirmk / README

diff --git a/subdirmk/README b/subdirmk/README
index 256fdbc8e7e8ef54b83ecdd9362ebd93225d0c28..e6da9eecd1f68b68ab930560236e802a741fb3cf 100644 (file)
--- a/subdirmk/README
+++ b/subdirmk/README
@@ -25,8 +25,8 @@ builds well).
 Basic approach
 --------------
 
 Basic approach
 --------------
 

-The developer is expected to write a makefile fragment in each
-relevant subdirectory called `Subdir.sd.mk'.
+The developer is expected to write a makefile fragment, in each
+relevant subdirectory, called `Subdir.sd.mk'.

 
 These fragments may contain ordinary make language.
 
 
 These fragments may contain ordinary make language.
 


@@ -66,8 +66,9 @@ But `foo' can also be a conventional target like `all'.
 Each subdirectory has its own `all' target.  For example a
 subdirectory `src' has a target `src/all'.  The rules for these are
 automatically generated from the settings of the per-directory
 Each subdirectory has its own `all' target.  For example a
 subdirectory `src' has a target `src/all'.  The rules for these are
 automatically generated from the settings of the per-directory

-&TARGETS variables.  (In src/Subdir.sd.mk, this of course refers to a
-make variable called src_TARGETS.)
+&TARGETS variables.  &TARGETS is magic in this way.  (In
+src/Subdir.sd.mk, &TARGES of course refers to a make variable called
+src_TARGETS.)

 
 The `all' target in a parent directory is taken to imply the `all'
 targets in all of its subdirectories, recursively.  And in the
 
 The `all' target in a parent directory is taken to imply the `all'
 targets in all of its subdirectories, recursively.  And in the


@@ -81,7 +82,7 @@ invocation at a time.
 
 You can define other per-directory recursive targets too: simply
 mention (usually, by setting) the variable &TARGETS_zonk, or whatever.
 
 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.  (&TARGETS is magic.)
+This will create a src/zonk target.

 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
 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


@@ -99,7 +100,14 @@ This lets you do per-directory boilerplate.  Some useful boilerplate
 is already provided in subdirmk, for you to reference like this:
   &:include subdirmk/cdeps.sd.mk
   &:include subdirmk/clean.sd.mk
 is already provided in subdirmk, for you to reference like this:
   &:include subdirmk/cdeps.sd.mk
   &:include subdirmk/clean.sd.mk

-(for example in Perdir.sd.mk).
+For example you could put that in Perdir.sd.mk.
+
+Global definitions
+------------------
+
+If want to set global variables, such as CC, that should only be done
+once.  You can put them in your top-level Subdir.sd.mk, or a separate
+file you `include' and declare using SUBDIRMK_MAKEFILES.

 
 Subdirectory templates `.sd.mk' vs plain autoconf templates `.mk.in'
 --------------------------------------------------------------------
 
 Subdirectory templates `.sd.mk' vs plain autoconf templates `.mk.in'
 --------------------------------------------------------------------


@@ -111,8 +119,10 @@ There are two kinds of template files.
  Processed by             &-substitution,         autoconf only
                           then autoconf
 
  Processed by             &-substitution,         autoconf only
                           then autoconf
 

+ Instantiated             Usu. once per subdir    Once only
+

  Need to be mentioned     No, but Subdir.sd.mk    All not in subdirmk/
  Need to be mentioned     No, but Subdir.sd.mk    All not in subdirmk/

- in configure.ac          via SUBDIRMK_SUBDIRS    via SUBDIRMK_MAKEFILES
+ in configure.ac?         via SUBDIRMK_SUBDIRS    via SUBDIRMK_MAKEFILES

 
  How to include           `&:include foo.sd.mk'   `include foo.mk'
                          in all relevant .sd.mk  in only one
 
  How to include           `&:include foo.sd.mk'   `include foo.mk'
                          in all relevant .sd.mk  in only one


@@ -123,77 +133,108 @@ 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.
 

-Global definitions
-------------------
-
-If want to set global variables, such as CC, that should only be done
-once.  The usual approach is to include 
-
-
-
-  subdirmk/cdeps.mk.in
-  subdirmk/cdeps.mk.in
-  
-
-
-
-
-
-
-  (None of this prevents
+Substitution syntax
+-------------------
+
+In general & expands to the subdirectory name when used for a
+filename, and to the subdirectory name with / replaced with _ for
+variable names.
+
+Note that & is processed *even in makefile comments*.  The substitutor
+does not understand make syntax, or shell syntax, at all.  However,
+the substitution rules are chosen to work well with constructs which
+are common in makefiles.
+
+In the notation below, we suppose that the substitution is being in
+done in a subdirectory sub/dir of the source tree.  In the RH column
+we describe the expansion at the top level, which is often a special
+case (in general in variable names we call that TOP rather than the
+empty string).
+
+&CAPS          =>      sub_dir_CAPS                    or TOP_CAPS
+&lc            =>      sub/dir/lc                      or lc
+       Here CAPS is any ASCII letter A-Z and lc is a-z.
+       The assumption is that filenames are usually lowercase and
+       variables usually uppercase.  Otherwise, use another syntax:
+
+&_             =>      sub_dir_                        or TOP_
+&/             =>      sub/dir/                        or nothing
+&=_            =>      sub_dir                         or TOP
+&=/            =>      sub/dir                         or .
+&^             =>      $(top_srcdir)/sub/dir           or $(top_srcdir)
+&~             =>      $(abs_top_srcdir)/sub/dir       or $(abs_top_srcdir)
+
+&&             =>      &&              for convenience in shell runes
+\&             =>      &               general escaping mechanism
+
+& 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.
+       This processing continues until a & preceded by lwsp,
+       or until EOL (the end of the line), or \ then EOL.

 
 

-
-
-
-
-  https://web.archive.org/web/20150330111905/http://miller.emu.id.au/pmiller/books/rmch/
-
-
-
-
-&CAPS          =>      subdir_CAPS                     or TOP_CAPS
-&lc            =>      subdir/lc                       or lc
-
-&_             =>      subdir_                         or TOP_
-&/             =>      subdir/                         or nothing
-&=_            =>      subdir                          or TOP
-&=/            =>      subdir                          or .
-&^             =>      $(top_srcdir)/subdir            or $(top_srcdir)
-&~             =>      $(abs_top_srcdir)/subdir        or $(abs_top_srcdir)
-
-&&             =>      &&
-\&             =>      &
-
-& thing thing... &     =>      each thing prefixed by &/ &^/ &~/ resp
-& ^ thing thing... &           each thing is any non-ws
-& ~ thing thing... &           & may be omitted before EOL or before \EOL
-                               other &'s not recognised
-
-start of line (maybe after ws):

 &:<directive> <args>....
 &:<directive> <args>....

-args are processed for & first
-&:include filename             filename should usually be foo.mk.in
-&:-include filename
-
-CAPS is [A-Z][0-9_A-Z]*(?!\w)
-lc is [a-z][-+,0-9_a-z]*(?!\w)
-
-&!<spaces or tabs>     disables & *until* EOL (and disappears)
-
-&!STUFF<lwsp>          STUFF is recognised instead of &
-                       the terminating lwsp is discarded too
-                       may also occur at eol
-
-eg notably
- STUFF!&       now & is recognised instead (ie back to normal)
- STUFFSTUFF    STUFF
-
-eg
- &!@@@         @@@ is recognised instead of &
- @@@!&         go back to &
-
-&TARGETS[_things]              is handled specially
-                               must be spelled precisely this way
-                               if no _things, means _all
-
-Also, `all' is weird in that it is present even if not specified
+       recognised at start of line only (possibly after lwsp)
+       args are processed for &
+
+&:include filename             filename should usually be foo.sd.mk
+&:-include filename            tolerate nonexistent file
+
+&!<lwsp>       disables & until EOL (and then disappears)
+
+&!STUFF
+       changes the escape sequence from & to literally STUFF
+       STUFF may be any series of of non-whitespace characters,
+       and is terminated by EOL or lwsp.  STUFF and the lwsp
+       is discarded.
+
+       After this, write STUFF instead of &, everywhere.
+       The effect is global and lasts until the next setting.
+       It takes effect on &:include'd files too, so maybe set
+       it back before using &:include.
+
+       Notably
+               STUFFSTUFF      =>      STUFF
+               \STUFF          =>      STUFF
+               STUFF!&         set escape back to &
+
+&TARGETS_things
+       Handled specially.  If mentioned, declares that
+       this subdirectory ought to have a target `things'.
+       (`all' if not specified).  The rule will be
+               &/things:: $(&TARGETS_things)
+
+       You may extend it by adding more :: rules for the target,
+       but the preferred style is to do things like this:
+               &TARGETS_check += & test-passed.stamp
+
+       It is important to mention &TARGETS_things at least once in
+       the context of each applicable directory, because it arranges
+       that the *parent* will also have a `things' target which
+       recursively implies this directory's `things'.
+
+       Must be spelled exactly &TARGETS_things.  &_TARGETS_things,
+       for example, does not work.  But mentioning it in a #-comment
+       *does* work because the & filter does not care about comments.
+
+       `all' is extra special: every directory has an `all'
+       target, which corresponds to &TARGETS.
+
+Subdirectory and variable naming
+--------------------------------
+
+The simple variable decoration scheme does not enforce a strict
+namespace distinction between parts of variable names which come from
+subdirectory names, and parts that mean something else.
+
+So it is a good idea to be a bit careful with your directory naming.
+`TOP', names that contain `_', and names that are similar to parts of
+make variables (whether conventional ones, or ones used in your
+project) are best avoided.
+
+If you name your variables in ALL CAPS and your subdirectories in
+lower case with `-' rather than `_', there will be no confusion.