`subdirmk' is an attempt to solve these problems (and it also slightly
alleviates some of the boilerplate needed to support out-of-tree
-builds well).
+builds well, and helps a bit with metaprogramming and rule writing).
Basic approach
--------------
The developer is expected to write a makefile fragment, in each
-relevant subdirectory, called `Subdir.sd.mk'.
+relevant subdirectory, called `Dir.sd.mk'.
These fragments may contain ordinary make language. Unqualified
filenames are relative to the build toplevel, and all commands all run
`the build directory corresponding to this .sd.mk file', etc.
There are a variety of convenient constructions.
-The result is that to a large extent, the Subdir.sd.mk has an easy way
+The result is that to a large extent, the Dir.sd.mk has an easy way
to namespace its "local" make variables, and an easy way to refer to
its "local" filenames (and filenames in general).
-The Subdir.sd.mk's are filtered, fed through autoconf in the usual way
+The Dir.sd.mk's are filtered, fed through autoconf in the usual way
(for @..@-substitutions) and included by one autogenerated toplevel
makefile.
which exists purely to capture ordinary make invocations and arrange
for something suitable to happen.
-Where there are dependencies between subdirectories, each Subdir.sd.mk
+Where there are dependencies between subdirectories, each Dir.sd.mk
can simply refer to files in other subdirectories directly.
Invocation, "recursive" per-directory targets
subdirectory `src' has a target `src/all'. The rules for these are
automatically generated from the settings of the per-directory
&TARGETS variables. &TARGETS is magic in this way. (In
-src/Subdir.sd.mk, &TARGETS of course refers to a make variable called
+src/Dir.sd.mk, &TARGETS of course refers to a make variable called
src_TARGETS.)
The `all' target in a parent directory is taken to imply the `all'
The files Prefix.sd.mk and Suffix.sd.mk in the toplevel of the source
are automatically processed before and after each individual
-directory's Subdir.sd.mk, and the &-substituted contents therefore
+directory's Dir.sd.mk, and the &-substituted contents therefore
appear once for each subdirectory.
This lets you do per-directory boilerplate. Some useful boilerplate
&:include subdirmk/clean.sd.mk
For example you could put that in Suffix.sd.mk.
-The top-level Subdir.sd.mk is the first makefile included after the
+The top-level Dir.sd.mk is the first makefile included after the
autogenerated `main.mk' which merely has some basic settings and
includes. So if you want to get in early and set global variables,
-put them near the top of Subdir.sd.mk.
+put them near the top of Dir.sd.mk.
The file Final.sd.mk in the toplevel directory is processed and
included after all the other files.
------------------
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
+once. You can put them in your top-level Dir.sd.mk, or a separate
file you `include' and declare using SUBDIRMK_MAKEFILES.
If you need different settings of variables like CC for different
subdirectories, you should probably do that with target-specific
variable settings. See the info node `(make) Target-specific'.
-Subdirectory templates `.sd.mk' vs plain autoconf templates `.mk.in'
+Directory templates `.sd.mk' vs plain autoconf templates `.mk.in'
--------------------------------------------------------------------
There are two kinds of template files.
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 Dir.sd.mk All not in subdirmk/
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
- (but not needed for Subdir.sd.mk
+ (but not needed for Dir.sd.mk
Prefix, Suffix, Final)
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.
-Tables of file reference syntaxes
----------------------------------
-
-In a nonrecursive makefile supporting out of tree builds there are
-three separate important distinctions between different file
-locations:
-
- (i) In the build tree, or in the source tree ?
-
- (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. 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...
- build source
-
- This directory & &^
- Top level . &~
-
-In more detail, with all the various options laid out:
-
- Recommended Relative paths in... Absolute paths in...
- for build source build source
-
- 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
- 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
-------------------
In general & expands to the subdirectory name when used for a
filename, and to the subdirectory name with / replaced with _ for
-variable names.
+variable names. (If your variables start with capital letters and
+your filenames with lowercase. Otherwise, use &/ or &_.)
Note that & is processed *even in makefile comments*. The substitutor
does not understand make syntax, or shell syntax, at all. However,
^ pathname of this subdirectory in source tree
~ pathname of top level of source tree
/ terminates the path escape } needed if next is
- _ terminates the var escape } not lwsp or space)
+ _ terminates the var escape } not letter or space)
. terminates path escape giving dir name (excluding /)
= terminates var escape giving only prefix part (rarely needed)
lwsp starts multi-word processing (see below)
So pathname syntax is a subset of:
- '&' [ '^' | '~' ] [ lc | '/' | '.' | '=' ]
+ '&' [ '^' | '~' ] [ lc | '/' | '.' ]
&& => && for convenience in shell runes
&\& => & general escaping mechanism
-&\$ => $
+&\$ => $ provided for $-doubling regimes
&\NEWLINE eats the newline and vanishes
&$VARIABLE => $(sub_dir_VARIABLE) or $(TOP_VARIABLE)
&:include filename filename should usually be [&]foo.sd.mk
&:-include filename tolerate nonexistent file
- filenames are relative to $(top_srcdir)
- RHS is &-expanded
+ RHS is &-expanded but filenames are relative to the top
+ srcdir. This implies that unqualified names are like &~/
+ whereas &/ is like &^/. &^ and &~ do not work here because
+ they expand to constructions involving literally
+ `$(top_srcdir)', but the RHS is not make-expanded.
&!<lwsp> disables & until EOL (and then disappears)
&# delete everything to end of line
(useful if the RHS contains unrecognised & constructions)
-&:changequote NEWQUOTE
- changes the escape sequence from & to literally NEWQUOTE
- NEWQUOTE may be any series of of non-whitespace characters,
- and is terminated by EOL or lwsp. The whole line is
- discarded.
-
- After this, write NEWQUOTE 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
- NEWQUOTENEWQUOTE => NEWQUOTENEWQUOTE
- NEWQUOTE\NEWQUOTE => NEWQUOTE
- NEWQUOTE\$ => $
- NEWQUOTE:changequote & set escape back to &
-
&TARGETS_things
Handled specially. If mentioned at the start of a line
(possibly following whitespace), declares that this
`all' is extra special: every directory has an `all'
target, which corresponds to &TARGETS.
+&:changequote NEWQUOTE
+ changes the escape sequence from & to literally NEWQUOTE
+ NEWQUOTE may be any series of of non-whitespace characters,
+ and is terminated by EOL or lwsp. The whole line is
+ discarded.
+
+ After this, write NEWQUOTE instead of &, everywhere.
+ The effect is unscoped and lasts until the next setting,
+ or until the end of the current directory's Suffix.sd.mk.
+ It takes effect on &:include'd files too, so maybe set
+ it back before using &:include.
+
+ Notably
+ NEWQUOTENEWQUOTE => NEWQUOTENEWQUOTE
+ NEWQUOTE\NEWQUOTE => NEWQUOTE
+ NEWQUOTE\$ => $
+ NEWQUOTE:changequote & set escape back to &
+
+
+Dollar doubling and macro assistance
+------------------------------------
+
+&$+ Starts dollar-doubling
+&$- Stops dollar-doubling
+ Both are idempotent and local to the file or context.
+
+Sometimes we will show $'s being doubled inside another construct.
+This means the content of the construct is $-doubled: $-doubling is
+locally enabled, and restored afterwards.
+
+&:macro NAME => define NAME
+STUFF $ THINGS .. STUFF $$ THINGS
+&:endm .. endef
+ NAME is processed for &
+
+&${..$..} => ${eval ${call ..$$..}}
+ (matches { } pairs to find the end)
+ content is $-doubled (unless it contains $- to turn that off)
+
+ Together &:macro and &${...} provide a more reasonable macro
+ facility than raw make. They solve the problem that make
+ expansions cannot directly generate multiple rules, variable,
+ etc.; instead, `$(eval )' must be used, but that re-expands
+ the argument, meaning that all the literal text must be
+ $-doubled. This applies to the macro text and to the
+ arguments. Also `$(eval $(call ...))' is an unfortunate syntax.
+ Hence &:macro and &${...}.
+
+While dollar-doubling:
+- - - - - - - - - - -
+
+$ => $$ including $'s produced by other
+ &-expansions not mentioned here
+
+&\$ => $
+&$NN => $(NN) where N are digits
+&$( => $(
+
+A few contexts do not support $-doubling, such as directive arguments
+or places where this might imply $-quadrupling. (There is no way to
+get $-quadrupling.)
+
+
+Tables of file reference syntaxes
+---------------------------------
+
+In a nonrecursive makefile supporting out of tree builds there are
+three separate important distinctions between different file
+locations:
+
+ (i) In the build tree, or in the source tree ?
+
+ (ii) In (or relative to) the subdirectory to which this Dir.sd.mk
+ relates, or relative to the project's top level ?
+
+ (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...
+ build source
+
+ This directory & &^
+ Top level . &~
+
+In more detail, with all the various options laid out:
+
+ Recommended Relative paths in... Absolute paths in...
+ for build source build source
+
+ 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
+ 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.)
+
Subdirectory and variable naming
--------------------------------
Use `git-subtree' to merge the subdirmk/ directory. You may find it
useful to symlink the DEVELOPER-CERTIFICATE file (git can store
symlinks as symlinks - just `git add' the link). And you probably
-want to mention the situation in your top-level COPYING.
+want to mention the situation in your top-level COPYING and HACKING.
Symlink autogen.sh into your project toplevel.
m4_include([subdirmk/subdirmk.ac])
SUBDIRMK_SUBDIRS([...list of subdirectories in relative syntax...])
-Write a Subdir.sd.mk in each directory. The toplevel one should
+Write a Dir.sd.mk in each directory. The toplevel one should
probably contain:
include subdirmk/usual.mk
-----
You can convert your project incrementally. Start with the top-level
-Makefile.in and rename it to Subdir.sd.mk, and add the appropriate
+Makefile.in and rename it to Dir.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.)
+your leisure. (You must be /sure/ that each recursive (non-subdirmk)
+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