X-Git-Url: https://www.chiark.greenend.org.uk/ucgi/~ian/git?p=subdirmk.git;a=blobdiff_plain;f=README;h=360afbd351686e5f2d0ebfde1a486d5ac4967b40;hp=e5ef4b4f5c28a1291e1d4b9c4e981d1ffb4f4eb7;hb=fbb6e8895fbdef49a07539657a6051175fdb6b27;hpb=f1789a0ae66174a95c8d629738eae98d40c084ac diff --git a/README b/README index e5ef4b4..360afbd 100644 --- a/README +++ b/README @@ -28,15 +28,17 @@ Basic approach 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. Unqualified +filenames are relative to the build toplevel, and all commands all run +there. However, the sigil & is treated specially. By and large, it refers to -`the current directory'. There are a variety of convenient -constructions. +`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 to namespace its "local" make variables, and an easy way to refer to -its "local" filenames. +its "local" filenames (and filenames in general). The Subdir.sd.mk's are filtered, fed through autoconf in the usual way (for @..@-substitutions) and included by one autogenerated toplevel @@ -103,6 +105,19 @@ is already provided in subdirmk, for you to reference like this: &:include subdirmk/clean.sd.mk For example you could put that in Perdir.sd.mk. +The top-level Subdir.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. + +subdirmk's filter script itself sets (only) these variables: + top_srcdir + abs_top_srcdir + SUBDIRMK_MAKEFILES + MAKEFILE_TEMPLATES +You are likely to want to define $(PWD), and shorter names for +top_srdir and abs_top_srcdir (we suggest $(src) and $(abs_src)). + Global definitions ------------------ @@ -138,6 +153,47 @@ 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 ------------------- @@ -162,57 +218,86 @@ empty string). 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) +&_ => sub_dir_ or TOP_ +&. => sub/dir or . + (This implies that `&./' works roughly like `&/', although + it can produce a needless `./') + +&= => sub_dir or TOP + +&^lc => $(top_srcdir)/sub/dir/lc +&^/ => $(top_srcdir)/sub/dir/ +&^. => $(top_srcdir)/sub/dir + +&~lc => $(top_srcdir)/lc +&~/ => $(top_srcdir)/ +&~. => $(top_srcdir) + +In general: + ^ 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 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 | '/' | '.' | '=' ] && => && for convenience in shell runes -\& => & general escaping mechanism + +&\& => & general escaping mechanism +&\$ => $ +&\NEWLINE eats the newline and vanishes + +&$VARIABLE => $(sub_dir_VARIABLE) or $(TOP_VARIABLE) + VARIABLE is ASCII starting with a letter and matching \w+ & thing thing... & -& ^ thing thing... & -& ~ 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. + 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. &: .... recognised at start of line only (possibly after lwsp) - args are processed for & -&:include filename filename should usually be foo.sd.mk +&:include filename filename should usually be [&]foo.sd.mk &:-include filename tolerate nonexistent file filenames are relative to $(top_srcdir) + RHS is &-expanded &! disables & until EOL (and then disappears) &# delete everything to end of line (useful if the RHS contains unrecognised & constructions) -&!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 - are discarded. +&: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 STUFF instead of &, everywhere. + 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 - STUFFSTUFF => STUFFSTUFF - \STUFF => STUFF - STUFF!& set escape back to & + NEWQUOTENEWQUOTE => NEWQUOTENEWQUOTE + NEWQUOTE\NEWQUOTE => NEWQUOTE + NEWQUOTE\$ => $ + NEWQUOTE:changequote & set escape back to & &TARGETS_things - Handled specially. If mentioned, declares that this + Handled specially. If mentioned at the start of a line + (possibly following whitespace), declares that this subdir ought to have a target `things'. The rule will be &/things:: $(&TARGETS_things) @@ -226,9 +311,9 @@ empty string). which recursively implies this directory's `things'. Must be spelled exactly &TARGETS_things. &_TARGETS_things, - for example, is not magic. But mentioning &TARGETS_things in - a #-comment *does* work because the & filter does not care - about comments. + for example, is not magic. To make the target exist + without providing any prerequisites for it, write a line + containing just `&TARGETS_things +='. `all' is extra special: every directory has an `all' target, which corresponds to &TARGETS. @@ -275,6 +360,38 @@ have: &:include subdirmk/cdeps.sd.mk &:include subdirmk/clean.sd.mk +Hints +----- + +You can convert your project incrementally. Start with the top-level +Makefile.in and rename it to Subdir.sd.mk, and add the appropriate +stuff to configure.ac, and fix everything up. Leave the existing +$(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. + +If you go back and forth between different versions of your code you +can sometimes find that `make' complains that one of your Subdir.sd.mk +files is missing: typically, if iot was used and therefore a +dependency in some other version of your code. If you run `make +clean' (or `make realclean') these dependencies are suppressed, which +will clear up the problem. + Legal information -----------------