X-Git-Url: https://www.chiark.greenend.org.uk/ucgi/~ian/git?p=subdirmk.git;a=blobdiff_plain;f=README;h=bbec51884700b9776f8f9491f1b6375b0a9c1e0d;hp=0ab3b50057b5ed23172f7fa60b911fd8c9d47e23;hb=83e89d6960a536ab393aaf081cf9209a32508045;hpb=172580f2d7fb712f40e036c1417718b443e4adb9 diff --git a/README b/README index 0ab3b50..bbec518 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 ------------------- @@ -163,22 +219,37 @@ empty string). variables usually uppercase. Otherwise, use another syntax: &_ => sub_dir_ or TOP_ -&/ => sub/dir/ or nothing &=_ => sub_dir or TOP + +&/ => sub/dir/ or nothing &=/ => sub/dir or . -&^ => $(top_srcdir)/sub/dir or $(top_srcdir) -&~ => $(abs_top_srcdir)/sub/dir or $(abs_top_srcdir) + +&^lc => $(top_srcdir)/sub/dir/lc +&^/ => $(top_srcdir)/sub/dir/ + +&~lc => $(top_srcdir)/lc +&~/ => $(top_srcdir)/ + +In general: + = return subdir without delimiter (not allowed with `^' `~') + ^ pathname of this subdirectory in source tree + ~ pathname of top level of source tree + / 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 | '/' ] && => && for convenience in shell runes \& => & general escaping mechanism & 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. @@ -282,15 +353,18 @@ 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. +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 there is no -separate-directory barrier stopping the different invocations ending -up trying to make the same targets at the same time, which causes -hideous racy lossage. There are ways to get this to work reliably but -it is advanced stuff. +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