X-Git-Url: https://www.chiark.greenend.org.uk/ucgi/~ian/git?p=subdirmk.git;a=blobdiff_plain;f=README;h=ef839d56d9e7669abf3143e172ab0efbcb334f3a;hp=e5ef4b4f5c28a1291e1d4b9c4e981d1ffb4f4eb7;hb=0a6dd433bf3969cf7dfa6dcfecfc1244a289c0b4;hpb=f1789a0ae66174a95c8d629738eae98d40c084ac diff --git a/README b/README index e5ef4b4..ef839d5 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 @@ -138,6 +140,43 @@ 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.) + +Path construction &-expansions are built from the following: + + Relative paths in... Absolute paths in... + build source build source + + This directory & &, &@ &@, + Top level . &; &@. &@; + +In more detail, with the various options for what comes next: + + Recommended Relative paths in... Absolute paths in... + for build source build source + + 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 &@;file + level any file &;/file &@./file &@;/file + several f g h &; f g h &@. f g h &@; f g h + .mk.in file $(src)/file $(abs)/file $(abs_src)/file + Substitution syntax ------------------- @@ -163,22 +202,47 @@ 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)/ + +&@lc => $(PWD)/sub/dir/lc &@/ => $(PWD)/sub/dir/ +&@.lc => $(PWD)/lc &@./ => $(PWD)/ +&@,lc => $(abs_top_srcdir)/sub/dir/lc &@,/ => $(abs_top_srcdir)/sub/dir/ +&@;lc => $(abs_top_srcdir)/lc &@;/ => $(abs_top_srcdir)/ + +In general: + = return subdir without delimiter (not allowed with `,' `;' `@') + , pathname of this subdirectory in source tree + ; pathname of top level of source tree + . pathname of this directory in build tree, `@' must be specified + @ absolute pathnames + / terminates the escape (needed if next is not lwsp or space) + lwsp starts multi-word processing (see below) + +So pathname syntax is a subset of: + '&' [ '@' ] [ ',' | ';' | '.' ] [ lc | '/' ] + + To avoid incomprehensible .sd.mk files, some combinations are not + allowed. For example `&=./' would mean `.' and `&./' would be the + empty string. Variations with `=' and one of `@' `,' `;' are + uncommon and must be written using make variables instead. && => && for convenience in shell runes \& => & general escaping mechanism -& thing thing... & -& ^ thing thing... & -& ~ thing thing... & +& thing thing... & &@ thing thing... & + &. thing thing... & +&, thing thing... & &@, thing thing... & +&; thing thing... & &@; thing thing... & Convenience syntax for prefixing multiple filenames. - Introduced by & followed by lwsp (space or tab). - Each lwsp-separated non-ws word is prefixed by &/ &^/ &~/ - respectively. No other & escapes are recognised. + Introduced by & followed by lwsp where lc could go. + Each lwsp-separated non-ws word is prefixed by &/ etc. + etc. respectively. No other & escapes are recognised. This processing continues until & preceded by lwsp, or until EOL (the end of the line), or \ then EOL. @@ -275,6 +339,31 @@ have: &:include subdirmk/cdeps.sd.mk &:include subdirmk/clean.sd.mk +Hints +----- + +You can convert your project incrementally. Start with the top-level +Makefile.in and rename it to Subdir.sd.mk, and add the appropriate +stuff to configure.ac, and fix everything up. Leave the existing +$(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 -----------------