X-Git-Url: https://www.chiark.greenend.org.uk/ucgi/~ian/git?p=subdirmk.git;a=blobdiff_plain;f=README;h=c4f9d0ea484881aba7058c604482957b948e727a;hp=7de4def345f95bdfa39f6da34992be894b22e11f;hb=bde6b293e235070d0997cfccd9e408127f49ff00;hpb=963054a07f6670d984c3e69280bde4832ca837d6 diff --git a/README b/README index 7de4def..c4f9d0e 100644 --- a/README +++ b/README @@ -20,13 +20,13 @@ style is not very ergonomic. The main difficulties are: `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 @@ -36,11 +36,11 @@ However, the sigil & is treated specially. By and large, it refers to `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. @@ -52,7 +52,7 @@ Each subdirectory is also provided with an autogenerated `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 @@ -69,7 +69,7 @@ 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. &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' @@ -98,7 +98,7 @@ Prefix.sd.mk, Suffix.sd.mk, Final.sd.mk, inclusion 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 @@ -107,10 +107,10 @@ is already provided in subdirmk, for you to reference like this: &: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. @@ -127,14 +127,14 @@ 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 +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. @@ -146,65 +146,25 @@ 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, @@ -243,18 +203,18 @@ 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 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 $(TOP_VARIABLE) @@ -290,7 +250,8 @@ So pathname syntax is a subset of: discarded. After this, write NEWQUOTE instead of &, everywhere. - The effect is global and lasts until the next setting. + The effect is unscoped and lasts until the next setting, + or until the end of the current directory's Suffix.sd.mk. It takes effect on &:include'd files too, so maybe set it back before using &:include. @@ -323,6 +284,92 @@ So pathname syntax is a subset of: `all' is extra special: every directory has an `all' target, which corresponds to &TARGETS. + +Dollar doubling and macro assistance +------------------------------------ + +&$+ 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 -------------------------------- @@ -344,7 +391,7 @@ Incorporating this into your project 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. @@ -353,7 +400,7 @@ In your configure.ac, say 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 @@ -369,13 +416,14 @@ 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 +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