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Re: [PATCH v2 1/1] Makefile: use `git ls-files` to list header files, if possible





On 04/03/2019 13:47, Johannes Schindelin via GitGitGadget wrote:
> From: Johannes Schindelin <johannes.schindelin@xxxxxx>
> 
> In d85b0dff72 (Makefile: use `find` to determine static header
> dependencies, 2014-08-25), we switched from a static list of header
> files to a dynamically-generated one, asking `find` to enumerate them.
> 
> Back in those days, we did not use `$(LIB_H)` by default, and many a
> `make` implementation seems smart enough not to run that `find` command
> in that case, so it was deemed okay to run `find` for special targets
> requiring this macro.
> 
> However, as of ebb7baf02f (Makefile: add a hdr-check target,
> 2018-09-19), $(LIB_H) is part of a global rule and therefore must be
> expanded. Meaning: this `find` command has to be run upon every
> `make` invocation. In the presence of many a worktree, this can tax the
> developers' patience quite a bit.
> 
> Even in the absence of worktrees or other untracked files and
> directories, the cost of I/O to generate that list of header files is
> simply a lot larger than a simple `git ls-files` call.
> 
> Therefore, just like in 335339758c (Makefile: ask "ls-files" to list
> source files if available, 2011-10-18), we now prefer to use `git
> ls-files` to enumerate the header files to enumerating them via `find`,
> falling back to the latter if the former failed (which would be the case
> e.g. in a worktree that was extracted from a source .tar file rather
> than from a clone of Git's sources).
> 
> This has one notable consequence: we no longer include `command-list.h`
> in `LIB_H`, as it is a generated file, not a tracked one, but that is

Heh, just to be _unnecessarily_ picky, but this is not always true.
The 'command-list.h' header is _sometimes_ not included in the LIB_H
variable - it simply depends on whether it has been generated by the
time the $(FIND) is called.

Obviously, not worth a re-roll. Otherwise, this LGTM.

Thanks!

ATB,
Ramsay Jones

> easily worked around. Of the three sites that use `LIB_H`, two
> (`LOCALIZED_C` and `CHK_HDRS`) already handle generated headers
> separately. In the third, the computed-dependency fallback, we can just
> add in a reference to $(GENERATED_H).
> 
> Likewise, we no longer include not-yet-tracked header files in `LIB_H`.
> 
> Given the speed improvements, these consequences seem a comparably small
> price to pay.
> 
> Signed-off-by: Johannes Schindelin <johannes.schindelin@xxxxxx>
> ---
>  Makefile | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/Makefile b/Makefile
> index c5240942f2..0c4712cb48 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -841,7 +841,8 @@ VCSSVN_LIB = vcs-svn/lib.a
>  
>  GENERATED_H += command-list.h
>  
> -LIB_H = $(shell $(FIND) . \
> +LIB_H := $(shell git ls-files '*.h' ':!t/' ':!Documentation/' 2>/dev/null || \
> +	$(FIND) . \
>  	-name .git -prune -o \
>  	-name t -prune -o \
>  	-name Documentation -prune -o \
> @@ -2363,7 +2364,7 @@ else
>  # should _not_ be included here, since they are necessary even when
>  # building an object for the first time.
>  
> -$(OBJECTS): $(LIB_H)
> +$(OBJECTS): $(LIB_H) $(GENERATED_H)
>  endif
>  
>  exec-cmd.sp exec-cmd.s exec-cmd.o: GIT-PREFIX
>