Re: [PATCH 2/4] maint.mk: expand the prohibit_doubled_word regex

[Ján Tomko]

On Fri, Jul 29, 2016 at 03:29:09PM -0600, Eric Blake wrote:
> On 07/26/2016 08:28 AM, Ján Tomko wrote:
> > This check has a static list of words that are checked for repetitions.
> > Expand it before running the perl script to avoid using expensive
> > captures.
> > ---
> >  ChangeLog    | 9 +++++++++
> >  top/maint.mk | 7 ++++++-
> >  2 files changed, 15 insertions(+), 1 deletion(-)

> > +prohibit_doubled_words_ = \
> > +    the then in an on if is it but for or at and do to
> > +# expand the regex before running the check to avoid using expensive captures
> > +prohibit_doubled_word_expanded_ = \
> > +    $(shell echo $(prohibit_doubled_words_) | sed -r 's/\b(\S+)\b/\1\\s\+\1/g')
>
> I bet GNU make has builtins that could do this operation without forking
> to $(shell).  This stage results in a variable containing:
>
> the\s\+the then\s\+then ...
>
> Maybe:
>
> $(join $(prohibit_doubled_words_),$(addprefix
> \s\+,$(prohibit_doubled_words_)))
>
> >  prohibit_doubled_word_RE_ ?= \
> > -  /\b(then?|[iao]n|i[fst]|but|f?or|at|and|[dt]o)\s+\1\b/gims
> > +    /\b(?:$(subst $(space),|,$(prohibit_doubled_word_expanded_)))\b/gims
>
> At any rate, you want to end up with the perl regex:
>
> \b(?:the\s\+the|then\s\+then|...)\b/gims
>
> >  prohibit_doubled_word_ =                                               \
> >      -e 'while ($(prohibit_doubled_word_RE_))'                          \
> >      $(perl_filename_lineno_text_)
>
> At any rate, I doubt my make fine-tuning matters, and you are definitely
> correct that avoiding back-references makes perl regexes more efficient.

I doubt there is any difference in performance, but using join and
addprefix could be more readable than sed.

Jan