On 2/6/19 5:05 PM, Peng Yu wrote: > On Wed, Feb 6, 2019 at 4:49 PM Eric Blake <ebl...@redhat.com> wrote: >> >> On 2/6/19 4:18 PM, Peng Yu wrote: >>> Hi, >>> >>> I deleted the file parser-built, and bash still compiles and an empty >>> parser-built file will be generated upon compilation. What is the >>> purpose of this file? Should it be deleted? Thanks. > >> parser-built is a witness that $(YACC) was run, even if the timestamps >> did not change (because the generated file did not change compared to >> last time). It exists in the file system so as to let make compute >> timestamp dependencies where we know the parser is up-to-date, even >> though the actual file we depend on has a timestamp that does NOT change >> (because we intentionally don't override it when there is no >> difference), all in order to minimize the time spent rebuilding the >> project when making a tweak to parse.y (for example, being able to tell >> the difference between a minor edit that changes a comment but not the >> generated parser, vs. a major edit that requires rebuilding other files >> to pick up the changes implied by the changed parser). > > I don't get the point. Should parser-built be deleted? If bash can be > compiled without it, why put it in the source tar.gz file?
Deleting it makes rebuild times longer, AND means that your build will depend on having a decent $(YACC) installed. The file is placed in the tar.gz so that downstream users can unpack bash (even if it corrupts timestamps), and still be able to './configure && make' without having bison installed; where only the upstream maintainer has to have bison. If you deleted the file and things still built, then you happen to have a good-enough bison installed, OR you got lucky and didn't make any changes to parser.y that would have resulted in changes where the fallback rule of copying the pre-built y.tab.h that shipped with the tarball disagrees with an actual y.tab.h that you would get if you did have bison installed. -- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3226 Virtualization: qemu.org | libvirt.org
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