On Mon, 25 Sep 2023 at 11:17, Tom Lane <t...@sss.pgh.pa.us> wrote: > Japin Li <japi...@hotmail.com> writes: >> I find src/backend/utils/mb/Unicode/Makefile has the following comments: > >>> # Note that while each script call produces two output files, to be >>> # parallel-make safe we need to split this into two rules. (See for >>> # example gram.y for more explanation.) > >> I could not find the explanation in gram.y easily. Would someone point >> it out for me? Thanks in advance! > > It's referring to this bit in src/backend/parser/Makefile: > > ----- > # There is no correct way to write a rule that generates two files. > # Rules with two targets don't have that meaning, they are merely > # shorthand for two otherwise separate rules. If we have an action > # that in fact generates two or more files, we must choose one of them > # as primary and show it as the action's output, then make all of the > # other output files dependent on the primary, like this. Furthermore, > # the "touch" action is essential, because it ensures that gram.h is > # marked as newer than (or at least no older than) gram.c. Without that, > # make is likely to try to rebuild gram.h in subsequent runs, which causes > # failures in VPATH builds from tarballs. > > gram.h: gram.c > touch $@ > > gram.c: BISONFLAGS += -d > gram.c: BISON_CHECK_CMD = $(PERL) $(srcdir)/check_keywords.pl $< > $(top_srcdir)/src/include/parser/kwlist.h > ----- > > This is indeed kind of confusing, because there's no explicit > reference to gram.y here --- the last two lines just tweak > the behavior of the default .y to .c rule. > > Maybe we should adjust the comment in Unicode/Makefile, but > I'm not sure what would be a better reference. > > regards, tom lane
Thank you! Maybe be reference src/backend/parser/Makefile is better than current. How about "See gram.h target's comment in src/backend/parser/Makefile" or just "See src/backend/parser/Makefile"? -- Regrads, Japin Li
