This was an important conflict. In the following expression:
def a: 0; . | a
Bison needs to decide between these two equally valid
parses:
(def a: 0; .) | a
def a: 0; (. | a)
For jq we want the second one, because the first results in
"a/0 is not defined". In the current parser the first parse
is a reduce and the second parse is a shift. Since Bison
prefers to shift in shift/reduce conflicts, we accidentally
got the correct behavior.
This commit adds a precedence level FUNCDEF which is lower
precedence than '|', meaning we explicitly choose the
correct parse.
Of course many unit tests already cover this case, but I
added one specifically for it.
Also flex is now optional.
The outputs of flex and bison are now committed. By default they get
built, but users who want to build from git can now
./configure --disable-maintainer-mode
to turn off the dependency on bison and flex.
Maintainers must, of course, commit the bison and/or flex outputs when
they make changes to parser.y and/or lexer.l, respectively.
David Tolnay