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fix repeat of preferred empty match #137

Merged
merged 1 commit into from
May 28, 2021
Merged

fix repeat of preferred empty match #137

merged 1 commit into from
May 28, 2021

Commits on May 27, 2021

  1. fix repeat of preferred empty match 

    Ports fix of golang/go#46123 to RE2/J.

Original go fix:

golang/go@2a61b3c

Change description from that commit:

In Perl mode, (|a)* should match an empty string at the start of the
input. Instead it matches as many a's as possible.
Because (|a)+ is handled correctly, matching only an empty string,
this leads to the paradox that e* can match more text than e+
(for e = (|a)) and that e+ is sometimes different from ee*.

The current code treats e* and e+ as the same structure, with
different entry points. In the case of e* the preference list ends up
not quite in the right order, in part because the "before e" and
"after e" states are the same state. Splitting them apart fixes the
preference list, and that can be done by compiling e* as if it were
(e+)?.

Fixes google#136.
    @sjamesr
    sjamesr committed May 27, 2021
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