Re: There's a bug in my LPeg code, but I can't find it

[Sean Conner <sean@...>]

It was thus said that the Great Daurnimator once stated:
> On 18 August 2018 at 12:12, Daurnimator <quae@daurnimator.com> wrote:
> > On 18 August 2018 at 10:33, Sean Conner <sean@conman.org> wrote:
> >>   Possibly related:
> >>
> >> a,b = x:match "/status#a" print(b)  -- prints 10 okay
> >> a,b = x:match "/status/#a" print(b) -- prints 8 WAT?
> > Your segment definition is incorrect: you have "either followed by end
> > of string, or at least one path character"
> > It should instead be "any number of path characters". i.e.
> >
> > segment         <- {~ pchar* ~}
> 
> I forgot to answer the second half here; though it's relatively the same answer.
> 
> path_empty      <- ! . {| |}
> 
> Should be
> 
> path_empty      <- {| |}

  I made the following changes:

diff --git a/url/url.lua b/url/url.lua
index 821a9ac..09b90ba 100644
--- a/url/url.lua
+++ b/url/url.lua
@@ -72,8 +72,8 @@ path_abempty    <- {| {:root: %istrue :} ( '/' segment)* |}
 path_absolute   <- {| {:root: %istrue :}   '/' (segment_nz ('/' segment)* )? |}
 path_noscheme   <- {| segment_nz_nc ('/' segment)* |}
 path_rootless   <- {| segment_nz    ('/' segment)* |}
-path_empty      <- ! . {| |}
-segment         <- ! . / {~ pchar+ ~}
+path_empty      <- {| |}
+segment         <- {~ pchar* ~}
 segment_nz      <- {~ pchar+ ~}
 segment_nz_nc   <- {~ (unreserved / pct_encoded / sub_delims / ';' / '@')+ ~}
 pchar           <-  unreserved / pct_encoded / sub_delims / ':' / '@'

  And I still get the same results:

url  = require "org.conman.parsers.url.url"
lpeg = require "lpeg"

x = url * lpeg.Cp()

_,b = x:match "/status"   print(b) -- 8, which is right
                    --^ here is position 8
_,b = x:match "/status/"  print(b) -- 9, which is right
                     --^ here is position 9
_,b = x:match "/status "  print(b) -- 8, which is right
                    --^ here is position 8
_,b = x:match "/status/ " print(b) -- 8, which is incorrect, shoule be 9
                     --^ here is *WHERE* is should be
                    --^ here is where it's returning

> A simple principle to work with is that you should almost never use
> EOF in a pattern that you intend to compose: leave that for the user.
> e.g. https://github.com/daurnimator/lua-http/blob/e3ed1a0a2a2eab4d149ea8560b1a9740bc54a8f9/http/request.lua#L46

  Fair enough.

  -spc