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Fix for 31456 -- replace with optional matching group fails when there is no match #31493

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Fix for 31456 -- replace with optional matching group fails when there is no match #31493

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8dd871a
Update regex.jl
tlienart Mar 27, 2019
e6abbda
Adding tests for replace (issue 31456)
tlienart Mar 28, 2019
8012cb9
removing trailing whitespace in comment
tlienart Mar 28, 2019
cd82403
removing trailing whitespace in test
tlienart Mar 28, 2019
254805e
Update pcre.jl
tlienart Apr 2, 2019
f416fd1
Update regex.jl
tlienart Apr 2, 2019
aed992e
Update util.jl
tlienart Apr 2, 2019
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3 changes: 3 additions & 0 deletions base/regex.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -363,6 +363,9 @@ macro s_str(string) SubstitutionString(string) end
replace_err(repl) = error("Bad replacement string: $repl")

function _write_capture(io, re, group)
# in the case of an optional group that doesn't match, don't write anything
# e.g. replace("The fox.", r"fox(es)?" => s"bus\1")
isa(re.match_data, Ptr{Nothing}) && return
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This doesn't look right --- isn't match_data always a Ptr?

We might have to modify substring_length_bynumber to return 0 in this error case, but I'm not sure whether that's the best way to do it.

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@tlienart tlienart Mar 29, 2019 •
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Ok yes. Looking at the PCRE2 doc for substring (https://code.woboq.org/qt5/qtbase/src/3rdparty/pcre2/src/pcre2_substring.c.html) L315 onwards, it returns a PCRE2_ERROR_UNSET code (-55) when it can't find a match.

So locally I did the following:

  1. modify substring_length_bynumber as suggested with
function substring_length_bynumber(match_data, number)
    s = Base.RefValue{Csize_t}()
    rc = ccall((:pcre2_substring_length_bynumber_8, PCRE_LIB), Cint,
          (Ptr{Cvoid}, UInt32, Ref{Csize_t}), match_data, number, s)
    if rc < 0
        rc == -55 && return 0
        error("PCRE error: $(err_message(rc))")
    end
    convert(Int, s[])
end
  1. modify _write_capture so that it doesn't go further when it has a length of 0 (otherwise the next PCRE function fails):
function _write_capture(io, re, group)
    len = substring_length_bynumber(re.match_data, group)
    len == 0 && return
    ensureroom(io, len+1)
    PCRE.substring_copy_bynumber(re.match_data, group,
        pointer(io.data, io.ptr), len+1)
    io.ptr += len
    io.size = max(io.size, io.ptr - 1)
end

And:

julia> replace("The quick fox quickly.", r"(quick)?\sfox(es)?\s(run)?" => s"\1 bus\2 \3")
"The quick bus quickly."

Should I try that in the PR or should I close it and let someone who knows more about PCRE take over? I've added that to the PR, feel free to close the PR if you think that's not the right approach, happy for someone more competent to do it (or tell me how it should be done)

len = PCRE.substring_length_bynumber(re.match_data, group)
ensureroom(io, len+1)
PCRE.substring_copy_bynumber(re.match_data, group,
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4 changes: 4 additions & 0 deletions test/strings/util.jl
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Expand Up @@ -272,6 +272,10 @@ end
# Issue 13332
@test replace("abc", 'b' => 2.1) == "a2.1c"

# Issue 31456
@test replace("The fox.", r"fox(es)?" => s"bus\1") == "The bus."
@test replace("The foxes.", r"fox(es)?" => s"bus\1") == "The buses."

# test replace with a count for String and GenericString
# check that replace is a no-op if count==0
for s in ["aaa", Test.GenericString("aaa")]
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