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mruby-regexp: test a lookbehind over a class that holds a stray byte #7219

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Merged
matz merged 1 commit into from
Aug 17, 2026
Merged

mruby-regexp: test a lookbehind over a class that holds a stray byte #7219

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29 changes: 29 additions & 0 deletions mrbgems/mruby-regexp/test/regexp_syntax.rb
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Original file line number Diff line number Diff line change
Expand Up @@ -911,6 +911,35 @@
assert_nil "aab".match(/(?<=Āa)b/)
end

assert("Regexp - lookbehind over a class holding a byte that spells no character") do
# Two things meet here that were built apart: a character class may hold a
# byte that starts no character, and the rewind steps back over characters.
# They agree on the unit already: such a byte is a character of its own,
# which is the step the forward match takes for it too, so a class holding
# one is measured as one character wide, the same as any other class.
#
# A subject whose bytes spell no character is refused wherever an encoding
# reads them, so the stray byte is put to a binary subject, which rewinds by
# bytes in either build.
assert_equal "x", "\xB5x".b.match(/(?<=[\xB5])x/)[0]
assert_equal 1, ("\xB5x".b =~ /(?<=[\xB5])x/)
if __ENCODING__ == "UTF-8"
assert_raise(ArgumentError) { "\xB5x" =~ /(?<=[\xB5])x/ }
# the byte written into a class is still asked about a character: Ā is
# C4 80, and the rewind steps back over the whole of it, so the class is
# handed U+0100 rather than either of its bytes
assert_nil ("Āx" =~ /(?<=[\x80])x/)
assert_nil ("Āx" =~ /(?<=[\xC4])x/)
assert_equal 1, ("Āx" =~ /(?<=[Ā])x/)
else
# a build that reads its strings by byte has one character per byte, so
# the same class does see the continuation byte, and only that one
assert_equal 1, ("\xB5x" =~ /(?<=[\xB5])x/)
assert_equal 2, ("\xC4\x80x" =~ /(?<=[\x80])x/)
assert_nil ("\xC4\x80x" =~ /(?<=[\xC4])x/)
end
end

assert("Regexp - lookbehind measures an ASCII-only class") do
assert_equal "x", "ax".match(/(?<=[a-z])x/)[0]
assert_nil "1x".match(/(?<=[a-z])x/)
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