Apparent regex bug involving `\_.' (and other newline-matching constructs)

Given a file containing the following 2 lines...

1a3

123xyz

...try the following tests, and note the unexpected results.

Case 1.1:

call cursor(1, 1)

echo searchpos('\%(\([a-z]\)\|\_.\)\{-}xyz', 'pcW')

=> [1, 1, 2]

Case 1.2:

call cursor(1, 2)

echo searchpos('\%(\([a-z]\)\|\_.\)\{-}xyz', 'pcW')

=> [2, 1, 1]

Question: Why does the \_. not permit earlier match at cursor pos (1, 2)?

Note: Clearly, submatch should be 2, not 1, but this error is simply a

consequence of the first error: since match doesn't begin on 1st line,

the "a" at cursor pos can't be captured.

Case 1.3:

call cursor(1, 3)

echo searchpos('\%(\([a-z]\)\|\_.\)\{-}xyz', 'pcW')

=> [2, 1, 1]

Note: Why isn't a match found at cursor pos (1, 3)?

Repeat these tests with a \zs in the pattern, and note how the capture

is matched unconditionally...

Case 2.1:

call cursor(1, 1)

echo searchpos('\%(\([a-z]\)\|\_.\)\{-}\zsxyz', 'pcW')

=> [2, 4, 2]

Case 2.2:

call cursor(1, 2)

echo searchpos('\%(\([a-z]\)\|\_.\)\{-}\zsxyz', 'pcW')

=> [2, 4, 2]

Case 2.3:

call cursor(1, 3)

echo searchpos('\%(\([a-z]\)\|\_.\)\{-}\zsxyz', 'pcW')

=> [2, 4, 2]

Note: Submatch should be 1, not 2, here. It's as though the \zs forces the

capture to match unconditionally.

Points to note... Originally, I thought the error had to do with the 'p' flag, but that appears not to be the case: the submatch errors are simply a consequence of the incorrectly determined start locations. Also, it appears the results would have been the same with * as they were with \{-}. Finally, the unexpected behavior is not limited to \_., but is seen even when (e.g.) explicit \n is used.

Thanks,

Brett Stahlman

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