[cmake-developers] regex replace bug?

[Matthew Woehlke]

While writing a command to invoke asciidoc, I thought I would use this 
little regex replace to get the output file name:

   string(REGEX REPLACE "([.][^.]+)?$" ".html" BAR "${FOO}")

However, CMake is throwing this error:

   string sub-command REGEX, mode REPLACE regex "([.][^.]+)?$" matched an
   empty string.

This doesn't seem right for two reasons:

1. The match (given an input 'foo.txt') should have been non-empty.
2. Even if the match is empty, the use of an anchor makes it definite 
and non-ambiguous, so replacement should succeed.

For point 2, I get a similar error if the match is '^' or '$', both of 
which I would have expected to be valid. (Silly perhaps if/when the 
expression is known when writing the replace rule, as using a regex 
replace is overkill for such a case, but still valid.)

For comparison, doing the replace with sed using the same expression 
works as expected (i.e. { 'foo', 'foo.txt' } -> 'foo.html'). In 
particular, while sed is understandably unhappy being asked to match and 
replace '' (empty pattern), '^' and '$' are both valid.

Is this expected behavior, or should I file a bug?

(And yes, I'm now using get_filename_component, but still...)

-- 
Matthew