mruby-regexp: quote the pattern as written in RegexpError messages - #7031

compile_error() formats the pattern the parser is reading. In /x mode that
is not the pattern the user wrote: mrb_re_compile() points c->src at the
buffer strip_extended() returns, so the message quotes text with the
free-spacing and the comments taken out.

Regexp.new("a # c\n[", Regexp::EXTENDED)
# CRuby: RegexpError (premature end of char-class: /a # c\n[/x)
# mruby: RegexpError (unterminated character class: /a[/)

The comment that explained the pattern is gone from the message, and so is the
position the reader would use to find the error. Anything the pass removes goes
with it:

Regexp.new("a b(", Regexp::EXTENDED)
# CRuby: RegexpError (end pattern with unmatched parenthesis: /a b(/x)
# mruby: RegexpError (unmatched '(': /ab(/)

This is a diagnostics bug, not a behavioural one. The same patterns are accepted
and rejected either way; only the text of the exception differs.

Change

re_compiler gains orig and orig_end next to src and src_end.
mrb_re_compile() sets them from its arguments before the extended-mode block
replaces pattern and len, and compile_error() quotes them instead of
src and src_end. The parser keeps reading the preprocessed text; this only
changes what gets quoted. Ordinary patterns see no difference, since c->src
is then already the caller's buffer.

The new pointer outlives the compile. The single caller is regexp_init(),
which stores the same String in @source before passing RSTRING_PTR(), so
the bytes stay rooted across the allocating mrb_format(). It also never
points into c->stripped, so the message no longer depends on the free order
in compile_error(); the comment there is updated to say what is quoted and
why rather than to state a lifetime constraint that no longer applies.

Out of scope

CRuby appends the flags, /a # c\n[/x. mruby's format string carries no flags
at all, for /x or for anything else, which is a separate difference. The
message wording (unterminated character class against CRuby's
premature end of char-class) is another one; this gem's messages differ from
Onigmo's throughout.

Tests

Two assert_raise_with_message cases in assert("Regexp extended mode (x flag)")
pin the whole message for a comment-bearing pattern and a whitespace-bearing
one. No existing assertion depended on the old text: the RegexpError cases in
this file are all assert_raise without a message.

rake test passes (1940 OK, 0 KO).

Summary by CodeRabbit

• Bug Fixes

  • Improved regular expression compilation errors in extended mode to display the original pattern, including whitespace and comments.
  • Preserved the correct pattern length in error messages for clearer diagnostics.

• Tests

  • Added coverage for unterminated character classes and unmatched opening parentheses in extended-mode regular expressions.