rust-hgignore: add a scripting command to print the hgignore regexp Add a command `script::hgignore --print-re` to print the hgignore regexp. One complication is that the `rootfilesin`-only matcher doesn't use a regular expression, and the existing converts it to something that's not a regular expression. We add code to handle that case. Since this command is now sufficient to generate a tidy-looking regexp for scripting, this frees up the "debug" command to report the internal regexp used by the regex engine, so we make that change too.

--- a/rust/hg-core/src/pre_regex.rs	Fri Dec 06 20:27:59 2024 +0000
+++ b/rust/hg-core/src/pre_regex.rs	Fri Dec 13 15:05:37 2024 +0000
@@ -19,6 +19,9 @@
     &RE_ESCAPE[c as usize]
 }
 
+/// An intermediate regular expression representation, that can be used
+/// both to compile down to a `Regex` for matching, or converted to
+/// a string directly for diagnostics.
 #[derive(Debug, Clone)]
 pub enum PreRegex {
     Empty,