$ may end any alternative in a pattern, not only the last

mvzr refuses $ anywhere but at the very end, so /h$|zz/ and Edit ,x/r$|pi/
were bad patterns while /zz|h$/ worked. Its matcher already ends an
alternative at .end, so a build-time patch, anchor-checked like the group
one, lets $ stand before | and ). The upstream report is in
docs/mvzr-group-backtrack.md.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

1 files changed, 22 insertions, 0 deletions

diff --git a/docs/mvzr-group-backtrack.md b/docs/mvzr-group-backtrack.md
index d074af62..867336a3 100644
--- a/docs/mvzr-group-backtrack.md
+++ b/docs/mvzr-group-backtrack.md
@@ -62,3 +62,25 @@ string end at `e`, so a group ending in either can accept a cut the full
 string would not; a continuation-passing matcher (each repeat trying the
 rest of the whole pattern) would be the full fix. `hasAlt` returning false
 at the group's own `)` is worth fixing too.
+
+# mvzr: `$` before `|` is a bad pattern
+
+A second report, same trunk. `compile` refuses `$` anywhere but at the
+very end of the pattern, so an anchored alternative must come last:
+
+```zig
+std.debug.assert(mvzr.compile("zz|h$") != null);
+std.debug.assert(mvzr.compile("h$|zz") == null); // expected a regex
+std.debug.assert(mvzr.compile("(h$|zz)") == null); // likewise
+```
+
+The parser's check is `if (i + 1 < in.len) bad_string = true`. The
+matcher already handles `.end` inside an alternative: `matchAlt` and
+`matchGroup` hand `matchPattern` each alternative as its own slice, and
+`.end` returns an empty rest, which ends that slice. So `$` can stand
+before `|` or `)` as well as last; pardes's patch:
+
+```zig
+'$' => {
+    if (i + 1 < in.len and in[i + 1] != '|' and in[i + 1] != ')') {
+```