$ 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, 18 insertions, 1 deletions

diff --git a/build.zig b/build.zig
index e63b7f4b..fb17afd8 100644
--- a/build.zig
+++ b/build.zig
@@ -500,7 +500,24 @@ pub fn build(b: *std.Build) void {
             \\
         ;
         if (std.mem.count(u8, budgeted, group_anchor) != 1) @panic("mvzr's matchGroup changed: redo its group backtracking in build.zig");
-        const patched = std.mem.replaceOwned(u8, b.allocator, budgeted, group_anchor, group_backoff) catch @panic("OOM");
+        const backed = std.mem.replaceOwned(u8, b.allocator, budgeted, group_anchor, group_backoff) catch @panic("OOM");
+        // `$` is refused anywhere but last, so `h$|zz` was a bad pattern
+        // while `zz|h$` was fine. An alternative or a group ends at `|` and
+        // `)`, and the matcher's `.end` ends the alternative it is in, so
+        // `$` may stand before either (docs/mvzr-group-backtrack.md).
+        const end_anchor =
+            \\            '$' => {
+            \\                if (i + 1 < in.len) {
+            \\
+        ;
+        const end_before_alt =
+            \\            '$' => {
+            \\                // pardes's patch (its build.zig): `$` may end an alternative.
+            \\                if (i + 1 < in.len and in[i + 1] != '|' and in[i + 1] != ')') {
+            \\
+        ;
+        if (std.mem.count(u8, backed, end_anchor) != 1) @panic("mvzr's parser changed: redo its `$` before `|` in build.zig");
+        const patched = std.mem.replaceOwned(u8, b.allocator, backed, end_anchor, end_before_alt) catch @panic("OOM");
         break :mvzr b.createModule(.{ .root_source_file = b.addWriteFiles().add("mvzr.zig", patched), .target = target, .optimize = optimize });
     };