A regular expression search is bounded by a step budget patched into mvzr, not windows and a repeat cap

The windows returned wrong matches: a candidate reaching a window's edge was
left to the next window, half a window on, which could answer a match starting
mid-token rather than the leftmost, and addr then pointed data's next write at
the wrong bytes. The repeat cap missed mvzr's own worst case, a chain of a?,
and alternation under a repeat, each exponential inside one mvzr call the
deadline could not interrupt; and it refused ordinary s/S patterns. build.zig
now patches the fetched mvzr at build time with a step counter on its
backtracking recursion (matchPattern), so a fresh fetch keeps it and a moved
anchor stops the build; regexp.zig gives each compiled pattern a budget, about
300 ms here, and a search that spends it fails as taking too long. Windows,
the cap and their special cases are gone, and matches are exact again.

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

1 files changed, 3 insertions, 4 deletions

diff --git a/src/ninep/addr.zig b/src/ninep/addr.zig
index 69e6dc77..cc7ca632 100644
--- a/src/ninep/addr.zig
+++ b/src/ninep/addr.zig
@@ -14,7 +14,6 @@ fn clip(n: usize) u32 {
 pub const e_no_match = "no match for regexp";
 pub const e_range = "address out of range";
 pub const e_regexp = "bad regular expression";
-pub const e_costly = "regular expression has more than four repeats";
 pub const e_slow = "regular expression search took too long";
 pub const e_syntax = "bad address syntax";
 
@@ -198,8 +197,8 @@ pub const Addr = struct {
             a.err = "no previous regular expression";
             return null;
         }
-        const rx = regexp_.Regex.compile(pat) catch |err| {
-            a.err = if (err == error.TooCostly) e_costly else e_regexp;
+        var rx = regexp_.Regex.compile(pat) catch {
+            a.err = e_regexp;
             return null;
         };
         const found = if (back) found: {
@@ -378,7 +377,7 @@ test "the address language, form by form" {
     for ([_][2][]const u8{
         .{ "zzz", e_syntax },         .{ "/nomatch/", e_no_match }, .{ "99", e_range },
         .{ "#999", e_range },         .{ "/a[/", e_regexp },        .{ "/(a/", e_regexp },
-        .{ "/*a/", e_regexp },        .{ "/a*b*c*d*e*/", e_costly },
+        .{ "/*a/", e_regexp },
     }) |c| {
         _ = th.wr(p, addr, "#0");
         try testing.expectEqualStrings(c[1], th.wr(p, addr, c[0]).reply.ename);