From ca379c5d149683216d930fb9bbe308fcc0f9a690 Mon Sep 17 00:00:00 2001
From: Chris Tate <chris@ctate.dev>
Date: Tue, 20 Oct 2026 19:38:31 -0500
Subject: [PATCH] Run exec on regular expressions held as any

exec on a regular expression held as an untyped value threw "Native RegExp
method has no lowering". It now returns Node's match array: the captures,
with undefined for one that did not participate, then index, input and
groups, or null without a match. Global and sticky expressions read and
advance lastIndex and reset it when nothing matches, as the typed exec
does.
---
 .../tests/corpus/6902-dyn-regexp-exec.js.json |  6 +++
 packages/runtime/src/scr_regex.c              | 18 +++++++
 tests/corpus/6902-dyn-regexp-exec.js          | 47 +++++++++++++++++++
 .../corpus-costs/6902-dyn-regexp-exec.js.json |  1 +
 4 files changed, 72 insertions(+)
 create mode 100644 packages/compiler/test/ts7/baselines/order-parity/tests/corpus/6902-dyn-regexp-exec.js.json
 create mode 100644 tests/corpus/6902-dyn-regexp-exec.js
 create mode 100644 tests/harness/corpus-costs/6902-dyn-regexp-exec.js.json

diff --git a/packages/compiler/test/ts7/baselines/order-parity/tests/corpus/6902-dyn-regexp-exec.js.json b/packages/compiler/test/ts7/baselines/order-parity/tests/corpus/6902-dyn-regexp-exec.js.json
new file mode 100644
index 000000000..46ca41b60
--- /dev/null
+++ b/packages/compiler/test/ts7/baselines/order-parity/tests/corpus/6902-dyn-regexp-exec.js.json
@@ -0,0 +1,6 @@
+{
+ "order": [
+  "<repo>/tests/corpus/6902-dyn-regexp-exec.js"
+ ],
+ "diags": []
+}
diff --git a/packages/runtime/src/scr_regex.c b/packages/runtime/src/scr_regex.c
index e4867ddf3..73440c110 100644
--- a/packages/runtime/src/scr_regex.c
+++ b/packages/runtime/src/scr_regex.c
@@ -2784,6 +2784,24 @@ static ScrDyn *scr_native_regex_invoke(void *ptr, ScrDyn *self, const char *meth
     scr_str_release(subject);
     return scr_exc_pending() ? NULL : scr_dyn_new_bool(matches);
   }
+  if (strcmp(method, "exec") == 0) {
+    /* The match array: each capture (undefined when it did not
+     * participate), then index, input and groups; null without a match.
+     * The exec itself reads and advances lastIndex. */
+    ScrStr *subject = scr_dyn_string_coerce_js(argc ? args[0] : scr_dyn_undefined());
+    if (!subject) return NULL;
+    ScrArr *row = scr_regex_exec(subject, re);
+    scr_str_release(subject);
+    if (!row) return scr_exc_pending() ? NULL : scr_dyn_new_null();
+    ScrDyn *match = scr_dyn_new_arr();
+    for (size_t k = 0; k < row->len; k++)
+      scr_dyn_arr_push(match, *scr_arr_state_ptr(row, k) == SCR_ARR_VALUE
+                                  ? scr_dyn_new_str((ScrStr *)(uintptr_t)row->data[k])
+                                  : scr_dyn_retain(scr_dyn_undefined()));
+    scr_arr_copy_metadata(row, match);
+    scr_arr_release(row);
+    return match;
+  }
   static const char message[] = "Native RegExp method has no lowering";
   scr_throw_error_msg_code(SCR_ERR_ERROR, message, sizeof message - 1, "SC2020");
   return NULL;
diff --git a/tests/corpus/6902-dyn-regexp-exec.js b/tests/corpus/6902-dyn-regexp-exec.js
new file mode 100644
index 000000000..a16a155c8
--- /dev/null
+++ b/tests/corpus/6902-dyn-regexp-exec.js
@@ -0,0 +1,47 @@
+// exec on a regular expression held as an untyped value returns Node's
+// match array: the captures (undefined for one that did not participate),
+// index, input and groups. Global and sticky expressions read and advance
+// lastIndex, and reset it when nothing matches.
+function dyn(value) {
+  return [value][0];
+}
+function show(label, match) {
+  if (match === null) return console.log(label, null);
+  console.log(label, JSON.stringify([...match]), match.index, match.input, JSON.stringify(match.groups), match.length);
+}
+
+const plain = dyn(/(\d+)-(x)?/);
+show("plain", plain.exec("a 12- b"));
+show("miss", plain.exec("none"));
+console.log("plain lastIndex", plain.lastIndex);
+
+const global = dyn(/o(.)/g);
+show("g1", global.exec("foo boo"));
+console.log("after g1", global.lastIndex);
+show("g2", global.exec("foo boo"));
+console.log("after g2", global.lastIndex);
+show("g3", global.exec("foo boo"));
+console.log("after g3", global.lastIndex);
+global.lastIndex = 5;
+show("from 5", global.exec("foo boo"));
+
+const sticky = dyn(/b/y);
+show("sticky miss", sticky.exec("ab"));
+sticky.lastIndex = 1;
+show("sticky hit", sticky.exec("ab"));
+console.log("sticky after", sticky.lastIndex);
+
+const named = dyn(/(?<year>\d{4})-(?<month>\d{2})(?:-(?<day>\d{2}))?/);
+const date = named.exec("on 2024-05");
+show("named", date);
+console.log("year", date.groups.year, "day", date.groups.day, Object.getPrototypeOf(date.groups) === null);
+
+const unicode = dyn(/\u{1F600}(.)/u);
+show("unicode", unicode.exec("x\u{1F600}y"));
+show("coerced", dyn(/1/).exec(123));
+const matches = [];
+const all = dyn(/a(\d)/g);
+let m;
+while ((m = all.exec("a1 a2 a3")) !== null) matches.push(m[1] + "@" + m.index);
+console.log("loop", matches.join(","), all.lastIndex);
+console.log("Array.isArray", Array.isArray(dyn(/x/).exec("x")));
diff --git a/tests/harness/corpus-costs/6902-dyn-regexp-exec.js.json b/tests/harness/corpus-costs/6902-dyn-regexp-exec.js.json
new file mode 100644
index 000000000..876c351cb
--- /dev/null
+++ b/tests/harness/corpus-costs/6902-dyn-regexp-exec.js.json
@@ -0,0 +1 @@
+{ "plain": 2611, "san": 3084 }