From 57896643822d2c63bebd95c3c9622f2f37d2f780 Mon Sep 17 00:00:00 2001
From: Jay Hemnani <193022578+jayhemnani9910@users.noreply.github.com>
Date: Thu, 22 Oct 2026 00:45:58 +0530
Subject: [PATCH] interpreter: match a bare regex against $0

---
 interpreter/src/ir/lower.rs |  5 ++++-
 tests/by-util/test_awk.rs   | 18 ++++++++++++++++++
 2 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/interpreter/src/ir/lower.rs b/interpreter/src/ir/lower.rs
index 20fbe42..af1160d 100644
--- a/interpreter/src/ir/lower.rs
+++ b/interpreter/src/ir/lower.rs
@@ -513,9 +513,12 @@ impl<'a> CodeGen<'a> {
                 TypedArg::new_cnt(self, val(buf.into()))
             }
             Atom::Regex(r) => {
+                // A bare `/re/` is `$0 ~ /re/`
+                let (arg, ty) = TypedArg::new_imm(0).into_arg();
+                self.emit(Instruction::LoadF { dest, arg, ty });
                 let buf = &*self.arena.alloc_slice_copy(r.as_ref());
                 let (rhs, tyr) = TypedArg::new_cnt(self, Value::new_regex(buf.into())).into_arg();
-                let (lhs, tyl) = TypedArg::new_imm(0).into_arg();
+                let (lhs, tyl) = TypedArg::new_reg(dest).into_arg();
                 self.emit(Instruction::Matches { dest, rhs, lhs, tyr, tyl });
                 TypedArg::new_reg(dest)
             }
diff --git a/tests/by-util/test_awk.rs b/tests/by-util/test_awk.rs
index 3e19faf..9f56c9f 100644
--- a/tests/by-util/test_awk.rs
+++ b/tests/by-util/test_awk.rs
@@ -881,3 +881,21 @@ fn mdim_in_array() {
         .succeeds()
         .stdout_is("1 1 1 1 0\n");
 }
+
+#[test]
+fn bare_regex_pattern_matches_record() {
+    ucmd()
+        .args(&["/b/ { print NR \": \" $0 } !/a/ { print \"no a\" }"])
+        .pipe_in("a b\nc\nab\n")
+        .succeeds()
+        .stdout_is("1: a b\nno a\n3: ab\n");
+}
+
+#[test]
+fn bare_regex_in_expression_matches_record() {
+    ucmd()
+        .arg(r#"{ n += /x/; if (/^y/) print "y", NR } END { print n }"#)
+        .pipe_in("x\ny\nxx\n")
+        .succeeds()
+        .stdout_is("y 2\n2\n");
+}