From d72229ff2c53adcf4b900846eb4c50b5cd13c989 Mon Sep 17 00:00:00 2001
From: yuyi <yuyi98@163.com>
Date: Mon, 14 Aug 2023 11:21:51 +0800
Subject: [PATCH] scanner: error early on an unsupported escape sequence in a
 string, like `\_` (fix #19131) (#19134)

---
 vlib/v/scanner/scanner.v                             | 5 +++++
 vlib/v/scanner/tests/unknown_escape_sequence_err.out | 5 +++++
 vlib/v/scanner/tests/unknown_escape_sequence_err.vv  | 3 +++
 3 files changed, 13 insertions(+)
 create mode 100644 vlib/v/scanner/tests/unknown_escape_sequence_err.out
 create mode 100644 vlib/v/scanner/tests/unknown_escape_sequence_err.vv

diff --git a/vlib/v/scanner/scanner.v b/vlib/v/scanner/scanner.v
index 6a102d439..2b96bfaae 100644
--- a/vlib/v/scanner/scanner.v
+++ b/vlib/v/scanner/scanner.v
@@ -1234,6 +1234,11 @@ fn (mut s Scanner) ident_string() string {
 				}
 				u_escapes_pos << s.pos - 1
 			}
+			// Unknown escape sequence
+			if c !in [`x`, `u`, `e`, `n`, `r`, `t`, `v`, `a`, `f`, `b`, `\\`, `\``, `$`, `@`, `?`, `{`, `}`, `'`, `"`]
+				&& !c.is_digit() {
+				s.error('`${c.ascii_str()}` unknown escape sequence')
+			}
 		}
 		// ${var} (ignore in vfmt mode) (skip \$)
 		if prevc == `$` && c == `{` && !is_raw
diff --git a/vlib/v/scanner/tests/unknown_escape_sequence_err.out b/vlib/v/scanner/tests/unknown_escape_sequence_err.out
new file mode 100644
index 000000000..eef4301d3
--- /dev/null
+++ b/vlib/v/scanner/tests/unknown_escape_sequence_err.out
@@ -0,0 +1,5 @@
+vlib/v/scanner/tests/unknown_escape_sequence_err.vv:2:14: error: `_` unknown escape sequence
+    1 | fn main() {
+    2 |     println('¯\_(ツ)_/¯')
+      |                ^
+    3 | }
diff --git a/vlib/v/scanner/tests/unknown_escape_sequence_err.vv b/vlib/v/scanner/tests/unknown_escape_sequence_err.vv
new file mode 100644
index 000000000..1e1a8af0f
--- /dev/null
+++ b/vlib/v/scanner/tests/unknown_escape_sequence_err.vv
@@ -0,0 +1,3 @@
+fn main() {
+	println('¯\_(ツ)_/¯')
+}
-- 
2.39.5