fix: render actual newline in terminal-sanitized error messages

sanitize_for_terminal() escaped every control char it saw, including
plain LF, so any multi-line diagnostic built from a hardcoded template
(e.g. the path-separator error in main.rs) came out on a TTY as the
literal 4-character sequence "\x0A" instead of a line break.

LF cannot draw, move the cursor, or exfiltrate data the way ESC- and
CSI/OSC-initiated sequences can, so it does not need the same defense
as those. CR is still escaped since it can overwrite the current line
and forge fake output.

Closes #2104

CHANGELOG.md

@@ -4,7 +4,8 @@
 -
 
 ## Bugfixes
--
+- Render actual newlines instead of the literal `\x0A` escape in multi-line error
+  messages printed to a terminal, see #2104
 
 # 10.5.0
 

src/sanitize.rs

@@ -3,11 +3,19 @@
 use std::borrow::Cow;
 use std::fmt::Write;
 
-/// True for any char that is neither printable nor permitted whitespace (only HT).
-/// Covers C0/C1/DEL, bidi overrides, zero-width and format chars, and tag chars.
+/// True for any char that is neither printable nor permitted whitespace (only HT
+/// and LF). Covers C0/C1/DEL, bidi overrides, zero-width and format chars, and tag
+/// chars.
+///
+/// LF is deliberately let through even though it is a C0 control: it only ever
+/// starts a new line and cannot draw, move the cursor or exfiltrate data the way
+/// ESC- and CSI/OSC-initiated sequences can, so escaping it just mangles the
+/// developer-authored multi-line diagnostics fd prints (see sharkdp/fd#2104).
+/// CR is still escaped: unlike LF it can overwrite the current line and forge
+/// fake output.
 #[inline]
 fn needs_escape(c: char) -> bool {
-    if c == '\t' {
+    if c == '\t' || c == '\n' {
         return false;
     }
     c.is_control()
@@ -107,8 +115,22 @@ mod tests {
     }
 
     #[test]
-    fn strips_newline() {
-        assert_eq!(sanitize_for_terminal("a\nb"), "a\\x0Ab");
+    fn preserves_newline() {
+        assert!(matches!(sanitize_for_terminal("a\nb"), Cow::Borrowed(_)));
+        assert_eq!(sanitize_for_terminal("a\nb"), "a\nb");
+    }
+
+    #[test]
+    fn preserves_real_newlines_in_diagnostics() {
+        // Multi-line diagnostics such as the path-separator error in main.rs use
+        // real newlines for readability; they carry no attacker-controlled bytes,
+        // so a bare '\n' must reach the terminal as an actual line break, not as
+        // the literal 4-character sequence "\x0A". See sharkdp/fd#2104.
+        let message = "The search pattern 'a/b' contains a path-separation character \
+            and will not lead to any search results.\n\n\
+            If you want to search for all files inside the 'a/b' directory, use a match-all pattern:\n\n  \
+            fd . 'a/b'";
+        assert_eq!(sanitize_for_terminal(message), message);
     }
 
     #[test]