Handle unterminated format string

src/lexer.rs

@@ -231,10 +231,14 @@ impl<'src> Lexer<'src> {
     // The width of the error site to highlight depends on the kind of error:
     let length = match kind {
       UnterminatedString | UnterminatedBacktick => {
-        let Some(kind) = StringKind::from_token_start(self.lexeme()) else {
-          return self.internal_error("Lexer::error: expected string or backtick token start");
-        };
-        kind.delimiter().len()
+        if self.lexeme().starts_with(Self::INTERPOLATION_END) {
+          Self::INTERPOLATION_END.len()
+        } else {
+          let Some(kind) = StringKind::from_token_start(self.lexeme()) else {
+            return self.internal_error("Lexer::error: expected string or backtick token start");
+          };
+          kind.delimiter().len()
+        }
       }
       // highlight the full token
       _ => self.lexeme().len(),

tests/format_string.rs

@@ -290,3 +290,19 @@ fn format_string_followed_by_recipe() {
     )
     .success();
 }
+
+#[test]
+fn unterminated_format_string_error() {
+  Test::new()
+    .justfile("x := f'{{}}")
+    .stderr(
+      "
+        error: unterminated string
+         ——▶ justfile:1:10
+          │
+        1 │ x := f'{{}}
+          │          ^^
+      ",
+    )
+    .failure();
+}