add find_last_uncommented

Author: rchaser53

src/comment.rs

@@ -976,6 +976,7 @@ fn left_trim_comment_line<'a>(line: &'a str, style: &CommentStyle<'_>) -> (&'a s
 
 pub(crate) trait FindUncommented {
     fn find_uncommented(&self, pat: &str) -> Option<usize>;
+    fn find_last_uncommented(&self, pat: &str) -> Option<usize>;
 }
 
 impl FindUncommented for str {
@@ -1001,6 +1002,19 @@ impl FindUncommented for str {
             None => Some(self.len() - pat.len()),
         }
     }
+
+    fn find_last_uncommented(&self, pat: &str) -> Option<usize> {
+        if let Some(left) = self.find_uncommented(pat) {
+            let mut result = left;
+            // add 1 to use find_last_uncommented for &str after pat
+            while let Some(next) = self[(result + 1)..].find_last_uncommented(pat) {
+                result += next + 1;
+            }
+            Some(result)
+        } else {
+            None
+        }
+    }
 }
 
 // Returns the first byte position after the first comment. The given string
@@ -1882,6 +1896,16 @@ mod test {
         check("\"/* abc", "abc", Some(4));
     }
 
+    #[test]
+    fn test_find_last_uncommented() {
+        fn check(haystack: &str, needle: &str, expected: Option<usize>) {
+            assert_eq!(expected, haystack.find_last_uncommented(needle));
+        }
+        check("foo test bar test", "test", Some(13));
+        check("test,", "test", Some(0));
+        check("nothing", "test", None);
+    }
+
     #[test]
     fn test_filter_normal_code() {
         let s = r#"