Allow parsing rename-only diffs (similarity score 100%)

Author: vrmiguel

src/parser.rs

@@ -99,6 +99,9 @@ fn patch(input: Input<'_>) -> IResult<Input<'_>, Patch> {
     if let Ok(patch) = binary_files_differ(input) {
         return Ok(patch);
     }
+    if let Ok(patch) = file_rename_only(input) {
+        return Ok(patch);
+    }
     let (input, files) = headers(input)?;
     let (input, hunks) = chunks(input)?;
     let (input, no_newline_indicator) = no_newline_indicator(input)?;
@@ -151,6 +154,36 @@ fn binary_files_differ(input: Input<'_>) -> IResult<Input<'_>, Patch> {
     ))
 }
 
+/// Parse patches with "similarity index 100%", i.e., patches where a file is renamed without any
+/// other change in its diff.
+///
+/// The `parse` function should handle rename diffs with similary index less than 100%, at least as per the test
+/// `parses_file_renames_with_some_diff`.
+fn file_rename_only(input: Input<'_>) -> IResult<Input<'_>, Patch> {
+    let (rest, _parsed) = take_until("\nsimilarity index 100%\n")(input)?;
+    let (rest, _parsed) = tag("\nsimilarity index 100%\n")(rest)?;
+
+    let (rest, old_name) = delimited(tag("rename from "), take_until("\n"), line_ending)(rest)?;
+
+    let (rest, new_name) = delimited(tag("rename to "), take_until("\n"), line_ending)(rest)?;
+
+    Ok((
+        rest,
+        Patch {
+            old: File {
+                path: Cow::Borrowed(&old_name),
+                meta: None,
+            },
+            new: File {
+                path: Cow::Borrowed(&new_name),
+                meta: None,
+            },
+            hunks: Vec::new(),
+            end_newline: false,
+        },
+    ))
+}
+
 // Header lines
 fn headers(input: Input<'_>) -> IResult<Input<'_>, (File, File)> {
     // Ignore any preamble lines in produced diffs

tests/parse_patch.rs

@@ -399,3 +399,20 @@ index d923f10..b47f160 100644
         .iter()
         .any(|line| matches!(line, Line::Add("use new_crate;"))));
 }
+
+#[test]
+fn parses_file_rename_with_100_pct_similarity() {
+    let sample = "\
+diff --git a/original-path.rs b/new-path.rs
+similarity index 100%
+rename from original-path.rs
+rename to new-path.rs
+";
+
+    let patches = Patch::from_multiple(sample).unwrap();
+
+    assert_eq!(patches.len(), 1);
+    assert_eq!(patches[0].old.path, "original-path.rs");
+    assert_eq!(patches[0].new.path, "new-path.rs");
+    assert!(patches[0].hunks.is_empty());
+}