Handle git diffs that only rename files

Fixes #20

Author: sourcefrog

CHANGELOG.md

@@ -8,8 +8,11 @@
 - `Patch` now has an additional `binary` field indicating a "binary files differ" message.
 
 ### Fixed
+
 - Issue #4: Fixed parsing of “No newline at end of file” markers so they are recognized even when not the final line of a hunk.
 
+- Issue #20: Handle patches containing git file renames with no changes. 
+
 ### Changed
 
 ## [v0.7]

src/ast.rs

@@ -30,12 +30,21 @@ impl fmt::Display for Patch<'_> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         // Display implementations typically hold up the invariant that there is no trailing
         // newline. This isn't enforced, but it allows them to work well with `println!`
+        let Patch { old, new, .. } = &self;
         if self.binary {
-            assert!(self.hunks.is_empty());
-            write!(f, "Binary files {} and {} differ", self.old, self.new)?;
+            assert!(
+                self.hunks.is_empty(),
+                "binary diff is not expected to have hunks"
+            );
+            write!(f, "Binary files {old} and {new} differ")?;
+        } else if self.hunks.is_empty() && old != new {
+            writeln!(f, "diff --git a/{old} b/{new}")?; // TODO: Perhaps should be emitted in every case?
+            writeln!(f, "similarity index 100%")?;
+            writeln!(f, "rename from {old}")?;
+            write!(f, "rename to {new}")?;
         } else {
-            writeln!(f, "--- {}", self.old)?;
-            write!(f, "+++ {}", self.new)?;
+            writeln!(f, "--- {old}")?;
+            write!(f, "+++ {new}")?;
             for (i, hunk) in self.hunks.iter().enumerate() {
                 writeln!(f)?;
                 if i == self.hunks.len() - 1 {

src/parser.rs

@@ -102,10 +102,10 @@ fn multiple_patches(input: Input) -> IResult<Input, Vec<Patch>> {
 }
 
 fn patch(input: Input) -> IResult<Input, Patch> {
+    let (input, _diff_command) = diff_command(input)?;
     if let Ok(patch) = file_rename_only(input) {
         return Ok(patch);
     }
-    let (input, _diff_command) = diff_command(input)?;
     let (input, _git_index) = git_index_line(input)?;
     if let Ok(patch) = binary_files_differ(input) {
         return Ok(patch);
@@ -172,14 +172,13 @@ 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.
+/// Attempt to match 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
+/// The `parse` function should handle rename diffs with similarity 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, _parsed) = tag("similarity index 100%\n")(input)?;
 
     let (rest, old_name) = delimited(tag("rename from "), take_until("\n"), line_ending)(rest)?;
 
@@ -815,4 +814,31 @@ mod tests {
 
         Ok(())
     }
+
+    #[test]
+    fn test_git_file_rename_without_changes() -> ParseResult<'static, ()> {
+        let sample = "\
+diff --git a/tests/test-utils/Cargo.toml b/test-utils/Cargo.toml
+similarity index 100%
+rename from tests/test-utils/Cargo.toml
+rename to test-utils/Cargo.toml
+";
+        let expected = Patch {
+            old: File {
+                path: "tests/test-utils/Cargo.toml".into(),
+                meta: None,
+            },
+            new: File {
+                path: "test-utils/Cargo.toml".into(),
+                meta: None,
+            },
+            hunks: Vec::new(),
+            old_missing_newline: false,
+            new_missing_newline: false,
+            binary: false,
+        };
+        test_parser!(patch(sample) -> expected);
+        assert_eq!(format!("{expected}\n"), sample);
+        Ok(())
+    }
 }

tests/wild-samples/git-multiple-file-moves.patch

@@ -0,0 +1,20 @@
+diff --git a/tests/test-utils/Cargo.toml b/test-utils/Cargo.toml
+similarity index 100%
+rename from tests/test-utils/Cargo.toml
+rename to test-utils/Cargo.toml
+diff --git a/tests/test-utils/src/io.rs b/test-utils/src/io.rs
+similarity index 100%
+rename from tests/test-utils/src/io.rs
+rename to test-utils/src/io.rs
+diff --git a/tests/test-utils/src/lib.rs b/test-utils/src/lib.rs
+similarity index 100%
+rename from tests/test-utils/src/lib.rs
+rename to test-utils/src/lib.rs
+diff --git a/tests/test-utils/src/read.rs b/test-utils/src/read.rs
+similarity index 100%
+rename from tests/test-utils/src/read.rs
+rename to test-utils/src/read.rs
+diff --git a/tests/test-utils/src/write.rs b/test-utils/src/write.rs
+similarity index 100%
+rename from tests/test-utils/src/write.rs
+rename to test-utils/src/write.rs

tests/wild-samples/git-only-file-moves.patch

@@ -0,0 +1,4 @@
+diff --git a/tests/test-utils/Cargo.toml b/test-utils/Cargo.toml
+similarity index 100%
+rename from tests/test-utils/Cargo.toml
+rename to test-utils/Cargo.toml