Emit 'mode [-+]x' instead of full file permission bits (#607)

Ref #583

2 files changed, 31 insertions, 7 deletions

diff --git a/src/parse.rs b/src/parse.rs
index 3329248b..8e93dd6a 100644
--- a/src/parse.rs
+++ b/src/parse.rs
@@ -162,9 +162,13 @@ pub fn get_file_change_description_from_file_paths(
                 plus_file,
                 FileEvent::ModeChange(old_mode),
                 FileEvent::ModeChange(new_mode),
-            ) if minus_file == plus_file => {
-                format!("{}: {} ⟶   {}", plus_file, old_mode, new_mode)
-            }
+            ) if minus_file == plus_file => match (old_mode.as_str(), new_mode.as_str()) {
+                // 100755 for executable and 100644 for non-executable are the only file modes Git records.
+                // https://medium.com/@tahteche/how-git-treats-changes-in-file-permissions-f71874ca239d
+                ("100644", "100755") => format!("{}: mode +x", plus_file),
+                ("100755", "100644") => format!("{}: mode -x", plus_file),
+                _ => format!("{}: {} ⟶   {}", plus_file, old_mode, new_mode),
+            },
             (minus_file, plus_file, _, _) if minus_file == plus_file => format!(
                 "{}{}",
                 format_label(&config.file_modified_label),
diff --git a/src/tests/test_example_diffs.rs b/src/tests/test_example_diffs.rs
index a4d0b854..82b12f52 100644
--- a/src/tests/test_example_diffs.rs
+++ b/src/tests/test_example_diffs.rs
@@ -1570,11 +1570,25 @@ src/align.rs:71: impl<'a> Alignment<'a> { │
     }
 
     #[test]
-    fn test_file_mode_change() {
+    fn test_file_mode_change_gain_executable_bit() {
         let config = integration_test_utils::make_config_from_args(&[]);
-        let output = integration_test_utils::run_delta(GIT_DIFF_FILE_MODE_CHANGE, &config);
+        let output = integration_test_utils::run_delta(
+            GIT_DIFF_FILE_MODE_CHANGE_GAIN_EXECUTABLE_BIT,
+            &config,
+        );
+        let output = strip_ansi_codes(&output);
+        assert!(output.contains(r"src/delta.rs: mode +x"));
+    }
+
+    #[test]
+    fn test_file_mode_change_lose_executable_bit() {
+        let config = integration_test_utils::make_config_from_args(&[]);
+        let output = integration_test_utils::run_delta(
+            GIT_DIFF_FILE_MODE_CHANGE_LOSE_EXECUTABLE_BIT,
+            &config,
+        );
         let output = strip_ansi_codes(&output);
-        assert!(output.contains(r"src/delta.rs: 100644 ⟶   100755"));
+        assert!(output.contains(r"src/delta.rs: mode -x"));
     }
 
     const GIT_DIFF_SINGLE_HUNK: &str = "\
@@ -2181,9 +2195,15 @@ Date:   Sun Nov 1 15:28:53 2020 -0500
 +]
 "#;
 
-    const GIT_DIFF_FILE_MODE_CHANGE: &str = "
+    const GIT_DIFF_FILE_MODE_CHANGE_GAIN_EXECUTABLE_BIT: &str = "
 diff --git a/src/delta.rs b/src/delta.rs
 old mode 100644
 new mode 100755
 ";
+
+    const GIT_DIFF_FILE_MODE_CHANGE_LOSE_EXECUTABLE_BIT: &str = "
+diff --git a/src/delta.rs b/src/delta.rs
+old mode 100755
+new mode 100644
+";
 }