Report permission changes

Fixes #605

3 files changed, 73 insertions, 2 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index c406a4934..14007e1cd 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -7,6 +7,10 @@ Added support for Salesforce Apex.
 Improved parsing of regex literals in Clojure and strictness
 annotations in Haskell.
 
+### Diffing
+
+Difftastic will now also report file permission changes.
+
 ### Display
 
 Fixed a rare crash when the last non-blank line had changes for
diff --git a/sample_files/compare.expected b/sample_files/compare.expected
index 61ce95301..c8b7cb46a 100644
--- a/sample_files/compare.expected
+++ b/sample_files/compare.expected
@@ -23,7 +23,7 @@ sample_files/change_outer_before.el sample_files/change_outer_after.el
 8ed3308b9eabd486bdbe9aa2e7dc9be6  -
 
 sample_files/chinese_before.po sample_files/chinese_after.po
-b5cf768305ee724d456aedfc20095226  -
+097250024d46c75a159b8a8efe9a1e51  -
 
 sample_files/clojure_before.clj sample_files/clojure_after.clj
 34a723cb5ec5a81f3ae5c01a64bca6c2  -
diff --git a/src/main.rs b/src/main.rs
index 76e45d98f..ba0e028be 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -73,6 +73,7 @@ use crate::parse::syntax;
 #[global_allocator]
 static GLOBAL: MiMalloc = MiMalloc;
 
+use std::fs::Permissions;
 use std::path::Path;
 use std::{env, thread};
 
@@ -330,6 +331,62 @@ fn main() {
     };
 }
 
+#[cfg(unix)]
+fn compare_permissions(lhs: &Permissions, rhs: &Permissions) -> Option<String> {
+    use std::os::unix::fs::PermissionsExt;
+
+    let lhs_mode = lhs.mode();
+    let rhs_mode = rhs.mode();
+
+    if lhs_mode != rhs_mode {
+        let lhs_mode = format!("{:o}", lhs_mode);
+        let rhs_mode = format!("{:o}", rhs_mode);
+        Some(format!(
+            "File permissions changed from {} to {}.",
+            lhs_mode, rhs_mode
+        ))
+    } else {
+        None
+    }
+}
+
+#[cfg(windows)]
+fn compare_permissions(lhs: &Permissions, rhs: &Permissions) -> Option<String> {
+    if lhs.readonly() != rhs.readonly() {
+        Some(format!(
+            "File permissions changed from {} to {}.",
+            if lhs.readonly() {
+                "readonly"
+            } else {
+                "read-write"
+            },
+            if rhs.readonly() {
+                "readonly"
+            } else {
+                "read-write"
+            },
+        ))
+    } else {
+        None
+    }
+}
+
+#[cfg(not(any(unix, windows)))]
+fn compare_permissions(_lhs: &Permissions, _rhs: &Permissions) -> Option<String> {
+    None
+}
+
+fn describe_permissions_change(lhs_path: &FileArgument, rhs_path: &FileArgument) -> Option<String> {
+    match (lhs_path, rhs_path) {
+        (FileArgument::NamedPath(lhs_path), FileArgument::NamedPath(rhs_path)) => {
+            let lhs_metadata = std::fs::metadata(lhs_path).ok()?;
+            let rhs_metadata = std::fs::metadata(rhs_path).ok()?;
+            compare_permissions(&lhs_metadata.permissions(), &rhs_metadata.permissions())
+        }
+        _ => None,
+    }
+}
+
 /// Print a diff between two files.
 fn diff_file(
     display_path: &str,
@@ -365,9 +422,19 @@ fn diff_file(
         rhs_src.retain(|c| c != '\r');
     }
 
+    let mut extra_info = renamed;
+    if let Some(permissions_change) = describe_permissions_change(lhs_path, rhs_path) {
+        if let Some(extra_info) = &mut extra_info {
+            extra_info.push('\n');
+            extra_info.push_str(&permissions_change);
+        } else {
+            extra_info = Some(permissions_change);
+        }
+    }
+
     diff_file_content(
         display_path,
-        renamed,
+        extra_info,
         lhs_path,
         rhs_path,
         &lhs_src,