added module update diff display

Cargo.toml

@@ -32,6 +32,7 @@ indicatif = "0.17.8"
 which = "6.0.3"
 regex = "1.10.6"
 toml_edit = "0.22.20"
+imara-diff = "0.1.7"
 
 [build-dependencies]
 cc="*"

src/cmd/update.rs

@@ -3,6 +3,8 @@ use anyhow::Result;
 use crate::cmd::{Execute, Update};
 use crate::cmd::include::get_head_commit_hash;
 use crate::toml::{get_repo_links, add_top_module, remove_top_module};
+use imara_diff::intern::InternedInput;
+use imara_diff::{diff, Algorithm, UnifiedDiffBuilder};
 
 impl Execute for Update {
     async fn execute(&self) -> Result<()> {
@@ -36,9 +38,24 @@ fn update_module(module_path: &str, commit: Option<&str>) -> Result<()> {
     let commit_hash = commit.unwrap_or(&head_commit_hash);
 
     println!("Updating module '{}' to commit '{}'", module_path, commit_hash);
+    let old_contents = std::fs::read_to_string(module_path)?;
     remove_top_module(&chosen_repo, module_path)?;
     add_top_module(&chosen_repo, module_path, commit_hash)?;
+    let new_contents = std::fs::read_to_string(module_path)?;
     println!("Module '{}' updated to commit '{}'", module_path, commit_hash);
 
+    display_diff(&old_contents, &new_contents);
+
     Ok(())
+}
+
+fn display_diff(old_contents: &str, new_contents: &str) {
+    let input = InternedInput::new(old_contents, new_contents);
+    let diff_output = diff(
+        Algorithm::Histogram,
+        &input,
+        UnifiedDiffBuilder::new(&input)
+    );
+
+    println!("Diff:\n{}", diff_output);
 }