Show diff of files when applying merges

Cargo.lock

@@ -2078,6 +2078,7 @@ dependencies = [
  "serde_yaml",
  "sha1",
  "sha2",
+ "similar",
  "tempfile",
  "tokio",
  "toml",
@@ -3294,6 +3295,12 @@ version = "0.3.7"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "d66dc143e6b11c1eddc06d5c423cfc97062865baf299914ab64caa38182078fe"
 
+[[package]]
+name = "similar"
+version = "2.6.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1de1d4f81173b03af4c0cbed3c898f6bff5b870e4a7f5d6f4057d62a7a4b686e"
+
 [[package]]
 name = "siphasher"
 version = "0.3.11"

mcmpmgr/Cargo.toml

@@ -17,6 +17,7 @@ serde_json = "1.0.128"
 serde_yaml = "0.9.34"
 sha1 = "0.10.6"
 sha2 = "0.10.8"
+similar = "2.6.0"
 tempfile = "3.12.0"
 tokio = { version = "1.39.2", features = ["full"] }
 toml = { version = "0.8.19", features = ["preserve_order"] }

mcmpmgr/src/modpack.rs

@@ -6,6 +6,7 @@ use crate::{
 };
 use anyhow::{Context, Result};
 use serde::{Deserialize, Serialize};
+use similar::{ChangeTag, TextDiff};
 use std::{
     collections::{BTreeMap, BTreeSet},
     path::{Path, PathBuf},
@@ -298,9 +299,20 @@ impl ModpackMeta {
                     )
                     .with_context(|| format!("Failed to merge file {src:?} -> {dst:?}"))?;
 
-                    std::fs::write(dst, merged_contents).with_context(|| {
+                    std::fs::write(dst, &merged_contents).with_context(|| {
                         format!("Failed to write merged contents of {src:?} -> {dst:?}")
                     })?;
+
+                    println!("Successfully merged {src:?} -> {dst:?}. See diff below:");
+                    let diff = TextDiff::from_lines(&dst_val, &merged_contents);
+                    for change in diff.iter_all_changes() {
+                        let sign = match change.tag() {
+                            ChangeTag::Delete => "-",
+                            ChangeTag::Insert => "+",
+                            ChangeTag::Equal => " ",
+                        };
+                        print!("{}{}", sign, change);
+                    }
                 } else {
                     println!("Syncing file {} -> {}", src.display(), dst.display());
                     std::fs::copy(src, dst)?;