Add comparison example

Cargo.toml

@@ -20,6 +20,10 @@ crate-type = ["cdylib", "rlib"]
 name = "merge-file"
 path = "examples/merge-file.rs"
 
+[[example]]
+name = "compare-with-diff-match-patch"
+path = "examples/compare-with-diff-match-patch.rs"
+
 [dependencies]
 serde = { version = "1.0.219", optional = true, features = ["derive"] }
 thiserror = "2.0.17"
@@ -48,6 +52,7 @@ serde = { version = "1.0.219", features = ["derive"] }
 serde_yaml = "0.9.34"
 test-case = "3.3.1"
 wasm-bindgen-test = "0.3.56"
+diff-match-patch-rs = "0.5"
 
 [profile.release]
 codegen-units = 1

examples/compare-with-diff-match-patch.rs

@@ -0,0 +1,92 @@
+use std::panic;
+
+use diff_match_patch_rs::{Compat, DiffMatchPatch, PatchInput};
+use reconcile_text::{BuiltinTokenizer, reconcile};
+
+fn dmp_merge(parent: &str, left: &str, right: &str) -> Option<String> {
+    let parent = parent.to_owned();
+    let left = left.to_owned();
+    let right = right.to_owned();
+
+    // diff-match-patch-rs can panic on some inputs, so we catch that.
+    panic::catch_unwind(|| {
+        let dmp = DiffMatchPatch::new();
+        let diffs = dmp.diff_main::<Compat>(&parent, &left).ok()?;
+        let patches = dmp
+            .patch_make(PatchInput::new_text_diffs(&parent, &diffs))
+            .ok()?;
+        let (result, _) = dmp.patch_apply(&patches, &right).ok()?;
+        Some(result)
+    })
+    .ok()
+    .flatten()
+}
+
+fn try_merge(parent: &str, left: &str, right: &str) {
+    let dmp_result = dmp_merge(parent, left, right);
+
+    let reconcile_result = reconcile(
+        parent,
+        &left.into(),
+        &right.into(),
+        &*BuiltinTokenizer::Word,
+    )
+    .apply()
+    .text();
+
+    println!("Parent: {parent:?}");
+    println!("Left:   {left:?}");
+    println!("Right:  {right:?}");
+    println!();
+    match dmp_result {
+        Some(r) => println!("diff-match-patch: {r:?}"),
+        None => println!("diff-match-patch: <panic or error>"),
+    }
+    println!("reconcile-text:   {reconcile_result:?}");
+    println!();
+}
+
+/// Demonstrates cases where diff-match-patch silently produces incorrect
+/// output, while reconcile-text preserves both users' edits correctly.
+///
+/// Run it with:
+/// `cargo run --example compare-with-diff-match-patch`
+fn main() {
+    // Example 1
+    // Two users edit the same short phrase. Alice replaces "old(!)" with
+    // "new improved", Bob replaces "broken" with "working". These are
+    // independent changes to adjacent words.
+    //
+    // diff-match-patch has no common ancestor, so it diffs parent → left
+    // and applies the patch to right. The character-level patches overlap
+    // and produce garbled text ("impovind"). It reports success.
+    //
+    // reconcile-text sees both changes relative to the parent and merges
+    // them cleanly.
+
+    println!("── Example 1: adjacent edits ──");
+    try_merge(
+        "old(!) broken code",
+        "new improved code",
+        "old(!) working code",
+    );
+
+    // Example 2
+    // Alice adds a sentence. Bob rewrites the surrounding text. Because
+    // diff-match-patch works without a common ancestor, Alice's entire
+    // sentence is silently lost.
+
+    println!("── Example 2: sentence lost ──");
+    // Alice adds a sentence in the middle of a paragraph. Bob rephrases
+    // the same paragraph. Because the patch context from Alice's edit no
+    // longer appears in Bob's version, diff-match-patch silently drops
+    // Alice's entire sentence.
+    //
+    // reconcile-text understands both edits relative to the common ancestor
+    // and keeps both.
+    try_merge(
+        "We used the existing parsing approach for processing. The output was saved to the database.",
+        "We used the existing parsing approach for processing. Always validate the schema! The output was saved to the database.",
+        "We adopted a brand new analysis pipeline for execution. The results were written to cloud storage.",
+    );
+}