Make migration notification not display if some bug causes no changes (#24578)

When working on #24442, I did a project wide replacement of
`AcceptInlineCompletion` with `AcceptEditPrediction`, as I was updating
the branch to mmain and that rename had happened. This also replaced it
in the migrator, causing the migration notification to always pop up on
keymap changes.

Checking if the migration actually changes the text makes it behave
better if this variety of bug happens in the future.

Release Notes:

- N/A

Cargo.lock

@@ -7878,6 +7878,7 @@ version = "0.1.0"
 dependencies = [
  "collections",
  "convert_case 0.7.1",
+ "log",
  "pretty_assertions",
  "streaming-iterator",
  "tree-sitter",

crates/migrator/Cargo.toml

@@ -15,6 +15,7 @@ doctest = false
 [dependencies]
 collections.workspace = true
 convert_case.workspace = true
+log.workspace = true
 streaming-iterator.workspace = true
 tree-sitter-json.workspace = true
 tree-sitter.workspace = true

crates/migrator/src/migrator.rs

@@ -29,11 +29,19 @@ fn migrate(text: &str, patterns: MigrationPatterns, query: &Query) -> Option<Str
     if edits.is_empty() {
         None
     } else {
-        let mut text = text.to_string();
-        for (range, replacement) in edits.into_iter().rev() {
-            text.replace_range(range, &replacement);
+        let mut new_text = text.to_string();
+        for (range, replacement) in edits.iter().rev() {
+            new_text.replace_range(range.clone(), replacement);
+        }
+        if new_text == text {
+            log::error!(
+                "Edits computed for configuration migration do not cause a change: {:?}",
+                edits
+            );
+            None
+        } else {
+            Some(new_text)
         }
-        Some(text)
     }
 }