Use Myers diff for snapshot list comparison.

packages/testing/composer.json

@@ -23,6 +23,7 @@
         "ext-json": "*",
         "ock/class-discovery": "self.version",
         "ock/helpers": "self.version",
+        "fisharebest/algorithm": "^1.6",
         "symfony/yaml": "^7.1.5"
     },
     "require-dev": {

packages/testing/src/Diff/ExportedArrayDiffer.php

@@ -4,6 +4,7 @@
 
 namespace Ock\Testing\Diff;
 
+use Fisharebest\Algorithm\MyersDiff;
 use Symfony\Component\Yaml\Tag\TaggedValue;
 
 class ExportedArrayDiffer implements DifferInterface {
@@ -107,76 +108,45 @@ protected function compareArrays(array $before, array $after, bool $could_be_lis
    * @return array|false
    */
   protected function compareLists(array $before, array $after): array|false {
-    $diff = $this->doCompareLists($before, $after);
-    if (!$diff || count($diff) === count($before) + count($after)) {
-      // The two lists are completely different.
+    $algorithm = new MyersDiff();
+    /** @var list<array{mixed, -1|0|1}> $myers_diff_solution */
+    $myers_diff_solution = $algorithm->calculate(
+      // The Myers diff actually works for non-strings.
+      // See https://github.com/fisharebest/algorithm/pull/9.
+      // @phpstan-ignore argument.type
+      $before,
+      // @phpstan-ignore argument.type
+      $after,
+      fn ($a, $b) => false !== $this->compareValues($a, $b),
+    );
+    if (count($myers_diff_solution) >= count($before) + count($after) - 1) {
+      // The two lists are too different.
       return false;
     }
-    return $diff;
-  }
-
-  /**
-   * Compares two lists recursively.
-   *
-   * @param list<mixed> $before
-   * @param list<mixed> $after
-   * @param int $i_before
-   * @param int $i_after
-   *
-   * @return array
-   */
-  protected function doCompareLists(array $before, array $after, int $i_before = 0, int $i_after = 0): array {
-    $diff = [];
-    while (true) {
-      if ($i_before >= count($before)) {
-        // There are more items in "after" list.
-        for (; $i_after < count($after); ++$i_after) {
-          $diff[] = new TaggedValue('add', $after[$i_after]);
-        }
-        return $diff;
+    $result = [];
+    $i_before = 0;
+    $i_after = 0;
+    foreach ($myers_diff_solution as [, $operation]) {
+      if ($operation === -1) {
+        $result[] = new TaggedValue('--', $before[$i_before]);
+        ++$i_before;
       }
-      if ($i_after >= count($after)) {
-        // There are more items in "before" list.
-        for (; $i_before < count($before); ++$i_before) {
-          $diff[] = new TaggedValue('--', $before[$i_before]);
-        }
-        return $diff;
+      elseif ($operation === 1) {
+        $result[] = new TaggedValue('add', $after[$i_after]);
+        ++$i_after;
       }
-      $item_diff = $this->compareValues($before[$i_before], $after[$i_after]);
-      if ($item_diff === []) {
-        // The two values are the same.
+      else {
+        $item_diff = $this->compareValues($before[$i_before], $after[$i_after]);
         ++$i_before;
         ++$i_after;
-        continue;
-      }
-      // The two items are completely different.
-      $diff_minus = $this->doCompareLists($before, $after, $i_before + 1, $i_after);
-      $diff_plus = $this->doCompareLists($before, $after, $i_before, $i_after + 1);
-      if ($item_diff !== false) {
-        $diff_eq = $this->doCompareLists($before, $after, $i_before + 1, $i_after + 1);
-        if (count($diff_eq) < count($diff_minus) && count($diff_eq) < count($diff_plus)) {
-          return [
-            ...$diff,
-            new TaggedValue('diff', $item_diff),
-            ...$diff_eq,
-          ];
+        #assert($item_diff !== false);
+        if ($item_diff === []) {
+          continue;
         }
-      }
-      if (count($diff_minus) <= count($diff_plus)) {
-        return [
-          ...$diff,
-          new TaggedValue('--', $before[$i_before]),
-          ...$diff_minus,
-        ];
-      }
-      else {
-        return [
-          ...$diff,
-          new TaggedValue('add', $after[$i_after]),
-          ...$diff_plus,
-        ];
+        $result[] = new TaggedValue('diff', $item_diff);
       }
     }
+    return $result;
   }
 
   protected function compareAssoc(array $before, array $after): array|false {

packages/testing/tests/fixtures/ExportedArrayDifferTest/list.change-assoc-value.yml

@@ -17,12 +17,12 @@ after:
     b: 'B orig'
   - after
 diff:
-  - !--
-    a: 'A orig'
-    b: 'B orig'
   - !add
     a: 'A changed'
     b: 'B changed'
   - !diff
     '~- a': 'A orig'
     '~+ a': 'A changed'
+  - !--
+    a: 'A orig'
+    b: 'B orig'

packages/testing/tests/fixtures/ExportedArrayDifferTest/list.hello.yml

@@ -5,5 +5,9 @@ after:
   - goodbye
   - world
 diff:
-  - !-- hello
-  - !add goodbye
+  '-':
+    - hello
+    - world
+  +:
+    - goodbye
+    - world

packages/testing/tests/fixtures/ExportedArrayDifferTest/list.insert-between-complex.yml

@@ -40,32 +40,44 @@ after:
       - '@drupal.proxy_original_service.paramconverter.menu_link'
       - drupal.proxy_original_service.paramconverter.menu_link
 diff:
-  - !add
-    - addConverter
+  '-':
     -
+      - addConverter
       -
-        class: Symfony\Component\DependencyInjection\Definition
-        getClass(): Drupal\ock\UI\ParamConverter\ParamConverter_Iface
-        getTags():
-          paramconverter:
-            - {  }
-      - Drupal\ock\UI\ParamConverter\ParamConverter_Iface
-  - !add
-    - addConverter
+        - '@drupal.proxy_original_service.paramconverter.menu_link'
+        - drupal.proxy_original_service.paramconverter.menu_link
+  +:
     -
+      - addConverter
       -
-        class: Symfony\Component\DependencyInjection\Definition
-        getArguments():
-          - '@Ock\Ock\Plugin\Map\PluginMapInterface'
-          -
-            class: Symfony\Component\DependencyInjection\TypedReference
-            $type: Psr\Log\LoggerInterface
-            $attributes:
-              -
-                class: Symfony\Component\DependencyInjection\Attribute\Autowire
-                $value: '@logger.channel.ock'
-        getClass(): Drupal\ock\UI\ParamConverter\ParamConverter_Plugin
-        getTags():
-          paramconverter:
-            - {  }
-      - Drupal\ock\UI\ParamConverter\ParamConverter_Plugin
+        -
+          class: Symfony\Component\DependencyInjection\Definition
+          getClass(): Drupal\ock\UI\ParamConverter\ParamConverter_Iface
+          getTags():
+            paramconverter:
+              - {  }
+        - Drupal\ock\UI\ParamConverter\ParamConverter_Iface
+    -
+      - addConverter
+      -
+        -
+          class: Symfony\Component\DependencyInjection\Definition
+          getArguments():
+            - '@Ock\Ock\Plugin\Map\PluginMapInterface'
+            -
+              class: Symfony\Component\DependencyInjection\TypedReference
+              $type: Psr\Log\LoggerInterface
+              $attributes:
+                -
+                  class: Symfony\Component\DependencyInjection\Attribute\Autowire
+                  $value: '@logger.channel.ock'
+          getClass(): Drupal\ock\UI\ParamConverter\ParamConverter_Plugin
+          getTags():
+            paramconverter:
+              - {  }
+        - Drupal\ock\UI\ParamConverter\ParamConverter_Plugin
+    -
+      - addConverter
+      -
+        - '@drupal.proxy_original_service.paramconverter.menu_link'
+        - drupal.proxy_original_service.paramconverter.menu_link