fix(Differ): use strict identity for old/new comparison to avoid numeric string coercion

PHP's spaceship operator treats numeric strings like '0' and '00000'
as equal, causing empty diffs. Replace with === and refactor to
bool $oldNewAreSame property.

Deprecate getOldNewComparison() in favor of getOldNewAreSame().

Fixes #94

Co-Authored-By: Claude <noreply@anthropic.com>
Signed-off-by: Jack Cherng <jfcherng@gmail.com>

Author: jfcherng

src/Differ.php

@@ -39,7 +39,7 @@ final class Differ
         'groupedOpcodesGnu' => [],
         'oldNoEolAtEofIdx' => -1,
         'newNoEolAtEofIdx' => -1,
-        'oldNewComparison' => 0,
+        'oldNewAreSame' => false,
     ];
 
     /**
@@ -84,10 +84,9 @@ final class Differ
     private int $newNoEolAtEofIdx = -1;
 
     /**
-     * @var int the result of comparing the old and the new with the spaceship operator
-     *          `-1` means `old < new`, `0` means `old == new`, `1` means `old > new`
+     * @var bool the result of spaceship operator comparing old and new (0 if they are the same, 1 if they are different)
      */
-    private int $oldNewComparison = 0;
+    private bool $oldNewAreSame = false;
 
     /**
      * @var int[][][] array containing the generated opcodes for the differences between the two items
@@ -232,12 +231,22 @@ public function getNewNoEolAtEofIdx(): int
         return $this->finalize()->newNoEolAtEofIdx;
     }
 
+    /**
+     * Check whether the old and the new are the same.
+     */
+    public function getOldNewAreSame(): bool
+    {
+        return $this->finalize()->oldNewAreSame;
+    }
+
     /**
      * Compare the old and the new with the spaceship operator.
+     *
+     * @deprecated Use getOldNewAreSame() instead
      */
     public function getOldNewComparison(): int
     {
-        return $this->finalize()->oldNewComparison;
+        return $this->getOldNewAreSame() ? 0 : 1;
     }
 
     /**
@@ -302,7 +311,7 @@ public function getGroupedOpcodes(): array
 
         $this->getGroupedOpcodesPre($old, $new);
 
-        if ($this->oldNewComparison === 0 && $this->options->fullContextIfIdentical) {
+        if ($this->oldNewAreSame && $this->options->fullContextIfIdentical) {
             $opcodes = [
                 [
                     [SequenceMatcher::OP_EQ, 0, \count($old), 0, \count($new)],
@@ -338,7 +347,7 @@ public function getGroupedOpcodesGnu(): array
 
         $this->getGroupedOpcodesGnuPre($old, $new);
 
-        if ($this->oldNewComparison === 0 && $this->options->fullContextIfIdentical) {
+        if ($this->oldNewAreSame && $this->options->fullContextIfIdentical) {
             $opcodes = [
                 [
                     [SequenceMatcher::OP_EQ, 0, \count($old), 0, \count($new)],
@@ -483,7 +492,7 @@ private function finalize(): self
 
             $this->oldNoEolAtEofIdx = $this->getOld(-1) === [''] ? -1 : \count($this->old);
             $this->newNoEolAtEofIdx = $this->getNew(-1) === [''] ? -1 : \count($this->new);
-            $this->oldNewComparison = $this->old <=> $this->new;
+            $this->oldNewAreSame = $this->old === $this->new;
 
             $this->sequenceMatcher->setOptions($this->options->toSequenceMatcherOptions());
         }

src/Renderer/AbstractRenderer.php

@@ -114,7 +114,7 @@ final public function render(Differ $differ): string
         $this->changesAreRaw = true;
 
         // the "no difference" situation may happen frequently
-        return $differ->getOldNewComparison() === 0 && !$differ->options->fullContextIfIdentical
+        return $differ->getOldNewAreSame() && !$differ->options->fullContextIfIdentical
             ? $this->getResultForIdenticals()
             : $this->renderWorker($differ);
     }

tests/DifferTest.php

@@ -67,4 +67,32 @@ public static function provideGetGroupedOpcodesCases(): iterable
             ],
         ];
     }
+
+    /**
+     * Test that numeric strings are compared as strings, not numbers.
+     *
+     * @covers \Jfcherng\Diff\Differ::getOldNewAreSame
+     *
+     * @see https://github.com/jfcherng/php-diff/issues/94
+     */
+    #[DataProvider('provideNumericStringComparisonCases')]
+    public function testNumericStringComparison(string $old, string $new, bool $expectedAreSame): void
+    {
+        $differ = new Differ(explode("\n", $old), explode("\n", $new));
+
+        self::assertSame($expectedAreSame, $differ->getOldNewAreSame());
+    }
+
+    /**
+     * Data provider for testNumericStringComparison.
+     */
+    public static function provideNumericStringComparisonCases(): iterable
+    {
+        return [
+            'zero vs multiple zeros' => ['0', '00000', false],
+            'identical zeros' => ['0', '0', true],
+            'numeric strings with different values' => ['1', '01', false],
+            'leading zeros' => ['007', '7', false],
+        ];
+    }
 }