Remove common prefixes and suffixes from actual and expected single-l…

…ine strings

src/ScalarComparator.php

@@ -57,6 +57,8 @@ public function assertEquals(mixed $expected, mixed $actual, float $delta = 0.0,
         }
 
         if ($expectedToCompare !== $actualToCompare && is_string($expected) && is_string($actual)) {
+            [$expected, $actual] = StringUtil::removeOverlongCommonPrefix($expected, $actual);
+
             throw new ComparisonFailure(
                 $expected,
                 $actual,

src/StringUtil.php

@@ -0,0 +1,55 @@
+<?php declare(strict_types=1);
+/*
+ * This file is part of sebastian/comparator.
+ *
+ * (c) Sebastian Bergmann <sebastian@phpunit.de>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+namespace SebastianBergmann\Comparator;
+
+use function str_replace;
+use function strlen;
+use function substr;
+
+/**
+ * @no-named-arguments Parameter names are not covered by the backward compatibility promise for PHPUnit
+ *
+ * @internal This class is not covered by the backward compatibility promise for PHPUnit
+ */
+final class StringUtil
+{
+    private const OVERLONG_PREFIX_THRESHOLD = 40;
+    private const KEEP_PREFIX_CHARS         = 15;
+
+    /**
+     * @return array{string, string}
+     */
+    public static function removeOverlongCommonPrefix(string $string1, string $string2): array
+    {
+        $commonPrefix = self::findCommonPrefix($string1, $string2);
+
+        if (strlen($commonPrefix) > self::OVERLONG_PREFIX_THRESHOLD) {
+            $string1 = str_replace(substr($commonPrefix, 0, -self::KEEP_PREFIX_CHARS), '...', $string1);
+            $string2 = str_replace(substr($commonPrefix, 0, -self::KEEP_PREFIX_CHARS), '...', $string2);
+        }
+
+        return [$string1, $string2];
+    }
+
+    private static function findCommonPrefix(string $string1, string $string2): string
+    {
+        $prefix = '';
+
+        for ($i = 0; $i < strlen($string1); $i++) {
+            if (!isset($string2[$i]) || $string1[$i] != $string2[$i]) {
+                break;
+            }
+
+            $prefix .= $string1[$i];
+        }
+
+        return $prefix;
+    }
+}

tests/unit/ArrayComparatorTest.php

@@ -124,6 +124,41 @@ public static function assertEqualsFailsProvider(): array
         ];
     }
 
+    /**
+     * @return non-empty-list<array{0: string, 1: array, 2: array, 3?: float, 4?: bool}>
+     */
+    public static function assertEqualsFailsWithDiffProvider(): array
+    {
+        return [
+            [
+                "
+--- Expected
++++ Actual
+@@ @@
+ Array (
+-    0 => 'Too short to cut XYZ'
++    0 => 'Too short to cut HERE'
+ )
+",
+                ['Too short to cut XYZ'],
+                ['Too short to cut HERE'],
+            ],
+            [
+                "
+--- Expected
++++ Actual
+@@ @@
+ Array (
+-    0 => '...important clue XYZ and more behind'
++    0 => '...important clue HERE and more behind'
+ )
+",
+                ['Some really long string that just keeps going and going and going but contains important clue XYZ and more behind'],
+                ['Some really long string that just keeps going and going and going but contains important clue HERE and more behind'],
+            ],
+        ];
+    }
+
     protected function setUp(): void
     {
         $this->comparator = new ArrayComparator;
@@ -178,4 +213,25 @@ public function testAssertEqualsFails(array $expected, array $actual, float $del
 
         $this->comparator->assertEquals($expected, $actual, $delta, $canonicalize);
     }
+
+    /**
+     * @param array<mixed> $expected
+     * @param array<mixed> $actual
+     */
+    #[DataProvider('assertEqualsFailsWithDiffProvider')]
+    public function testAssertEqualsFailsWithDiff(
+        string $expectedDiff,
+        array $expected,
+        array $actual,
+        float $delta = 0.0,
+        bool $canonicalize = false
+    ): void {
+        try {
+            $this->comparator->assertEquals($expected, $actual, $delta, $canonicalize);
+            $this->fail('Expected ComparisonFailure not thrown');
+        } catch (ComparisonFailure $e) {
+            $this->assertEquals('Failed asserting that two arrays are equal.', $e->getMessage());
+            $this->assertEquals($expectedDiff, $e->getDiff());
+        }
+    }
 }

tests/unit/ScalarComparatorTest.php

@@ -123,6 +123,48 @@ public static function assertEqualsFailsProvider(): array
         ];
     }
 
+    /**
+     * @return non-empty-list<array{0: string, 1: string, 2: string}>
+     */
+    public static function assertEqualsFailsWithDiffProvider(): array
+    {
+        return [
+            [
+                "
+--- Expected
++++ Actual
+@@ @@
+-'string'
++'other string'
+",
+                'string',
+                'other string',
+            ],
+            [
+                "
+--- Expected
++++ Actual
+@@ @@
+-'...ch will be cut HERE some trailer'
++'...ch will be cut XYZ some trailer'
+",
+                'too too too long string which will be cut HERE some trailer',
+                'too too too long string which will be cut XYZ some trailer',
+            ],
+            [
+                "
+--- Expected
++++ Actual
+@@ @@
+-'...ch will be cut HERE some llooooooooonnng llooooooooonnng llooooooooonnng llooooooooonnng trailer'
++'...ch will be cut XYZ some llooooooooonnng llooooooooonnng llooooooooonnng llooooooooonnng trailer'
+",
+                'too too too long string which will be cut HERE some llooooooooonnng llooooooooonnng llooooooooonnng llooooooooonnng trailer',
+                'too too too long string which will be cut XYZ some llooooooooonnng llooooooooonnng llooooooooonnng llooooooooonnng trailer',
+            ],
+        ];
+    }
+
     #[DataProvider('acceptsSucceedsProvider')]
     public function testAcceptsSucceeds(mixed $expected, mixed $actual): void
     {
@@ -160,4 +202,16 @@ public function testAssertEqualsFails(mixed $expected, mixed $actual, string $me
 
         (new ScalarComparator)->assertEquals($expected, $actual);
     }
+
+    #[DataProvider('assertEqualsFailsWithDiffProvider')]
+    public function testAssertEqualsFailsWithDiff(string $expectedDiff, string $expected, string $actual): void
+    {
+        try {
+            (new ScalarComparator)->assertEquals($expected, $actual);
+            $this->fail('Expected ComparisonFailure not thrown');
+        } catch (ComparisonFailure $e) {
+            $this->assertEquals('Failed asserting that two strings are equal.', $e->getMessage());
+            $this->assertEquals($expectedDiff, $e->getDiff());
+        }
+    }
 }