Improve failed phpt test diff

In case of multiline placeholder %a or %A we try to match
multiple lines at the same time.

The tricky part is to keep the expected output and the real
output in sync since they can be different in size and amount
of lines.

Co-authored-by: Volker Dusch <github@wallbash.com>
Co-authored-by: Sebastian Feldmann <sf@sebastian-feldmann.info>

Author: sebastianfeldmann

src/Framework/Constraint/String/StringMatchesFormatDescription.php

@@ -11,6 +11,9 @@
 
 use const DIRECTORY_SEPARATOR;
 use const PHP_EOL;
+use function array_slice;
+use function array_splice;
+use function count;
 use function explode;
 use function implode;
 use function preg_match;
@@ -60,30 +63,68 @@ protected function failureDescription(mixed $other): string
         return 'string matches format description';
     }
 
+    /**
+     * Returns a useful diff with the 'actual' differences.
+     *
+     * The expected string can contain placeholders like %s and %d.
+     * By using 'diff' such placeholders compared to the real output are
+     * always objectively different, although we don't want to show them as different.
+     *
+     * This method removes the objective differences by figuring out if an objective
+     * difference is allowed by a placeholder.
+     *
+     * The final result should only contain the differences that caused the failing test.
+     */
     protected function additionalFailureDescription(mixed $other): string
     {
-        $from = explode("\n", $this->formatDescription);
-        $to   = explode("\n", $this->convertNewlines($other));
+        $expected = explode("\n", $this->formatDescription);
+        $output   = explode("\n", $this->convertNewlines($other));
+
+        for ($oIndex = 0, $eIndex = 0, $length = count($output); $oIndex < $length; $oIndex++) {
+            $multiLineMatch = false;
 
-        foreach ($from as $index => $line) {
-            if (isset($to[$index]) && $line !== $to[$index]) {
-                $line = $this->regularExpressionForFormatDescription($line);
+            if (isset($expected[$eIndex]) && $expected[$eIndex] !== $output[$oIndex]) {
+                $regEx     = $this->regularExpressionForFormatDescription($expected[$eIndex]);
+                $compareTo = $output[$oIndex];
+                $matches   = [];
+
+                // if we do a multiline match we have to consider all following lines as well
+                if ($this->isMultilineMatch($expected[$eIndex])) {
+                    $multiLineMatch = true;
+                    $compareTo      = implode("\n", array_slice($output, $oIndex));
+                }
 
-                if (preg_match($line, $to[$index]) > 0) {
-                    $from[$index] = $to[$index];
+                if (preg_match($regEx, $compareTo, $matches) > 0) {
+                    $lines = 1;
+
+                    // if we matched multiple lines we have to sync $expected and $output
+                    if ($multiLineMatch) {
+                        $lines = count(explode("\n", $matches[0]));
+                    }
+                    // we sync at least one line
+                    $expected[$eIndex] = $output[$oIndex];
+
+                    // for multiline matches we sync the matched lines to $expected
+                    for ($i = 1; $i < $lines; $i++) {
+                        $eIndex++;
+                        $oIndex++;
+                        array_splice($expected, $eIndex, 0, [$output[$oIndex]]);
+                    }
                 }
             }
+            $eIndex++;
         }
+        $expectedString = implode("\n", $expected);
+        $outputString   = implode("\n", $output);
 
-        $from = implode("\n", $from);
-        $to   = implode("\n", $to);
-
-        return $this->differ()->diff($from, $to);
+        return $this->differ()->diff($expectedString, $outputString);
     }
 
     private function regularExpressionForFormatDescription(string $string): string
     {
-        $string = strtr(
+        // only add the end of string check ($) for single line comparisons
+        $endOfLine = $this->isMultilineMatch($string) ? '' : '$';
+        $string    = strtr(
             preg_quote($string, '/'),
             [
                 '%%' => '%',
@@ -102,7 +143,7 @@ private function regularExpressionForFormatDescription(string $string): string
             ],
         );
 
-        return '/^' . $string . '$/s';
+        return '/^' . $string . $endOfLine . '/s';
     }
 
     private function convertNewlines(string $text): string
@@ -114,4 +155,9 @@ private function differ(): Differ
     {
         return new Differ(new UnifiedDiffOutputBuilder("--- Expected\n+++ Actual\n"));
     }
+
+    private function isMultilineMatch(string $line): bool
+    {
+        return preg_match('#%a#i', $line) > 0;
+    }
 }