Improve bless tests script to minimize diffs

Compute the diff between the old EXPECTF and the new output and
don't touch lines that still match the old EXPECTF. This reduces
the amount of manual fixup necessary after running bless_tests.php.

scripts/dev/bless_tests.php

@@ -19,13 +19,26 @@
     }
 
     $phpt = file_get_contents($path);
+    $out = file_get_contents($outPath);
+
     if (false !== strpos($phpt, '--XFAIL--')) {
         // Don't modify expected output of XFAIL tests
         continue;
     }
 
-    $out = file_get_contents($outPath);
-    $out = normalizeOutput($out);
+    // Don't update EXPECTREGEX tests
+    if (!preg_match('/--EXPECT(F?)--(.*)$/s', $phpt, $matches)) {
+        continue;
+    }
+
+    $oldExpect = trim($matches[2]);
+    $isFormat = $matches[1] == 'F';
+    if ($isFormat) {
+        $out = generateMinimallyDifferingOutput($out, $oldExpect);
+    } else {
+        $out = normalizeOutput($out);
+    }
+
     $phpt = insertOutput($phpt, $out);
     file_put_contents($path, $phpt);
 }
@@ -62,9 +75,160 @@ function normalizeOutput(string $out): string {
     return $out;
 }
 
+function formatToRegex(string $format): string {
+    $result = preg_quote($format, '/');
+    $result = str_replace('%d', '\d+', $result);
+    $result = str_replace('%s', '[^\r\n]+', $result);
+    return "/^$result$/s";
+}
+
+function generateMinimallyDifferingOutput(string $out, string $oldExpect) {
+    $outLines = explode("\n", $out);
+    $oldExpectLines = explode("\n", $oldExpect);
+    $differ = new Differ(function($oldExpect, $new) {
+        if (strpos($oldExpect, '%') === false) {
+            return $oldExpect === $new;
+        }
+        return preg_match(formatToRegex($oldExpect), $new);
+    });
+    $diff = $differ->diff($oldExpectLines, $outLines);
+
+    $result = [];
+    foreach ($diff as $elem) {
+        if ($elem->type == DiffElem::TYPE_KEEP) {
+            $result[] = $elem->old;
+        } else if ($elem->type == DiffElem::TYPE_ADD) {
+            $result[] = normalizeOutput($elem->new);
+        }
+    }
+    return implode("\n", $result);
+}
+
 function insertOutput(string $phpt, string $out): string {
     return preg_replace_callback('/--EXPECTF?--.*$/s', function($matches) use($out) {
         $F = strpos($out, '%') !== false ? 'F' : '';
         return "--EXPECT$F--\n" . $out . "\n";
     }, $phpt);
 }
+
+/**
+ * Implementation of the the Myers diff algorithm.
+ *
+ * Myers, Eugene W. "An O (ND) difference algorithm and its variations."
+ * Algorithmica 1.1 (1986): 251-266.
+ */
+
+class DiffElem
+{
+    const TYPE_KEEP = 0;
+    const TYPE_REMOVE = 1;
+    const TYPE_ADD = 2;
+
+    /** @var int One of the TYPE_* constants */
+    public $type;
+    /** @var mixed Is null for add operations */
+    public $old;
+    /** @var mixed Is null for remove operations */
+    public $new;
+
+    public function __construct(int $type, $old, $new) {
+        $this->type = $type;
+        $this->old = $old;
+        $this->new = $new;
+    }
+}
+
+class Differ
+{
+    private $isEqual;
+
+    /**
+     * Create differ over the given equality relation.
+     *
+     * @param callable $isEqual Equality relation with signature function($a, $b) : bool
+     */
+    public function __construct(callable $isEqual) {
+        $this->isEqual = $isEqual;
+    }
+
+    /**
+     * Calculate diff (edit script) from $old to $new.
+     *
+     * @param array $old Original array
+     * @param array $new New array
+     *
+     * @return DiffElem[] Diff (edit script)
+     */
+    public function diff(array $old, array $new) {
+        list($trace, $x, $y) = $this->calculateTrace($old, $new);
+        return $this->extractDiff($trace, $x, $y, $old, $new);
+    }
+
+    private function calculateTrace(array $a, array $b) {
+        $n = \count($a);
+        $m = \count($b);
+        $max = $n + $m;
+        $v = [1 => 0];
+        $trace = [];
+        for ($d = 0; $d <= $max; $d++) {
+            $trace[] = $v;
+            for ($k = -$d; $k <= $d; $k += 2) {
+                if ($k === -$d || ($k !== $d && $v[$k-1] < $v[$k+1])) {
+                    $x = $v[$k+1];
+                } else {
+                    $x = $v[$k-1] + 1;
+                }
+
+                $y = $x - $k;
+                while ($x < $n && $y < $m && ($this->isEqual)($a[$x], $b[$y])) {
+                    $x++;
+                    $y++;
+                }
+
+                $v[$k] = $x;
+                if ($x >= $n && $y >= $m) {
+                    return [$trace, $x, $y];
+                }
+            }
+        }
+        throw new \Exception('Should not happen');
+    }
+
+    private function extractDiff(array $trace, int $x, int $y, array $a, array $b) {
+        $result = [];
+        for ($d = \count($trace) - 1; $d >= 0; $d--) {
+            $v = $trace[$d];
+            $k = $x - $y;
+
+            if ($k === -$d || ($k !== $d && $v[$k-1] < $v[$k+1])) {
+                $prevK = $k + 1;
+            } else {
+                $prevK = $k - 1;
+            }
+
+            $prevX = $v[$prevK];
+            $prevY = $prevX - $prevK;
+
+            while ($x > $prevX && $y > $prevY) {
+                $result[] = new DiffElem(DiffElem::TYPE_KEEP, $a[$x-1], $b[$y-1]);
+                $x--;
+                $y--;
+            }
+
+            if ($d === 0) {
+                break;
+            }
+
+            while ($x > $prevX) {
+                $result[] = new DiffElem(DiffElem::TYPE_REMOVE, $a[$x-1], null);
+                $x--;
+            }
+
+            while ($y > $prevY) {
+                $result[] = new DiffElem(DiffElem::TYPE_ADD, null, $b[$y-1]);
+                $y--;
+            }
+        }
+        return array_reverse($result);
+    }
+}