Robustly fuse files together with arc weld

Summary: Fixes T8236. I played around with a lot of variations of this but in the end it felt like the simple version was best.

Test Plan: Ran `arc weld a.txt b.txt`, observed very robust fusion of materials.

Maniphest Tasks: T8236

Differential Revision: https://secure.phabricator.com/D19081

src/__phutil_library_map__.php

@@ -398,6 +398,7 @@ phutil_register_library_map(array(
     'ArcanistVariableVariableXHPASTLinterRule' => 'lint/linter/xhpast/rules/ArcanistVariableVariableXHPASTLinterRule.php',
     'ArcanistVariableVariableXHPASTLinterRuleTestCase' => 'lint/linter/xhpast/rules/__tests__/ArcanistVariableVariableXHPASTLinterRuleTestCase.php',
     'ArcanistVersionWorkflow' => 'workflow/ArcanistVersionWorkflow.php',
+    'ArcanistWeldWorkflow' => 'workflow/ArcanistWeldWorkflow.php',
     'ArcanistWhichWorkflow' => 'workflow/ArcanistWhichWorkflow.php',
     'ArcanistWorkflow' => 'workflow/ArcanistWorkflow.php',
     'ArcanistWorkingCopyIdentity' => 'workingcopyidentity/ArcanistWorkingCopyIdentity.php',
@@ -816,6 +817,7 @@ phutil_register_library_map(array(
     'ArcanistVariableVariableXHPASTLinterRule' => 'ArcanistXHPASTLinterRule',
     'ArcanistVariableVariableXHPASTLinterRuleTestCase' => 'ArcanistXHPASTLinterRuleTestCase',
     'ArcanistVersionWorkflow' => 'ArcanistWorkflow',
+    'ArcanistWeldWorkflow' => 'ArcanistWorkflow',
     'ArcanistWhichWorkflow' => 'ArcanistWorkflow',
     'ArcanistWorkflow' => 'Phobject',
     'ArcanistWorkingCopyIdentity' => 'Phobject',

src/workflow/ArcanistWeldWorkflow.php

@@ -0,0 +1,133 @@
+<?php
+
+final class ArcanistWeldWorkflow extends ArcanistWorkflow {
+
+  public function getWorkflowName() {
+    return 'weld';
+  }
+
+  public function getCommandSynopses() {
+    return phutil_console_format(<<<EOTEXT
+      **weld** [options] __file__ __file__ ...
+EOTEXT
+      );
+  }
+
+  public function getCommandHelp() {
+    return phutil_console_format(<<<EOTEXT
+          Robustly fuse two or more files together. The resulting joint is
+          much stronger than the one created by tools like __cat__.
+EOTEXT
+      );
+  }
+
+  public function getArguments() {
+    return array(
+      '*' => 'files',
+    );
+  }
+
+  public function run() {
+    $files = $this->getArgument('files');
+    if (count($files) < 2) {
+      throw new ArcanistUsageException(
+        pht('Specify two or more files to weld together.'));
+    }
+
+    $buffer = array();
+    foreach ($files as $file) {
+      $data = Filesystem::readFile($file);
+      if (!strlen($data)) {
+        continue;
+      }
+      $lines = phutil_split_lines($data, true);
+
+      $overlap = mt_rand(16, 32);
+
+      if (count($buffer) > 6) {
+        $overlap = min($overlap, ceil(count($buffer) / 2));
+      }
+
+      if (count($lines) > 6) {
+        $overlap = min($overlap, ceil(count($lines) / 2));
+      }
+
+      $overlap = min($overlap, count($buffer));
+      $overlap = min($overlap, count($lines));
+
+      $buffer_len = count($buffer);
+      for ($ii = 0; $ii < $overlap; $ii++) {
+        $buffer[$buffer_len - $overlap + $ii] = $this->weldLines(
+          $buffer[$buffer_len - $overlap + $ii],
+          $lines[$ii],
+          ($ii + 0.5) / $overlap);
+      }
+
+      for ($ii = $overlap; $ii < count($lines); $ii++) {
+        $buffer[] = $lines[$ii];
+      }
+    }
+
+    echo implode('', $buffer);
+  }
+
+  private function weldLines($u, $v, $bias) {
+    $newline = null;
+    $matches = null;
+
+    if (preg_match('/([\r\n]+)\z/', $u, $matches)) {
+      $newline = $matches[1];
+    }
+
+    if (preg_match('/([\r\n]+)\z/', $v, $matches)) {
+      $newline = $matches[1];
+    }
+
+    $u = rtrim($u, "\r\n");
+    $v = rtrim($v, "\r\n");
+
+    $u = phutil_utf8v_combined($u);
+    $v = phutil_utf8v_combined($v);
+
+    $len = max(count($u), count($v));
+
+    while (count($u) < $len) {
+      $u[] = ' ';
+    }
+    while (count($v) < $len) {
+      $v[] = ' ';
+    }
+
+    $rand_max = mt_getrandmax();
+
+    $result = array();
+    for ($ii = 0; $ii < $len; $ii++) {
+      $uc = $u[$ii];
+      $vc = $v[$ii];
+
+      $threshold = $bias;
+      if ($uc == ' ') {
+        $threshold = 1;
+      }
+
+      if ($vc == ' ') {
+        $threshold = 0;
+      }
+
+      if ((mt_rand() / $rand_max) > $threshold) {
+        $r = $uc;
+      } else {
+        $r = $vc;
+      }
+
+      $result[] = $r;
+    }
+
+    if ($newline !== null) {
+      $result[] = $newline;
+    }
+
+    return implode('', $result);
+  }
+
+}