Add linting for syntax brought in by unresolved merge conflicts.

Summary:
Add linting capability for detecting files which contain
syntax introduced by unresolved merge conflicts. The detection is
file-type-agnostic (the only requirement is that the file is a text
file).

Test Plan:
Tested in three ways.

The first way is to add all three forms of syntax to a file to
indicate a merge conflict. HPHP will pick this up as a syntax error
before this linter reaches it.

The second way is to add the syntax in a comment. In that case, this
linter will show three warnings. For example:

    $ arc lint ArcanistMergeConflictLinter.php
    >>> Lint for arcanist/src/lint/linter/ArcanistMergeConflictLinter.php:

       Warning  (MERGECONFLICT1) Unresolved merge conflict
        This syntax indicates there is still an unresolved merge conflict.

                  20
                  21     foreach ($lines as $lineno => $line) {
                  22 /*
        >>>       23 >>>>>>>
                  24
                  25 =======

       Warning  (MERGECONFLICT1) Unresolved merge conflict
        This syntax indicates there is still an unresolved merge conflict.

                  22 /*
                  23 >>>>>>>
                  24
        >>>       25 =======
                  26
                  27 <<<<<<<

       Warning  (MERGECONFLICT1) Unresolved merge conflict
        This syntax indicates there is still an unresolved merge conflict.

                  24
                  25 =======
                  26
        >>>       27 <<<<<<<
                  28
                  29 */

The last test was to test on various different file types, including
JavaScript, PHP, an animated GIF, a PNG, and a Bash file to make sure
the file type detection worked. Each of the aforementioned tests
passed.

Reviewers: vrana, epriestley

Reviewed By: epriestley

CC: aran, epriestley, Korvin

Maniphest Tasks: T2547

Differential Revision: https://secure.phabricator.com/D4966

src/__phutil_library_map__.php

@@ -96,6 +96,7 @@ phutil_register_library_map(array(
     'ArcanistMercurialAPI' => 'repository/api/ArcanistMercurialAPI.php',
     'ArcanistMercurialParser' => 'repository/parser/ArcanistMercurialParser.php',
     'ArcanistMercurialParserTestCase' => 'repository/parser/__tests__/ArcanistMercurialParserTestCase.php',
+    'ArcanistMergeConflictLinter' => 'lint/linter/ArcanistMergeConflictLinter.php',
     'ArcanistNoEffectException' => 'exception/usage/ArcanistNoEffectException.php',
     'ArcanistNoEngineException' => 'exception/usage/ArcanistNoEngineException.php',
     'ArcanistNoLintLinter' => 'lint/linter/ArcanistNoLintLinter.php',
@@ -232,6 +233,7 @@ phutil_register_library_map(array(
     'ArcanistMarkCommittedWorkflow' => 'ArcanistBaseWorkflow',
     'ArcanistMercurialAPI' => 'ArcanistRepositoryAPI',
     'ArcanistMercurialParserTestCase' => 'ArcanistTestCase',
+    'ArcanistMergeConflictLinter' => 'ArcanistLinter',
     'ArcanistNoEffectException' => 'ArcanistUsageException',
     'ArcanistNoEngineException' => 'ArcanistUsageException',
     'ArcanistNoLintLinter' => 'ArcanistLinter',

src/lint/engine/PhutilLintEngine.php

@@ -57,6 +57,15 @@ class PhutilLintEngine extends ArcanistLintEngine {
       ->setXHPASTLinter($xhpast_linter)
       ->setPaths($php_paths);
 
+    $merge_conflict_linter = id(new ArcanistMergeConflictLinter());
+
+    foreach ($paths as $path) {
+      $merge_conflict_linter->addPath($path);
+      $merge_conflict_linter->addData($path, $this->loadData($path));
+    }
+
+    $linters[] = $merge_conflict_linter;
+
     return $linters;
   }
 

src/lint/linter/ArcanistLinter.php

@@ -243,4 +243,9 @@ abstract class ArcanistLinter {
     return self::GRANULARITY_FILE;
   }
 
+  public function isBinaryFile($path) {
+    // Note that we need the lint engine set before this can be used.
+    return ArcanistDiffUtils::isHeuristicBinaryFile($this->getData($path));
+  }
+
 }

src/lint/linter/ArcanistMergeConflictLinter.php

@@ -0,0 +1,50 @@
+<?php
+
+/**
+ * Checks files for unresolved merge conflicts.
+ *
+ * @group linter
+ */
+final class ArcanistMergeConflictLinter extends ArcanistLinter {
+  const LINT_MERGECONFLICT = 1;
+
+  public function willLintPaths(array $paths) {
+    return;
+  }
+
+  public function lintPath($path) {
+    if ($this->isBinaryFile($path)) {
+      return;
+    }
+
+    $lines = phutil_split_lines($this->getData($path), false);
+
+    foreach ($lines as $lineno => $line) {
+      // An unresolved merge conflict will contain a series of seven
+      // '<', '=', or '>'.
+      if (preg_match('/^(>{7}|<{7}|={7})$/', $line)) {
+        $this->raiseLintAtLine(
+          $lineno + 1,
+          0,
+          self::LINT_MERGECONFLICT,
+          "This syntax indicates there is an unresolved merge conflict.");
+      }
+    }
+  }
+
+  public function getLinterName() {
+    return "MERGECONFLICT";
+  }
+
+  public function getLintSeverityMap() {
+    return array(
+      self::LINT_MERGECONFLICT => ArcanistLintSeverity::SEVERITY_ERROR
+    );
+  }
+
+  public function getLintNameMap() {
+    return array(
+      self::LINT_MERGECONFLICT => "Unresolved merge conflict"
+    );
+  }
+}