Allow caching lint results

Summary:
There is one big decision: How to get linters version.
I've created `getCacheVersion()` which is supposed to be bumped every time engine or any linter is changed.
This is not very nice but the other alternative (detect this automatically) seems worse:

- The engine may be outside repo and may or may not be under version control so getting its version through something like `git log` may not be even possible.
- If it is in the same repo then every rebase will obsolete the whole cache.

Even though bumping the version manually is PITA I still think it's a better solution.

Test Plan:
  $ time arc lint --cache 1
  # verified file
  $ arc arc lint --cache 1
  # added some debug output to see the cached results
  # also observed better time (.57 s instead of 2.19 s)

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Maniphest Tasks: T2036

Differential Revision: https://secure.phabricator.com/D4006

src/lint/ArcanistLintMessage.php

@@ -48,6 +48,8 @@ final class ArcanistLintMessage {
       'severity'    => $this->getSeverity(),
       'name'        => $this->getName(),
       'description' => $this->getDescription(),
+      'original'    => $this->getOriginalText(),
+      'replacement' => $this->getReplacementText(),
     );
   }
 

src/lint/engine/ArcanistLintEngine.php

@@ -165,22 +165,6 @@ abstract class ArcanistLintEngine {
     $stopped = array();
     $linters = $this->buildLinters();
 
-    if (!$linters) {
-      throw new ArcanistNoEffectException("No linters to run.");
-    }
-
-    $have_paths = false;
-    foreach ($linters as $linter) {
-      if ($linter->getPaths()) {
-        $have_paths = true;
-        break;
-      }
-    }
-
-    if (!$have_paths) {
-      throw new ArcanistNoEffectException("No paths are lintable.");
-    }
-
     $exceptions = array();
     foreach ($linters as $linter_name => $linter) {
       try {
@@ -251,6 +235,22 @@ abstract class ArcanistLintEngine {
       }
     }
 
+    if (!$linters) {
+      throw new ArcanistNoEffectException("No linters to run.");
+    }
+
+    $have_paths = false;
+    foreach ($linters as $linter) {
+      if ($linter->getPaths()) {
+        $have_paths = true;
+        break;
+      }
+    }
+
+    if (!$have_paths) {
+      throw new ArcanistNoEffectException("No paths are lintable.");
+    }
+
     if ($exceptions) {
       throw new PhutilAggregateException('Some linters failed:', $exceptions);
     }
@@ -291,7 +291,7 @@ abstract class ArcanistLintEngine {
     return false;
   }
 
-  private function getResultForPath($path) {
+  public function getResultForPath($path) {
     if (empty($this->results[$path])) {
       $result = new ArcanistLintResult();
       $result->setPath($path);
@@ -336,6 +336,10 @@ abstract class ArcanistLintEngine {
     return $this;
   }
 
+  public function getCacheVersion() {
+    return 0;
+  }
+
   protected function getPEP8WithTextOptions() {
     // E101 is subset of TXT2 (Tab Literal).
     // E501 is same as TXT3 (Line Too Long).

src/workflow/ArcanistDiffWorkflow.php

@@ -354,6 +354,13 @@ EOTEXT
           'Run lint and unit tests on background. '.
           '"0" to disable, "1" to enable (default).',
       ),
+      'cache' => array(
+        'param' => 'bool',
+        'help' => "0 to disable lint cache (default), 1 to enable.",
+        'passthru' => array(
+          'lint' => true,
+        ),
+      ),
       '*' => 'paths',
     );
 

src/workflow/ArcanistLintWorkflow.php

@@ -120,6 +120,10 @@ EOTEXT
             array_keys(ArcanistLintSeverity::getLintSeverities())).
           "'. Defaults to '".self::DEFAULT_SEVERITY."'.",
       ),
+      'cache' => array(
+        'param' => 'bool',
+        'help' => "0 to disable cache (default), 1 to enable.",
+      ),
       '*' => 'paths',
     );
   }
@@ -132,6 +136,15 @@ EOTEXT
     return true;
   }
 
+  private function getCacheKey() {
+    return implode("\n", array(
+      get_class($this->engine),
+      $this->getArgument('severity', self::DEFAULT_SEVERITY),
+      $this->getArgument('lintall'),
+      $this->engine->getCacheVersion(),
+    ));
+  }
+
   public function run() {
     $working_copy = $this->getWorkingCopy();
 
@@ -176,6 +189,25 @@ EOTEXT
     $engine->setMinimumSeverity(
       $this->getArgument('severity', self::DEFAULT_SEVERITY));
 
+    $cached = false;
+    if ($this->getArgument('cache')) {
+      $paths = array_combine($paths, $paths);
+      $cache = $this->readScratchJSONFile('lint-cache.json');
+      $cache = idx($cache, $this->getCacheKey(), array());
+      foreach ($cache as $path => $messages) {
+        $messages = idx($messages, md5_file($engine->getFilePathOnDisk($path)));
+        // TODO: Some linters work with the whole directory.
+        if ($messages !== null) {
+          foreach ($messages as $message) {
+            $engine->getResultForPath($path)->addMessage(
+              ArcanistLintMessage::newFromDictionary($message));
+          }
+          $cached = true;
+          unset($paths[$path]);
+        }
+      }
+    }
+
     // Propagate information about which lines changed to the lint engine.
     // This is used so that the lint engine can drop warning messages
     // concerning lines that weren't in the change.
@@ -201,8 +233,12 @@ EOTEXT
     try {
       $engine->run();
     } catch (Exception $ex) {
+      if ($ex instanceof ArcanistNoEffectException && $cached) {
+        // Swallow.
+      } else {
         $failed = $ex;
       }
+    }
 
     $results = $engine->getResults();
 
@@ -365,6 +401,24 @@ EOTEXT
     }
     $this->unresolvedMessages = $unresolved;
 
+    if ($this->getArgument('cache')) {
+      $cached = array();
+      foreach ($results as $result) {
+        $path = $result->getPath();
+        $hash = md5_file($engine->getFilePathOnDisk($path));
+        $cached[$path] = array($hash => array());
+        foreach ($result->getMessages() as $message) {
+          if (!$message->isPatchApplied()) {
+            $cached[$path][$hash][] = $message->toDictionary();
+          }
+        }
+      }
+      $cache = $this->readScratchJSONFile('lint-cache.json');
+      $cache[$this->getCacheKey()] = $cached;
+      // TODO: Garbage collection.
+      $this->writeScratchJSONFile('lint-cache.json', $cache);
+    }
+
     // Take the most severe lint message severity and use that
     // as the result code.
     if ($has_errors) {