diff --git a/src/lint/ArcanistLintMessage.php b/src/lint/ArcanistLintMessage.php
index cce74e5e..25f193d7 100644
--- a/src/lint/ArcanistLintMessage.php
+++ b/src/lint/ArcanistLintMessage.php
@@ -1,188 +1,198 @@
 <?php
 
 /**
  * Message emitted by a linter, like an error or warning.
  *
  * @group lint
  */
 final class ArcanistLintMessage {
 
   protected $path;
   protected $line;
   protected $char;
   protected $code;
   protected $severity;
   protected $name;
   protected $description;
   protected $originalText;
   protected $replacementText;
   protected $appliedToDisk;
   protected $dependentMessages = array();
   protected $obsolete;
+  protected $uncacheable;
 
   public static function newFromDictionary(array $dict) {
     $message = new ArcanistLintMessage();
 
     $message->setPath($dict['path']);
     $message->setLine($dict['line']);
     $message->setChar($dict['char']);
     $message->setCode($dict['code']);
     $message->setSeverity($dict['severity']);
     $message->setName($dict['name']);
     $message->setDescription($dict['description']);
     if (isset($dict['original'])) {
       $message->setOriginalText($dict['original']);
     }
     if (isset($dict['replacement'])) {
       $message->setReplacementText($dict['replacement']);
     }
     return $message;
   }
 
   public function toDictionary() {
     return array(
       'path'        => $this->getPath(),
       'line'        => $this->getLine(),
       'char'        => $this->getChar(),
       'code'        => $this->getCode(),
       'severity'    => $this->getSeverity(),
       'name'        => $this->getName(),
       'description' => $this->getDescription(),
       'original'    => $this->getOriginalText(),
       'replacement' => $this->getReplacementText(),
     );
   }
 
   public function setPath($path) {
     $this->path = $path;
     return $this;
   }
 
   public function getPath() {
     return $this->path;
   }
 
   public function setLine($line) {
     $this->line = $line;
     return $this;
   }
 
   public function getLine() {
     return $this->line;
   }
 
   public function setChar($char) {
     $this->char = $char;
     return $this;
   }
 
   public function getChar() {
     return $this->char;
   }
 
   public function setCode($code) {
     $this->code = $code;
     return $this;
   }
 
   public function getCode() {
     return $this->code;
   }
 
   public function setSeverity($severity) {
     $this->severity = $severity;
     return $this;
   }
 
   public function getSeverity() {
     return $this->severity;
   }
 
   public function setName($name) {
     $this->name = $name;
     return $this;
   }
 
   public function getName() {
     return $this->name;
   }
 
   public function setDescription($description) {
     $this->description = $description;
     return $this;
   }
 
   public function getDescription() {
     return $this->description;
   }
 
   public function setOriginalText($original) {
     $this->originalText = $original;
     return $this;
   }
 
   public function getOriginalText() {
     return $this->originalText;
   }
 
   public function setReplacementText($replacement) {
     $this->replacementText = $replacement;
     return $this;
   }
 
   public function getReplacementText() {
     return $this->replacementText;
   }
 
   public function isError() {
     return $this->getSeverity() == ArcanistLintSeverity::SEVERITY_ERROR;
   }
 
   public function isWarning() {
     return $this->getSeverity() == ArcanistLintSeverity::SEVERITY_WARNING;
   }
 
   public function isAutofix() {
     return $this->getSeverity() == ArcanistLintSeverity::SEVERITY_AUTOFIX;
   }
 
   public function hasFileContext() {
     return ($this->getLine() !== null);
   }
 
   public function setObsolete($obsolete) {
     $this->obsolete = $obsolete;
     return $this;
   }
 
   public function getObsolete() {
     return $this->obsolete;
   }
 
   public function isPatchable() {
     return ($this->getReplacementText() !== null) &&
            ($this->getReplacementText() !== $this->getOriginalText());
   }
 
   public function didApplyPatch() {
     if ($this->appliedToDisk) {
       return $this;
     }
     $this->appliedToDisk = true;
     foreach ($this->dependentMessages as $message) {
       $message->didApplyPatch();
     }
     return $this;
   }
 
   public function isPatchApplied() {
     return $this->appliedToDisk;
   }
 
+  public function setUncacheable($bool) {
+    $this->uncacheable = $bool;
+    return $this;
+  }
+
+  public function isUncacheable() {
+    return $this->uncacheable;
+  }
+
   public function setDependentMessages(array $messages) {
     assert_instances_of($messages, 'ArcanistLintMessage');
     $this->dependentMessages = $messages;
     return $this;
   }
 
 }
diff --git a/src/lint/engine/ArcanistLintEngine.php b/src/lint/engine/ArcanistLintEngine.php
index cbf7670a..8d4845f2 100644
--- a/src/lint/engine/ArcanistLintEngine.php
+++ b/src/lint/engine/ArcanistLintEngine.php
@@ -1,383 +1,389 @@
 <?php
 
 /**
  * Manages lint execution. When you run 'arc lint' or 'arc diff', Arcanist
  * checks your .arcconfig to see if you have specified a lint engine in the
  * key "lint.engine". The engine must extend this class. For example:
  *
  *  lang=js
  *  {
  *    // ...
  *    "lint.engine" : "ExampleLintEngine",
  *    // ...
  *  }
  *
  * The lint engine is given a list of paths (generally, the paths that you
  * modified in your change) and determines which linters to run on them. The
  * linters themselves are responsible for actually analyzing file text and
  * finding warnings and errors. For example, if the modified paths include some
  * JS files and some Python files, you might want to run JSLint on the JS files
  * and PyLint on the Python files.
  *
  * You can also run multiple linters on a single file. For instance, you might
  * run one linter on all text files to make sure they don't have trailing
  * whitespace, or enforce tab vs space rules, or make sure there are enough
  * curse words in them.
  *
  * Because lint engines are pretty custom to the rules of a project, you will
  * generally need to build your own. Fortunately, it's pretty easy (and you
  * can use the prebuilt //linters//, you just need to write a little glue code
  * to tell Arcanist which linters to run). For a simple example of how to build
  * a lint engine, see @{class:ExampleLintEngine}.
  *
  * You can test an engine like this:
  *
  *   arc lint --engine ExampleLintEngine --lintall some_file.py
  *
  * ...which will show you all the lint issues raised in the file.
  *
  * See @{article@phabricator:Arcanist User Guide: Customizing Lint, Unit Tests
  * and Workflows} for more information about configuring lint engines.
  *
  * @group lint
  * @stable
  */
 abstract class ArcanistLintEngine {
 
   protected $workingCopy;
   protected $paths = array();
   protected $fileData = array();
 
   protected $charToLine = array();
   protected $lineToFirstChar = array();
   private $cachedResults;
   private $cacheVersion;
   private $results = array();
   private $minimumSeverity = ArcanistLintSeverity::SEVERITY_DISABLED;
 
   private $changedLines = array();
   private $commitHookMode = false;
   private $hookAPI;
 
   private $enableAsyncLint = false;
   private $postponedLinters = array();
 
   public function __construct() {
 
   }
 
   public function setWorkingCopy(ArcanistWorkingCopyIdentity $working_copy) {
     $this->workingCopy = $working_copy;
     return $this;
   }
 
   public function getWorkingCopy() {
     return $this->workingCopy;
   }
 
   public function setPaths($paths) {
     $this->paths = $paths;
     return $this;
   }
 
   public function getPaths() {
     return $this->paths;
   }
 
   public function setPathChangedLines($path, $changed) {
     if ($changed === null) {
       $this->changedLines[$path] = null;
     } else {
       $this->changedLines[$path] = array_fill_keys($changed, true);
     }
     return $this;
   }
 
   public function getPathChangedLines($path) {
     return idx($this->changedLines, $path);
   }
 
   public function setFileData($data) {
     $this->fileData = $data + $this->fileData;
     return $this;
   }
 
   public function setCommitHookMode($mode) {
     $this->commitHookMode = $mode;
     return $this;
   }
 
   public function setHookAPI(ArcanistHookAPI $hook_api) {
     $this->hookAPI  = $hook_api;
     return $this;
   }
 
   public function getHookAPI() {
     return $this->hookAPI;
   }
 
   public function setEnableAsyncLint($enable_async_lint) {
     $this->enableAsyncLint = $enable_async_lint;
     return $this;
   }
 
   public function getEnableAsyncLint() {
     return $this->enableAsyncLint;
   }
 
   public function loadData($path) {
     if (!isset($this->fileData[$path])) {
       if ($this->getCommitHookMode()) {
         $this->fileData[$path] = $this->getHookAPI()
           ->getCurrentFileData($path);
       } else {
         $disk_path = $this->getFilePathOnDisk($path);
         $this->fileData[$path] = Filesystem::readFile($disk_path);
       }
     }
     return $this->fileData[$path];
   }
 
   public function pathExists($path) {
     if ($this->getCommitHookMode()) {
       $file_data = $this->loadData($path);
       return ($file_data !== null);
     } else {
       $disk_path = $this->getFilePathOnDisk($path);
       return Filesystem::pathExists($disk_path);
     }
   }
 
   public function getFilePathOnDisk($path) {
     return Filesystem::resolvePath(
       $path,
       $this->getWorkingCopy()->getProjectRoot());
   }
 
   public function setMinimumSeverity($severity) {
     $this->minimumSeverity = $severity;
     return $this;
   }
 
   public function getCommitHookMode() {
     return $this->commitHookMode;
   }
 
   public function run() {
     $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.");
     }
 
     $versions = array($this->getCacheVersion());
     foreach ($linters as $linter) {
       $versions[] = get_class($linter).':'.$linter->getCacheVersion();
     }
     $this->cacheVersion = crc32(implode("\n", $versions));
 
     $exceptions = array();
     foreach ($linters as $linter_name => $linter) {
       try {
         $linter->setEngine($this);
         if (!$linter->canRun()) {
           continue;
         }
         $paths = $linter->getPaths();
 
+        $cache_granularity = $linter->getCacheGranularity();
+
         foreach ($paths as $key => $path) {
           // Make sure each path has a result generated, even if it is empty
           // (i.e., the file has no lint messages).
           $result = $this->getResultForPath($path);
           if (isset($stopped[$path])) {
             unset($paths[$key]);
           }
-          // TODO: Some linters work with the whole directory.
           if (isset($this->cachedResults[$path][$this->cacheVersion])) {
-            unset($paths[$key]);
+            if ($cache_granularity == ArcanistLinter::GRANULARITY_FILE) {
+              unset($paths[$key]);
+            }
           }
         }
         $paths = array_values($paths);
 
         if ($paths) {
           $linter->willLintPaths($paths);
           foreach ($paths as $path) {
             $linter->willLintPath($path);
             $linter->lintPath($path);
             if ($linter->didStopAllLinters()) {
               $stopped[$path] = true;
             }
           }
         }
 
         $minimum = $this->minimumSeverity;
         foreach ($linter->getLintMessages() as $message) {
           if (!ArcanistLintSeverity::isAtLeastAsSevere($message, $minimum)) {
             continue;
           }
           if (!$this->isRelevantMessage($message)) {
             continue;
           }
+          if ($cache_granularity != ArcanistLinter::GRANULARITY_FILE) {
+            $message->setUncacheable(true);
+          }
           $result = $this->getResultForPath($message->getPath());
           $result->addMessage($message);
         }
       } catch (Exception $ex) {
         if (!is_string($linter_name)) {
           $linter_name = get_class($linter);
         }
         $exceptions[$linter_name] = $ex;
       }
     }
 
     if ($this->cachedResults) {
       foreach ($this->cachedResults as $path => $messages) {
         foreach (idx($messages, $this->cacheVersion, array()) as $message) {
           $this->getResultForPath($path)->addMessage(
             ArcanistLintMessage::newFromDictionary($message));
         }
       }
     }
 
     foreach ($this->results as $path => $result) {
       $disk_path = $this->getFilePathOnDisk($path);
       $result->setFilePathOnDisk($disk_path);
       if (isset($this->fileData[$path])) {
         $result->setData($this->fileData[$path]);
       } else if ($disk_path && Filesystem::pathExists($disk_path)) {
         // TODO: this may cause us to, e.g., load a large binary when we only
         // raised an error about its filename. We could refine this by looking
         // through the lint messages and doing this load only if any of them
         // have original/replacement text or something like that.
         try {
           $this->fileData[$path] = Filesystem::readFile($disk_path);
           $result->setData($this->fileData[$path]);
         } catch (FilesystemException $ex) {
           // Ignore this, it's noncritical that we access this data and it
           // might be unreadable or a directory or whatever else for plenty
           // of legitimate reasons.
         }
       }
     }
 
     if ($exceptions) {
       throw new PhutilAggregateException('Some linters failed:', $exceptions);
     }
 
     return $this->results;
   }
 
   /**
    * @param dict<string path, dict<int version, list<dict message>>>
    * @return this
    */
   public function setCachedResults(array $results) {
     $this->cachedResults = $results;
     return $this;
   }
 
   public function getResults() {
     return $this->results;
   }
 
   abstract protected function buildLinters();
 
   private function isRelevantMessage($message) {
     // When a user runs "arc lint", we default to raising only warnings on
     // lines they have changed (errors are still raised anywhere in the
     // file). The list of $changed lines may be null, to indicate that the
     // path is a directory or a binary file so we should not exclude
     // warnings.
 
     $changed = $this->getPathChangedLines($message->getPath());
 
     if ($changed === null || $message->isError() || !$message->getLine()) {
       return true;
     }
 
     $last_line = $message->getLine();
     if ($message->getOriginalText()) {
       $last_line += substr_count($message->getOriginalText(), "\n");
     }
 
     for ($l = $message->getLine(); $l <= $last_line; $l++) {
       if (!empty($changed[$l])) {
         return true;
       }
     }
 
     return false;
   }
 
   protected function getResultForPath($path) {
     if (empty($this->results[$path])) {
       $result = new ArcanistLintResult();
       $result->setPath($path);
       $result->setCacheVersion($this->cacheVersion);
       $this->results[$path] = $result;
     }
     return $this->results[$path];
   }
 
   public function getLineAndCharFromOffset($path, $offset) {
     if (!isset($this->charToLine[$path])) {
       $char_to_line = array();
       $line_to_first_char = array();
 
       $lines = explode("\n", $this->loadData($path));
       $line_number = 0;
       $line_start = 0;
       foreach ($lines as $line) {
         $len = strlen($line) + 1; // Account for "\n".
         $line_to_first_char[] = $line_start;
         $line_start += $len;
         for ($ii = 0; $ii < $len; $ii++) {
           $char_to_line[] = $line_number;
         }
         $line_number++;
       }
       $this->charToLine[$path] = $char_to_line;
       $this->lineToFirstChar[$path] = $line_to_first_char;
     }
 
     $line = $this->charToLine[$path][$offset];
     $char = $offset - $this->lineToFirstChar[$path][$line];
 
     return array($line, $char);
   }
 
   public function getPostponedLinters() {
     return $this->postponedLinters;
   }
 
   public function setPostponedLinters(array $linters) {
     $this->postponedLinters = $linters;
     return $this;
   }
 
   protected function getCacheVersion() {
     return 0;
   }
 
   protected function getPEP8WithTextOptions() {
     // E101 is subset of TXT2 (Tab Literal).
     // E501 is same as TXT3 (Line Too Long).
     // W291 is same as TXT6 (Trailing Whitespace).
     // W292 is same as TXT4 (File Does Not End in Newline).
     // W293 is same as TXT6 (Trailing Whitespace).
     return '--ignore=E101,E501,W291,W292,W293';
   }
 
 }
diff --git a/src/lint/linter/ArcanistLinter.php b/src/lint/linter/ArcanistLinter.php
index 0c20fab9..909aa71b 100644
--- a/src/lint/linter/ArcanistLinter.php
+++ b/src/lint/linter/ArcanistLinter.php
@@ -1,214 +1,223 @@
 <?php
 
 /**
  * Implements lint rules, like syntax checks for a specific language.
  *
  * @group linter
  * @stable
  */
 abstract class ArcanistLinter {
 
+  const GRANULARITY_FILE = 1;
+  const GRANULARITY_DIRECTORY = 2;
+  const GRANULARITY_REPOSITORY = 3;
+  const GRANULARITY_GLOBAL = 4;
+
   protected $paths  = array();
   protected $data   = array();
   protected $engine;
   protected $activePath;
   protected $messages = array();
 
   protected $stopAllLinters = false;
 
   private $customSeverityMap = array();
   private $config = array();
 
   public function setCustomSeverityMap(array $map) {
     $this->customSeverityMap = $map;
     return $this;
   }
 
   public function setConfig(array $config) {
     $this->config = $config;
     return $this;
   }
 
   protected function getConfig($key, $default = null) {
     return idx($this->config, $key, $default);
   }
 
   public function getActivePath() {
     return $this->activePath;
   }
 
   public function stopAllLinters() {
     $this->stopAllLinters = true;
     return $this;
   }
 
   public function didStopAllLinters() {
     return $this->stopAllLinters;
   }
 
   public function addPath($path) {
     $this->paths[$path] = $path;
     return $this;
   }
 
   public function setPaths(array $paths) {
     $this->paths = $paths;
     return $this;
   }
 
   public function getPaths() {
     return array_values($this->paths);
   }
 
   public function addData($path, $data) {
     $this->data[$path] = $data;
     return $this;
   }
 
   protected function getData($path) {
     if (!array_key_exists($path, $this->data)) {
       $this->data[$path] = $this->getEngine()->loadData($path);
     }
     return $this->data[$path];
   }
 
   public function setEngine(ArcanistLintEngine $engine) {
     $this->engine = $engine;
     return $this;
   }
 
   protected function getEngine() {
     return $this->engine;
   }
 
   public function getCacheVersion() {
     return 0;
   }
 
   public function getLintMessageFullCode($short_code) {
     return $this->getLinterName().$short_code;
   }
 
   public function getLintMessageSeverity($code) {
     $map = $this->customSeverityMap;
     if (isset($map[$code])) {
       return $map[$code];
     }
 
     $map = $this->getLintSeverityMap();
     if (isset($map[$code])) {
       return $map[$code];
     }
 
     return ArcanistLintSeverity::SEVERITY_ERROR;
   }
 
   public function isMessageEnabled($code) {
     return ($this->getLintMessageSeverity($code) !==
             ArcanistLintSeverity::SEVERITY_DISABLED);
   }
 
   public function getLintMessageName($code) {
     $map = $this->getLintNameMap();
     if (isset($map[$code])) {
       return $map[$code];
     }
     return "Unknown lint message!";
   }
 
   protected function addLintMessage(ArcanistLintMessage $message) {
     if (!$this->getEngine()->getCommitHookMode()) {
       $root = $this->getEngine()->getWorkingCopy()->getProjectRoot();
       $path = Filesystem::resolvePath($message->getPath(), $root);
       $message->setPath(Filesystem::readablePath($path, $root));
     }
     $this->messages[] = $message;
     return $message;
   }
 
   public function getLintMessages() {
     return $this->messages;
   }
 
   protected function raiseLintAtLine(
     $line,
     $char,
     $code,
     $desc,
     $original = null,
     $replacement = null) {
 
     $dict = array(
       'path'          => $this->getActivePath(),
       'line'          => $line,
       'char'          => $char,
       'code'          => $this->getLintMessageFullCode($code),
       'severity'      => $this->getLintMessageSeverity($code),
       'name'          => $this->getLintMessageName($code),
       'description'   => $desc,
     );
 
     if ($original !== null) {
       $dict['original'] = $original;
     }
     if ($replacement !== null) {
       $dict['replacement'] = $replacement;
     }
 
     return $this->addLintMessage(ArcanistLintMessage::newFromDictionary($dict));
   }
 
   protected function raiseLintAtPath(
     $code,
     $desc) {
 
     return $this->raiseLintAtLine(null, null, $code, $desc, null, null);
   }
 
   protected function raiseLintAtOffset(
     $offset,
     $code,
     $desc,
     $original = null,
     $replacement = null) {
 
     $path = $this->getActivePath();
     $engine = $this->getEngine();
     if ($offset === null) {
       $line = null;
       $char = null;
     } else {
       list($line, $char) = $engine->getLineAndCharFromOffset($path, $offset);
     }
 
     return $this->raiseLintAtLine(
       $line + 1,
       $char + 1,
       $code,
       $desc,
       $original,
       $replacement);
   }
 
   public function willLintPath($path) {
     $this->stopAllLinters = false;
     $this->activePath = $path;
   }
 
   public function canRun() {
     return true;
   }
 
   abstract public function willLintPaths(array $paths);
   abstract public function lintPath($path);
   abstract public function getLinterName();
 
   public function getLintSeverityMap() {
     return array();
   }
 
   public function getLintNameMap() {
     return array();
   }
 
+  public function getCacheGranularity() {
+    return self::GRANULARITY_FILE;
+  }
+
 }
diff --git a/src/lint/linter/ArcanistPhutilLibraryLinter.php b/src/lint/linter/ArcanistPhutilLibraryLinter.php
index c7a31e52..7b7ebe76 100644
--- a/src/lint/linter/ArcanistPhutilLibraryLinter.php
+++ b/src/lint/linter/ArcanistPhutilLibraryLinter.php
@@ -1,174 +1,179 @@
 <?php
 
 /**
  * Applies lint rules for Phutil libraries. We enforce three rules:
  *
  *   # If you use a symbol, it must be defined somewhere.
  *   # If you define a symbol, it must not duplicate another definition.
  *   # If you define a class or interface in a file, it MUST be the only symbol
  *     defined in that file.
  *
  * @group linter
  */
 final class ArcanistPhutilLibraryLinter extends ArcanistLinter {
 
   const LINT_UNKNOWN_SYMBOL               = 1;
   const LINT_DUPLICATE_SYMBOL             = 2;
   const LINT_ONE_CLASS_PER_FILE           = 3;
 
   public function getLintNameMap() {
     return array(
       self::LINT_UNKNOWN_SYMBOL         => 'Unknown Symbol',
       self::LINT_DUPLICATE_SYMBOL       => 'Duplicate Symbol',
       self::LINT_ONE_CLASS_PER_FILE     => 'One Class Per File',
     );
   }
 
   public function getLinterName() {
     return 'PHL';
   }
 
   public function getLintSeverityMap() {
     return array();
   }
 
   public function willLintPaths(array $paths) {
     if (!xhpast_is_available()) {
       throw new Exception(xhpast_get_build_instructions());
     }
 
     // NOTE: For now, we completely ignore paths and just lint every library in
     // its entirety. This is simpler and relatively fast because we don't do any
     // detailed checks and all the data we need for this comes out of module
     // caches.
 
     $bootloader = PhutilBootloader::getInstance();
     $libs = $bootloader->getAllLibraries();
 
     // Load the up-to-date map for each library, without loading the library
     // itself. This means lint results will accurately reflect the state of
     // the working copy.
 
     $arc_root = dirname(phutil_get_library_root('arcanist'));
     $bin = "{$arc_root}/scripts/phutil_rebuild_map.php";
 
     $symbols = array();
     foreach ($libs as $lib) {
       // Do these one at a time since they individually fanout to saturate
       // available system resources.
       $future = new ExecFuture(
         '%s --show --quiet --ugly -- %s',
         $bin,
         phutil_get_library_root($lib));
       $symbols[$lib] = $future->resolveJSON();
     }
 
     $all_symbols = array();
     foreach ($symbols as $library => $map) {
       // Check for files which declare more than one class/interface in the same
       // file, or mix function definitions with class/interface definitions. We
       // must isolate autoloadable symbols to one per file so the autoloader
       // can't end up in an unresolvable cycle.
       foreach ($map as $file => $spec) {
         $have = idx($spec, 'have', array());
 
         $have_classes =
           idx($have, 'class', array()) +
           idx($have, 'interface', array());
         $have_functions = idx($have, 'function');
 
         if ($have_functions && $have_classes) {
           $function_list = implode(', ', array_keys($have_functions));
           $class_list = implode(', ', array_keys($have_classes));
           $this->raiseLintInLibrary(
             $library,
             $file,
             end($have_functions),
             self::LINT_ONE_CLASS_PER_FILE,
             "File '{$file}' mixes function ({$function_list}) and ".
             "class/interface ({$class_list}) definitions in the same file. ".
             "A file which declares a class or an interface MUST ".
             "declare nothing else.");
         } else if (count($have_classes) > 1) {
           $class_list = implode(', ', array_keys($have_classes));
           $this->raiseLintInLibrary(
             $library,
             $file,
             end($have_classes),
             self::LINT_ONE_CLASS_PER_FILE,
             "File '{$file}' declares more than one class or interface ".
             "({$class_list}). A file which declares a class or interface MUST ".
             "declare nothing else.");
         }
       }
 
       // Check for duplicate symbols: two files providing the same class or
       // function.
       foreach ($map as $file => $spec) {
         $have = idx($spec, 'have', array());
         foreach (array('class', 'function', 'interface') as $type) {
           $libtype = ($type == 'interface') ? 'class' : $type;
           foreach (idx($have, $type, array()) as $symbol => $offset) {
             if (empty($all_symbols[$libtype][$symbol])) {
               $all_symbols[$libtype][$symbol] = array(
                 'library' => $library,
                 'file'    => $file,
                 'offset'  => $offset,
               );
               continue;
             }
 
             $osrc = $all_symbols[$libtype][$symbol]['file'];
             $olib = $all_symbols[$libtype][$symbol]['library'];
 
             $this->raiseLintInLibrary(
               $library,
               $file,
               $offset,
               self::LINT_DUPLICATE_SYMBOL,
               "Definition of {$type} '{$symbol}' in '{$file}' in library ".
               "'{$library}' duplicates prior definition in '{$osrc}' in ".
               "library '{$olib}'.");
           }
         }
       }
     }
 
     foreach ($symbols as $library => $map) {
       // Check for unknown symbols: uses of classes, functions or interfaces
       // which are not defined anywhere. We reference the list of all symbols
       // we built up earlier.
       foreach ($map as $file => $spec) {
         $need = idx($spec, 'need', array());
         foreach (array('class', 'function', 'interface') as $type) {
           $libtype = ($type == 'interface') ? 'class' : $type;
           foreach (idx($need, $type, array()) as $symbol => $offset) {
             if (!empty($all_symbols[$libtype][$symbol])) {
               // Symbol is defined somewhere.
               continue;
             }
 
             $this->raiseLintInLibrary(
               $library,
               $file,
               $offset,
               self::LINT_UNKNOWN_SYMBOL,
               "Use of unknown {$type} '{$symbol}'. This symbol is not defined ".
               "in any loaded phutil library.");
           }
         }
       }
     }
   }
 
   private function raiseLintInLibrary($library, $path, $offset, $code, $desc) {
     $root = phutil_get_library_root($library);
 
     $this->activePath = $root.'/'.$path;
     $this->raiseLintAtOffset($offset, $code, $desc);
   }
 
   public function lintPath($path) {
     return;
   }
+
+  public function getCacheGranularity() {
+    return self::GRANULARITY_GLOBAL;
+  }
+
 }
diff --git a/src/workflow/ArcanistLintWorkflow.php b/src/workflow/ArcanistLintWorkflow.php
index 10e8a37b..fce3eccb 100644
--- a/src/workflow/ArcanistLintWorkflow.php
+++ b/src/workflow/ArcanistLintWorkflow.php
@@ -1,446 +1,458 @@
 <?php
 
 /**
  * Runs lint rules on changes.
  *
  * @group workflow
  */
 class ArcanistLintWorkflow extends ArcanistBaseWorkflow {
 
   const RESULT_OKAY       = 0;
   const RESULT_WARNINGS   = 1;
   const RESULT_ERRORS     = 2;
   const RESULT_SKIP       = 3;
   const RESULT_POSTPONED  = 4;
 
   const DEFAULT_SEVERITY = ArcanistLintSeverity::SEVERITY_ADVICE;
 
   private $unresolvedMessages;
   private $shouldLintAll;
   private $shouldAmendChanges = false;
   private $shouldAmendWithoutPrompt = false;
   private $shouldAmendAutofixesWithoutPrompt = false;
   private $engine;
   private $postponedLinters;
 
   public function getWorkflowName() {
     return 'lint';
   }
 
   public function setShouldAmendChanges($should_amend) {
     $this->shouldAmendChanges = $should_amend;
     return $this;
   }
 
   public function setShouldAmendWithoutPrompt($should_amend) {
     $this->shouldAmendWithoutPrompt = $should_amend;
     return $this;
   }
 
   public function setShouldAmendAutofixesWithoutPrompt($should_amend) {
     $this->shouldAmendAutofixesWithoutPrompt = $should_amend;
     return $this;
   }
 
   public function getCommandSynopses() {
     return phutil_console_format(<<<EOTEXT
       **lint** [__options__] [__paths__]
       **lint** [__options__] --rev [__rev__]
 EOTEXT
       );
   }
 
   public function getCommandHelp() {
     return phutil_console_format(<<<EOTEXT
           Supports: git, svn, hg
           Run static analysis on changes to check for mistakes. If no files
           are specified, lint will be run on all files which have been modified.
 EOTEXT
       );
   }
 
   public function getArguments() {
     return array(
       'lintall' => array(
         'help' =>
           "Show all lint warnings, not just those on changed lines."
       ),
       'rev' => array(
         'param' => 'revision',
         'help' => "Lint changes since a specific revision.",
         'supports' => array(
           'git',
           'hg',
         ),
         'nosupport' => array(
           'svn' => "Lint does not currently support --rev in SVN.",
         ),
       ),
       'output' => array(
         'param' => 'format',
         'help' =>
           "With 'summary', show lint warnings in a more compact format. ".
           "With 'json', show lint warnings in machine-readable JSON format. ".
           "With 'compiler', show lint warnings in suitable for your editor."
       ),
       'engine' => array(
         'param' => 'classname',
         'help' =>
           "Override configured lint engine for this project."
       ),
       'apply-patches' => array(
         'help' =>
           'Apply patches suggested by lint to the working copy without '.
           'prompting.',
         'conflicts' => array(
           'never-apply-patches' => true,
         ),
       ),
       'never-apply-patches' => array(
         'help' => 'Never apply patches suggested by lint.',
         'conflicts' => array(
           'apply-patches' => true,
         ),
       ),
       'amend-all' => array(
         'help' =>
         'When linting git repositories, amend HEAD with all patches '.
         'suggested by lint without prompting.',
       ),
       'amend-autofixes' => array(
         'help' =>
           'When linting git repositories, amend HEAD with autofix '.
           'patches suggested by lint without prompting.',
       ),
       'severity' => array(
         'param' => 'string',
         'help' =>
           "Set minimum message severity. One of: '".
           implode(
             "', '",
             array_keys(ArcanistLintSeverity::getLintSeverities())).
           "'. Defaults to '".self::DEFAULT_SEVERITY."'.",
       ),
       'cache' => array(
         'param' => 'bool',
         'help' => "0 to disable cache (default), 1 to enable.",
       ),
       '*' => 'paths',
     );
   }
 
   public function requiresWorkingCopy() {
     return true;
   }
 
   public function requiresRepositoryAPI() {
     return true;
   }
 
   private function getCacheKey() {
     return implode("\n", array(
       get_class($this->engine),
       $this->getArgument('severity', self::DEFAULT_SEVERITY),
       $this->shouldLintAll,
     ));
   }
 
   public function run() {
     $working_copy = $this->getWorkingCopy();
 
     $engine = $this->getArgument('engine');
     if (!$engine) {
       $engine = $working_copy->getConfigFromAnySource('lint.engine');
       if (!$engine) {
         throw new ArcanistNoEngineException(
           "No lint engine configured for this project. Edit .arcconfig to ".
           "specify a lint engine.");
       }
     }
 
     $rev = $this->getArgument('rev');
     $paths = $this->getArgument('paths');
 
     if ($rev && $paths) {
       throw new ArcanistUsageException("Specify either --rev or paths.");
     }
 
     $this->shouldLintAll = $this->getArgument('lintall');
     if ($paths) {
       // NOTE: When the user specifies paths, we imply --lintall and show all
       // warnings for the paths in question. This is easier to deal with for
       // us and less confusing for users.
       $this->shouldLintAll = true;
     }
 
     $paths = $this->selectPathsForWorkflow($paths, $rev);
 
     if (!class_exists($engine) ||
         !is_subclass_of($engine, 'ArcanistLintEngine')) {
       throw new ArcanistUsageException(
         "Configured lint engine '{$engine}' is not a subclass of ".
         "'ArcanistLintEngine'.");
     }
 
     $engine = newv($engine, array());
     $this->engine = $engine;
     $engine->setWorkingCopy($working_copy);
 
     $engine->setMinimumSeverity(
       $this->getArgument('severity', self::DEFAULT_SEVERITY));
 
     if ($this->getArgument('cache')) {
       $cache = $this->readScratchJSONFile('lint-cache.json');
       $cache = idx($cache, $this->getCacheKey(), array());
+      $cache = array_intersect_key($cache, array_flip($paths));
       $cached = array();
       foreach ($cache as $path => $messages) {
-        $messages = idx($messages, md5_file($engine->getFilePathOnDisk($path)));
+        $abs_path = $engine->getFilePathOnDisk($path);
+        if (!Filesystem::pathExists($abs_path)) {
+          continue;
+        }
+        $messages = idx($messages, md5_file($abs_path));
         if ($messages !== null) {
           $cached[$path] = $messages;
         }
       }
       $engine->setCachedResults($cached);
     }
 
     // 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.
     $engine->setPaths($paths);
     if (!$this->shouldLintAll) {
       foreach ($paths as $path) {
         // Note that getChangedLines() returns null to indicate that a file
         // is binary or a directory (i.e., changed lines are not relevant).
         $engine->setPathChangedLines(
           $path,
           $this->getChangedLines($path, 'new'));
       }
     }
 
     // Enable possible async linting only for 'arc diff' not 'arc lint'
     if ($this->getParentWorkflow()) {
       $engine->setEnableAsyncLint(true);
     } else {
       $engine->setEnableAsyncLint(false);
     }
 
     $failed = null;
     try {
       $engine->run();
     } catch (Exception $ex) {
       $failed = $ex;
     }
 
     $results = $engine->getResults();
 
     // It'd be nice to just return a single result from the run method above
     // which contains both the lint messages and the postponed linters.
     // However, to maintain compatibility with existing lint subclasses, use
     // a separate method call to grab the postponed linters.
     $this->postponedLinters = $engine->getPostponedLinters();
 
     if ($this->getArgument('never-apply-patches')) {
       $apply_patches = false;
     } else {
       $apply_patches = true;
     }
 
     if ($this->getArgument('apply-patches')) {
       $prompt_patches = false;
     } else {
       $prompt_patches = true;
     }
 
     if ($this->getArgument('amend-all')) {
       $this->shouldAmendChanges = true;
       $this->shouldAmendWithoutPrompt = true;
     }
 
     if ($this->getArgument('amend-autofixes')) {
       $prompt_autofix_patches = false;
       $this->shouldAmendChanges = true;
       $this->shouldAmendAutofixesWithoutPrompt = true;
     } else {
       $prompt_autofix_patches = true;
     }
 
     $wrote_to_disk = false;
 
     switch ($this->getArgument('output')) {
       case 'json':
         $renderer = new ArcanistLintJSONRenderer();
         $prompt_patches = false;
         $apply_patches = $this->getArgument('apply-patches');
         break;
       case 'summary':
         $renderer = new ArcanistLintSummaryRenderer();
         break;
       case 'compiler':
         $renderer = new ArcanistLintLikeCompilerRenderer();
         $prompt_patches = false;
         $apply_patches = $this->getArgument('apply-patches');
         break;
       default:
         $renderer = new ArcanistLintConsoleRenderer();
         $renderer->setShowAutofixPatches($prompt_autofix_patches);
         break;
     }
 
     $all_autofix = true;
 
     $console = PhutilConsole::getConsole();
 
     foreach ($results as $result) {
       $result_all_autofix = $result->isAllAutofix();
 
       if (!$result->getMessages() && !$result_all_autofix) {
         continue;
       }
 
       if (!$result_all_autofix) {
         $all_autofix = false;
       }
 
       $lint_result = $renderer->renderLintResult($result);
       if ($lint_result) {
         $console->writeOut('%s', $lint_result);
       }
 
       if ($apply_patches && $result->isPatchable()) {
         $patcher = ArcanistLintPatcher::newFromArcanistLintResult($result);
 
         if ($prompt_patches &&
             !($result_all_autofix && !$prompt_autofix_patches)) {
           $old_file = $result->getFilePathOnDisk();
           if (!Filesystem::pathExists($old_file)) {
             $old_file = '/dev/null';
           }
           $new_file = new TempFile();
           $new = $patcher->getModifiedFileContent();
           Filesystem::writeFile($new_file, $new);
 
           // TODO: Improve the behavior here, make it more like
           // difference_render().
           list(, $stdout, $stderr) =
             exec_manual("diff -u %s %s", $old_file, $new_file);
           $console->writeOut('%s', $stdout);
           $console->writeErr('%s', $stderr);
 
           $prompt = phutil_console_format(
             "Apply this patch to __%s__?",
             $result->getPath());
           if (!$console->confirm($prompt, $default_no = false)) {
             continue;
           }
         }
 
         $patcher->writePatchToDisk();
         $wrote_to_disk = true;
       }
     }
 
     $repository_api = $this->getRepositoryAPI();
     if ($wrote_to_disk &&
         ($repository_api instanceof ArcanistGitAPI) &&
         $this->shouldAmendChanges) {
 
       if ($this->shouldAmendWithoutPrompt ||
           ($this->shouldAmendAutofixesWithoutPrompt && $all_autofix)) {
         $console->writeOut(
           "<bg:yellow>** LINT NOTICE **</bg> Automatically amending HEAD ".
           "with lint patches.\n");
         $amend = true;
       } else {
         $amend = $console->confirm("Amend HEAD with lint patches?");
       }
 
       if ($amend) {
         execx(
           '(cd %s; git commit -a --amend -C HEAD)',
           $repository_api->getPath());
       } else {
         throw new ArcanistUsageException(
           "Sort out the lint changes that were applied to the working ".
           "copy and relint.");
       }
     }
 
     if ($this->getArgument('output') == 'json') {
       // NOTE: Required by save_lint.php in Phabricator.
       return 0;
     }
 
     if ($failed) {
       throw $failed;
     }
 
     $unresolved = array();
     $has_warnings = false;
     $has_errors = false;
 
     foreach ($results as $result) {
       foreach ($result->getMessages() as $message) {
         if (!$message->isPatchApplied()) {
           if ($message->isError()) {
             $has_errors = true;
           } else if ($message->isWarning()) {
             $has_warnings = true;
           }
           $unresolved[] = $message;
         }
       }
     }
     $this->unresolvedMessages = $unresolved;
 
     $cache = $this->readScratchJSONFile('lint-cache.json');
     $cached = idx($cache, $this->getCacheKey(), array());
     if ($cached || $this->getArgument('cache')) {
       foreach ($results as $result) {
         $path = $result->getPath();
         if (!$this->getArgument('cache')) {
           unset($cached[$path]);
           continue;
         }
-        $hash = md5_file($engine->getFilePathOnDisk($path));
+        $abs_path = $engine->getFilePathOnDisk($path);
+        if (!Filesystem::pathExists($abs_path)) {
+          continue;
+        }
+        $hash = md5_file($abs_path);
         $version = $result->getCacheVersion();
         $cached[$path] = array($hash => array($version => array()));
         foreach ($result->getMessages() as $message) {
+          if ($message->isUncacheable()) {
+            continue;
+          }
           if (!$message->isPatchApplied()) {
             $cached[$path][$hash][$version][] = $message->toDictionary();
           }
         }
       }
       $cache[$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) {
       $result_code = self::RESULT_ERRORS;
     } else if ($has_warnings) {
       $result_code = self::RESULT_WARNINGS;
     } else if (!empty($this->postponedLinters)) {
       $result_code = self::RESULT_POSTPONED;
     } else {
       $result_code = self::RESULT_OKAY;
     }
 
     if (!$this->getParentWorkflow()) {
       if ($result_code == self::RESULT_OKAY) {
         $console->writeOut('%s', $renderer->renderOkayResult());
       }
     }
 
     return $result_code;
   }
 
   public function getUnresolvedMessages() {
     return $this->unresolvedMessages;
   }
 
   public function getPostponedLinters() {
     return $this->postponedLinters;
   }
 
 }