diff --git a/src/configuration/ArcanistConfigurationManager.php b/src/configuration/ArcanistConfigurationManager.php
--- a/src/configuration/ArcanistConfigurationManager.php
+++ b/src/configuration/ArcanistConfigurationManager.php
@@ -258,7 +258,7 @@
   }
 
   public function getUserConfigurationFileLocation() {
-    if (strlen($this->customArcrcFilename)) {
+    if ($this->customArcrcFilename !== null) {
       return $this->customArcrcFilename;
     }
 
diff --git a/src/filesystem/PhutilDirectoryFixture.php b/src/filesystem/PhutilDirectoryFixture.php
--- a/src/filesystem/PhutilDirectoryFixture.php
+++ b/src/filesystem/PhutilDirectoryFixture.php
@@ -28,6 +28,8 @@
   }
 
   public function getPath($to_file = null) {
+    $to_file = phutil_string_cast($to_file);
+
     return $this->path.'/'.ltrim($to_file, '/');
   }
 
diff --git a/src/future/exec/ExecFuture.php b/src/future/exec/ExecFuture.php
--- a/src/future/exec/ExecFuture.php
+++ b/src/future/exec/ExecFuture.php
@@ -192,11 +192,18 @@
    * @task interact
    */
   public function read() {
-    $stdout = $this->readStdout();
+    $stdout_value = $this->readStdout();
+
+    $stderr = $this->stderr;
+    if ($stderr === null) {
+      $stderr_value = '';
+    } else {
+      $stderr_value = substr($stderr, $this->stderrPos);
+    }
 
     $result = array(
-      $stdout,
-      (string)substr($this->stderr, $this->stderrPos),
+      $stdout_value,
+      $stderr_value,
     );
 
     $this->stderrPos = $this->getStderrBufferLength();
@@ -209,7 +216,14 @@
       $this->updateFuture(); // Sync
     }
 
-    $result = (string)substr($this->stdout, $this->stdoutPos);
+    $stdout = $this->stdout;
+
+    if ($stdout === null) {
+      $result = '';
+    } else {
+      $result = substr($stdout, $this->stdoutPos);
+    }
+
     $this->stdoutPos = $this->getStdoutBufferLength();
 
     return $result;
diff --git a/src/lint/linter/ArcanistXMLLinter.php b/src/lint/linter/ArcanistXMLLinter.php
--- a/src/lint/linter/ArcanistXMLLinter.php
+++ b/src/lint/linter/ArcanistXMLLinter.php
@@ -27,7 +27,11 @@
   }
 
   public function getCacheVersion() {
-    return LIBXML_VERSION;
+    if (defined('LIBXML_VERSION')) {
+      return LIBXML_VERSION;
+    } else {
+      return 'unavailable';
+    }
   }
 
   public function lintPath($path) {
diff --git a/src/lint/linter/__tests__/ArcanistLinterTestCase.php b/src/lint/linter/__tests__/ArcanistLinterTestCase.php
--- a/src/lint/linter/__tests__/ArcanistLinterTestCase.php
+++ b/src/lint/linter/__tests__/ArcanistLinterTestCase.php
@@ -51,6 +51,13 @@
   private function lintFile($file, ArcanistLinter $linter) {
     $linter = clone $linter;
 
+    if (!$linter->canRun()) {
+      $this->assertSkipped(
+        pht(
+          'Linter "%s" can not run.',
+          get_class($linter)));
+    }
+
     $contents = Filesystem::readFile($file);
     $contents = preg_split('/^~{4,}\n/m', $contents);
     if (count($contents) < 2) {
@@ -283,9 +290,12 @@
   }
 
   private function compareTransform($expected, $actual) {
+    $expected = phutil_string_cast($expected);
+
     if (!strlen($expected)) {
       return;
     }
+
     $this->assertEqual(
       $expected,
       $actual,
diff --git a/src/lint/linter/xhpast/rules/ArcanistPHPCompatibilityXHPASTLinterRule.php b/src/lint/linter/xhpast/rules/ArcanistPHPCompatibilityXHPASTLinterRule.php
--- a/src/lint/linter/xhpast/rules/ArcanistPHPCompatibilityXHPASTLinterRule.php
+++ b/src/lint/linter/xhpast/rules/ArcanistPHPCompatibilityXHPASTLinterRule.php
@@ -155,7 +155,9 @@
       if ($this->windowsVersion) {
         $windows = idx($compat_info['functions_windows'], $name);
 
-        if ($windows === false) {
+        if ($windows === null) {
+          // This function has no special Windows considerations.
+        } else if ($windows === false) {
           $this->raiseLintAtNode(
             $node,
             pht(
diff --git a/src/lint/linter/xhpast/rules/ArcanistParentMemberReferenceXHPASTLinterRule.php b/src/lint/linter/xhpast/rules/ArcanistParentMemberReferenceXHPASTLinterRule.php
--- a/src/lint/linter/xhpast/rules/ArcanistParentMemberReferenceXHPASTLinterRule.php
+++ b/src/lint/linter/xhpast/rules/ArcanistParentMemberReferenceXHPASTLinterRule.php
@@ -55,7 +55,12 @@
             }
           }
 
-          if (version_compare($this->version, '5.4.0', '>=') || !$in_closure) {
+          $version_target = $this->version;
+          if ($version_target === null) {
+            $version_target = phpversion();
+          }
+
+          if (version_compare($version_target, '5.4.0', '>=') || !$in_closure) {
             $this->raiseLintAtNode(
               $class_ref,
               pht(
diff --git a/src/lint/linter/xhpast/rules/ArcanistSelfMemberReferenceXHPASTLinterRule.php b/src/lint/linter/xhpast/rules/ArcanistSelfMemberReferenceXHPASTLinterRule.php
--- a/src/lint/linter/xhpast/rules/ArcanistSelfMemberReferenceXHPASTLinterRule.php
+++ b/src/lint/linter/xhpast/rules/ArcanistSelfMemberReferenceXHPASTLinterRule.php
@@ -42,7 +42,12 @@
             }
           }
 
-          if (version_compare($this->version, '5.4.0', '>=') || !$in_closure) {
+          $version_target = $this->version;
+          if (!$version_target) {
+            $version_target = phpversion();
+          }
+
+          if (version_compare($version_target, '5.4.0', '>=') || !$in_closure) {
             $this->raiseLintAtNode(
               $class_ref,
               pht(
diff --git a/src/parser/ArcanistBundle.php b/src/parser/ArcanistBundle.php
--- a/src/parser/ArcanistBundle.php
+++ b/src/parser/ArcanistBundle.php
@@ -639,8 +639,7 @@
     $old_path = $change->getOldPath();
     $type = $change->getType();
 
-    if (!strlen($old_path) ||
-        $type == ArcanistDiffChangeType::TYPE_ADD) {
+    if ($old_path === '' || $type == ArcanistDiffChangeType::TYPE_ADD) {
       $old_path = null;
     }
 
@@ -1023,7 +1022,7 @@
         if ($is_64bit) {
           for ($count = 4; $count >= 0; $count--) {
             $val = $accum % 85;
-            $accum = $accum / 85;
+            $accum = (int)($accum / 85);
             $slice .= $map[$val];
           }
         } else {
diff --git a/src/parser/ArcanistDiffParser.php b/src/parser/ArcanistDiffParser.php
--- a/src/parser/ArcanistDiffParser.php
+++ b/src/parser/ArcanistDiffParser.php
@@ -217,7 +217,7 @@
       $line = $this->nextLine();
     }
 
-    if (strlen($message)) {
+    if ($message !== null && strlen($message)) {
       // If we found a message during pre-parse steps, add it to the resulting
       // changes here.
       $change = $this->buildChange(null)
@@ -582,10 +582,13 @@
 
         $ok = false;
         $match = null;
-        foreach ($patterns as $pattern) {
-          $ok = preg_match('@^'.$pattern.'@', $line, $match);
-          if ($ok) {
-            break;
+
+        if ($line !== null) {
+          foreach ($patterns as $pattern) {
+            $ok = preg_match('@^'.$pattern.'@', $line, $match);
+            if ($ok) {
+              break;
+            }
           }
         }
 
@@ -774,7 +777,7 @@
       $this->nextLine();
       $this->parseGitBinaryPatch();
       $line = $this->getLine();
-      if (preg_match('/^literal/', $line)) {
+      if ($line !== null && preg_match('/^literal/', $line)) {
         // We may have old/new binaries (change) or just a new binary (hg add).
         // If there are two blocks, parse both.
         $this->parseGitBinaryPatch();
@@ -920,11 +923,11 @@
       $hunk->setNewOffset($matches[3]);
 
       // Cover for the cases where length wasn't present (implying one line).
-      $old_len = idx($matches, 2);
+      $old_len = idx($matches, 2, '');
       if (!strlen($old_len)) {
         $old_len = 1;
       }
-      $new_len = idx($matches, 4);
+      $new_len = idx($matches, 4, '');
       if (!strlen($new_len)) {
         $new_len = 1;
       }
@@ -1041,7 +1044,7 @@
         $line = $this->nextNonemptyLine();
       }
 
-    } while (preg_match('/^@@ /', $line));
+    } while (($line !== null) && preg_match('/^@@ /', $line));
   }
 
   protected function buildChange($path = null) {
diff --git a/src/parser/PhutilBugtraqParser.php b/src/parser/PhutilBugtraqParser.php
--- a/src/parser/PhutilBugtraqParser.php
+++ b/src/parser/PhutilBugtraqParser.php
@@ -85,7 +85,7 @@
       $captured_text = $capture['text'];
       $captured_offset = $capture['at'];
 
-      if (strlen($select_regexp)) {
+      if ($select_regexp !== null) {
         $selections = null;
         preg_match_all(
           $select_regexp,
diff --git a/src/parser/PhutilEmailAddress.php b/src/parser/PhutilEmailAddress.php
--- a/src/parser/PhutilEmailAddress.php
+++ b/src/parser/PhutilEmailAddress.php
@@ -13,6 +13,7 @@
   private $domainName;
 
   public function __construct($email_address = null) {
+    $email_address = phutil_string_cast($email_address);
     $email_address = trim($email_address);
 
     $matches = null;
@@ -89,7 +90,7 @@
 
   public function getAddress() {
     $address = $this->localPart;
-    if (strlen($this->domainName)) {
+    if ($this->domainName !== null && strlen($this->domainName)) {
       $address .= '@'.$this->domainName;
     }
     return $address;
diff --git a/src/parser/PhutilURI.php b/src/parser/PhutilURI.php
--- a/src/parser/PhutilURI.php
+++ b/src/parser/PhutilURI.php
@@ -171,14 +171,19 @@
       }
     }
 
-    if (strlen($protocol) || strlen($auth) || strlen($domain)) {
+    $has_protocol = ($protocol !== null) && strlen($protocol);
+    $has_auth = ($auth !== null);
+    $has_domain = ($domain !== null) && strlen($domain);
+    $has_port = ($port !== null) && strlen($port);
+
+    if ($has_protocol || $has_auth || $has_domain) {
       if ($this->isGitURI()) {
         $prefix = "{$auth}{$domain}";
       } else {
         $prefix = "{$protocol}://{$auth}{$domain}";
       }
 
-      if (strlen($port)) {
+      if ($has_port) {
         $prefix .= ':'.$port;
       }
     }
diff --git a/src/parser/aast/api/AASTNodeList.php b/src/parser/aast/api/AASTNodeList.php
--- a/src/parser/aast/api/AASTNodeList.php
+++ b/src/parser/aast/api/AASTNodeList.php
@@ -80,6 +80,7 @@
 
 /* -(  Countable  )---------------------------------------------------------- */
 
+  #[\ReturnTypeWillChange]
   public function count() {
     return count($this->ids);
   }
@@ -87,22 +88,27 @@
 
 /* -(  Iterator  )----------------------------------------------------------- */
 
+  #[\ReturnTypeWillChange]
   public function current() {
     return $this->list[$this->key()];
   }
 
+  #[\ReturnTypeWillChange]
   public function key() {
     return $this->ids[$this->pos];
   }
 
+  #[\ReturnTypeWillChange]
   public function next() {
     $this->pos++;
   }
 
+  #[\ReturnTypeWillChange]
   public function rewind() {
     $this->pos = 0;
   }
 
+  #[\ReturnTypeWillChange]
   public function valid() {
     return $this->pos < count($this->ids);
   }
diff --git a/src/serviceprofiler/PhutilServiceProfiler.php b/src/serviceprofiler/PhutilServiceProfiler.php
--- a/src/serviceprofiler/PhutilServiceProfiler.php
+++ b/src/serviceprofiler/PhutilServiceProfiler.php
@@ -137,7 +137,7 @@
 
           $uri = phutil_censor_credentials($data['uri']);
 
-          if (strlen($proxy)) {
+          if ($proxy !== null) {
             $desc = "{$proxy} >> {$uri}";
           } else {
             $desc = $uri;
diff --git a/src/unit/renderer/ArcanistUnitConsoleRenderer.php b/src/unit/renderer/ArcanistUnitConsoleRenderer.php
--- a/src/unit/renderer/ArcanistUnitConsoleRenderer.php
+++ b/src/unit/renderer/ArcanistUnitConsoleRenderer.php
@@ -65,9 +65,10 @@
       50   => "<fg:green>%s</fg><fg:yellow>{$star}</fg> ",
       200  => '<fg:green>%s</fg>  ',
       500  => '<fg:yellow>%s</fg>  ',
-      INF  => '<fg:red>%s</fg>  ',
     );
 
+    $least_acceptable = '<fg:red>%s</fg>  ';
+
     $milliseconds = $seconds * 1000;
     $duration = $this->formatTime($seconds);
     foreach ($acceptableness as $upper_bound => $formatting) {
@@ -75,7 +76,8 @@
         return phutil_console_format($formatting, $duration);
       }
     }
-    return phutil_console_format(end($acceptableness), $duration);
+
+    return phutil_console_format($least_acceptable, $duration);
   }
 
   private function formatTime($seconds) {
diff --git a/src/utils/PhutilArray.php b/src/utils/PhutilArray.php
--- a/src/utils/PhutilArray.php
+++ b/src/utils/PhutilArray.php
@@ -29,6 +29,7 @@
 /* -(  Countable Interface  )------------------------------------------------ */
 
 
+  #[\ReturnTypeWillChange]
   public function count() {
     return count($this->data);
   }
@@ -37,22 +38,27 @@
 /* -(  Iterator Interface  )------------------------------------------------- */
 
 
+  #[\ReturnTypeWillChange]
   public function current() {
     return current($this->data);
   }
 
+  #[\ReturnTypeWillChange]
   public function key() {
     return key($this->data);
   }
 
+  #[\ReturnTypeWillChange]
   public function next() {
     return next($this->data);
   }
 
+  #[\ReturnTypeWillChange]
   public function rewind() {
     reset($this->data);
   }
 
+  #[\ReturnTypeWillChange]
   public function valid() {
     return (key($this->data) !== null);
   }
@@ -61,18 +67,22 @@
 /* -(  ArrayAccess Interface  )---------------------------------------------- */
 
 
+  #[\ReturnTypeWillChange]
   public function offsetExists($key) {
     return array_key_exists($key, $this->data);
   }
 
+  #[\ReturnTypeWillChange]
   public function offsetGet($key) {
     return $this->data[$key];
   }
 
+  #[\ReturnTypeWillChange]
   public function offsetSet($key, $value) {
     $this->data[$key] = $value;
   }
 
+  #[\ReturnTypeWillChange]
   public function offsetUnset($key) {
     unset($this->data[$key]);
   }
diff --git a/src/utils/PhutilCallbackFilterIterator.php b/src/utils/PhutilCallbackFilterIterator.php
--- a/src/utils/PhutilCallbackFilterIterator.php
+++ b/src/utils/PhutilCallbackFilterIterator.php
@@ -18,6 +18,7 @@
     $this->callback = $callback;
   }
 
+  #[\ReturnTypeWillChange]
   public function accept() {
     return call_user_func($this->callback, $this->current());
   }
diff --git a/src/workflow/ArcanistDiffWorkflow.php b/src/workflow/ArcanistDiffWorkflow.php
--- a/src/workflow/ArcanistDiffWorkflow.php
+++ b/src/workflow/ArcanistDiffWorkflow.php
@@ -701,7 +701,7 @@
       $this->revisionID = $revision_id;
 
       $revision['message'] = $this->getArgument('message');
-      if (!strlen($revision['message'])) {
+      if ($revision['message'] === null) {
         $update_messages = $this->readScratchJSONFile('update-messages.json');
 
         $update_messages[$revision_id] = $this->getUpdateMessage(
@@ -1740,9 +1740,12 @@
     if ($template == '') {
       $comments = $this->getDefaultUpdateMessage();
 
+      $comments = phutil_string_cast($comments);
+      $comments = rtrim($comments);
+
       $template = sprintf(
         "%s\n\n# %s\n#\n# %s\n# %s\n#\n# %s\n#  $ %s\n\n",
-        rtrim($comments),
+        $comments,
         pht(
           'Updating %s: %s',
           "D{$fields['revisionID']}",
@@ -2360,7 +2363,7 @@
     if (strlen($branch)) {
       $upstream_path = $api->getPathToUpstream($branch);
       $remote_branch = $upstream_path->getRemoteBranchName();
-      if (strlen($remote_branch)) {
+      if ($remote_branch !== null) {
         return array(
           array(
             'type' => 'branch',
@@ -2374,7 +2377,7 @@
     // If "arc.land.onto.default" is configured, use that.
     $config_key = 'arc.land.onto.default';
     $onto = $this->getConfigFromAnySource($config_key);
-    if (strlen($onto)) {
+    if ($onto !== null) {
       return array(
         array(
           'type' => 'branch',
diff --git a/src/workflow/ArcanistWorkflow.php b/src/workflow/ArcanistWorkflow.php
--- a/src/workflow/ArcanistWorkflow.php
+++ b/src/workflow/ArcanistWorkflow.php
@@ -154,7 +154,7 @@
       }
 
       $help = $information->getHelp();
-      if (strlen($help)) {
+      if ($help !== null) {
         // Unwrap linebreaks in the help text so we don't get weird formatting.
         $help = preg_replace("/(?<=\S)\n(?=\S)/", ' ', $help);
 
diff --git a/support/lib/extract-symbols.php b/support/lib/extract-symbols.php
--- a/support/lib/extract-symbols.php
+++ b/support/lib/extract-symbols.php
@@ -219,7 +219,13 @@
     $symbol = array_shift($params);
     $type = 'function';
     $symbol_value = $symbol->getStringLiteralValue();
-    $pos = strpos($symbol_value, '::');
+
+    if ($symbol_value !== null) {
+      $pos = strpos($symbol_value, '::');
+    } else {
+      $pos = false;
+    }
+
     if ($pos) {
       $type = 'class';
       $symbol_value = substr($symbol_value, 0, $pos);