diff --git a/src/toolset/workflow/ArcanistShellCompleteWorkflow.php b/src/toolset/workflow/ArcanistShellCompleteWorkflow.php
index fa87d5ad..b3e7b2fa 100644
--- a/src/toolset/workflow/ArcanistShellCompleteWorkflow.php
+++ b/src/toolset/workflow/ArcanistShellCompleteWorkflow.php
@@ -1,623 +1,638 @@
 <?php
 
 final class ArcanistShellCompleteWorkflow
   extends ArcanistWorkflow {
 
   public function getWorkflowName() {
     return 'shell-complete';
   }
 
   public function getWorkflowInformation() {
     $help = pht(<<<EOTEXT
 Install shell completion so you can use the "tab" key to autocomplete
 commands and flags in your shell for Arcanist toolsets and workflows.
 
 The **bash** shell is supported.
 
 **Installing Completion**
 
 To install shell completion, run the command:
 
   $ arc shell-complete
 
 This will install shell completion into your current shell. After installing,
 you may need to start a new shell (or open a new terminal window) to pick up
 the updated configuration.
 
 Once installed, completion should work across all Arcanist toolsets.
 
 **Using Completion**
 
 After completion is installed, use the "tab" key to automatically complete
 workflows and flags. For example, if you type:
 
   $ arc diff --draf<tab>
 
 ...your shell should automatically expand the flag to:
 
   $ arc diff --draft
 
 **Updating Completion**
 
 To update shell completion, run the same command:
 
   $ arc shell-complete
 
 You can update shell completion without reinstalling it by running:
 
   $ arc shell-complete --generate
 
 You may need to update shell completion if:
 
   - you install new Arcanist toolsets; or
   - you move the Arcanist directory; or
   - you upgrade Arcanist and the new version fixes shell completion bugs.
 EOTEXT
 );
 
     return $this->newWorkflowInformation()
       ->setHelp($help);
   }
 
   public function getWorkflowArguments() {
     return array(
       $this->newWorkflowArgument('current')
         ->setParameter('cursor-position')
         ->setHelp(
           pht(
             'Internal. Current term in the argument list being completed.')),
       $this->newWorkflowArgument('generate')
         ->setHelp(
           pht(
             'Regenerate shell completion rules, without installing any '.
             'configuration.')),
       $this->newWorkflowArgument('shell')
         ->setParameter('shell-name')
         ->setHelp(
           pht(
             'Install completion support for a particular shell.')),
       $this->newWorkflowArgument('argv')
         ->setWildcard(true),
     );
   }
 
   public function runWorkflow() {
     $log = $this->getLogEngine();
 
     $argv = $this->getArgument('argv');
 
     $is_generate = $this->getArgument('generate');
     $is_shell = (bool)strlen($this->getArgument('shell'));
     $is_current = $this->getArgument('current');
 
     if ($argv) {
       $should_install = false;
       $should_generate = false;
 
       if ($is_generate) {
         throw new PhutilArgumentUsageException(
           pht(
             'You can not use "--generate" when completing arguments.'));
       }
 
       if ($is_shell) {
         throw new PhutilArgumentUsageException(
           pht(
             'You can not use "--shell" when completing arguments.'));
       }
 
     } else if ($is_generate) {
       $should_install = false;
       $should_generate = true;
 
       if ($is_current) {
         throw new PhutilArgumentUsageException(
           pht(
             'You can not use "--current" when generating rules.'));
       }
 
       if ($is_shell) {
         throw new PhutilArgumentUsageException(
           pht(
             'The flags "--generate" and "--shell" are mutually exclusive. '.
             'The "--shell" flag selects which shell to install support for, '.
             'but the "--generate" suppresses installation.'));
       }
 
     } else {
       $should_install = true;
       $should_generate = true;
 
       if ($is_current) {
         throw new PhutilArgumentUsageException(
           pht(
             'You can not use "--current" when installing support.'));
       }
     }
 
     if ($should_install) {
       $this->runInstall();
     }
 
     if ($should_generate) {
       $this->runGenerate();
     }
 
     if ($should_install || $should_generate) {
       $log->writeHint(
         pht('NOTE'),
         pht(
           'You may need to open a new terminal window or launch a new shell '.
           'before the changes take effect.'));
       return 0;
     }
 
     $this->runAutocomplete();
   }
 
   private function runInstall() {
     $log = $this->getLogEngine();
 
     $shells = array(
       array(
         'key' => 'bash',
         'path' => '/bin/bash',
         'file' => '.profile',
         'source' => 'hooks/bash-completion.sh',
       ),
     );
     $shells = ipull($shells, null, 'key');
 
     $shell = $this->getArgument('shell');
     if (!$shell) {
       $shell = $this->detectShell($shells);
     } else {
       $shell = $this->selectShell($shells, $shell);
     }
 
     $spec = $shells[$shell];
     $file = $spec['file'];
     $home = getenv('HOME');
 
     if (!strlen($home)) {
       throw new PhutilArgumentUsageException(
         pht(
           'The "HOME" environment variable is not defined, so this workflow '.
           'can not identify where to install shell completion.'));
     }
 
     $file_path = getenv('HOME').'/'.$file;
     $file_display = '~/'.$file;
 
     if (Filesystem::pathExists($file_path)) {
       $file_path = Filesystem::resolvePath($file_path);
       $data = Filesystem::readFile($file_path);
       $is_new = false;
     } else {
       $data = '';
       $is_new = true;
     }
 
     $line = csprintf(
       'source %R # arcanist-shell-complete',
       $this->getShellPath($spec['source']));
 
     $matches = null;
     $replace = preg_match(
       '/(\s*\n)?[^\n]+# arcanist-shell-complete\s*(\n\s*)?/',
       $data,
       $matches,
       PREG_OFFSET_CAPTURE);
 
     $log->writeSuccess(
       pht('INSTALL'),
       pht('Installing shell completion support for "%s".', $shell));
 
     if ($replace) {
       $replace_pos = $matches[0][1];
       $replace_line = $matches[0][0];
       $replace_len = strlen($replace_line);
       $replace_display = trim($replace_line);
 
       if ($replace_pos === 0) {
         $new_line = $line."\n";
       } else {
         $new_line = "\n\n".$line."\n";
       }
 
       $new_data = substr_replace($data, $new_line, $replace_pos, $replace_len);
 
       if ($new_data === $data) {
         // If we aren't changing anything in the file, just skip the write
         // completely.
         $needs_write = false;
 
         $log->writeStatus(
           pht('SKIP'),
           pht('Shell completion for "%s" is already installed.', $shell));
 
         return;
       }
 
       echo tsprintf(
         "%s\n\n    %s\n\n%s\n\n    %s\n",
         pht(
           'To update shell completion support for "%s", your existing '.
           '"%s" file will be modified. This line will be removed:',
           $shell,
           $file_display),
         $replace_display,
         pht('This line will be added:'),
         $line);
 
       $prompt = pht('Rewrite this file?');
     } else {
       if ($is_new) {
         $new_data = $line."\n";
 
         echo tsprintf(
           "%s\n\n    %s\n",
           pht(
             'To install shell completion support for "%s", a new "%s" file '.
             'will be created with this content:',
             $shell,
             $file_display),
           $line);
 
         $prompt = pht('Create this file?');
       } else {
         $new_data = rtrim($data)."\n\n".$line."\n";
 
         echo tsprintf(
           "%s\n\n     %s\n",
           pht(
             'To install shell completion support for "%s", this line will be '.
             'added to your existing "%s" file:',
             $shell,
             $file_display),
           $line);
 
         $prompt = pht('Append to this file?');
       }
     }
 
     // TOOLSETS: Generalize prompting.
 
     if (!phutil_console_confirm($prompt, false)) {
       throw new PhutilArgumentUsageException(pht('Aborted.'));
     }
 
     Filesystem::writeFile($file_path, $new_data);
 
     $log->writeSuccess(
       pht('INSTALLED'),
       pht(
         'Installed shell completion support for "%s" to "%s".',
         $shell,
         $file_display));
   }
 
   private function selectShell(array $shells, $shell_arg) {
     foreach ($shells as $shell) {
       if ($shell['key'] === $shell_arg) {
         return $shell_arg;
       }
     }
 
     throw new PhutilArgumentUsageException(
       pht(
         'The shell "%s" is not supported. Supported shells are: %s.',
         $shell_arg,
         implode(', ', ipull($shells, 'key'))));
   }
 
   private function detectShell(array $shells) {
     // NOTE: The "BASH_VERSION" and "ZSH_VERSION" shell variables are not
     // passed to subprocesses, so we can't inspect them to figure out which
     // shell launched us. If we could figure this out in some other way, it
     // would be nice to do so.
 
     // Instead, just look at "SHELL" (the user's startup shell).
 
     $log = $this->getLogEngine();
 
     $detected = array();
     $log->writeStatus(
       pht('DETECT'),
       pht('Detecting current shell...'));
 
     $shell_env = getenv('SHELL');
     if (!strlen($shell_env)) {
       $log->writeWarning(
         pht('SHELL'),
         pht(
           'The "SHELL" environment variable is not defined, so it can '.
           'not be used to detect the shell to install rules for.'));
     } else {
       $found = false;
       foreach ($shells as $shell) {
         if ($shell['path'] !== $shell_env) {
           continue;
         }
 
         $found = true;
         $detected[] = $shell['key'];
 
         $log->writeSuccess(
           pht('SHELL'),
           pht(
             'The "SHELL" environment variable has value "%s", so the '.
             'target shell was detected as "%s".',
             $shell_env,
             $shell['key']));
       }
 
       if (!$found) {
         $log->writeStatus(
           pht('SHELL'),
           pht(
             'The "SHELL" environment variable does not match any recognized '.
             'shell.'));
       }
     }
 
     if (!$detected) {
       throw new PhutilArgumentUsageException(
         pht(
           'Unable to detect any supported shell, so autocompletion rules '.
           'can not be installed. Use "--shell" to select a shell.'));
     } else if (count($detected) > 1) {
       throw new PhutilArgumentUsageException(
         pht(
           'Multiple supported shells were detected. Unable to determine '.
           'which shell to install autocompletion rules for. Use "--shell" '.
           'to select a shell.'));
     }
 
     return head($detected);
   }
 
   private function runGenerate() {
     $log = $this->getLogEngine();
 
     $toolsets = ArcanistToolset::newToolsetMap();
 
     $log->writeStatus(
       pht('GENERATE'),
       pht('Generating shell completion rules...'));
 
     $shells = array('bash');
     foreach ($shells as $shell) {
 
       $rules = array();
       foreach ($toolsets as $toolset) {
         $rules[] = $this->newCompletionRules($toolset, $shell);
       }
       $rules = implode("\n", $rules);
 
       $rules_path = $this->getShellPath('rules/'.$shell.'-rules.sh');
 
       // If a write wouldn't change anything, skip the write. This allows
       // "arc shell-complete" to work if "arcanist/" is on a read-only NFS
       // filesystem or something unusual like that.
 
       $skip_write = false;
       if (Filesystem::pathExists($rules_path)) {
         $current = Filesystem::readFile($rules_path);
         if ($current === $rules) {
           $skip_write = true;
         }
       }
 
       if ($skip_write) {
         $log->writeStatus(
           pht('SKIP'),
           pht(
             'Rules are already up to date for "%s" in: %s',
             $shell,
             Filesystem::readablePath($rules_path)));
       } else {
         Filesystem::writeFile($rules_path, $rules);
         $log->writeStatus(
           pht('RULES'),
           pht(
             'Wrote updated completion rules for "%s" to: %s.',
             $shell,
             Filesystem::readablePath($rules_path)));
       }
     }
   }
 
   private function newCompletionRules(ArcanistToolset $toolset, $shell) {
     $template_path = $this->getShellPath('templates/'.$shell.'-template.sh');
     $template = Filesystem::readFile($template_path);
 
     $variables = array(
       'BIN' => $toolset->getToolsetKey(),
     );
 
     foreach ($variables as $key => $value) {
       $template = str_replace('{{{'.$key.'}}}', $value, $template);
     }
 
     return $template;
   }
 
   private function getShellPath($to_file = null) {
     $arc_root = dirname(phutil_get_library_root('arcanist'));
     return $arc_root.'/support/shell/'.$to_file;
   }
 
   private function runAutocomplete() {
     $argv = $this->getArgument('argv');
     $argc = count($argv);
 
     $pos = $this->getArgument('current');
     if (!$pos) {
       $pos = $argc - 1;
     }
 
     if ($pos > $argc) {
       throw new ArcanistUsageException(
         pht(
           'Argument position specified with "--current" ("%s") is greater '.
           'than the number of arguments provided ("%s").',
           new PhutilNumber($pos),
           new PhutilNumber($argc)));
     }
 
     $workflows = $this->getRuntime()->getWorkflows();
 
     // NOTE: This isn't quite right. For example, "arc --con<tab>" will
     // try to autocomplete workflows named "--con", but it should actually
     // autocomplete global flags and suggest "--config".
 
     $is_workflow = ($pos <= 1);
 
     if ($is_workflow) {
       // NOTE: There was previously some logic to try to filter impossible
       // workflows out of the completion list based on the VCS in the current
       // working directory: for example, if you're in an SVN working directory,
       // "arc a" is unlikely to complete to "arc amend" because "amend" does
       // not support SVN. It's not clear this logic is valuable, but we could
       // consider restoring it if good use cases arise.
 
       // TOOLSETS: Restore the ability for workflows to opt out of shell
       // completion. It is exceptionally unlikely that users want to shell
       // complete obscure or internal workflows, like "arc shell-complete"
       // itself. Perhaps a good behavior would be to offer these as
       // completions if they are the ONLY available completion, since a user
       // who has typed "arc shell-comp<tab>" likely does want "shell-complete".
 
       $complete = array();
       foreach ($workflows as $workflow) {
         $complete[] = $workflow->getWorkflowName();
       }
 
       foreach ($this->getConfig('aliases') as $alias) {
         if ($alias->getException()) {
           continue;
         }
 
         if ($alias->getToolset() !== $this->getToolsetKey()) {
           continue;
         }
 
         $complete[] = $alias->getTrigger();
       }
 
-      // Remove invalid possibilities. For example, if the user has typed
-      // "skun<tab>", it obviously can't complete to "zebra". We don't really
-      // need to do this filtering ourselves: the shell completion will
-      // automatically match things for us even if we emit impossible results.
-      // However, it's a little easier to debug the raw output if we clean it
-      // up here before printing it out.
       $partial = $argv[$pos];
-      foreach ($complete as $key => $candidate) {
-        if (strncmp($partial, $candidate, strlen($partial))) {
-          unset($complete[$key]);
-        }
-      }
+      $complete = $this->getMatches($complete, $partial);
 
       if ($complete) {
         return $this->suggestStrings($complete);
       } else {
         return $this->suggestNothing();
       }
 
     } else {
       // TOOLSETS: We should resolve aliases before picking a workflow, so
       // that if you alias "arc draft" to "arc diff --draft", we can suggest
       // other "diff" flags when you type "arc draft --q<tab>".
 
       // TOOLSETS: It's possible the workflow isn't in position 1. The user
       // may be running "arc --trace diff --dra<tab>", for example.
 
       $workflow = idx($workflows, $argv[1]);
       if (!$workflow) {
         return $this->suggestNothing();
       }
 
       $arguments = $workflow->getWorkflowArguments();
       $arguments = mpull($arguments, null, 'getKey');
+      $current = idx($argv, $pos, '');
 
       $argument = null;
       $prev = idx($argv, $pos - 1, null);
       if (!strncmp($prev, '--', 2)) {
         $prev = substr($prev, 2);
         $argument = idx($arguments, $prev);
       }
 
       // If the last argument was a "--thing" argument, test if "--thing" is
       // a parameterized argument. If it is, the next argument should be a
       // parameter.
 
       if ($argument && strlen($argument->getParameter())) {
         if ($argument->getIsPathArgument()) {
-          return $this->suggestPaths();
+          return $this->suggestPaths($current);
         } else {
           return $this->suggestNothing();
         }
 
         // TOOLSETS: We can allow workflows and arguments to provide a specific
         // list of completeable values, like the "--shell" argument for this
         // workflow.
       }
 
       $flags = array();
       $wildcard = null;
       foreach ($arguments as $argument) {
         if ($argument->getWildcard()) {
           $wildcard = $argument;
           continue;
         }
 
         $flags[] = '--'.$argument->getKey();
       }
 
-      $current = idx($argv, $pos, '');
-      $matches = array();
-      if (strlen($current)) {
-        foreach ($flags as $possible) {
-          if (!strncmp($possible, $current, strlen($current))) {
-            $matches[] = $possible;
-          }
-        }
-      }
+      $matches = $this->getMatches($flags, $current);
 
       // If whatever the user is completing does not match the prefix of any
       // flag, try to autcomplete a wildcard argument if it has some kind of
       // meaningful completion. For example, "arc lint READ<tab>" should
       // autocomplete a file.
 
       if (!$matches && $wildcard) {
 
         // TOOLSETS: There was previously some very questionable support for
         // autocompleting branches here. This could be moved into Arguments
         // and Workflows.
 
         if ($wildcard->getIsPathArgument()) {
-          return $this->suggestPaths();
+          return $this->suggestPaths($current);
         }
       }
 
       return $this->suggestStrings($matches);
     }
   }
 
-  private function suggestPaths() {
-    echo "FILE\n";
+  private function suggestPaths($prefix) {
+    // NOTE: We are returning a directive to the bash script to run "compgen"
+    // for us rather than running it ourselves. If we run:
+    //
+    //   compgen -A file -- %s
+    //
+    // ...from this context, it fails (exits with error code 1 and no output)
+    // if the prefix is "foo\ ", on my machine. See T9116 for some dicussion.
+    echo "<compgen:file>";
     return 0;
   }
 
   private function suggestNothing() {
-    echo "ARGUMENT\n";
-    return 0;
+    return $this->suggestStrings(array());
   }
 
   private function suggestStrings(array $strings) {
-    echo implode(' ', $strings)."\n";
+    sort($strings);
+    echo implode("\n", $strings);
     return 0;
   }
 
+  private function getMatches(array $candidates, $prefix) {
+    $matches = array();
+
+    if (strlen($prefix)) {
+      foreach ($candidates as $possible) {
+        if (!strncmp($possible, $prefix, strlen($prefix))) {
+          $matches[] = $possible;
+        }
+      }
+
+      // If we matched nothing, try a case-insensitive match.
+      if (!$matches) {
+        foreach ($candidates as $possible) {
+          if (!strncasecmp($possible, $prefix, strlen($prefix))) {
+            $matches[] = $possible;
+          }
+        }
+      }
+    } else {
+      $matches = $candidates;
+    }
+
+    return $matches;
+  }
+
 }
diff --git a/support/shell/templates/bash-template.sh b/support/shell/templates/bash-template.sh
index ae622347..e2e8047e 100644
--- a/support/shell/templates/bash-template.sh
+++ b/support/shell/templates/bash-template.sh
@@ -1,23 +1,22 @@
 _arcanist_complete_{{{BIN}}} ()
 {
   COMPREPLY=()
 
-  CUR="${COMP_WORDS[COMP_CWORD]}"
-  OPTS=$(echo | {{{BIN}}} shell-complete --current ${COMP_CWORD} -- ${COMP_WORDS[@]} 2>/dev/null)
+  RESULT=$(echo | {{{BIN}}} shell-complete \
+    --current ${COMP_CWORD} \
+    -- \
+    "${COMP_WORDS[@]}" \
+    2>/dev/null)
 
   if [ $? -ne 0 ]; then
     return $?
   fi
 
-  if [ "$OPTS" = "FILE" ]; then
-    COMPREPLY=( $(compgen -f -- ${CUR}) )
-    return 0
+  if [ "$RESULT" == "<compgen:file>" ]; then
+    RESULT=$( compgen -A file -- ${COMP_WORDS[COMP_CWORD]} )
   fi
 
-  if [ "$OPTS" = "ARGUMENT" ]; then
-    return 0
-  fi
-
-  COMPREPLY=( $(compgen -W "${OPTS}" -- ${CUR}) )
+  local IFS=$'\n'
+  COMPREPLY=( $RESULT )
 }
 complete -F _arcanist_complete_{{{BIN}}} -o filenames {{{BIN}}}