Update ArcanistMercurialAPI to support getting the current commit ref

Summary:
Mercurial does not have an implementation for querying commit symbol hardpoints, which is what the "arc amend" workflow uses.

This provides an implementation for Mercurial as well as updating `ArcanistMercurialAPI` to specify the current working directory symbol as `.`.

Additionally removed an erroneous early return in `ArcanistAmendWorkflow` which prevents a check against uncommitted changes.

Fixes T13665

Test Plan:
1. I created a diff on a Mercurial revision.
2. I updated the revisions summary in phabricator.
3. I ran `arc amend` and it successfully amended the local commit with the updated commit message.
4. I modified a file in the repository and left the change uncommitted.
5. I ran `arc amend` and verified that it reported an error due to uncommited commits.

I ran the following commands to verify that they resolved to the correct commits
1. `arc inspect --explore -- 'commit(674492bb460)'` properly matched the right commit as a commit hash prefix
2. `arc inspect --explore -- 'commit(674492bb4606666d5321feb38d2a467a8733c786)'` properly matched the right commit as a full commit hash
3. `arc inspect --explore -- 'commit(master)'` properly matched the right commit as a bookmark
4. `arc inspect --explore -- 'commit(tip)'` properly matched the right commit as a tag
5. `arc inspect --explore -- 'commit(.)'` properly matched the right commit as the working directory
6. `arc inspect --explore -- 'commit(cafe)'` properly matched the right commit as a commit hash prefix
7. I created a 'cafe' bookmark on a changeset
8. `arc inspect --explore -- 'commit(cafe)'` properly matched the right commit as a bookmark
9. `arc inspect --explore -- 'commit(67449)'` properly matched the right commit as a revision number
10. `arc inspect --explore -- 'commit(2147483648)'` properly did not match any revision (no python exception)
11. `arc inspect --explore -- 'commit(0)'` properly matched the first commit

Reviewers: #blessed_reviewers, epriestley

Reviewed By: #blessed_reviewers, epriestley

Subscribers: Korvin, epriestley

Maniphest Tasks: T13665

Differential Revision: https://secure.phabricator.com/D21716

src/__phutil_library_map__.php

@@ -346,6 +346,7 @@ phutil_register_library_map(array(
     'ArcanistMercurialAPI' => 'repository/api/ArcanistMercurialAPI.php',
     'ArcanistMercurialCommitGraphQuery' => 'repository/graph/query/ArcanistMercurialCommitGraphQuery.php',
     'ArcanistMercurialCommitMessageHardpointQuery' => 'query/ArcanistMercurialCommitMessageHardpointQuery.php',
+    'ArcanistMercurialCommitSymbolCommitHardpointQuery' => 'ref/commit/ArcanistMercurialCommitSymbolCommitHardpointQuery.php',
     'ArcanistMercurialLandEngine' => 'land/engine/ArcanistMercurialLandEngine.php',
     'ArcanistMercurialLocalState' => 'repository/state/ArcanistMercurialLocalState.php',
     'ArcanistMercurialParser' => 'repository/parser/ArcanistMercurialParser.php',
@@ -1404,6 +1405,7 @@ phutil_register_library_map(array(
     'ArcanistMercurialAPI' => 'ArcanistRepositoryAPI',
     'ArcanistMercurialCommitGraphQuery' => 'ArcanistCommitGraphQuery',
     'ArcanistMercurialCommitMessageHardpointQuery' => 'ArcanistWorkflowMercurialHardpointQuery',
+    'ArcanistMercurialCommitSymbolCommitHardpointQuery' => 'ArcanistWorkflowMercurialHardpointQuery',
     'ArcanistMercurialLandEngine' => 'ArcanistLandEngine',
     'ArcanistMercurialLocalState' => 'ArcanistRepositoryLocalState',
     'ArcanistMercurialParser' => 'Phobject',

src/ref/commit/ArcanistMercurialCommitSymbolCommitHardpointQuery.php

@@ -0,0 +1,204 @@
+<?php
+
+final class ArcanistMercurialCommitSymbolCommitHardpointQuery
+  extends ArcanistWorkflowMercurialHardpointQuery {
+
+  public function getHardpoints() {
+    return array(
+      ArcanistCommitSymbolRef::HARDPOINT_OBJECT,
+    );
+  }
+
+  protected function canLoadRef(ArcanistRef $ref) {
+    return ($ref instanceof ArcanistCommitSymbolRef);
+  }
+
+  public function loadHardpoint(array $refs, $hardpoint) {
+    $symbol_map = array();
+    foreach ($refs as $key => $ref) {
+      $symbol_map[$key] = $ref->getSymbol();
+    }
+
+    $symbol_set = array_fuse($symbol_map);
+    foreach ($symbol_set as $symbol) {
+      $this->validateSymbol($symbol);
+    }
+
+    $api = $this->getRepositoryAPI();
+
+    // Using "hg log" with repeated "--rev arguments will have the following
+    // behaviors which need accounted for:
+    // 1. If any one revision is invalid then the entire command will fail. To
+    //    work around this the revset uses a trick where specifying a pattern
+    //    for the bookmark() or tag() predicates instead of a literal won't
+    //    result in failure if the pattern isn't found.
+    // 2. Multiple markers that resolve to the same node will only be included
+    //    once in the output. Because of this the order of output can't be
+    //    relied upon to match up with the requested symbol. To work around
+    //    this, the template used must also output any associated symbols to
+    //    match back to. Because of this there is no reasonable way to resolve
+    //    symbols with Mercurial-supported modifiers such as 'symbol^'.
+    // 3. The working directory can't be identified directly, instead a special
+    //    template conditional is used to include 'CWD' as the second item in
+    //    the output if the node is also the working directory, or 'NOTCWD'
+    //    otherwise. This needs included before the tags/bookmarks in order to
+    //    distinguish it from some repository using that same name for a tag or
+    //    bookmark.
+
+    $pattern = array();
+    $arguments = array();
+
+    $pattern[] = 'log';
+
+    $pattern[] = '--template %s';
+    $arguments[] = "{rev}\1".
+                   "{node}\1".
+                   "{ifcontains(rev, revset('parents()'), 'CWD', 'NOTCWD')}\1".
+                   "{tags % '{tag}\2'}{bookmarks % '{bookmark}\2'}\3";
+
+    foreach ($symbol_set as $symbol) {
+      // This is the one symbol that wouldn't be a bookmark or tag
+      if ($symbol === '.') {
+        $pattern[] = '--rev .';
+        continue;
+      }
+
+      $predicates = array();
+
+      if (ctype_xdigit($symbol)) {
+        // Commit hashes are 40 characters
+        if (strlen($symbol) <= 40) {
+          $predicates[] = hgsprintf('id("%s")', $symbol);
+        }
+      }
+
+      if (ctype_digit($symbol)) {
+        // This is 2^32-1 which is (typically) the maximum size of an int in
+        // Python -- passing anything higher than this to rev() will result
+        // in a Python exception.
+        if ($symbol <= 2147483647) {
+          $predicates[] = hgsprintf('rev("%s")', $symbol);
+        }
+      } else {
+        // Mercurial disallows using numbers as marker names.
+        $re_symbol = preg_quote($symbol);
+        $predicates[] = hgsprintf('bookmark("re:^%s$")', $re_symbol);
+        $predicates[] = hgsprintf('tag("re:^%s$")', $re_symbol);
+      }
+
+      $pattern[] = '--rev %s';
+      $arguments[] = implode(' or ', $predicates);
+    }
+
+    $pattern = implode(' ', $pattern);
+    array_unshift($arguments, $pattern);
+
+    $future = call_user_func_array(
+      array($api, 'newFuture'),
+      $arguments);
+
+    list($stdout) = (yield $this->yieldFuture($future));
+
+    $lines = explode("\3", $stdout);
+
+    $hash_map = array();
+    $node_list = array();
+
+    foreach ($lines as $line) {
+      $parts = explode("\1", $line, 4);
+
+      if (empty(array_filter($parts))) {
+        continue;
+      } else if (count($parts) === 3) {
+        list($rev, $node, $cwd) = $parts;
+        $markers = array();
+      } else if (count($parts) === 4) {
+        list($rev, $node, $cwd, $markers) = $parts;
+        $markers = array_filter(explode("\2", $markers));
+      } else {
+        throw new Exception(
+          pht('Execution of "hg log" emitted an unexpected line ("%s").',
+            $line));
+      }
+
+      $node_list[] = $node;
+
+      if (in_array($rev, $symbol_set)) {
+        if (!isset($hash_map[$rev])) {
+          $hash_map[$rev] = $node;
+        } else if ($hash_map[$rev] !== $node) {
+          $hash_map[$rev] = '';
+        }
+      }
+
+      foreach ($markers as $marker) {
+        if (!isset($hash_map[$marker])) {
+          $hash_map[$marker] = $node;
+        } else if ($hash_map[$marker] !== $node) {
+          $hash_map[$marker] = '';
+        }
+      }
+
+      // The log template will mark the working directory node with 'CWD' which
+      // we insert for the special marker '.' for the working directory, used
+      // by ArcanistMercurialAPI::newCurrentCommitSymbol().
+      if ($cwd === 'CWD') {
+        if (!isset($hash_map['.'])) {
+          $hash_map['.'] = $node;
+        } else if ($hash_map['.'] !== $node) {
+          $hash_map['.'] = '';
+        }
+      }
+    }
+
+    // Changeset hashes can be prefixes but also collide with other markers.
+    // Consider 'cafe' which could be a bookmark or also a changeset hash
+    // prefix. Mercurial will always allow markers to take precedence over
+    // changeset hashes when resolving, so only populate symbols that match
+    // hashes after all other entries are populated, to avoid the hash taing
+    // a spot which a marker might match.
+    foreach ($node_list as $node) {
+      foreach ($symbol_set as $symbol) {
+        if (str_starts_with($node, $symbol)) {
+          if (!isset($hash_map[$symbol])) {
+            $hash_map[$symbol] = $node;
+          }
+        }
+      }
+    }
+
+    // Remove entries resulting in collisions, which set empty string values
+    $hash_map = array_filter($hash_map);
+
+    $results = array();
+    foreach ($symbol_map as $key => $symbol) {
+      if (isset($hash_map[$symbol])) {
+        $results[$key] = $hash_map[$symbol];
+      }
+    }
+
+    foreach ($results as $key => $result) {
+      if ($result === null) {
+        continue;
+      }
+
+      $ref = id(new ArcanistCommitRef())
+        ->setCommitHash($result);
+
+      $results[$key] = $ref;
+    }
+
+    yield $this->yieldMap($results);
+  }
+
+  private function validateSymbol($symbol) {
+    if (strpos($symbol, "\n") !== false) {
+      throw new Exception(
+        pht(
+          'Commit symbol "%s" contains a newline. This is not a valid '.
+          'character in a Mercurial commit symbol.',
+          addcslashes($symbol, "\\\n")));
+    }
+  }
+
+}

src/repository/api/ArcanistMercurialAPI.php

@@ -454,6 +454,10 @@ final class ArcanistMercurialAPI extends ArcanistRepositoryAPI {
     }
   }
 
+  protected function newCurrentCommitSymbol() {
+    return $this->getWorkingCopyRevision();
+  }
+
   public function getWorkingCopyRevision() {
     return '.';
   }

src/workflow/ArcanistAmendWorkflow.php

@@ -164,8 +164,6 @@ EOTEXT
         ->execute();
     }
 
-    return;
-
     if ($api->getUncommittedChanges()) {
       // TODO: Make this class of error show the uncommitted changes.