Help Mercurial build a parse trees with a few hundred items

Summary: Ref T5896. See that task and inline for a description.

Test Plan:
  - Ran `bin/repository refs HGTESTX --trace`, saw sensible commands and a reasonable result.
  - Faked the heads, set chunk size to 2, got this correct output from the algorithm:

> (((((((((1 or 2) or (3 or 4)) or ((5 or 6) or (7 or 8))) or (((9 or 10) or (11 or 12)) or ((13 or 14) or (15 or 16)))) or ((((17 or 18) or (19 or 20)) or ((21 or 22) or (23 or 24))) or (((25 or 26) or (27 or 28)) or ((29 or 30) or (31 or 32))))) or (((((33 or 34) or (35 or 36)) or ((37 or 38) or (39 or 40))) or (((41 or 42) or (43 or 44)) or ((45 or 46) or (47 or 48)))) or ((((49 or 50) or (51 or 52)) or ((53 or 54) or (55 or 56))) or (((57 or 58) or (59 or 60)) or ((61 or 62) or (63 or 64)))))) or ((((((65 or 66) or (67 or 68)) or ((69 or 70) or (71 or 72))) or (((73 or 74) or (75 or 76)) or ((77 or 78) or (79 or 80)))) or ((((81 or 82) or (83 or 84)) or ((85 or 86) or (87 or 88))) or (((89 or 90) or (91 or 92)) or ((93 or 94) or (95 or 96))))) or (((((97 or 98) or (99 or 100)) or ((101 or 102) or (103 or 104))) or (((105 or 106) or (107 or 108)) or ((109 or 110) or (111 or 112)))) or ((((113 or 114) or (115 or 116)) or ((117 or 118) or (119 or 120))) or (((121 or 122) or (123 or 124)) or ((125 or 126) or (127 or 128))))))) or (((((((129 or 130) or (131 or 132)) or ((133 or 134) or (135 or 136))) or (((137 or 138) or (139 or 140)) or ((141 or 142) or (143 or 144)))) or ((((145 or 146) or (147 or 148)) or ((149 or 150) or (151 or 152))) or (((153 or 154) or (155 or 156)) or ((157 or 158) or (159 or 160))))) or (((((161 or 162) or (163 or 164)) or ((165 or 166) or (167 or 168))) or (((169 or 170) or (171 or 172)) or ((173 or 174) or (175 or 176)))) or ((((177 or 178) or (179 or 180)) or ((181 or 182) or (183 or 184))) or (((185 or 186) or (187 or 188)) or ((189 or 190) or (191 or 192)))))) or ((((((193 or 194) or (195 or 196)) or ((197 or 198) or (199 or 200))) or (((201 or 202) or (203 or 204)) or ((205 or 206) or (207 or 208)))) or ((((209 or 210) or (211 or 212)) or ((213 or 214) or (215 or 216))) or (((217 or 218) or (219 or 220)) or ((221 or 222) or (223 or 224))))) or (((((225 or 226) or (227 or 228)) or ((229 or 230) or (231 or 232))) or (((233 or 234) or (235 or 236)) or ((237 or 238) or (239 or 240)))) or ((((241 or 242) or (243 or 244)) or ((245 or 246) or (247 or 248))) or (((249 or 250) or (251 or 252)) or ((253 or 254) or (255 or 256)))))))) or ((((((((257 or 258) or (259 or 260)) or ((261 or 262) or (263 or 264))) or (((265 or 266) or (267 or 268)) or ((269 or 270) or (271 or 272)))) or ((((273 or 274) or (275 or 276)) or ((277 or 278) or (279 or 280))) or (((281 or 282) or (283 or 284)) or ((285 or 286) or (287 or 288))))) or (((((289 or 290) or (291 or 292)) or ((293 or 294) or (295 or 296))) or (((297 or 298) or (299 or 300)) or ((301 or 302) or (303 or 304)))) or ((((305 or 306) or (307 or 308)) or ((309 or 310) or (311 or 312))) or (((313 or 314) or (315 or 316)) or ((317 or 318) or (319 or 320)))))) or ((((((321 or 322) or (323 or 324)) or ((325 or 326) or (327 or 328))) or (((329 or 330) or (331 or 332)) or ((333 or 334) or (335 or 336)))) or ((((337 or 338) or (339 or 340)) or ((341 or 342) or (343 or 344))) or (((345 or 346) or (347 or 348)) or ((349 or 350) or (351 or 352))))) or (((((353 or 354) or (355 or 356)) or ((357 or 358) or (359 or 360))) or (((361 or 362) or (363 or 364)) or ((365 or 366) or (367 or 368)))) or ((((369 or 370) or (371 or 372)) or ((373 or 374) or (375 or 376))) or (((377 or 378) or (379 or 380)) or ((381 or 382) or (383 or 384))))))) or (((((((385 or 386) or (387 or 388)) or ((389 or 390) or (391 or 392))) or (((393 or 394) or (395 or 396)) or ((397 or 398) or (399 or 400)))) or ((((401 or 402) or (403 or 404)) or ((405 or 406) or (407 or 408))) or (((409 or 410) or (411 or 412)) or ((413 or 414) or (415 or 416))))) or (((((417 or 418) or (419 or 420)) or ((421 or 422) or (423 or 424))) or (((425 or 426) or (427 or 428)) or ((429 or 430) or (431 or 432)))) or ((((433 or 434) or (435 or 436)) or ((437 or 438) or (439 or 440))) or (((441 or 442) or (443 or 444)) or ((445 or 446) or (447 or 448)))))) or ((((((449 or 450) or (451 or 452)) or ((453 or 454) or (455 or 456))) or (((457 or 458) or (459 or 460)) or ((461 or 462) or (463 or 464)))) or ((((465 or 466) or (467 or 468)) or ((469 or 470) or (471 or 472))) or (((473 or 474) or (475 or 476)) or ((477 or 478) or (479 or 480))))) or (((((481 or 482) or (483 or 484)) or ((485 or 486) or (487 or 488))) or (((489 or 490) or (491 or 492)) or ((493 or 494) or (495 or 496)))) or ((((497 or 498) or (499 or 500)) or ((501 or 502) or (503 or 504))) or (((505 or 506) or (507 or 508)) or ((509 or 510) or (511 or 512)))))))))

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: chad, epriestley

Maniphest Tasks: T5896

Differential Revision: https://secure.phabricator.com/D12549

src/applications/repository/engine/PhabricatorRepositoryRefEngine.php

@@ -262,15 +262,36 @@ final class PhabricatorRepositoryRefEngine
     switch ($vcs) {
       case PhabricatorRepositoryType::REPOSITORY_TYPE_MERCURIAL:
         if ($all_closing_heads) {
-          $escheads = array();
+          $parts = array();
           foreach ($all_closing_heads as $head) {
-            $escheads[] = hgsprintf('%s', $head);
+            $parts[] = hgsprintf('%s', $head);
           }
-          $escheads = implode(' or ', $escheads);
+
+          // See T5896. Mercurial can not parse an "X or Y or ..." rev list
+          // with more than about 300 items, because it exceeds the maximum
+          // allowed recursion depth. Split all the heads into chunks of
+          // 256, and build a query like this:
+          //
+          //   ((1 or 2 or ... or 255) or (256 or 257 or ... 511))
+          //
+          // If we have more than 65535 heads, we'll do that again:
+          //
+          //   (((1 or ...) or ...) or ((65536 or ...) or ...))
+
+          $chunk_size = 256;
+          while (count($parts) > $chunk_size) {
+            $chunks = array_chunk($parts, $chunk_size);
+            foreach ($chunks as $key => $chunk) {
+              $chunks[$key] = '('.implode(' or ', $chunk).')';
+            }
+            $parts = array_values($chunks);
+          }
+          $parts = '('.implode(' or ', $parts).')';
+
           list($stdout) = $this->getRepository()->execxLocalCommand(
             'log --template %s --rev %s',
             '{node}\n',
-            hgsprintf('%s', $new_head).' - ('.$escheads.')');
+            hgsprintf('%s', $new_head).' - '.$parts);
         } else {
           list($stdout) = $this->getRepository()->execxLocalCommand(
             'log --template %s --rev %s',