Okay here's an interesting one I came across...
1. Create a revision with changes
2. Modify the local commit to revert the changes, resulting in an empty commit
3. Notably, `arc diff` will report a Usage Exception of "no changes found", and not update the diff
4. However running `arc land` will result in an exception such that the commit is published, the revision throws an error when attempting to view it, and browsing history results in a different type of error. This lands the local change with it being out of sync from the phabricator revision.
```lang=console
$ hg add
$ hg book test
$ hg ci -m "test commit"
$ arc diff
# fill in details
$ hg revert -r test^ --all
$ hg amend
$ arc diff
# Usage Exception
$ arc land test
```
Arcanist (while running `arc land`):
```lang=console
[2021-09-14 21:35:33] EXCEPTION: (CommandException) Command failed with error #255!
COMMAND
hg --encoding utf-8 prune --rev '(fb1b33613c73cf6478efb40c7e2051841f3d87ea::)'
STDOUT
(empty)
STDERR
abort: cannot prune public changesets: fb1b33613c73
(see 'hg help phases' for details)
at [<arcanist>/src/future/exec/ExecFuture.php:421]
arcanist(head=master, ref.master=d246a0656259, custom=2)
#0 ExecFuture::raiseResultError(array) called at [<arcanist>/src/future/exec/ExecFuture.php:325]
#1 ExecFuture::resolvex() called at [<arcanist>/src/repository/api/ArcanistRepositoryAPI.php:399]
#2 ArcanistRepositoryAPI::execxLocal(string, string) called at [<arcanist>/src/land/engine/ArcanistMercurialLandEngine.php:1168]
#3 ArcanistMercurialLandEngine::pruneBranches(array) called at [<arcanist>/src/land/engine/ArcanistLandEngine.php:1304]
#4 ArcanistLandEngine::execute() called at [<arcanist>/src/workflow/ArcanistLandWorkflow.php:344]
#5 ArcanistLandWorkflow::runWorkflow(PhutilArgumentParser) called at [<arcanist>/src/workflow/ArcanistWorkflow.php:227]
#6 ArcanistWorkflow::executeWorkflow(PhutilArgumentParser) called at [<arcanist>/src/toolset/ArcanistPhutilWorkflow.php:21]
#7 ArcanistPhutilWorkflow::execute(PhutilArgumentParser) called at [<arcanist>/src/parser/argument/PhutilArgumentParser.php:492]
#8 PhutilArgumentParser::parseWorkflowsFull(array) called at [<arcanist>/src/runtime/ArcanistRuntime.php:171]
#9 ArcanistRuntime::executeCore(array) called at [<arcanist>/src/runtime/ArcanistRuntime.php:37]
#10 ArcanistRuntime::execute(array) called at [<arcanist>/support/init/init-arcanist.php:6]
#11 require_once(string) called at [<arcanist>/bin/arc:10]
```
Browsing Revision:
```lang=console
2021/09/13 16:48:03 [error] 59551#59551: *285042 FastCGI sent in stderr: "PHP message: [2021-09-13 15:48:03] EXCEPTION: (RuntimeException) min(): Array must contain at least one element at [<arcanist>/src/error/PhutilErrorHandler.php:262]
PHP message: arcanist(head=mim, ref.mim=4f70fcffa8a5), phabricator(head=mim, ref.mim=885d9fc25231, custom=11)
#0 <#2> PhutilErrorHandler::handleError(integer, string, string, integer, array)
called at [<arcanist>/src/error/PhutilErrorHandler.php:262]
#1 <#2> min(array)
called at [<phabricator>/src/infrastructure/diff/engine/PhabricatorInlineCommentAdjustmentEngine.php:146]
#2 <#2> PhabricatorInlineCommentAdjustmentEngine::execute()
called at [<phabricator>/src/applications/differential/engine/DifferentialRevisionTimelineEngine.php:68]
#3 <#2> DifferentialRevisionTimelineEngine::newTimelineView()
called at [<phabricator>/src/applications/transactions/engine/PhabricatorTimelineEngine.php:70]
#4 <#2> PhabricatorTimelineEngine::buildTimelineView()
called at [<phabricator>/src/applications/base/controller/PhabricatorController.php:520]
#5 <#2> PhabricatorController::buildTransactionTimeline(DifferentialRevision, DifferentialTransactionQuery, NULL, array)
called at [<phabricator>/src/applications/differential/controller/DifferentialRevisionViewController.php:1150]
#6 <#2> DifferentialRevisionViewController::buildTransactions(DifferentialRevision, DifferentialDiff, DifferentialDiff, array, array)
called at [<phabricator>/src/applications/differential/controller/DifferentialRevisionViewController.php:353]
#7 <#2> DifferentialRevisionViewController::handleRequest(AphrontRequest)
called at [<phabricator>/src/aphront/configuration/AphrontApplicationConfiguration.php:284]
#8 phlog(RuntimeException)
called at [<phabricator>/src/aphront/handler/PhabricatorDefaultRequestExceptionHandler.php:41]
#9 PhabricatorDefaultRequestExceptionHandler::handleRequestThr
```
Browsing Diffusion (namely, loading a file while the published changeset is head, and trying to Skip past commit):
```lang=console
2021/09/14 12:38:11 [error] 59548#59548: *310503 FastCGI sent in stderr: "PHP message: [2021-09-14 11:38:11] EXCEPTION: (RuntimeException) reset() expects parameter 1 to be array, null given at [<arcanist>/src/error/PhutilErrorHandler.php:262]
PHP message: arcanist(head=mim, ref.mim=4f70fcffa8a5), phabricator(head=mim, ref.mim=885d9fc25231, custom=11)
#0 <#2> PhutilErrorHandler::handleError(integer, string, string, integer, array)
called at [<arcanist>/src/error/PhutilErrorHandler.php:262]
#1 <#2> reset(NULL)
called at [<phabricator>/src/applications/diffusion/query/DiffusionRenameHistoryQuery.php:100]
#2 <#2> DiffusionRenameHistoryQuery::loadCommitSequence(string)
called at [<phabricator>/src/applications/diffusion/query/DiffusionRenameHistoryQuery.php:45]
#3 <#2> DiffusionRenameHistoryQuery::loadOldFilename()
called at [<phabricator>/src/applications/diffusion/controller/DiffusionBrowseController.php:666]
#4 <#2> DiffusionBrowseController::buildBeforeResponse(string)
called at [<phabricator>/src/applications/diffusion/controller/DiffusionBrowseController.php:108]
#5 <#2> DiffusionBrowseController::browseFile()
called at [<phabricator>/src/applications/diffusion/controller/DiffusionBrowseController.php:46]
#6 <#2> DiffusionBrowseController::handleRequest(AphrontRequest)
called at [<phabricator>/src/aphront/configuration/AphrontApplicationConfiguration.php:284]
#7 phlog(RuntimeException)
called at [<phabricator>/src/aphront/handler/PhabricatorDefaultRequestExceptionHandler.php:41]
#8 PhabricatorDefaultRequestExceptionHandler::handleRequestThrowable(AphrontRequest, RuntimeException)
called at [<phabricator>/src/aphront/configuration/AphrontApplicationConfiguration.php:751]
#9 AphrontApplicationConfiguration::handleThrowable(RuntimeException)
called at [<phabricator>/src/aphront/configuration/AphrontApplicationConfiguration.php:296]
#10 AphrontApplicationConfigura
```
Running `./bin/repository reparse` of the commit throws an error that it can't parse an empty diff
```lang=console
[cspeck@repo-testing1]$ ./bin/repository reparse --message --change --publish d132c1b0b602d0a403d74629e120e25b91dade54
[ ] 0.0%[2021-09-14 16:53:19] EXCEPTION: (Exception) Can't parse an empty diff! at [<arcanist>/src/parser/ArcanistDiffParser.php:191]
arcanist(head=mim, ref.mim=4f70fcffa8a5), phabricator(head=mim, ref.mim=885d9fc25231, custom=11)
#0 <#2> ArcanistDiffParser::parseDiff(string) called at [<phabricator>/src/applications/diffusion/herald/HeraldCommitAdapter.php:271]
#1 <#2> HeraldCommitAdapter::loadCommitDiff() called at [<phabricator>/src/applications/diffusion/herald/HeraldCommitAdapter.php:286]
#2 phlog(Exception) called at [<phabricator>/src/applications/diffusion/herald/HeraldCommitAdapter.php:289]
#3 HeraldCommitAdapter::loadDiffContent(string) called at [<phabricator>/src/applications/diffusion/herald/DiffusionCommitDiffContentAddedHeraldField.php:17]
#4 DiffusionCommitDiffContentAddedHeraldField::getHeraldFieldValue(PhabricatorRepositoryCommit) called at [<phabricator>/src/applications/herald/adapter/HeraldAdapter.php:143]
#5 HeraldAdapter::getHeraldField(string) called at [<phabricator>/src/applications/herald/engine/HeraldEngine.php:650]
#6 HeraldEngine::getObjectFieldValue(string) called at [<phabricator>/src/applications/herald/engine/HeraldEngine.php:622]
#7 HeraldEngine::getProfiledObjectFieldValue(HeraldCommitAdapter, string) called at [<phabricator>/src/applications/herald/engine/HeraldEngine.php:506]
#8 HeraldEngine::doesConditionMatch(HeraldRule, HeraldCondition, HeraldCommitAdapter) called at [<phabricator>/src/applications/herald/engine/HeraldEngine.php:421]
#9 HeraldEngine::getRuleMatchResult(HeraldRule, HeraldCommitAdapter) called at [<phabricator>/src/applications/herald/engine/HeraldEngine.php:166]
#10 HeraldEngine::applyRules(array, HeraldCommitAdapter) called at [<phabricator>/src/applications/herald/engine/HeraldEngine.php:52]
#11 HeraldEngine::loadAndApplyRules(HeraldCommitAdapter) called at [<phabricator>/src/applications/transactions/editor/PhabricatorApplicationTransactionEditor.php:3916]
#12 PhabricatorApplicationTransactionEditor::applyHeraldRules(PhabricatorRepositoryCommit, array) called at [<phabricator>/src/applications/transactions/editor/PhabricatorApplicationTransactionEditor.php:1286]
#13 PhabricatorApplicationTransactionEditor::applyTransactions(PhabricatorRepositoryCommit, array) called at [<phabricator>/src/applications/repository/worker/PhabricatorRepositoryCommitPublishWorker.php:124]
#14 PhabricatorRepositoryCommitPublishWorker::applyTransactions(PhabricatorUser, PhabricatorRepository, PhabricatorRepositoryCommit) called at [<phabricator>/src/applications/repository/worker/PhabricatorRepositoryCommitPublishWorker.php:80]
#15 PhabricatorRepositoryCommitPublishWorker::publishCommit(PhabricatorRepository, PhabricatorRepositoryCommit) called at [<phabricator>/src/applications/repository/worker/PhabricatorRepositoryCommitPublishWorker.php:20]
#16 PhabricatorRepositoryCommitPublishWorker::parseCommit(PhabricatorRepository, PhabricatorRepositoryCommit) called at [<phabricator>/src/applications/repository/worker/PhabricatorRepositoryCommitParserWorker.php:72]
#17 PhabricatorRepositoryCommitParserWorker::doWork() called at [<phabricator>/src/infrastructure/daemon/workers/PhabricatorWorker.php:124]
#18 PhabricatorWorker::executeTask() called at [<phabricator>/src/infrastructure/daemon/workers/PhabricatorWorker.php:166]
#19 PhabricatorWorker::scheduleTask(string, array, array) called at [<phabricator>/src/applications/repository/management/PhabricatorRepositoryManagementReparseWorkflow.php:263]
#20 PhabricatorRepositoryManagementReparseWorkflow::execute(PhutilArgumentParser) called at [<arcanist>/src/parser/argument/PhutilArgumentParser.php:492]
#21 PhutilArgumentParser::parseWorkflowsFull(array) called at [<arcanist>/src/parser/argument/PhutilArgumentParser.php:377]
#22 PhutilArgumentParser::parseWorkflows(array) called at [<phabricator>/scripts/repository/manage_repositories.php:22]
```
Versions
|arcanist (client)|`d246a06562593670f62951fed0541e2a894f9788`|(5 Sep 2021)|`master`|
|arcanist (server)|`4f70fcffa8a5`|Jun 5 2021|`stable`|
|phabricator|`885d9fc25231`|Jul 7 2021|This is a branch off of `193798385bd3a7f72dca255e44f8112f4f8fc155` Jun 25 2021 stable branch with a very minor unrelated modification|