Presubmit scripts can perform automated checks on the files in your change and the description of your change, and either fail your attempt to upload or commit, show a warning that you must acknowledge before uploading/committing, or simply show an informational message as part of the output of gcl
.
Generally you want the same tests for upload and committing, but there are exceptions.
Firstly, the commit bot can autofix various problems, so these problems only need to be checked on commit (to check that they have been fixed), not on upload (another good reason to use the commit queue!). Secondly, you can skip slow tests on upload and only run them on commit, if running these every time slows development too much, but this can result in problems only being caught at the last minute, and thus requiring last-minute changes after you think they're good to go.
Bypassing tests
To skip the scripts on upload, use the --bypass-hooks
flag, as in:
git cl upload --bypass-hooks
To skip the scripts on commit, use --bypass-hooks and directly commit your change.
You should only do these if necessary, as the presubmit scripts are there for a reason, but they're not perfect.
If you have trouble with a presubmit script, it's preferable to fix it, rather than simply bypassing it. See depot_tools: sending patches for how to contribute.
Design
When you run gcl upload
or gcl commit
, gcl
will look for all files named PRESUBMIT.py
in folders enclosing the files in your change, up to the repository root.
For each such file, it will load the file into the Python interpreter and then call either the CheckChangeOnUpload
or CheckChangeOnCommit
function depending on whether you are calling [gcl upload] or [gcl commit].
The same applies to git-cl upload
, git-cl dcommit
and git-cl push
.
Please note that presubmit scripts are a best-effort kind of thing; they do not prevent users from submitting without running the scripts, since one can always dcommit, and in fact there is a --bypass-hooks (formerly --no_presubmit
) flag to gcl that skips presubmit checks. Further, since they use the local copy of the PRESUBMIT.py
files, users must sync their repos before the latest presubmit checks will run when they upload or submit.
More subtly, presubmit scripts do not guarantee invariants: even if presubmit scripts pass prior to submission to CQ, once all changes land, the scripts may fail! This is because 2 changes may individually pass the tests, and the patches both apply cleanly together, but the combined change does not pass tests. Since presubmit/precommit scripts run at upload or at start of CQ steps, if two such changes are in the CQ at the same time, they can both pass, both be enqueued, and both land, at which point the tests start failing. A common example is change 1 adding a new test, and change 2 changing existing tests. After they both land, there is a new test in the old style (from change 1), which is out of sync with the new tests (from change 2).
Writing tests
To create a new test, either create a new PRESUBMIT.py script or edit an existing one, adding a new function for your test.
To check your changes, first commit locally (else git-cl
will complain about the dirty tree), then:
To test the upload checks (i.e., to run CheckChangeOnUpload
):
git cl presubmit --upload
To test the submit checks (i.e., to run CheckChangeOnCommit
):
git cl presubmit
The functions must match these method signatures. You do not need to define both functions if you're only interested in one type of event, and if you want to run the same tests in both events, just have them both call a single underlying function:
def CheckChangeOnUpload(input_api, output_api):
pass
def CheckChangeOnCommit(input_api, output_api):
pass
The input_api
parameter is an object through which you can get information about the change. Using the output_api
you can create result objects.
Both CheckChangeOnXXX
functions must return a list or tuple of result objects, or an empty list or tuple if there is nothing to report. The types of result objects you may use are output_api.PresubmitError
(a critical error), output_api.PresubmitPromptWarning
(a warning the user must acknowledge before the command will continue) and output_api.PresubmitNotifyResult
(a message that should be shown). Each takes a message parameter, and optional "items" and "long_text" parameters.
Version 2
Presubmit version 2 reduces some of the overhead of managing which checks are executed on upload and/or submit. To enable presubmit version 2, in the global scope of your presubmit script, define:
PRESUBMIT_VERSION = '2.0.0'
In presubmit version 2, you are not required to use CheckChangeOnUpload
and CheckChangeOnCommit
as your entry points. Any function that begins with the prefix Check
will be executed, receiving input_api
and output_api as its parameters.
CheckXXX
functions that end in Upload
will only be executed on upload and CheckXXX
functions that end in Commit
will only be executed on commit. CheckXXX
functions that do not end in either suffix will be executed at both upload and commit. The format of return values of CheckChangeOnXXX
functions is the same as for CheckChangeOnUpload/
CheckChangeOnCommit
. This makes existing presubmit scripts backwards compatible with presubmit version 2 provided there are no functions in the global scope of the script
that begin with Check
.
InputApi
The input_api
parameter is an object of type presubmit.InputApi
; see class InputApi
in presubmit_support.py
for implementation.
This object can be used to transform from local to repository paths and vice versa, and to get information on the files in the change that are contained in the same directory as your PRESUBMIT.py
file or subdirectories thereof.
The input_api.change
object represents the change itself. Using this object you can retrieve the description of the change, any key-value pairs in the description (e.g. BUG=123), and details on all of the files in the change (not just the ones contained by the directory your PRESUBMIT.py
file resides in).
An input_api.canned_checks
object contains a set of ready-made checks that you can easily add to your presubmit script.
The os/os.path
module is available as input_api.os_path
, so you do not need to import this yourself.
Files in the API are represented by an AffectedFile
object through which you can query the LocalPath()
, ServerPath()
, and the Action()
being performed ('A', 'M' or 'D').
The input_api.is_committing
attribute indicates whether the CL is being committed or just uploaded. This is particularly useful if you wish the same test to be run for both upload and committing, but with different behavior. A common pattern is to prompt a warning on upload, but an error on committing, which allows a CL to be uploaded and reviewed even if the test fails, but not committed (without dcommit). This can be done as follows:
if input_api.is_committing:
message_type = output_api.PresubmitError
else:
message_type = output_api.PresubmitPromptWarning
Caveats
It is possible to run arbitrary Python code in the presubmit scripts. To avoid side effects and hard-to-debug errors, it is safest to run tests in subprocesses. The InputApi object provides various facilities to assist with this; see example below.
Please note that you should not use any functions or attributes on the API objects that begin with an underscore (_) as these are private functions that may change, whereas all public functions will be retained through future versions of the API.
Details and Example
The most detailed documentation for the presubmit API is in its implementation code.
The canned checks are good examples of what you can do with the presubmit API.
An example simple file might be as follows:
def CheckChange(input_api, output_api):
results = []
results += input_api.canned_checks.CheckDoNotSubmit(input_api, output_api)
results += input_api.canned_checks.CheckChangeHasNoTabs(input_api, output_api)
results += input_api.canned_checks.CheckLongLines(input_api, output_api)
# Require a BUG= line and a HOW_TO_TEST= line.
if not input_api.change.BUG or not input_api.change.HOW_TO_TEST:
results += [output_api.PresubmitError(
'Must provide a BUG= line and a HOW_TO_TEST line.')]
return results
def CheckChangeOnUpload(input_api, output_api):
return CheckChange(input_api, output_api)
def CheckChangeOnCommit(input_api, output_api):
return CheckChange(input_api, output_api)
A simple example of a custom command (call from
CheckChangeOnUpload
or
CheckChangeOnCommit
) is:
def MyTest(input_api, output_api):
test_path = input_api.os_path.join(input_api.PresubmitLocalPath(), 'my_test.py')
cmd_name = 'my_test'
if input_api.platform == 'win32':
# Windows needs some help.
cmd = [input_api.python_executable, test_path]
else:
cmd = [test_path]
test_cmd = input_api.Command(
name=cmd_name,
cmd=cmd,
kwargs={},
message=output_api.PresubmitPromptWarning)
if input_api.verbose:
print('Running ' + cmd_name)
return input_api.RunTests([test_cmd])