In particular, it lets the implementation function access the current target's label, attributes, configuration, and the providers of its dependencies. It has methods for declaring output files and the actions that produce them.
Context objects essentially live for the duration of the call to the implementation function. It is not useful to access these objects outside of their associated function. See the Rules page for more information.
Members
- actions
- aspect_ids
- attr
- bin_dir
- build_file_path
- build_setting_value
- configuration
- coverage_instrumented
- created_actions
- disabled_features
- exec_groups
- executable
- expand_location
- expand_make_variables
- features
- file
- files
- fragments
- genfiles_dir
- info_file
- label
- outputs
- resolve_command
- resolve_tools
- rule
- runfiles
- split_attr
- super
- target_platform_has_constraint
- toolchains
- var
- version_file
- workspace_name
actions
actions ctx.actionsContains methods for declaring output files and the actions that produce them.
aspect_ids
list ctx.aspect_idsA list of ids for all aspects applied to the target. Only available in aspect implementation functions.
attr
struct ctx.attrA struct to access the values of the attributes. The values are provided by the user (if not, a default value is used). The attributes of the struct and the types of their values correspond to the keys and values of the
attrs
dict provided to the rule
function. See example of use.
bin_dir
root ctx.bin_dirThe root corresponding to bin directory.
build_file_path
string ctx.build_file_pathDeprecated: Use
ctx.label.package + '/BUILD'
. The path to the BUILD file for this rule, relative to the source root.
build_setting_value
unknown ctx.build_setting_valueValue of the build setting represented by the current target. If this isn't the context for an instance of a rule that sets the
build_setting
attribute, reading this is an error.
configuration
configuration ctx.configurationThe default configuration. See the configuration type for more details.
coverage_instrumented
bool ctx.coverage_instrumented(target=None)Returns whether code coverage instrumentation should be generated when performing compilation actions for this rule or, if
target
is provided, the rule specified by that Target. (If a non-rule or a Starlark rule Target is provided, this returns False.) Checks if the sources of the current rule (if no Target is provided) or the sources of Target should be instrumented based on the --instrumentation_filter and --instrument_test_targets config settings. This differs from coverage_enabled
in the configuration, which notes whether coverage data collection is enabled for the entire run, but not whether a specific target should be instrumented.
Parameters
Parameter | Description |
---|---|
target
|
Target; or None ;
default is None A Target specifying a rule. If not provided, defaults to the current rule. |
created_actions
StarlarkValue ctx.created_actions()For rules with _skylark_testable set to
True
, this returns an Actions
provider representing all actions created so far for the current rule. For all other rules, returns None
. Note that the provider is not updated when subsequent actions are created, so you will have to call this function again if you wish to inspect them. This is intended to help write tests for rule-implementation helper functions, which may take in a
ctx
object and create actions on it.
disabled_features
list ctx.disabled_featuresThe set of features that are explicitly disabled by the user for this rule.
exec_groups
ExecGroupCollection ctx.exec_groupsA collection of the execution groups available for this rule, indexed by their name. Access with
ctx.exec_groups[name_of_group]
.
executable
struct ctx.executableA
struct
containing executable files defined in label type attributes marked as executable=True
. The struct fields correspond to the attribute names. Each value in the struct is either a File
or None
. If an optional attribute is not specified in the rule then the corresponding struct value is None
. If a label type is not marked as executable=True
, no corresponding struct field is generated. See example of use.
expand_location
string ctx.expand_location(input, targets=[])Expands all
$(location ...)
templates in the given string by replacing $(location //x)
with the path of the output file of target //x. Expansion only works for labels that point to direct dependencies of this rule or that are explicitly listed in the optional argument targets
. $(location ...)
will cause an error if the referenced target has multiple outputs. In this case, please use $(locations ...)
since it produces a space-separated list of output paths. It can be safely used for a single output file, too.This function is useful to let the user specify a command in a BUILD file (like for
genrule
). In other cases, it is often better to manipulate labels directly.
Parameters
Parameter | Description |
---|---|
input
|
string;
required String to be expanded. |
targets
|
sequence of Targets;
default is [] List of targets for additional lookup information. |
None
.
expand_make_variables
string ctx.expand_make_variables(attribute_name, command, additional_substitutions)Deprecated. Use ctx.var to access the variables instead.
Returns a string after expanding all references to "Make variables". The variables must have the following format:
$(VAR_NAME)
. Also, $$VAR_NAME
expands to $VAR_NAME
. Examples:ctx.expand_make_variables("cmd", "$(MY_VAR)", {"MY_VAR": "Hi"}) # == "Hi" ctx.expand_make_variables("cmd", "$$PWD", {}) # == "$PWD"Additional variables may come from other places, such as configurations. Note that this function is experimental.
Parameters
Parameter | Description |
---|---|
attribute_name
|
string;
required The attribute name. Used for error reporting. |
command
|
string;
required The expression to expand. It can contain references to "Make variables". |
additional_substitutions
|
dict;
required Additional substitutions to make beyond the default make variables. |
features
list ctx.featuresThe set of features that are explicitly enabled by the user for this rule. See example of use.
file
struct ctx.fileA
struct
containing files defined in label type attributes marked as allow_single_file
. The struct fields correspond to the attribute names. The struct value is always a File
or None
. If an optional attribute is not specified in the rule then the corresponding struct value is None
. If a label type is not marked as allow_single_file
, no corresponding struct field is generated. It is a shortcut for:list(ctx.attr.<ATTR>.files)[0]In other words, use
file
to access the (singular) default output of a dependency. See example of use.
files
struct ctx.filesA
struct
containing files defined in label or label list type attributes. The struct fields correspond to the attribute names. The struct values are list
of File
s. It is a shortcut for:[f for t in ctx.attr.<ATTR> for f in t.files]In other words, use
files
to access the default outputs of a dependency. See example of use.
fragments
fragments ctx.fragmentsAllows access to configuration fragments in target configuration.
genfiles_dir
root ctx.genfiles_dirThe root corresponding to genfiles directory.
info_file
File ctx.info_fileThe file that is used to hold the non-volatile workspace status for the current build request. See documentation for --workspace_status_command for more information.
label
Label ctx.labelThe label of the target currently being analyzed.
outputs
structure ctx.outputsA pseudo-struct containing all the predeclared output files, represented by
File
objects. See the Rules page for more information and examples.This field does not exist on aspect contexts, since aspects do not have predeclared outputs.
The fields of this object are defined as follows. It is an error if two outputs produce the same field name or have the same label.
- If the rule declares an
outputs
dict, then for every entry in the dict, there is a field whose name is the key and whose value is the correspondingFile
. - For every attribute of type
attr.output
that the rule declares, there is a field whose name is the attribute's name. If the target specified a label for that attribute, then the field value is the correspondingFile
; otherwise the field value isNone
. - For every attribute of type
attr.output_list
that the rule declares, there is a field whose name is the attribute's name. The field value is a list ofFile
objects corresponding to the labels given for that attribute in the target, or an empty list if the attribute was not specified in the target. - (Deprecated) If the rule is marked
executable
ortest
, there is a field named"executable"
, which is the default executable. It is recommended that instead of using this, you pass another file (either predeclared or not) to theexecutable
arg ofDefaultInfo
.
resolve_command
tuple ctx.resolve_command(command='', attribute=None, expand_locations=False, make_variables=None, tools=[], label_dict={}, execution_requirements={})(Experimental) Returns a tuple
(inputs, command, empty list)
of the list of resolved inputs and the argv list for the resolved command both of them suitable for passing as the same-named arguments of the ctx.action
method.Note for Windows users: this method requires Bash (MSYS2). Consider using
resolve_tools()
instead (if that fits your needs). The empty list is returned as the third member of the tuple for backwards compatibility.
Parameters
Parameter | Description |
---|---|
command
|
string;
default is '' Command to resolve. |
attribute
|
string; or None ;
default is None Name of the associated attribute for which to issue an error, or None. |
expand_locations
|
bool;
default is False Shall we expand $(location) variables? See ctx.expand_location() for more details. |
make_variables
|
dict; or None ;
default is None Make variables to expand, or None. |
tools
|
sequence of Targets;
default is [] List of tools (list of targets). |
label_dict
|
dict;
default is {} Dictionary of resolved labels and the corresponding list of Files (a dict of Label : list of Files). |
execution_requirements
|
dict;
default is {} Information for scheduling the action to resolve this command. See tags for useful keys. |
resolve_tools
tuple ctx.resolve_tools(tools=[])Returns a tuple
(inputs, empty list)
of the depset of resolved inputs required to run the tools, suitable for passing as the same-named argument of the ctx.actions.run
and ctx.actions.run_shell
methods. In contrast to
ctx.resolve_command
, this method does not require that Bash be installed on the machine, so it's suitable for rules built on Windows. The empty list is returned as part of the tuple for backward compatibility.
Parameters
Parameter | Description |
---|---|
tools
|
sequence of Targets;
default is [] List of tools (list of targets). |
rule
rule_attributes ctx.ruleRule attributes descriptor for the rule that the aspect is applied to. Only available in aspect implementation functions.
runfiles
runfiles ctx.runfiles(files=[], transitive_files=None, collect_data=False, collect_default=False, symlinks={}, root_symlinks={})Creates a runfiles object.
Parameters
Parameter | Description |
---|---|
files
|
sequence of Files;
default is [] The list of files to be added to the runfiles. |
transitive_files
|
depset of Files; or None ;
default is None The (transitive) set of files to be added to the runfiles. The depset should use the default order (which, as the name implies, is the default).
|
collect_data
|
bool;
default is False Use of this parameter is not recommended. See runfiles guide. Whether to collect the data runfiles from the dependencies in srcs, data and deps attributes. |
collect_default
|
bool;
default is False Use of this parameter is not recommended. See runfiles guide. Whether to collect the default runfiles from the dependencies in srcs, data and deps attributes. |
symlinks
|
dict; or depset of SymlinkEntrys;
default is {} Either a SymlinkEntry depset or the map of symlinks to be added to the runfiles. Symlinks are always added under the main workspace's runfiles directory (e.g. <runfiles_root>/_main/<symlink_path> , not the directory corresponding to the current target's repository. See Runfiles symlinks in the rules guide.
|
root_symlinks
|
dict; or depset of SymlinkEntrys;
default is {} Either a SymlinkEntry depset or a map of symlinks to be added to the runfiles. See Runfiles symlinks in the rules guide. |
split_attr
struct ctx.split_attrA struct to access the values of attributes with split configurations. If the attribute is a label list, the value of split_attr is a dict of the keys of the split (as strings) to lists of the ConfiguredTargets in that branch of the split. If the attribute is a label, then the value of split_attr is a dict of the keys of the split (as strings) to single ConfiguredTargets. Attributes with split configurations still appear in the attr struct, but their values will be single lists with all the branches of the split merged together.
super
unknown ctx.super()Experimental: Calls parent's implementation function and returns its providers
target_platform_has_constraint
bool ctx.target_platform_has_constraint(constraintValue)Returns true if the given constraint value is part of the current target platform.
Parameters
Parameter | Description |
---|---|
constraintValue
|
ConstraintValueInfo;
required The constraint value to check the target platform against. |
toolchains
ToolchainContext ctx.toolchainsToolchains for the default exec group of this rule.
var
dict ctx.varDictionary (String to String) of configuration variables.
version_file
File ctx.version_fileThe file that is used to hold the volatile workspace status for the current build request. See documentation for --workspace_status_command for more information.
workspace_name
string ctx.workspace_nameThe name of the workspace, which is effectively the execution root name and runfiles prefix for the main repo. If
--enable_bzlmod
is on, this is the fixed string _main
. Otherwise, this is the workspace name as defined in the WORKSPACE file.