ctx
A context object that is passed to the implementation function for a rule or aspect. It provides access to the information and methods needed to analyze the current target.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
- default_provider
- disabled_features
- executable
- expand_location
- expand_make_variables
- features
- file
- files
- fragments
- genfiles_dir
- host_configuration
- host_fragments
- label
- new_file
- outputs
- resolve_command
- resolve_tools
- rule
- runfiles
- split_attr
- target_platform_has_constraint
- toolchains
- var
- workspace_name
actions
actions ctx.actionsContains methods for declaring output files and the actions that produce them.
aspect_ids
list ctx.aspect_idsReturns a list 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_pathReturns path to the BUILD file for this rule, relative to the source root.
build_setting_value
unknown ctx.build_setting_valueExperimental. This field is experimental and subject to change at any time. Do not depend on it.
Returns the value of the build setting that is represented by the current target. It is an error to access this field for rules that do not set the build_setting
attribute in their rule definition.
configuration
configuration ctx.configurationReturns the 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
|
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.
default_provider
Provider ctx.default_providerDeprecated. Use DefaultInfo instead.
disabled_features
list ctx.disabled_featuresReturns the set of features that are explicitly disabled by the user for this rule.
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 to be expanded. |
targets
|
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
|
The attribute name. Used for error reporting. |
command
|
The expression to expand. It can contain references to "Make variables". |
additional_substitutions
|
Additional substitutions to make beyond the default make variables. |
features
list ctx.featuresReturns the 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.
host_configuration
configuration ctx.host_configurationReturns the host configuration. See the configuration type for more details.
host_fragments
fragments ctx.host_fragmentsAllows access to configuration fragments in host configuration.
label
Label ctx.labelThe label of the target currently being analyzed.
new_file
File ctx.new_file(var1, var2=unbound, var3=unbound)DEPRECATED. Use ctx.actions.declare_file.
Creates a file object. There are four possible signatures to this method:
- new_file(filename): Creates a file object with the given filename in the current package.
- new_file(file_root, filename): Creates a file object with the given filename under the given file root.
- new_file(sibling_file, filename): Creates a file object in the same directory as the given sibling file.
- new_file(file_root, sibling_file, suffix): Creates a file object with same base name of the sibling_file but with different given suffix, under the given file root.
Does not actually create a file on the file system, just declares that some action will do so. You must create an action that generates the file. If the file should be visible to other rules, declare a rule output instead when possible. Doing so enables Bazel to associate a label with the file that rules can refer to (allowing finer dependency control) instead of referencing the whole rule.
Parameters
Parameter | Description |
---|---|
var1
|
|
var2
|
|
var3
|
outputs
ClassObject 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, input_manifests)
of the list of resolved inputs, the argv list for the resolved command, and the runfiles metadata required to run the command, all 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).
Parameters
Parameter | Description |
---|---|
command
|
Command to resolve. |
attribute
|
Name of the associated attribute for which to issue an error, or None. |
expand_locations
|
Shall we expand $(location) variables? See ctx.expand_location() for more details. |
make_variables
|
Make variables to expand, or None. |
tools
|
List of tools (list of targets). |
label_dict
|
Dictionary of resolved labels and the corresponding list of Files (a dict of Label : list of Files). |
execution_requirements
|
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, input_manifests)
of the depset of resolved inputs and the runfiles metadata required to run the tools, both of them suitable for passing as the same-named arguments of the ctx.actions.run
method.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.
Parameters
Parameter | Description |
---|---|
tools
|
List of tools (list of targets). |
rule
rule_attributes ctx.ruleReturns rule attributes descriptor for the rule that 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
|
The list of files to be added to the runfiles. |
transitive_files
|
The (transitive) set of files to be added to the runfiles. The depset should use the |
collect_data
|
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
|
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
|
The map of symlinks to be added to the runfiles, prefixed by workspace name. |
root_symlinks
|
The map of symlinks to be added to the runfiles. |
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.
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
|
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.
workspace_name
string ctx.workspace_nameReturns the workspace name as defined in the WORKSPACE file.