actions

Module providing functions to create actions. Access this module using ctx.actions.

Members

• args
• declare_directory
• declare_file
• declare_symlink
• do_nothing
• expand_template
• map_directory
• run
• run_shell
• symlink
• template_dict
• write

args

Args actions.args()

Returns an Args object that can be used to build memory-efficient command lines.

declare_directory

File actions.declare_directory(filename, *, sibling=None)

Declares that the rule or aspect creates a directory with the given name, in the current package. You must create an action that generates the directory. The contents of the directory are not directly accessible from Starlark, but can be expanded in an action command with Args.add_all(). Only regular files and directories can be in the expanded contents of a declare_directory.

Parameters

ParameterDescriptionfilenamestring; required

If no ‘sibling’ provided, path of the new directory, relative to the current package. Otherwise a base name for a file (‘sibling’ defines a directory). siblingFile; or None; default is None

A file that lives in the same directory as the newly declared directory. The file must be in the current package.

declare_file

File actions.declare_file(filename, *, sibling=None)

Declares that the rule or aspect creates a file with the given filename. If sibling is not specified, the file name is relative to the package directory, otherwise the file is in the same directory as sibling. Files cannot be created outside of the current package.

Remember that in addition to declaring a file, you must separately create an action that emits the file. Creating that action will require passing the returned File object to the action’s construction function.

Note that predeclared output files do not need to be (and cannot be) declared using this function. You can obtain their File objects from ctx.outputs instead. See example of use.

Parameters

ParameterDescriptionfilenamestring; required

If no ‘sibling’ provided, path of the new file, relative to the current package. Otherwise a base name for a file (‘sibling’ determines a directory). siblingFile; or None; default is None

A file that lives in the same directory as the newly created file. The file must be in the current package.

declare_symlink

File actions.declare_symlink(filename, *, sibling=None)

Declares that the rule or aspect creates a symlink with the given name in the current package. You must create an action that generates this symlink. Bazel will never dereference this symlink and will transfer it verbatim to sandboxes or remote executors. Symlinks inside tree artifacts are not currently supported.

Parameters

ParameterDescriptionfilenamestring; required

If no ‘sibling’ provided, path of the new symlink, relative to the current package. Otherwise a base name for a file (‘sibling’ defines a directory). siblingFile; or None; default is None

A file that lives in the same directory as the newly declared symlink.

do_nothing

None actions.do_nothing(*, mnemonic, inputs=[])

Creates an empty action that neither executes a command nor produces any output, but that is useful for inserting ‘extra actions’.

Parameters

ParameterDescriptionmnemonicstring; required

A one-word description of the action, for example, CppCompile or GoLink. inputssequence of File s; or depset; default is []

List of the input files of the action.

expand_template

None actions.expand_template(*, template, output, substitutions={}, is_executable=False, computed_substitutions=unbound)

Creates a template expansion action. When the action is executed, it will generate a file based on a template. Parts of the template will be replaced using the substitutions dictionary, in the order the substitutions are specified. Whenever a key of the dictionary appears in the template (or a result of a previous substitution), it is replaced with the associated value. There is no special syntax for the keys. You may, for example, use curly braces to avoid conflicts (for example, {KEY}). See example of use.

Parameters

ParameterDescriptiontemplateFile; required

The template file, which is a UTF-8 encoded text file. outputFile; required

The output file, which is a UTF-8 encoded text file. substitutionsdict; default is {}

Substitutions to make when expanding the template. is_executablebool; default is False

Whether the output file should be executable. computed_substitutionsTemplateDict; default is unbound

Substitutions to make when expanding the template.

map_directory

None actions.map_directory(*, input_directories, additional_inputs={}, output_directories, tools, additional_params={}, execution_requirements=None, exec_group=None, toolchain=None, use_default_shell_env=False, env=None, mnemonic=None, implementation)

Creates multiple actions based on the files within one or more input directories, to output one or more output directories.

Parameters

ParameterDescriptioninput_directoriesdict of File s; required

A dictionary mapping of strings to input directories, as declared by ctx.actions.declare_directory() (only directories are allowed as values here). The values specify the directories that we want expanded to access their files in the implementation function. The keys (strings) act as identifiers to easily reference a specific directory in the implementation function. additional_inputsdict; default is {}

A dictionary of mapping of strings to additional inputs (only files, FilesToRunProvider(s) and Depset(s) are allowed here). The values specify any additional inputs that we want to make accessible to actions created by the implementation function. The keys (strings) act as identifiers to easily reference a specific input from within the implementation function. output_directoriesdict of File s; required

A dictionary mapping of strings to output directories, as declared by ctx.actions.declare_directory(). The values specify the output directories that we want to generate by the actions created by the implementation function. The keys (strings) act as identifiers to easily reference a specific output directory from within the implementation function. toolsdict; required

A dictionary mapping of strings to tools (only files, FilesToRunProvider(s) and Depset(s) are allowed here). The values specify the tools that we want to make accessible to actions created by the implementation function. The keys (strings) act as identifiers to easily reference a specific tool from within the implementation function. additional_paramsdict; default is {}

A dictionary mapping of strings to additional parameters (only string, boolean and integer values are allowed here). The values specify any additional parameters that we want to make accessible to the implementation function that could be used to influence its behavior. The keys (strings) act as identifiers to easily reference a specific parameter from within the implementation function. execution_requirementsdict; or None; default is None

Information for scheduling the created actions. See tags for useful keys. exec_groupstring; or None; default is None

Run the created actions on the given exec group’s execution platform. If none, uses the target’s default execution platform. toolchainLabel; or string; or None; default is None

Toolchain type of the executable or tools used by the created actions.

If executable and tools are not coming from a toolchain, set this parameter to None.

If executable and tools are coming from a toolchain, toolchain type must be set so that the created actions execute on the correct execution platform.

Note that the rule which creates these actions needs to define this toolchain inside its ‘rule()’ function.

When toolchain and exec_group parameters are both set, exec_group will be used. An error is raised in case the exec_group doesn’t specify the same toolchain.

use_default_shell_envbool; default is False

Whether the created actions should use the default shell environment, which consists of a few OS-dependent variables as well as variables set via --action_env.

If both use_default_shell_env and env are set to True, values set in env will overwrite the default shell environment.

envdict; or None; default is None

Sets the dictionary of environment variables.

If both use_default_shell_env and env are set to True, values set in env will overwrite the default shell environment.

mnemonicstring; or None; default is None

A one-word description of the created actions, for example, CppCompile or GoLink. implementationfunction; required

A Starlark function that gets called after input directories have been built to generate actions that output files to the specified output directories. This function is passed the following arguments:

• template_ctx (positional): A template_ctx object that can be used to create actions.
• input_directories (keyword-only): A dictionary mapping from the string keys of the input_directories argument of actions.map_directory() to their values’ corresponding ExpandedDirectory objects.
• output_directories (keyword-only): The value of the output_directories argument of actions.map_directory(); a dictionary mapping from strings to output directories.
• additional_inputs (keyword-only): The value of the additional_inputs argument of actions.map_directory(); a dictionary mapping from strings to input files.
• tools (keyword-only): The value of the tools argument of actions.map_directory(); a dictionary mapping from strings to tools.
• additional_params (keyword-only): The value of the additional_params argument of actions.map_directory(); a dictionary mapping from strings to strings, booleans, or integers.

This function must be top-level, i.e. lambdas and nested functions are not allowed.

run

None actions.run(*, outputs, inputs=[], unused_inputs_list=None, executable, tools=unbound, arguments=[], mnemonic=None, progress_message=None, use_default_shell_env=False, env=None, execution_requirements=None, input_manifests=None, exec_group=None, shadowed_action=None, resource_set=None, toolchain=unbound)

Creates an action that runs an executable. See example of use.

Parameters

ParameterDescriptionoutputssequence of File s; required

List of the output files of the action. inputssequence of File s; or depset; default is []

List or depset of the input files of the action. unused_inputs_listFile; or None; default is None

File containing list of inputs unused by the action.

The content of this file (generally one of the outputs of the action) corresponds to the list of input files that were not used during the whole action execution. Any change in those files must not affect in any way the outputs of the action.

executableFile; or string; or FilesToRunProvider; required

The executable file to be called by the action. toolssequence; or depset; default is unbound

List or depset of any tools needed by the action. Tools are executable inputs that may have their own runfiles which are automatically made available to the action.

When a list is provided, it can be a heterogenous collection of:

• File s
• FilesToRunProvider instances
• depset s of File s

File s from ctx.executable and FilesToRunProvider s which are directly in the list will have their runfiles automatically added. All tools are implicitly added as inputs.

argumentssequence; default is []

Command line arguments of the action. Must be a list of strings or actions.args() objects. mnemonicstring; or None; default is None

A one-word description of the action, for example, CppCompile or GoLink. progress_messagestring; or None; default is None

Progress message to show to the user during the build, for example, “Compiling foo.cc to create foo.o”. The message may contain %{label}, %{input}, or %{output} patterns, which are substituted with label string, first input, or output’s path, respectively. Prefer to use patterns instead of static strings, because the former are more efficient. use_default_shell_envbool; default is False

Whether the action should use the default shell environment, which consists of a few OS-dependent variables as well as variables set via --action_env.

If both use_default_shell_env and env are set to True, values set in env will overwrite the default shell environment.

envdict; or None; default is None

Sets the dictionary of environment variables.

If both use_default_shell_env and env are set to True, values set in env will overwrite the default shell environment.

execution_requirementsdict; or None; default is None

Information for scheduling the action. See tags for useful keys. input_manifestssequence; or None; default is None

Legacy argument. Ignored. exec_groupstring; or None; default is None

Runs the action on the given exec group’s execution platform. If none, uses the target’s default execution platform. shadowed_actionAction; default is None

Runs the action using the given shadowed action’s inputs and environment added to the action’s inputs list and environment. The action environment can overwrite any of the shadowed action’s environment variables. If none, uses only the action’s inputs and given environment. resource_set callable; or None; default is None

A callback function that returns a resource set dictionary, used to estimate resource usage at execution time if this action is run locally.

The function accepts two positional arguments: a string representing an OS name (e.g. “osx”), and an integer representing the number of inputs to the action. The returned dictionary may contain the following entries, each of which may be a float or an int:

• “cpu”: number of CPUs; default 1
• “memory”: in MB; default 250
• “local_test”: number of local tests; default 1

If this parameter is set to None , the default values are used.

The callback must be top-level (lambda and nested functions aren’t allowed).

toolchainLabel; or string; or None; default is unbound

Toolchain type of the executable or tools used in this action.

If executable and tools are not coming from a toolchain, set this parameter to `None`.

If executable and tools are coming from a toolchain, toolchain type must be set so that the action executes on the correct execution platform.

Note that the rule which creates this action needs to define this toolchain inside its ‘rule()’ function.

When `toolchain` and `exec_group` parameters are both set, `exec_group` will be used. An error is raised in case the `exec_group` doesn’t specify the same toolchain.

run_shell

None actions.run_shell(*, outputs, inputs=[], tools=unbound, arguments=[], mnemonic=None, command, progress_message=None, use_default_shell_env=False, env=None, execution_requirements=None, input_manifests=None, exec_group=None, shadowed_action=None, resource_set=None, toolchain=unbound)

Creates an action that runs a shell command. See example of use.

Parameters

ParameterDescriptionoutputssequence of File s; required

List of the output files of the action. inputssequence of File s; or depset; default is []

List or depset of the input files of the action. toolssequence of File s; or depset; default is unbound

List or depset of any tools needed by the action. Tools are executable inputs that may have their own runfiles which are automatically made available to the action.

When a list is provided, it can be a heterogenous collection of:

• File s
• FilesToRunProvider instances
• depset s of File s

File s from ctx.executable and FilesToRunProvider s which are directly in the list will have their runfiles automatically added. All tools are implicitly added as inputs.

argumentssequence; default is []

Command line arguments of the action. Must be a list of strings or actions.args() objects.

Bazel passes the elements in this attribute as arguments to the command.The command can access these arguments using shell variable substitutions such as $1, $2, etc. Note that since Args objects are flattened before indexing, if there is an Args object of unknown size then all subsequent strings will be at unpredictable indices. It may be useful to use $@ (to retrieve all arguments) in conjunction with Args objects of indeterminate size.

In the case where command is a list of strings, this parameter may not be used.

mnemonicstring; or None; default is None

A one-word description of the action, for example, CppCompile or GoLink. commandstring; or sequence of string s; required

Shell command to execute. This may either be a string (preferred) or a sequence of strings (deprecated).

If command is a string, then it is executed as if by sh -c <command> "" <arguments> — that is, the elements in arguments are made available to the command as $1, $2 (or %1, %2 if using Windows batch), etc. If arguments contains any actions.args() objects, their contents are appended one by one to the command line, so $ i can refer to individual strings within an Args object. Note that if an Args object of unknown size is passed as part of arguments, then the strings will be at unknown indices; in this case the $@ shell substitution (retrieve all arguments) may be useful.

(Deprecated) If command is a sequence of strings, the first item is the executable to run and the remaining items are its arguments. If this form is used, the arguments parameter must not be supplied. Note that this form is deprecated and will soon be removed. It is disabled with `—incompatible_run_shell_command_string`. Use this flag to verify your code is compatible.

Bazel uses the same shell to execute the command as it does for genrules.

progress_messagestring; or None; default is None

Progress message to show to the user during the build, for example, “Compiling foo.cc to create foo.o”. The message may contain %{label}, %{input}, or %{output} patterns, which are substituted with label string, first input, or output’s path, respectively. Prefer to use patterns instead of static strings, because the former are more efficient. use_default_shell_envbool; default is False

Whether the action should use the default shell environment, which consists of a few OS-dependent variables as well as variables set via --action_env.

If both use_default_shell_env and env are set to True, values set in env will overwrite the default shell environment.

envdict; or None; default is None

Sets the dictionary of environment variables.

If both use_default_shell_env and env are set to True, values set in env will overwrite the default shell environment.

execution_requirementsdict; or None; default is None

Information for scheduling the action. See tags for useful keys. input_manifestssequence; or None; default is None

Legacy argument. Ignored. exec_groupstring; or None; default is None

Runs the action on the given exec group’s execution platform. If none, uses the target’s default execution platform. shadowed_actionAction; default is None

Runs the action using the given shadowed action’s discovered inputs added to the action’s inputs list. If none, uses only the action’s inputs. resource_set callable; or None; default is None

A callback function for estimating resource usage if run locally. See ctx.actions.run(). toolchainLabel; or string; or None; default is unbound

Toolchain type of the executable or tools used in this action.

If executable and tools are not coming from a toolchain, set this parameter to `None`.

If executable and tools are coming from a toolchain, toolchain type must be set so that the action executes on the correct execution platform.

Note that the rule which creates this action needs to define this toolchain inside its ‘rule()’ function.

When `toolchain` and `exec_group` parameters are both set, `exec_group` will be used. An error is raised in case the `exec_group` doesn’t specify the same toolchain.

symlink

None actions.symlink(*, output, target_file=None, target_path=None, is_executable=False, progress_message=None)

Creates an action that writes a symlink in the file system.

This function must be called with exactly one of target_file or target_path specified.

When you use target_file, declare output with declare_file() or declare_directory() and match the type of target_file. This makes the symlink point to target_file. Bazel invalidates the output of this action whenever the target of the symlink or its contents change.

Otherwise, when you use target_path, declare output with declare_symlink()). In this case, the symlink points to target_path. Bazel never resolves the symlink and the output of this action is invalidated only when the text contents of the symlink (that is, the value of readlink()) changes. In particular, this can be used to create a dangling symlink.

Parameters

ParameterDescriptionoutputFile; required

The output of this action. target_fileFile; or None; default is None

The File that the output symlink will point to. target_pathstring; or None; default is None

The exact path that the output symlink will point to. No normalization or other processing is applied. is_executablebool; default is False

May only be used with target_file, not target_path. If true, when the action is executed, the target_file’s path is checked to confirm that it is executable, and an error is reported if it is not. Setting is_executable to False does not mean the target is not executable, just that no verification is done.

This feature does not make sense for target_path because dangling symlinks might not exist at build time.

progress_messagestring; or None; default is None

Progress message to show to the user during the build.

template_dict

TemplateDict actions.template_dict()

Returns a TemplateDict object for memory-efficient template expansion.

write

None actions.write(output, content, is_executable=False, *, mnemonic=None)

Creates a file write action. When the action is executed, it will write the given content to a file. This is used to generate files using information available in the analysis phase. If the file is large and with a lot of static content, consider using expand_template.

Parameters

ParameterDescriptionoutputFile; required

The output file. contentstring; or Args; required

the contents of the file. May be a either a string or an actions.args() object. is_executablebool; default is False

Whether the output file should be executable. mnemonicstring; or None; default is None

A one-word description of the action, for example, CppCompile or GoLink.