module_ctx

The context of the module extension containing helper functions and information about pertinent tags across the dependency graph. You get a module_ctx object as an argument to the implementation function when you create a module extension.

Members

• download
• download_and_extract
• execute
• extension_metadata
• extract
• facts
• file
• getenv
• is_dev_dependency
• modules
• os
• path
• read
• report_progress
• root_module_has_non_dev_dependency
• watch
• which

download

unknown module_ctx.download(url, output='', sha256='', executable=False, allow_fail=False, canonical_id='', auth={}, headers={}, *, integrity='', block=True)

Downloads a file to the output path for the provided url and returns a struct containing success, a flag which is true if the download completed successfully, and if successful, a hash of the file with the fields sha256 and integrity. When sha256 or integrity is user specified, setting an explicit canonical_id is highly recommended. e.g. get_default_canonical_id

Parameters

Parameter	Description
url	string; or Iterable of strings; required List of mirror URLs referencing the same file.
output	string; or Label; or path; default is '' path to the output file, relative to the repository directory.
sha256	string; default is '' The expected SHA-256 hash of the file downloaded. This must match the SHA-256 hash of the file downloaded. It is a security risk to omit the SHA-256 as remote files can change. At best omitting this field will make your build non-hermetic. It is optional to make development easier but should be set before shipping. If provided, the repository cache will first be checked for a file with the given hash; a download will only be attempted if the file was not found in the cache. After a successful download, the file will be added to the cache.
executable	bool; default is False Set the executable flag on the created file, false by default.
allow_fail	bool; default is False If set, indicate the error in the return value instead of raising an error for failed downloads.
canonical_id	string; default is '' If set, restrict cache hits to those cases where the file was added to the cache with the same canonical id. By default caching uses the checksum (sha256 or integrity).
auth	dict; default is {} An optional dict specifying authentication information for some of the URLs.
headers	dict; default is {} An optional dict specifying http headers for all URLs.
integrity	string; default is '' Expected checksum of the file downloaded, in Subresource Integrity format. This must match the checksum of the file downloaded. It is a security risk to omit the checksum as remote files can change. At best omitting this field will make your build non-hermetic. It is optional to make development easier but should be set before shipping. If provided, the repository cache will first be checked for a file with the given checksum; a download will only be attempted if the file was not found in the cache. After a successful download, the file will be added to the cache.
block	bool; default is True If set to false, the call returns immediately and instead of the regular return value, it returns a token with one single method, wait(), which blocks until the download is finished and returns the usual return value or throws as usual.

download_and_extract

struct module_ctx.download_and_extract(url, output='', sha256='', type='', strip_prefix='', allow_fail=False, canonical_id='', auth={}, headers={}, *, integrity='', rename_files={})

Downloads a file to the output path for the provided url, extracts it, and returns a struct containing success, a flag which is true if the download completed successfully, and if successful, a hash of the file with the fields sha256 and integrity. When sha256 or integrity is user specified, setting an explicit canonical_id is highly recommended. e.g. get_default_canonical_id

Parameters

Parameter	Description
url	string; or Iterable of strings; required List of mirror URLs referencing the same file.
output	string; or Label; or path; default is '' Path to the directory where the archive will be unpacked, relative to the repository directory.
sha256	string; default is '' The expected SHA-256 hash of the file downloaded. This must match the SHA-256 hash of the file downloaded. It is a security risk to omit the SHA-256 as remote files can change. At best omitting this field will make your build non-hermetic. It is optional to make development easier but should be set before shipping. If provided, the repository cache will first be checked for a file with the given hash; a download will only be attempted if the file was not found in the cache. After a successful download, the file will be added to the cache.
type	string; default is '' The archive type of the downloaded file. By default, the archive type is determined from the file extension of the URL. If the file has no extension, you can explicitly specify either “zip”, “jar”, “war”, “aar”, “nupkg”, “whl”, “tar”, “tar.gz”, “tgz”, “gz”, “tar.xz”, “txz”, “xz”, “tar.zst”, “tzst”, “zst”, “tar.bz2”, “tbz”, “bz2”, “ar”, “deb” or “7z” here.
strip_prefix	string; default is '' A directory prefix to strip from the extracted files. Many archives contain a top-level directory that contains all files in the archive. Instead of needing to specify this prefix over and over in the build_file, this field can be used to strip it from extracted files. For compatibility, this parameter may also be used under the deprecated name stripPrefix.
allow_fail	bool; default is False If set, indicate the error in the return value instead of raising an error for failed downloads.
canonical_id	string; default is '' If set, restrict cache hits to those cases where the file was added to the cache with the same canonical id. By default caching uses the checksum (sha256 or integrity).
auth	dict; default is {} An optional dict specifying authentication information for some of the URLs.
headers	dict; default is {} An optional dict specifying http headers for all URLs.
integrity	string; default is '' Expected checksum of the file downloaded, in Subresource Integrity format. This must match the checksum of the file downloaded. It is a security risk to omit the checksum as remote files can change. At best omitting this field will make your build non-hermetic. It is optional to make development easier but should be set before shipping. If provided, the repository cache will first be checked for a file with the given checksum; a download will only be attempted if the file was not found in the cache. After a successful download, the file will be added to the cache.
rename_files	dict; default is {} An optional dict specifying files to rename during the extraction. Archive entries with names exactly matching a key will be renamed to the value, prior to any directory prefix adjustment. This can be used to extract archives that contain non-Unicode filenames, or which have files that would extract to the same path on case-insensitive filesystems.

execute

exec_result module_ctx.execute(arguments, timeout=600, environment={}, quiet=True, working_directory="")

Executes the command given by the list of arguments. The execution time of the command is limited by timeout (in seconds, default 600 seconds). This method returns an exec_result structure containing the output of the command. The environment map can be used to override some environment variables to be passed to the process.

Parameters

Parameter	Description
arguments	sequence; required List of arguments, the first element should be the path to the program to execute.
timeout	int; default is 600 Maximum duration of the command in seconds (default is 600 seconds).
environment	dict; default is {} Force some environment variables to be set to be passed to the process. The value can be None to remove the environment variable.
quiet	bool; default is True If stdout and stderr should be printed to the terminal.
working_directory	string; default is "" Working directory for command execution. Can be relative to the repository root or absolute. The default is the repository root.

extension_metadata

extension_metadata module_ctx.extension_metadata(*, root_module_direct_deps=None, root_module_direct_dev_deps=None, reproducible=False, facts={})

Constructs an opaque object that can be returned from the module extension’s implementation function to provide metadata about the repositories generated by the extension to Bazel.

Parameters

Parameter	Description
root_module_direct_deps	sequence of strings; or string; or None; default is None The names of the repositories that the extension considers to be direct dependencies of the root module. If the root module imports additional repositories or does not import all of these repositories via use_repo, Bazel will print a warning when the extension is evaluated, instructing the user to run bazel mod tidy to fix the use_repo calls automatically. If one of root_module_direct_deps and will print a warning and a fixup command when the extension is evaluated. If one of root_module_direct_deps and root_module_direct_dev_deps is specified, the other has to be as well. The lists specified by these two parameters must be disjoint. Exactly one of root_module_direct_deps and root_module_direct_dev_deps can be set to the special value "all", which is treated as if a list with the names of all repositories generated by the extension was specified as the value.
root_module_direct_dev_deps	sequence of strings; or string; or None; default is None The names of the repositories that the extension considers to be direct dev dependencies of the root module. If the root module imports additional repositories or does not import all of these repositories via use_repo on an extension proxy created with use_extension(..., dev_dependency = True), Bazel will print a warning when the extension is evaluated, instructing the user to run bazel mod tidy to fix the use_repo calls automatically. If one of root_module_direct_deps and root_module_direct_dev_deps is specified, the other has to be as well. The lists specified by these two parameters must be disjoint. Exactly one of root_module_direct_deps and root_module_direct_dev_deps can be set to the special value "all", which is treated as if a list with the names of all repositories generated by the extension was specified as the value.
reproducible	bool; default is False States that this module extension ensures complete reproducibility, thereby it should not be stored in the lockfile.
facts	dict of strings; default is {} A JSON-like dict that is made available to future executions of this extension via the module_ctx.facts property. This is useful for extensions that want to preserve universally true facts such as the hashes of artifacts in an immutable repository. Bazel may shallowly merge multiple facts dicts returned by different versions of the extension in order to resolve merge conflicts on the MODULE.bazel.lock file, as if by applying the dict.update() method or the `	` operator in Starlark. Extensions should use facts for key-value storage only and ensure that the key uniquely determines the value, although perhaps only via additional information and network access. An extension can opt out of this merging by providing a dict with a single, fixed top-level key and an arbitrary value. Note that the value provided here may be read back by a different version of the extension, so either include a version number or use a schema that is unlikely to result in ambiguities.

extract

None module_ctx.extract(archive, output='', strip_prefix='', *, rename_files={}, watch_archive='auto', type='')

Extract an archive to the repository directory.

Parameters

Parameter	Description
archive	string; or Label; or path; required path to the archive that will be unpacked, relative to the repository directory.
output	string; or Label; or path; default is '' path to the directory where the archive will be unpacked, relative to the repository directory.
strip_prefix	string; default is '' a directory prefix to strip from the extracted files. Many archives contain a top-level directory that contains all files in the archive. Instead of needing to specify this prefix over and over in the build_file, this field can be used to strip it from extracted files. For compatibility, this parameter may also be used under the deprecated name stripPrefix.
rename_files	dict; default is {} An optional dict specifying files to rename during the extraction. Archive entries with names exactly matching a key will be renamed to the value, prior to any directory prefix adjustment. This can be used to extract archives that contain non-Unicode filenames, or which have files that would extract to the same path on case-insensitive filesystems.
watch_archive	string; default is 'auto' whether to watch the archive file. Can be the string ‘yes’, ‘no’, or ‘auto’. Passing ‘yes’ is equivalent to immediately invoking the watch() method; passing ‘no’ does not attempt to watch the file; passing ‘auto’ will only attempt to watch the file when it is legal to do so (see watch() docs for more information.
type	string; default is '' The archive type of the downloaded file. By default, the archive type is determined from the file extension of the URL. If the file has no extension, you can explicitly specify either “zip”, “jar”, “war”, “aar”, “nupkg”, “whl”, “tar”, “tar.gz”, “tgz”, “gz”, “tar.xz”, “txz”, “xz”, “tar.zst”, “tzst”, “zst”, “tar.bz2”, “tbz”, “bz2”, “ar”, “deb” or “7z” here.

facts

Facts module_ctx.facts

The JSON-like dict returned by a previous execution of this extension in the facts parameter of extension_metadata or else {}. This is useful for extensions that want to preserve universally true facts such as the hashes of artifacts in an immutable repository. Note that the returned value may have been created by a different version of the extension, which may have used a different schema.

file

None module_ctx.file(path, content='', executable=True, legacy_utf8=False)

Generates a file in the repository directory with the provided content.

Parameters

Parameter	Description
path	string; or Label; or path; required Path of the file to create, relative to the repository directory.
content	string; default is '' The content of the file to create, empty by default.
executable	bool; default is True Set the executable flag on the created file, true by default.
legacy_utf8	bool; default is False No-op. This parameter is deprecated and will be removed in a future version of Bazel.

getenv

string module_ctx.getenv(name, default=None)

Returns the value of an environment variable name as a string if exists, or default if it doesn’t.

When building incrementally, any change to the value of the variable named by name will cause this repository to be re-fetched.

Parameters

Parameter	Description
name	string; required Name of desired environment variable.
default	string; or None; default is None Default value to return if name is not found.

May return None.

is_dev_dependency

bool module_ctx.is_dev_dependency(tag)

Returns whether the given tag was specified on the result of a use_extension call with devDependency = True.

Parameters

Parameter	Description
tag	bazel_module_tag; required A tag obtained from bazel_module.tags.

modules

list module_ctx.modules

A list of all the Bazel modules in the external dependency graph that use this module extension, each of which is a bazel_module object that exposes all the tags it specified for this extension. The iteration order of this dictionary is guaranteed to be the same as breadth-first search starting from the root module.

os

repository_os module_ctx.os

A struct to access information from the system.

path

path module_ctx.path(path)

Returns a path from a string, label, or path. If this context is a repository_ctx, a relative path will resolve relative to the repository directory. If it is a module_ctx, a relative path will resolve relative to a temporary working directory for this module extension. If the path is a label, it will resolve to the path of the corresponding file. Note that remote repositories and module extensions are executed during the analysis phase and thus cannot depends on a target result (the label should point to a non-generated file). If path is a path, it will return that path as is.

Parameters

Parameter	Description
path	string; or Label; or path; required string, Label or path from which to create a path from.

read

string module_ctx.read(path, *, watch='auto')

Reads the content of a file on the filesystem.

Parameters

Parameter	Description
path	string; or Label; or path; required Path of the file to read from.
watch	string; default is 'auto' Whether to watch the file. Can be the string ‘yes’, ‘no’, or ‘auto’. Passing ‘yes’ is equivalent to immediately invoking the watch() method; passing ‘no’ does not attempt to watch the file; passing ‘auto’ will only attempt to watch the file when it is legal to do so (see watch() docs for more information.

report_progress

None module_ctx.report_progress(status='')

Updates the progress status for the fetching of this repository or module extension.

Parameters

Parameter	Description
status	string; default is '' string describing the current status of the fetch progress.

root_module_has_non_dev_dependency

bool module_ctx.root_module_has_non_dev_dependency

Whether the root module uses this extension as a non-dev dependency.

watch

None module_ctx.watch(path)

Tells Bazel to watch for changes to the given path, whether or not it exists, or whether it’s a file or a directory. Any changes to the file or directory will invalidate this repository or module extension, and cause it to be refetched or re-evaluated next time.

“Changes” include changes to the contents of the file (if the path is a file); if the path was a file but is now a directory, or vice versa; and if the path starts or stops existing. Notably, this does not include changes to any files under the directory if the path is a directory. For that, use path.readdir() instead.

Note that attempting to watch paths inside the repo currently being fetched, or inside the working directory of the current module extension, will result in an error. A module extension attempting to watch a path outside the current Bazel workspace will also result in an error.

Parameters

Parameter	Description
path	string; or Label; or path; required Path of the file to watch.

which

path module_ctx.which(program)

Returns the path of the corresponding program or None if there is no such program in the path.

Parameters

Parameter	Description
program	string; required Program to find in the path.

May return None.