bazel-lib/docs/copy_file.md

A rule that copies a file to another place.

native.genrule() is sometimes used to copy files (often wishing to rename them). The 'copy_file' rule does this with a simpler interface than genrule.

The rule uses a Bash command on Linux/macOS/non-Windows, and a cmd.exe command on Windows (no Bash is required).

This fork of bazel-skylib's copy_file adds DirectoryPathInfo support and allows multiple copy_file in the same package.

Choosing execution requirements

Copy actions can be very numerous, especially when used on third-party dependency packages.

By default, we set the execution_requirements of actions we spawn to be non-sandboxed and run locally, not reading or writing to a remote cache. For the typical user this is the fastest, because it avoids the overhead of creating a sandbox and making network calls for every file being copied.

If you use Remote Execution and Build-without-the-bytes, then you'll want the copy action to occur on the remote machine instead, since the inputs and outputs stay in the cloud and don't need to be brought to the local machine where Bazel runs.

Other reasons to allow copy actions to run remotely:

• Bazel prints an annoying warning "[action] uses implicit fallback from sandbox to local, which is deprecated because it is not hermetic"
• When the host and exec platforms have different architectures, toolchain resolution runs the wrong binary locally, see https://github.com/aspect-build/bazel-lib/issues/466

To disable our copy_use_local_execution flag, put this in your .bazelrc file:

# with Bazel 6.4 or greater:

# Disable default for execution_requirements of copy actions
common --@aspect_bazel_lib//lib:copy_use_local_execution=false

# with Bazel 6.3 or earlier:

# Disable default for execution_requirements of copy actions
build --@aspect_bazel_lib//lib:copy_use_local_execution=false
fetch --@aspect_bazel_lib//lib:copy_use_local_execution=false
query --@aspect_bazel_lib//lib:copy_use_local_execution=false

copy_file

copy_file(name, src, out, is_executable, allow_symlink, kwargs)

Copies a file or directory to another location.

native.genrule() is sometimes used to copy files (often wishing to rename them). The 'copy_file' rule does this with a simpler interface than genrule.

This rule uses a Bash command on Linux/macOS/non-Windows, and a cmd.exe command on Windows (no Bash is required).

If using this rule with source directories, it is recommended that you use the --host_jvm_args=-DBAZEL_TRACK_SOURCE_DIRECTORIES=1 startup option so that changes to files within source directories are detected. See c64421bc35 for more context.

PARAMETERS

Name	Description	Default Value
name	Name of the rule.	none
src	A Label. The file to make a copy of. (Can also be the label of a rule that generates a file.)	none
out	Path of the output file, relative to this package.	none
is_executable	A boolean. Whether to make the output file executable. When True, the rule's output can be executed using bazel run and can be in the srcs of binary and test rules that require executable sources. WARNING: If allow_symlink is True, src must also be executable.	False
allow_symlink	A boolean. Whether to allow symlinking instead of copying. When False, the output is always a hard copy. When True, the output can be a symlink, but there is no guarantee that a symlink is created (i.e., at the time of writing, we don't create symlinks on Windows). Set this to True if you need fast copying and your tools can handle symlinks (which most UNIX tools can).	False
kwargs	further keyword arguments, e.g. visibility	none

copy_file_action

copy_file_action(ctx, src, dst, dir_path, is_windows)

Factory function that creates an action to copy a file from src to dst.

If src is a TreeArtifact, dir_path must be specified as the path within the TreeArtifact to the file to copy.

This helper is used by copy_file. It is exposed as a public API so it can be used within other rule implementations.

To use copy_file_action in your own rules, you need to include the toolchains it uses in your rule definition. For example:

load("@aspect_bazel_lib//lib:copy_file.bzl", "COPY_FILE_TOOLCHAINS")

my_rule = rule(
    ...,
    toolchains = COPY_FILE_TOOLCHAINS,
)

PARAMETERS

Name	Description	Default Value
ctx	The rule context.	none
src	The source file to copy or TreeArtifact to copy a single file out of.	none
dst	The destination file.	none
dir_path	If src is a TreeArtifact, the path within the TreeArtifact to the file to copy.	None
is_windows	Deprecated and unused	None