Bazel: Consider a WORKSPACE `alias` rule

[cgrushko]

Something like:

WORKSPACE:

http_archive(
    name = "com_google_protobuf",
    ...
)

alias(
    name = "com_google_protobuf_cc",
    actual = "com_google_protobuf",
)

Depending on com_google_protobuf_cc would be equivalent to com_google_protobuf.

The use-case is highlighted in
https://groups.google.com/forum/#!topic/bazel-discuss/859ybHQZnuI

[laszlocsomor]

How about bind()?

[cgrushko]

bind() doesn't do what I describe above.

[kchodorow]

--override_repository=com_google_protobuf_cc=/path/to/com_google_protobuf can technically do this.

I still disagree with your premise. A repository should be ~a project. Also, if you're aliasing these, all of these repositories need to have the exact same targets, which is awkward.

IIUC, the concern is that @com_google_protobuf_java has one implementation and @com_google_protobuf_javalite has another and some projects will want to use them interchangably? That seems like it can be handled at several other levels.

[cgrushko]

will want to use them interchangably?

They need to be used together in the same code base (e.g., Java code that's reused between server and Android).

[kchodorow]

That sounds like it should be handled at the configuration layer.

[jayconrod]

Without aliases, what is the the best practice for renaming a workspace? I would expect aliases to be the main tool for this, and I don't see how renaming would work without them.

Suppose I have a project that uses @io_bazel_rules_go, but at some point, that repository changes its name to @build_bazel_rules_go. I may have some dependencies that refer to it using the new name and some using the old name.

[gertvdijk]

Without aliases, what is the the best practice for renaming a workspace?

I have the same question really. This stops me from making a transition when renaming WORKSPACE rule names in dependency (or consumer) projects. Would be great leave some aliases to cover a certain transition period.

Bumped into this when trying to build a JGit development tree in Gerrit. One of the two decided it was a good idea to rename all the rules to a new format. (mailing list discussion)

[dslomov]

This is implemented with repository remapping

[Globegitter]

@dslomov How is that solved with repository remapping? The link provided only shows an example with local_repository. How can I apply a remapping for the current workspace, i.e. myproject in the example?

[Globegitter]

Also there is still missing documentation of this new field here: https://docs.bazel.build/versions/master/be/workspace.html#local_repository

[nicolov]

Repository remapping does remap labels in the BUILD files, but won't do anything to labels in .bzl files. This makes the feature useless when project have their own macros in .bzl files. As a reference, I've tried to make TensorFlow use @com_google_protobuf instead of @protobuf_archive to avoid double compilations.

[dslomov]

Repository remapping does remap labels in the BUILD files, but won't do anything to labels in .bzl files.

It should also remap labels in .bzl files as well - do you have a repro where it does not work?

This makes the feature useless when project have their own macros in .bzl files. As a reference, I've tried to make TensorFlow use @com_google_protobuf instead of @protobuf_archive to avoid double compilations.

[dslomov]

@dslomov How is that solved with repository remapping? The link provided only shows an example with local_repository. How can I apply a remapping for the current workspace, i.e. myproject in the example?

Every repository rule has a repo_mapping argument, not just local_repository.
What do you mean by "apply a remapping for the current workspace, i.e. myproject in the example?".

If a repository you depend on wants to refer to @some_repo but you want that to mean the main project, you can do the following:

workspace(name = "myproject")

http_archive(
       name = "xyz", ....,
       repo_mapping = { "@some_repo" : "@myproject" }
)

[nicolov]

It should also remap labels in .bzl files as well - do you have a repro where it does not work?

I have remapped @protobuf_archive to @com_google_protobuf when adding tensorflow to my project's workspace. This worked, but then my build was crashing when trying to use a tensorflow skylark rule that still tried to add @protobuf_archive as a dep/

[Globegitter]

@dslomov What I mean is, I want to be able to alias the external repository itself in my current workspace. So In the example you gave, I suppose I would want something like:

workspace(
    name = "myproject",
    repo_mapping  = { "@xyz": "@abc" },
)

http_archive(
       name = "xyz", ....,
       repo_mapping = { "@some_repo" : "@myproject" }
)

or as the issue creator suggested:

workspace(name = "myproject")

http_archive(
       name = "xyz", ....,
       repo_mapping = { "@some_repo" : "@myproject" }
)

alias(
    name = "abc",
    actual = "xyz",
)

As far as I can see from the documentation that is currently not possible, or am I wrong here?

My concrete use-case is we use yarn_install with an internal workspace name, but the name npm seems to become the standard for this workspace, so to make our internal migration easier I would like to be able to have two names for the same external repository that we can reference in our own BUILD files.

Hope that clarifies the problem.

[dslomov]

Hmm, why don't you just call the xyz repository abc?

[dslomov]

Ah I see, sorry... What forces you to use npm as a name?

[Globegitter]

rules_nodejs started to use @npm as its default name for its dependencies. E.g. see: https://github.com/bazelbuild/rules_nodejs/blob/master/packages/jasmine/src/jasmine_node_test.bzl#L31 So it is just that we can be compatible with the default.

Also I have started to write a plugin for gazelle to auto generate BUILD files, and while it is probably possible to add an option to provide a custom name, I would like to just assume npm for now for simplicity.

Renaming things permanently is a bigger task due to internal reasons, even if it is possible in an automated manner. So being able to alias the name in our current workspace would be preferable. It also would make it simpler to change workspace names of some of our own private external dependencies with a transition period.

[Globegitter]

@dslomov any more thoughts on this?

[Globegitter]

@dslomov Another use-case that just came up when implementing toolchaings for rules_nodejs is that per default we provide a nodejs repository for each supported platform with the name nodejs_<os>_<arch> but for usability and backwards-compatibility reasons it would be nice to provide an alias of the nodejs_<host_os>_<host_arch> to just nodejs as users do interact occasionally directly with tool provided in that repository, e.g. the package manager but also sometimes even node directly to get access to the repl etc. In this case though we would want to generate the alias and provide a .bzl file with it.

[kayasoze]

I suggest this bug be reopened, as the use-case identified by @Globegitter, which I share the need for, remains unsolved.

[dslomov]

If the usage is in your own project, why can't you just rename the references with a simple search and replace? It is more maintainable and less confusing than aliases.
If your other dependencies expect different names, use repo_mapping to remap.

[ccate]

mature projects (ie the family of protobuf projects) have over time changed the names of expected repos, as well as their strategies for fetching dependencies. Working with older versions of protobuf is a nightmare. I believe the request for aliasing repo's is valid.

[chrXiTer]

https://github.com/bazelbuild/rules_python

2019-07-26: The canonical name of this repo has been changed from @io_bazel_rules_python to just @rules_python, in accordance with convention. Please update your WORKSPACE file and labels that reference this repo accordingly.

https://github.com/bazelbuild/rules_python/blob/master/python/pip.bzl

if "rules_python" not in native.existing_rules():
message = "=" * 79 + """\n\
It appears that you are trying to import rules_python without using its
canonical name, "@rules_python". This does not work. Please change your
WORKSPACE file to import this repo with name = "rules_python" instead.
"""
if "io_bazel_rules_python" in native.existing_rules():
message += """\n\
Note that the previous name of "@io_bazel_rules_python" is no longer used.
See https://github.com/bazelbuild/rules_python/issues/203 for context.
"""
message += "=" * 79
fail(message)

MD TNND

Life is so hard

[TheButlah]

This looks like an important and relevant feature - why is this issue still closed?

[TheButlah]

Followup: I agree with @dslomov's point that aliasing repos are not necessary within the main workspace, as you should in theory have full control over that code and be able to find and replace to a name of your choice. Repo mapping fits the rest of the use cases - allowing a translation between the main workspace and the external workspaces names.

However, I'm having the exact same issue as @nicolov. In my case I refer to the flatbuffers repo as @flatbuffers instead of @com_github_google_flatbuffers. In order to compile a flatbuffers schema, I load a macro from the flatbuffers workspace. The loading of the macro via @flatbuffers works fine, but the contents of the macro itself references @com_github_google_flatbuffers in its body. I expected that providing repo_mapping to the http_archive rule I used to add the flatbuffers workspace would have translated this, but it did not - when the macro expands in my main workspace, it references the longer name, and therefore I get a compilation error about a non-existing repository.