Failed to coerce attr `licenses` when using `vendor=false` on a crate containing license metadata

[Fletcher Nichol]

As mentioned in #11:

so you might encounter wonky targets such as:

rust_library(
    ...
    licenses = ["../../../home/steveklabnik/.cargo/registry/src/index.crates.io-6f17d22bba15001f/owo-colors-3.5.0/LICENSE"],
)

Funny enough, this is precisely the issue I was running into this afternoon, and with the owo-colors LICENSE location, leading to a buck2 targets //... error like:

❯ buck2 targets //...
File changed: root//third-party/BUCK
Error parsing root//third-party
Error evaluating build file: `root//third-party:BUCK`

Caused by:
    Traceback (most recent call last):
      * third-party/BUCK:800, in <module>
          third_party_rust_library(
      * third-party/reindeer.bzl:20, in third_party_rust_library
          native.rust_library(
    error: Error coercing attribute `licenses` of `root//third-party:owo-colors-3.5.0`
      --> third-party/reindeer.bzl:20:5
       |
    20 |       native.rust_library(
       |  _____^
    21 | |         doctests = False,
    22 | |         **kwargs
    23 | |     )
       | |_____^
       |


    Error coercing attribute `licenses` of `root//third-party:owo-colors-3.5.0`

    Caused by:
        0: Error coercing attribute `licenses` of type `attrs.list(attrs.source(), default=[])`
        1: Error coercing ["../../../../../.cargo/registry/src/github.com-1ecc6299db9ec823/owo-colors-3.5.0/LICENSE"]
        2: Error coercing "../../../../../.cargo/registry/src/github.com-1ecc6299db9ec823/owo-colors-3.5.0/LICENSE"
        3: Couldn't coerce `../../../../../.cargo/registry/src/github.com-1ecc6299db9ec823/owo-colors-3.5.0/LICENSE` as a source.
             Error when treated as a target: Invalid absolute target pattern `../../../../../.cargo/registry/src/github.com-1ecc6299db9ec823/owo-colors-3.5.0/LICENSE` is not allowed: Expected a `:`, a trailing `/...` or the literal `...`.
             Error when treated as a path: expected a normalized path but got an un-normalized path instead: `../../../../../.cargo/registry/src/github.com-1ecc6299db9ec823/owo-colors-3.5.0/LICENSE`

Failed to parse 1 package
Build ID: ee2088e2-0803-4464-8ee0-18bc1c64be56
Jobs completed: 4. Time elapsed: 0.0s.

I was operating under the assumption that the relative path to LICENSE was outside the Buck2 package. Ideally, what would be a reasonable value for the third_party_rust_library rule's licenses argument? I'm working backwards in Reindeer's code to understand, so forgive a newcomer 😄

[David Tolnay]

Sorry about the breakage.

I think the correct behavior would be to not emit a licenses attribute at all in this mode.

licenses is not meaningful to any code in the prelude as far as I know. The only uses are by external tools, which are able to do things like:

$ buck2 uquery 'kind("rust_library", //...)' --output-attribute license
{
  "root//third-party:owo-colors-3.5.0": {
    "licenses": [
      "root//third-party/vendor/owo-colors-3.5.0/LICENSE"
    ]
  },
  ...
}

[David Tolnay]

In the short term, you can unblock yourself without reindeer changes by adding a macro (or maybe you already have one).

# third-party/defs.bzl

def rust_library(**kwargs):
    kwargs.pop("licenses", None)
    native.rust_library(**kwargs)

# reindeer.toml

[buck]
buckfile_imports = """
load("//third_party/defs.bzl", "rust_library")
"""

(Reindeer will still put the bad paths into your generated targets, but it won't break your build anymore.)

[Fletcher Nichol]

Confirmed that's working great, thank you! 🎉