Cryptic error when package.json is missing a name

[yjabri]

Is your feature request related to a problem? Please describe.
I was trying out the experimental JavaScript backend and running some "unfriendly" behavior. I've included a minimal reproduction repo to try the following in.

Run pants tailor ::. It populates foo/BUILD with

package_json()

Run pants tailor :: again. You'll get

$ pants tailor ::
14:56:17.68 [ERROR] 1 Exception encountered:

Engine traceback:
  in `tailor` goal

KeyError: 'name'

In a non minimal repo I had package_json() populate like package_json(name="foo0") since I had a python distribution with the same name. Given KeyError: 'name' it feels like tailor is writing an invalid target to the BUILD file. Also running pants help targets package_json doesn't enumerate a name field.

It took me some time to realize this had nothing to do with the BUILD file but instead that my package.json was missing a name.

Describe the solution you'd like
A more explicit message should be given to the caller that package.json needs to have a name the first time pants tailor (or any goal that consumes the file) is called.

Describe alternatives you've considered

Additional context

[huonw]

Thanks for the reproducer. I can reproduce.

---

For someone debugging, here's the stack trace output pants --print-stacktrace tailor ::

09:44:13.39 [ERROR] 1 Exception encountered:

Engine traceback:
  in root
    ..
  in pants.core.goals.tailor.tailor
    `tailor` goal

Traceback (most recent call last):
  File "/Users/huon/Library/Caches/nce/f46d2c12132bad9c27e0dd509186c190371abfe1add7e5ca42245466f35bea81/bindings/venvs/2.20.0/lib/python3.9/site-packages/pants/core/goals/tailor.py", line 650, in tailor
    specs_paths = await Get(SpecsPaths, Specs, specs)
  File "/Users/huon/Library/Caches/nce/f46d2c12132bad9c27e0dd509186c190371abfe1add7e5ca42245466f35bea81/bindings/venvs/2.20.0/lib/python3.9/site-packages/pants/engine/internals/selectors.py", line 124, in __await__
    result = yield self
  File "/Users/huon/Library/Caches/nce/f46d2c12132bad9c27e0dd509186c190371abfe1add7e5ca42245466f35bea81/bindings/venvs/2.20.0/lib/python3.9/site-packages/pants/engine/internals/specs_rules.py", line 313, in resolve_specs_paths
    unfiltered_include_targets, ignore_targets, include_paths, ignore_paths = await MultiGet(
  File "/Users/huon/Library/Caches/nce/f46d2c12132bad9c27e0dd509186c190371abfe1add7e5ca42245466f35bea81/bindings/venvs/2.20.0/lib/python3.9/site-packages/pants/engine/internals/selectors.py", line 436, in MultiGet
    return await _MultiGet((__arg0, __arg1, __arg2, __arg3))
  File "/Users/huon/Library/Caches/nce/f46d2c12132bad9c27e0dd509186c190371abfe1add7e5ca42245466f35bea81/bindings/venvs/2.20.0/lib/python3.9/site-packages/pants/engine/internals/selectors.py", line 174, in __await__
    result = yield self.gets
  File "/Users/huon/Library/Caches/nce/f46d2c12132bad9c27e0dd509186c190371abfe1add7e5ca42245466f35bea81/bindings/venvs/2.20.0/lib/python3.9/site-packages/pants/engine/internals/specs_rules.py", line 258, in resolve_addresses_from_raw_specs
    without_file_owners, with_file_owners = await MultiGet(
  File "/Users/huon/Library/Caches/nce/f46d2c12132bad9c27e0dd509186c190371abfe1add7e5ca42245466f35bea81/bindings/venvs/2.20.0/lib/python3.9/site-packages/pants/engine/internals/selectors.py", line 406, in MultiGet
    return await _MultiGet((__arg0, __arg1))
  File "/Users/huon/Library/Caches/nce/f46d2c12132bad9c27e0dd509186c190371abfe1add7e5ca42245466f35bea81/bindings/venvs/2.20.0/lib/python3.9/site-packages/pants/engine/internals/selectors.py", line 174, in __await__
    result = yield self.gets
  File "/Users/huon/Library/Caches/nce/f46d2c12132bad9c27e0dd509186c190371abfe1add7e5ca42245466f35bea81/bindings/venvs/2.20.0/lib/python3.9/site-packages/pants/engine/internals/specs_rules.py", line 183, in addresses_from_raw_specs_without_file_owners
    target_parametrizations_list = await MultiGet(
  File "/Users/huon/Library/Caches/nce/f46d2c12132bad9c27e0dd509186c190371abfe1add7e5ca42245466f35bea81/bindings/venvs/2.20.0/lib/python3.9/site-packages/pants/engine/internals/selectors.py", line 376, in MultiGet
    return await _MultiGet(tuple(__arg0))
  File "/Users/huon/Library/Caches/nce/f46d2c12132bad9c27e0dd509186c190371abfe1add7e5ca42245466f35bea81/bindings/venvs/2.20.0/lib/python3.9/site-packages/pants/engine/internals/selectors.py", line 174, in __await__
    result = yield self.gets
  File "/Users/huon/Library/Caches/nce/f46d2c12132bad9c27e0dd509186c190371abfe1add7e5ca42245466f35bea81/bindings/venvs/2.20.0/lib/python3.9/site-packages/pants/engine/internals/graph.py", line 349, in resolve_target_parametrizations
    all_generated = await MultiGet(
  File "/Users/huon/Library/Caches/nce/f46d2c12132bad9c27e0dd509186c190371abfe1add7e5ca42245466f35bea81/bindings/venvs/2.20.0/lib/python3.9/site-packages/pants/engine/internals/selectors.py", line 376, in MultiGet
    return await _MultiGet(tuple(__arg0))
  File "/Users/huon/Library/Caches/nce/f46d2c12132bad9c27e0dd509186c190371abfe1add7e5ca42245466f35bea81/bindings/venvs/2.20.0/lib/python3.9/site-packages/pants/engine/internals/selectors.py", line 174, in __await__
    result = yield self.gets
  File "/Users/huon/Library/Caches/nce/f46d2c12132bad9c27e0dd509186c190371abfe1add7e5ca42245466f35bea81/bindings/venvs/2.20.0/lib/python3.9/site-packages/pants/backend/javascript/package_json.py", line 735, in all_package_json
    await Get(
  File "/Users/huon/Library/Caches/nce/f46d2c12132bad9c27e0dd509186c190371abfe1add7e5ca42245466f35bea81/bindings/venvs/2.20.0/lib/python3.9/site-packages/pants/engine/internals/selectors.py", line 124, in __await__
    result = yield self
  File "/Users/huon/Library/Caches/nce/f46d2c12132bad9c27e0dd509186c190371abfe1add7e5ca42245466f35bea81/bindings/venvs/2.20.0/lib/python3.9/site-packages/pants/backend/javascript/package_json.py", line 709, in read_package_jsons
    await MultiGet(
  File "/Users/huon/Library/Caches/nce/f46d2c12132bad9c27e0dd509186c190371abfe1add7e5ca42245466f35bea81/bindings/venvs/2.20.0/lib/python3.9/site-packages/pants/engine/internals/selectors.py", line 376, in MultiGet
    return await _MultiGet(tuple(__arg0))
  File "/Users/huon/Library/Caches/nce/f46d2c12132bad9c27e0dd509186c190371abfe1add7e5ca42245466f35bea81/bindings/venvs/2.20.0/lib/python3.9/site-packages/pants/engine/internals/selectors.py", line 174, in __await__
    result = yield self.gets
  File "/Users/huon/Library/Caches/nce/f46d2c12132bad9c27e0dd509186c190371abfe1add7e5ca42245466f35bea81/bindings/venvs/2.20.0/lib/python3.9/site-packages/pants/backend/javascript/package_json.py", line 688, in parse_package_json
    name=parsed_package_json["name"],
  File "/Users/huon/Library/Caches/nce/f46d2c12132bad9c27e0dd509186c190371abfe1add7e5ca42245466f35bea81/bindings/venvs/2.20.0/lib/python3.9/site-packages/pants/util/frozendict.py", line 77, in __getitem__
    return self._data[k]
KeyError: 'name'