Confusing error message when conda-lock fails to parse meta.yaml

[arthurp]

I'm pretty sure my meta.yaml is too complex for conda-lock to process. I'm fine with this. However, the error message is very confusing because it comes from inside jinja2:

$ conda-lock lock -p linux-64  -f conda_recipe/meta.yaml 
[...]
TypeError: no loader for this environment specified

Full error message

$ conda-lock lock -p linux-64  -f conda_recipe/meta.yaml 
generating lockfile for linux-64
Traceback (most recent call last):
  File "/home/amp/LocalInstalls/conda/miniconda3/envs/katana-dev/bin/conda-lock", line 10, in <module>
    sys.exit(main())
  File "/home/amp/LocalInstalls/conda/miniconda3/envs/katana-dev/lib/python3.8/site-packages/click/core.py", line 829, in __call__
    return self.main(*args, **kwargs)
  File "/home/amp/LocalInstalls/conda/miniconda3/envs/katana-dev/lib/python3.8/site-packages/click/core.py", line 782, in main
    rv = self.invoke(ctx)
  File "/home/amp/LocalInstalls/conda/miniconda3/envs/katana-dev/lib/python3.8/site-packages/click/core.py", line 1259, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
  File "/home/amp/LocalInstalls/conda/miniconda3/envs/katana-dev/lib/python3.8/site-packages/click/core.py", line 1066, in invoke
    return ctx.invoke(self.callback, **ctx.params)
  File "/home/amp/LocalInstalls/conda/miniconda3/envs/katana-dev/lib/python3.8/site-packages/click/core.py", line 610, in invoke
    return callback(*args, **kwargs)
  File "/home/amp/LocalInstalls/conda/miniconda3/envs/katana-dev/lib/python3.8/site-packages/conda_lock/conda_lock.py", line 598, in lock
    run_lock(
  File "/home/amp/LocalInstalls/conda/miniconda3/envs/katana-dev/lib/python3.8/site-packages/conda_lock/conda_lock.py", line 504, in run_lock
    make_lock_files(
  File "/home/amp/LocalInstalls/conda/miniconda3/envs/katana-dev/lib/python3.8/site-packages/conda_lock/conda_lock.py", line 274, in make_lock_files
    lock_specs = parse_source_files(
  File "/home/amp/LocalInstalls/conda/miniconda3/envs/katana-dev/lib/python3.8/site-packages/conda_lock/conda_lock.py", line 420, in parse_source_files
    parse_meta_yaml_file(src_file, platform, include_dev_dependencies)
  File "/home/amp/LocalInstalls/conda/miniconda3/envs/katana-dev/lib/python3.8/site-packages/conda_lock/src_parser/meta_yaml.py", line 99, in parse_meta_yaml_file
    rendered = t.render()
  File "/home/amp/.local/lib/python3.8/site-packages/jinja2/environment.py", line 1090, in render
    self.environment.handle_exception()
  File "/home/amp/.local/lib/python3.8/site-packages/jinja2/environment.py", line 832, in handle_exception
    reraise(*rewrite_traceback_stack(source=source))
  File "/home/amp/.local/lib/python3.8/site-packages/jinja2/_compat.py", line 28, in reraise
    raise value.with_traceback(tb)
  File "<template>", line 1, in top-level template code
TypeError: no loader for this environment specified

The meta.yaml file involved is: https://github.com/KatanaGraph/katana/blob/9a63b012a09b5261ec5b12b06c51f3f576713df4/conda_recipe/meta.yaml

The error is the same with conda-lock versions (the message above is from 0.8.0):

• conda-lock 0.8.0 pyhd8ed1ab_0 conda-forge
• conda-lock 0.8.1.dev2+g2702768 pypi_0 pypi (installed with pip install .)

[mariusvniekerk]

yeah the meta.yaml support only really works for very simple conda recipes without lots of fancy templates. For your case you are probably better off locking from an environment.yaml

[arthurp]

Definitely. :-) Hence the issue being about the error, not the failure itself.