[workspaces] Better error handling of non-dependent package

[climblinne]

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Hello,

I am testing the workspace feature on Windows 10, Conan 1.6.1 & CMake 3.12.1.
When I just add a new library, which have no dependency (D = copy of C), I got this error message:

λ conan install . -if=build
Using conanws.yml file from C:\work\dsp\test\conan-workspace-example_additonal_D_without_dependency\conan-workspace-example
Workspace: Installing...
Requirements
    HelloA/root@project/develop from 'conanws.yml' - Workspace
    HelloB/0.1@user/testing from 'conanws.yml' - Workspace
    HelloC/0.1@user/testing from 'conanws.yml' - Workspace
Packages
    HelloA/root@project/develop:8562c08f9b976eb0eada9e5b55718f5f7733bc9a - Workspace
    HelloB/0.1@user/testing:19056882ab002381c35270bdb67b66b12d5b6ea6 - Workspace
    HelloC/0.1@user/testing:6cc50b139b9c3d27b3e9042d5f5372d327b3a9f7 - Workspace

Workspace HelloC: Generator cmake created conanbuildinfo.cmake
Workspace HelloC: Generated conaninfo.txt
Workspace HelloC: Generated conanbuildinfo.txt
Workspace HelloB: Generator cmake created conanbuildinfo.cmake
Workspace HelloB: Generated conaninfo.txt
Workspace HelloB: Generated conanbuildinfo.txt
Workspace HelloA: Generator cmake created conanbuildinfo.cmake
Workspace HelloA: Generated conaninfo.txt
Workspace HelloA: Generated conanbuildinfo.txt
Traceback (most recent call last):
  File "c:\tools\python3\lib\site-packages\conans\model\ref.py", line 70, in loads
    name, version, user, channel = tokens
ValueError: not enough values to unpack (expected 4, got 1)

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "c:\tools\python3\lib\site-packages\conans\client\command.py", line 314, in install
    reference = ConanFileReference.loads(args.path_or_reference)
  File "c:\tools\python3\lib\site-packages\conans\model\ref.py", line 73, in loads
    "OpenCV/1.0.6@user/stable" % text)
conans.errors.ConanException: Wrong package recipe reference .
Write something like OpenCV/1.0.6@user/stable

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "c:\tools\python3\lib\site-packages\conans\client\command.py", line 1230, in run
    method(args[0][1:])
  File "c:\tools\python3\lib\site-packages\conans\client\command.py", line 325, in install
    install_folder=args.install_folder)
  File "c:\tools\python3\lib\site-packages\conans\client\conan_api.py", line 79, in wrapper
    return f(*args, **kwargs)
  File "c:\tools\python3\lib\site-packages\conans\client\conan_api.py", line 466, in install
    manager.install_workspace(profile, workspace, remote, build, update)
  File "c:\tools\python3\lib\site-packages\conans\client\manager.py", line 218, in install_workspace
    workspace.generate()
  File "c:\tools\python3\lib\site-packages\conans\model\workspace.py", line 114, in generate
    build_folder = workspace_package.build_folder
  File "c:\tools\python3\lib\site-packages\conans\model\workspace.py", line 38, in build_folder
    folder = self._evaluate(self._build_folder)
  File "c:\tools\python3\lib\site-packages\conans\model\workspace.py", line 70, in _evaluate
    settings = self.conanfile.settings
AttributeError: 'NoneType' object has no attribute 'settings'

ERROR: 'NoneType' object has no attribute 'settings'

The error message is not really self explaining.
It would be much better to handle, when something like
"Error: Could not integrate HelloD, because no dependency to root exists"
would come as an error. Also I think, that may be just a warning (or asking) and still integrating in the workspace would also be fine.
The demo project is here:
conan-workspace-example_additonal_D_without_dependency.zip

Best regards

Jan

[lasote]

@memsharded the ugliness of the error (the ValueError: not enough values to unpack (expected 4, got 1) not the real error itself) is fixed at https://github.com/conan-io/conan/pull/3350/files with the command.py change.

[memsharded]

Workspaces were removed in 2.0, but the plan is to resume work on them in the 2.X roadmap.
Please track progress in #12466, closing this