Poetry install fails with maximum recursion limit reached

[vduseev]

Summary

We need to bump up poetry version to preview because poetry < 1.1.0 fails to resolve azure-identity library. Thus builds fail.

How to reproduce

1. Fresh git clone
2. Latest stable poetry release 1.0.10
3. poetry install -E yaml -E toml -E azure -E aws

Updating dependencies
Resolving dependencies... (126.2s)

[RecursionError]
maximum recursion depth exceeded

What happens

Turns out this optional dependency: azure-identity = {version = "^1.4.0", optional = true} has msal-extension as one of its requirements.

msal-extension in turn specifies 2 versions of portalocker depending on the OS and python verison (see AzureAD/microsoft-authentication-extensions-for-python#62)

portalocker~=1.6;platform_system=='Windows'",
portalocker~=1.0;platform_system!='Windows'"

This issue was discussed on Azure SDK for Python repository and it was decided that its poetry's fault (Azure/azure-sdk-for-python#12625).

The issue was fixed recently since poetry 1.1.0a2: python-poetry/poetry#1238

What should happen

Poetry now support such cases and should resolve correctly. After we fix this Travis build should work again.