Twine no longer prompts or resolves from keyring

[jaraco]

Following the acceptance of #426, TWINE_USERNAME is no longer honored and the default value of '' seems to be used instead, even if no ~/.pypirc is present.

Steps to Reproduce

With keyring configured with credentials and master checked out to ~/p/pypa/twine,

draft $ pip download --no-deps pip                                                                                                                                                       
Collecting pip
  Using cached https://files.pythonhosted.org/packages/46/dc/7fd5df840efb3e56c8b4f768793a237ec4ee59891959d6a215d63f727023/pip-19.0.1-py2.py3-none-any.whl
  Saved ./pip-19.0.1-py2.py3-none-any.whl
Successfully downloaded pip
draft $ env TWINE_USERNAME=jaraco pip-run '~/p/pypa/twine[keyring]' -- -m twine upload pip*.whl                                                                                                                    
Processing /Users/jaraco/p/pypa/twine
Collecting pkginfo>=1.4.2 (from twine==1.12.1)
  Using cached https://files.pythonhosted.org/packages/e6/d5/451b913307b478c49eb29084916639dc53a88489b993530fed0a66bab8b9/pkginfo-1.5.0.1-py2.py3-none-any.whl
Collecting readme_renderer>=21.0 (from twine==1.12.1)
  Using cached https://files.pythonhosted.org/packages/c3/7e/d1aae793900f36b097cbfcc5e70eef82b5b56423a6c52a36dce51fedd8f0/readme_renderer-24.0-py2.py3-none-any.whl
Collecting requests!=2.15,!=2.16,>=2.5.0 (from twine==1.12.1)
  Using cached https://files.pythonhosted.org/packages/7d/e3/20f3d364d6c8e5d2353c72a67778eb189176f08e873c9900e10c0287b84b/requests-2.21.0-py2.py3-none-any.whl
Collecting requests-toolbelt!=0.9.0,>=0.8.0 (from twine==1.12.1)
  Using cached https://files.pythonhosted.org/packages/60/ef/7681134338fc097acef8d9b2f8abe0458e4d87559c689a8c306d0957ece5/requests_toolbelt-0.9.1-py2.py3-none-any.whl
Collecting setuptools>=0.7.0 (from twine==1.12.1)
  Using cached https://files.pythonhosted.org/packages/d1/6a/4b2fcefd2ea0868810e92d519dacac1ddc64a2e53ba9e3422c3b62b378a6/setuptools-40.8.0-py2.py3-none-any.whl
Collecting tqdm>=4.14 (from twine==1.12.1)
  Using cached https://files.pythonhosted.org/packages/76/4c/103a4d3415dafc1ddfe6a6624333971756e2d3dd8c6dc0f520152855f040/tqdm-4.30.0-py2.py3-none-any.whl
Collecting keyring (from twine==1.12.1)
  Using cached https://files.pythonhosted.org/packages/28/01/06f2e55264994a89d543ee37f2cfc4af85800824a8ca5c6532f715ff41a9/keyring-17.1.1-py2.py3-none-any.whl
Collecting docutils>=0.13.1 (from readme_renderer>=21.0->twine==1.12.1)
  Using cached https://files.pythonhosted.org/packages/36/fa/08e9e6e0e3cbd1d362c3bbee8d01d0aedb2155c4ac112b19ef3cae8eed8d/docutils-0.14-py3-none-any.whl
Collecting Pygments (from readme_renderer>=21.0->twine==1.12.1)
  Using cached https://files.pythonhosted.org/packages/13/e5/6d710c9cf96c31ac82657bcfb441df328b22df8564d58d0c4cd62612674c/Pygments-2.3.1-py2.py3-none-any.whl
Collecting six (from readme_renderer>=21.0->twine==1.12.1)
  Using cached https://files.pythonhosted.org/packages/73/fb/00a976f728d0d1fecfe898238ce23f502a721c0ac0ecfedb80e0d88c64e9/six-1.12.0-py2.py3-none-any.whl
Collecting bleach>=2.1.0 (from readme_renderer>=21.0->twine==1.12.1)
  Using cached https://files.pythonhosted.org/packages/ab/05/27e1466475e816d3001efb6e0a85a819be17411420494a1e602c36f8299d/bleach-3.1.0-py2.py3-none-any.whl
Collecting chardet<3.1.0,>=3.0.2 (from requests!=2.15,!=2.16,>=2.5.0->twine==1.12.1)
  Using cached https://files.pythonhosted.org/packages/bc/a9/01ffebfb562e4274b6487b4bb1ddec7ca55ec7510b22e4c51f14098443b8/chardet-3.0.4-py2.py3-none-any.whl
Collecting certifi>=2017.4.17 (from requests!=2.15,!=2.16,>=2.5.0->twine==1.12.1)
  Using cached https://files.pythonhosted.org/packages/9f/e0/accfc1b56b57e9750eba272e24c4dddeac86852c2bebd1236674d7887e8a/certifi-2018.11.29-py2.py3-none-any.whl
Collecting idna<2.9,>=2.5 (from requests!=2.15,!=2.16,>=2.5.0->twine==1.12.1)
  Using cached https://files.pythonhosted.org/packages/14/2c/cd551d81dbe15200be1cf41cd03869a46fe7226e7450af7a6545bfc474c9/idna-2.8-py2.py3-none-any.whl
Collecting urllib3<1.25,>=1.21.1 (from requests!=2.15,!=2.16,>=2.5.0->twine==1.12.1)
  Using cached https://files.pythonhosted.org/packages/62/00/ee1d7de624db8ba7090d1226aebefab96a2c71cd5cfa7629d6ad3f61b79e/urllib3-1.24.1-py2.py3-none-any.whl
Collecting entrypoints (from keyring->twine==1.12.1)
  Using cached https://files.pythonhosted.org/packages/ac/c6/44694103f8c221443ee6b0041f69e2740d89a25641e62fb4f2ee568f2f9c/entrypoints-0.3-py2.py3-none-any.whl
Collecting webencodings (from bleach>=2.1.0->readme_renderer>=21.0->twine==1.12.1)
  Using cached https://files.pythonhosted.org/packages/f4/24/2a3e3df732393fed8b3ebf2ec078f05546de641fe1b667ee316ec1dcf3b7/webencodings-0.5.1-py2.py3-none-any.whl
Building wheels for collected packages: twine
  Building wheel for twine (setup.py) ... done
  Stored in directory: /private/var/folders/c6/v7hnmq453xb6p2dbz1gqc6rr0000gn/T/pip-ephem-wheel-cache-fhtn_rdf/wheels/90/ca/66/3db8b67d59f0fb1b9732c90aad29a220f1dcb3b92d43280d40
Successfully built twine
Installing collected packages: pkginfo, docutils, Pygments, six, webencodings, bleach, readme-renderer, chardet, certifi, idna, urllib3, requests, requests-toolbelt, setuptools, tqdm, entrypoints, keyring, twine
Successfully installed Pygments-2.3.1 bleach-3.1.0 certifi-2018.11.29 chardet-3.0.4 docutils-0.14 entrypoints-0.3 idna-2.8 keyring-17.1.1 pkginfo-1.5.0.1 readme-renderer-24.0 requests-2.21.0 requests-toolbelt-0.9.1 setuptools-40.8.0 six-1.12.0 tqdm-4.30.0 twine-1.12.1 urllib3-1.24.1 webencodings-0.5.1
Uploading distributions to https://upload.pypi.org/legacy/
Uploading pip-19.0.1-py2.py3-none-any.whl
100%|████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████| 1.30M/1.30M [00:01<00:00, 930kB/s]
NOTE: Try --verbose to see response content.
HTTPError: 403 Client Error: Invalid or non-existent authentication information. for url: https://upload.pypi.org/legacy/

[jaraco]

I think I better understand the issue here. The issue isn't that the blank username is overriding the TWINE_USERNAME variable, but that the blank password is now overriding the keyring fallback, because of how the keyring behavior is treated as a silent "prompt".

[sigmavirus24]

Well done @jaraco