Wrong metadata generated for old Python versions

• I am on the latest Poetry version.
• I have searched the issues of this repo and believe that this is not a duplicate.
• If an exception occurs when executing a command, I executed it again in debug mode (-vvv option).

• OS version and name: Ubuntu 20.04.2 LTS / WSL2
• Poetry version: 1.1.5
• Link of a Gist with the contents of your pyproject.toml file: https://gist.github.com/tueda/4c591340c44139b31093a84c4e63d05e#file-pyproject-toml

Issue

Although Poetry doesn't run with old Python versions like 2.6, as far as I understand, developing packages supporting Python 2.6 should be still supported by Poetry (running with a newer Python).

But it seems that source distributions and wheels generated by poetry build have wrong metadata for old Python versions.
Example:

[tool.poetry.dependencies]
python = "~2.6 || ~2.7 || ^3.2"

Poetry generates:

Metadata-Version: 2.1
Name: example
Version: 0.1.0
Summary: 
Author: Your Name
Author-email: you@example.com
Requires-Python: >=2.7, !=3.0.*, !=3.1.*
Classifier: Programming Language :: Python :: 2
Classifier: Programming Language :: Python :: 2.7
Classifier: Programming Language :: Python :: 3
Classifier: Programming Language :: Python :: 3.4
Classifier: Programming Language :: Python :: 3.5
Classifier: Programming Language :: Python :: 3.6
Classifier: Programming Language :: Python :: 3.7
Classifier: Programming Language :: Python :: 3.8
Classifier: Programming Language :: Python :: 3.9

So, 2.6 is omitted in Requires-Python (same for python_requires in setup.py). 3.2 and 3.3 are also missing in the classifiers.

Reproduce the issue with the linked pyproject.toml and poetry build, then inspect the generated source-distribution and wheel metadata. Check how the Python constraint becomes Requires-Python and classifiers; done means Python 2.6 appears in Requires-Python and Python 3.2 and 3.3 are represented in the classifiers.