Better error message when signing up with social and unable to link

[corradio]

Links:

• Feature request: Automatically connecting an account to an already registered email pennersr/django-allauth#418 (comment)
• https://stackoverflow.com/questions/28897220/django-allauth-social-account-connect-to-existing-account-on-login

Internal Server Error: /accounts/social/signup/

IntegrityError at /accounts/social/signup/
duplicate key value violates unique constraint "account_emailaddress_email_key"
DETAIL: Key (email)=(xx@electricitymaps.com) already exists.

Request Method: POST
Request URL: https://polynomial.so/accounts/social/signup/
Django Version: 4.1.7
Python Executable: /usr/local/bin/python
Python Version: 3.9.16
Python Path: ['/code', '/code', '/usr/local/bin', '/usr/local/lib/python39.zip', '/usr/local/lib/python3.9', '/usr/local/lib/python3.9/lib-dynload', '/root/.local/lib/python3.9/site-packages', '/usr/local/lib/python3.9/site-packages']
Server time: Wed, 22 Mar 2023 14:57:27 +0000
Installed Applications:
['django.contrib.admin',
'django.contrib.auth',
'django.contrib.contenttypes',
'django.contrib.sessions',
'django.contrib.messages',
'django.contrib.staticfiles',
'django_jsonform',
'allauth',
'allauth.account',
'allauth.socialaccount',
'allauth.socialaccount.providers.google',
'allauth.socialaccount.providers.linkedin_oauth2',
'compressor',
'mainapp']
Installed Middleware:
['django.middleware.security.SecurityMiddleware',
'whitenoise.middleware.WhiteNoiseMiddleware',
'django.contrib.sessions.middleware.SessionMiddleware',
'django.middleware.common.CommonMiddleware',
'django.middleware.csrf.CsrfViewMiddleware',
'django.contrib.auth.middleware.AuthenticationMiddleware',
'django.contrib.messages.middleware.MessageMiddleware',
'django.middleware.clickjacking.XFrameOptionsMiddleware']

Traceback (most recent call last):
File "/usr/local/lib/python3.9/site-packages/allauth/account/utils.py", line 313, in send_email_confirmation
email_address = EmailAddress.objects.get_for_user(user, email)
File "/usr/local/lib/python3.9/site-packages/allauth/account/managers.py", line 63, in get_for_user
raise self.model.DoesNotExist()

During handling of the above exception (), another exception occurred:
File "/usr/local/lib/python3.9/site-packages/django/db/models/query.py", line 929, in get_or_create
return self.get(**kwargs), False
File "/usr/local/lib/python3.9/site-packages/django/db/models/query.py", line 650, in get
raise self.model.DoesNotExist(

[corradio]

Note: we can't auto log in as we'd need to verify that the social email address is verified (else someone could be impersonating). This is only possible with Google and is provider dependant.

Update: a new user friendly error is now shown since c12bc39:

[corradio]

Action: add a better error message, see pennersr/django-allauth#215 (comment)
Depends on #107

Note: we should let the providers define their verified flag on email addresses and avoid overriding it. For example, even if we know LinkedIn addresses are supposed to be verified, it is unclear if the user added a new email that hasn't been verified yet.