Fix bug, when ':dependent => :destroy' option violates foreign key constraints, issue #12380
Moved explanation of `--mountable` option up

The example code uses `--mountable`. In previous version this was followed by an explanation of the `--full` option, which doesn't make sense. Later on in the text this is better explained. I moved this explanation up without repeating too much.
skip migration check if adapter doesn't support it
Prevent state leak.
Remove redundant code.
Parsing DATABASE_URI, use URI#hostname: it's smarter about IPv6

Fixes #15705.
SecurePassword - Validate password must be less than or equal to 72
See #14591, Reason - BCrypt hash function can handle maximum 72 characters.
Merge pull request #15708 from akshay-vishnoi/secure_password

SecurePassword - Validate password must be less than or equal to 72
Added changelog for #15708 [ci skip]
Move cleanup into teardown, delete obsolete code.
Cleaned up the `has_secure_password` test cases

* Grouped the valid test cases in one place
* Make the length of the generated password obvious
* Removed two wrong (copy-and-pasted) test cases
Make sure restoration always happen.
Merge pull request #15710 from zuhao/refactor_actionview_digestor_test

Make sure restoration always happen.
Avoid hard-coded value in test setup and teardown.
Clean up I18n stored translations after test.
Add test cases for Hash#asset_valid_keys
Merge pull request #15712 from zuhao/refactor_actionview_javascript_helper_test

Avoid hard-coded value in test setup and teardown.
Use `@existing_user` while updating existing user, fixing - #ee4e86
pg guide, use the term `database views` to be specific. [ci skip]
Merge pull request #15717 from akshay-vishnoi/test-cases

Use `@existing_user` while updating existing user, fixing - ee4e86