make `change_column_null` reversible. Closes #13576.

Closes #13623.
Minor typos fix [ci skip]
Move finish_template as the last public method in the generator
Fix typo [ci skip]
Merge pull request #13634 from jwworth/master

Fix typo [ci skip]
refactor generator tests to use block form of Tempfile
Merge pull request #13637 from craftsmen/app-generator-minor-fix

Move finish_template as the last public method defined in the generator
add a more restricted codepath for templates fixes #13390
clear cache on body close so that cache remains during rendering

fixes #13547

The body may use the local cache during rendering.  `call`ing the app
doesn't mean that rendering is finished, so we need to wait until
`close` is called on the body.
change to "check out"
MySQL version 4.1 was EOL on December 31, 2009
We should at least recommend modern versions of MySQL to users.
Merge pull request #13644 from zzak/doc_mysql_config_template

MySQL version 4.1 was EOL on December 31, 2009 [ci-skip]
Adding Hash#compact and Hash#compact! methods

  * Adding Hash#compact and Hash#compact! methods
  * Using Ruby 1.9 syntax on documentation
  * Updating guides for `Hash#compact` and `Hash#compact!` methods
  * Updating CHANGELOG for ActiveSupport
  * Removing unecessary protected method and lambda for `Hash#compact` implementations
  * Performing `Hash#compact` implementation - https://gist.github.com/tinogomes/8332883
  * fixing order position
  * Fixing typo
Merge pull request #13632 from tinogomes/master

Adding Hash#compact and Hash#compact! methods
Check `respond_to` before delegation due to: https://github.com/ruby/ruby/commit/d781caaf313b8649948c107bba277e5ad7307314
Revert "ask the fixture set for the sql statements"

This reverts commit 026d0555685087845b74dd87a0417b5a164b1c13.

Conflicts:
	activerecord/lib/active_record/fixtures.rb

Fixes #13383
Merge branch 'master' into ruby-2.2

* master:
  Revert "ask the fixture set for the sql statements"
Ensure Active Record connection consistency

Currently Active Record can be configured via the environment variable `DATABASE_URL` or by manually injecting a hash of values which is what Rails does, reading in `database.yml` and setting Active Record appropriately. Active Record expects to be able to use `DATABASE_URL` without the use of Rails, and we cannot rip out this functionality without deprecating. This presents a problem though when both config is set, and a `DATABASE_URL` is present. Currently the `DATABASE_URL` should "win" and none of the values in `database.yml` are used. This is somewhat unexpected to me if I were to set values such as `pool` in the `production:` group of `database.yml` they are ignored.

There are many ways that active record initiates a connection today:

- Stand Alone (without rails)
  - `rake db:<tasks>`
  - ActiveRecord.establish_connection
 
- With Rails
  - `rake db:<tasks>`
  - `rails <server> | <console>`
  - `rails dbconsole`


We should make all of these behave exactly the same way. The best way to do this is to put all of this logic in one place so it is guaranteed to be used.

Here is my prosed matrix of how this behavior should work:

```
No database.yml
No DATABASE_URL
=> Error
```

```
database.yml present
No DATABASE_URL
=> Use database.yml configuration
```

```
No database.yml
DATABASE_URL present
=> use DATABASE_URL configuration
```

```
database.yml present
DATABASE_URL present
=> Merged into `url` sub key. If both specify `url` sub key, the `database.yml` `url`
   sub key "wins". If other paramaters `adapter` or `database` are specified in YAML,
   they are discarded as the `url` sub key "wins".
```

### Implementation

Current implementation uses `ActiveRecord::Base.configurations` to resolve and merge all connection information before returning. This is achieved through a utility class: `ActiveRecord::ConnectionHandling::MergeAndResolveDefaultUrlConfig`.

To understand the exact behavior of this class, it is best to review the behavior in activerecord/test/cases/connection_adapters/connection_handler_test.rb though it should match the above proposal.
Improve ERB dependency detection.

The current implementation can't handle some special cases of oddly-formatted Ruby. Now we are able to detect them:

* Multi-line arguments on the `render` call
* Strings containing quotes, e.g. `"something's wrong"`
* Multiple kinds of identifiers - instance variables, class variables and globals
* Method chains as arguments for the `render` call

Also, this fix reduces the rate of "false positives" which showed up when we had calls/access to identifiers containing `render`, like `surrender` and `rendering`.
Avoid scanning multiple render calls as a single match.

Each chunk of text coming after `render` is now handled individually as a possible list of arguments.