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Deprecating Ember.Logger #297

merged 9 commits into from Mar 2, 2018
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- 2018-01-17
- RFC PR: 0297
- Ember Issue: (leave this empty)

# Deprecation of Ember.Logger

## Summary

This RFC recommends the deprecation and eventual removal of `Ember.Logger`.

## Motivation

There are a variety of features of Ember designed to support old browsers,
features that are no longer needed. `Ember.Logger` came into being because
the browser support for the console was inconsistent. In some browsers,
like Internet Explorer 9, the console only existed when the developer tools
panel was open, which caused null references and program crashes when run
with the console closed. `Ember.Logger` provided methods that would route to
the console when it was available.

With Ember 3.x, Ember no longer supports these older browsers, and hence this
feature no longer serves a purpose. Removing it will make Ember smaller and

## Detailed design

For the most part, this is a 1:1 substitution of the global `console` object
for `Ember.Logger`. However, Node only added support for `console.debug` in
Node version 9. If we wish to support earlier versions of Node, our codemod
will need to use `console.log`, rather than `console.debug`, as the
replacement for `Logger.debug`. For users who don't care about Node or are
specifying Node version 9 as their minimum, we could use `console.debug`.

### Within the framework

Remove the following direct uses of `Ember.Logger` from the ember.js and
ember-data projects:

* `ember-debug`:
* deprecate (`ember-debug\lib\deprecate.js`) - `Logger.warn`
* debug (`ember-debug\lib\index.js`) - ``
* warn (`ember-debug\lib\warn.js`) - `Logger.warn`
* `ember-routing` (`ember-routing\lib\system\router.js`):
* transitioned to - `Logger.log`
* preparing to transition to - `Logger.log`
* intermediate-transitioned to - `Logger.log`
* `ember-testing`:
* Testing paused (`ember-testing\lib\helpers\pause_test.js`) - ``
* Catch-all handler (`ember-testing\lib\test\adapter.js`) - `Logger.error`
* `ember-data`:
* `tests\test-helper.js`- `Logger.log`

Adjust all test code that redirects logging and sets it back:

* `ember\tests\routing\basic_test.js` (adjust)
* `ember-application\tests\system\dependency_injection\default_resolver_test.js` (adjust)
* `ember-application\tests\system\logging_test.js` (remove?)
* `ember-glimmer\tests\integration\helpers\log-test.js` (remove?)

Note: None of the uses of `Ember.Logger` in `ember.js` or `ember-data` involve
`Ember.debug`, so that issue doesn't affect the Ember.js code directly.

Add deprecation warnings to the implementation: `ember-console\lib\index.js`.
Bear in mind that the deprecation mechanism in `ember-debug` currently calls
`Logger.warn`, so the `ember-debug` code should be changed _first_ or adding
the deprecation warning will create a deep recursion.

The log and debug messages emitted by Ember for deprecations and assertions

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locks Jan 19, 2018


You might want to slightly rephrase this section to specifically indicate that it is Ember.warn and friends that are noops in production.

are not emitted on production. However, this is because they are suppressed
by the ember-debug module, which currently consumes `Ember.Logger`, _not_
by `Ember.Logger` itself. Hence, replacing calls to `Ember.Logger` with
direct calls to the console will not affect this behavior.

### Codemod

Provide a codemod that developers can use to switch references to the methods
of `Ember.Logger` to use the corresponding `console` methods instead. I
will definitely need help here.

### Add-On Developers

The following high-impact add-ons (9 or 10 or a * on EmberObserver) use
`Ember.Logger` and should probably be given an early heads-up to adjust
their code to use `console` before this RFC is implemented. This will limit
the level of pain that their users experience when the deprecation is released.

In the order of their number of references to `Ember.Logger`:

* `ember-concurrency` (15)
* `ember-cli-deprecation-workflow` (9)
* `ember-stripe-service` (9)
* `semantic-ui-ember` (7)
* `ember-resolver` (6)
* `ember-cli-page-object` (4)
* `ember-cli-sentry` (3)
* `ember-islands` (3)
* `ember-states` (3)
* `ember-cli-pagination` (2)
* `ember-cli-clipboard` (1)
* `ember-cli-fastboot` (1)
* `ember-elsewhere` (1)
* `ember-i18n` (1)
* `ember-simple-auth-token` (1)
* `ember-svg-jar` (1)
* `liquid-fire` (1)

For details, see

## How we teach this

### Communication of change

We need to inform users that `Ember.Logger` will be deprecated and in what
release it will occur.

### Official code bases and documentation

We do not currently actively teach the use of `Ember.Logger`. We will need to
remove any passing references to `Ember.Logger` from the Ember guides
from the Super Rentals tutorial, and anywhere else it appears on the website.

Once it is gone from the code, we also need to verify it no longer appears in
the API listings.

We must provide an entry in the deprecation guide for this change:
* offering instruction for using the codemod to perform the change automatically
with before and after code samples.
* describing the issue with using console.debug on node versions
earlier than Node 9 and what provision the codemod has made to deal with it.
* describing alternative ways of dealing with eslint's `no-console` messages.

## Drawbacks

191 add-ons in Ember Inspector are using `Ember.Logger`. It has been there and
documented for a long time. So this deprecation will cause some level of change
on many projects.

This, of course, can be said for almost any deprecation, and Ember's
disciplined approach to deprecation has been repeatedly shown to ease things.
Providing a codemod to replace `Ember.Logger` calls with the corresponding
console calls should make this transition relatively painless. Also, only
twenty of those add-ons have more than six references to `Ember.Logger`.
If this is characteristic of the user base, the level of effort to make
the change, even by hand, should be very small for most users.

Those using `Logger.debug` as something different from `Logger.log`may have at
least a theoretical concern. Under the covers `Logger.debug` only calls
`console.debug` if it exists, calling `console.log` otherwise. The only
platform where the difference between the two is visible in the console is on
Safari. We can encourage folks with a tangible, practical concern about this to
speak up during the comment period, but I don't anticipate this will have much

## Alternatives

1. Leave things as they are, perhaps providing an `@ember/console` module

2. Extract `Ember.Logger` into its own (tiny) `@ember/console` package as
a shim for users.

## Unresolved questions

How do we deal with `Logger.debug` in the codemod?

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locks Jan 19, 2018


A suggestion: Try making the question a sub-header and not use bullet points for all of the answer.

* Do we provide separate options for those who might use Node versions
earlier than 9 and those who are confident they will only use Node
version 9 or later?
* Do we have the codemod inject a polyfill for `console.debug` that calls
* Do we provide one separately for the user to apply?
* Or does that become a fastboot concern, since that's the primary driver
for running ember projects in node?

What do we do about the eslint `no-console` flag?

* Some developers are using `Ember.Logger` right now to work around it,
while others are providing their own logging service, and others are just
providing override comments.
* Currently, `no-console` is in the default set of flags set with eslint,
and ember-cli doesn't override the defaults in its set of flags to turn it off.
* Should we turn it off in the ember-cli settings?
* Or should that be left as a user decision?

I'm inclined toward the latter.
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