☂️ Migrate iOS embedder objective-c code to ARC (Auto Reference Counting)

[cyanglaz]

Most of the files in ios Embedder and some shared darwin codes use MRC(Manual Reference Counting).

Manual Reference Counting is easy to make memory management mistake with. Objecgtive-C with Manual Reference Counting is not pleasant to work with, often scaring away contributors.

Migrate all the objective-C code to ARC will boosts Flutter's stability on iOS and making contributing to Flutter iOS embedder more efficient.

This is an umbrella issue tracks all the work needs to be done to migrate the iOS embedder to ARC:

1. Temporarily enable Objective-C smart pointers (scoped_nsobject, scoped_block etc) to work with both ARC and MRC.
2. Migrate all Objective-C files to ARC.
3. [iOS] Eliminate ARC __bridge casts where possible #155943
4. Remove the support of Objective-C smart pointers

[chinmaygarde]

Is there a general issue for this that include macOS?

[cyanglaz]

Is there a general issue for this that include macOS?

macOS is already in ARC so I didn't create an issue for macOS. I can't think of any impact it could cause on macOS. Loop in @cbracken for might insights.

[cbracken]

Correct -- we're already building with ARC for macOS. I can't remember if the shared code in '//flutter/platform/darwin/common' is built with ARC enabled or not.

[cbracken]

To answer my own question, the bulk of the common code is ARC-enabled.
https://github.com/flutter/engine/blob/cc925b0021330759e18960e1ccbd7e55dec3c375/shell/platform/darwin/common/BUILD.gn#L61-L63