[pigeon] Allow multi instance support with message channel name suffix

[tarrinneal]

Adds the ability to instantiate any api using a suffix string to allow for unique instances.

partial flutter/flutter#66710

Pre-launch Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I read the Tree Hygiene wiki page, which explains my responsibilities.
• I read and followed the relevant style guides and ran the auto-formatter. (Unlike the flutter/flutter repo, the flutter/packages repo does use dart format.)
• I signed the CLA.
• The title of the PR starts with the name of the package surrounded by square brackets, e.g. [shared_preferences]
• I listed at least one issue that this PR fixes in the description above.
• I updated pubspec.yaml with an appropriate new version according to the pub versioning philosophy, or this PR is exempt from version changes.
• I updated CHANGELOG.md to add a description of the change, following repository CHANGELOG style.
• I updated/added relevant documentation (doc comments with ///).
• I added new tests to check the change I am making, or this PR is test-exempt.
• All existing and new tests are passing.

If you need help, consider asking for advice on the #hackers-new channel on Discord.

[stuartmorgan-g]

With the changes below the tests run, but there's a bad allocation exception being thrown that I'm still looking into.

[tarrinneal]

This is fully ready for review @stuartmorgan @hellohuanlin and @bparrishMines for anyone who wants to give it a look

[hellohuanlin]

reviewed the ios part

[unknown-undefined]

It appears there could be a bug within the Objective-C generator in c55a91673d7b. Specifically, the issue involves the messageChannelSuffix being repeatedly modified in the generated code. Initially, it's changed to .messageChannelSuffix, but with subsequent generations, an additional dot is prepended each time, leading to ..messageChannelSuffix, then ...messageChannelSuffix, and so on, eventually resulting in .......messageChannelSuffix.

  {
      messageChannelSuffix = messageChannelSuffix.length > 0 ? [NSString stringWithFormat: @".%@", messageChannelSuffix] : @"";
    FlutterBasicMessageChannel *channel =
      [[FlutterBasicMessageChannel alloc]
        initWithName:[NSString stringWithFormat:@"%@%@", @"SDK.joinChannel", messageChannelSuffix]
        binaryMessenger:binaryMessenger
        codec:SDKGetCodec()];
   ...
  }
  {
      messageChannelSuffix = messageChannelSuffix.length > 0 ? [NSString stringWithFormat: @".%@", messageChannelSuffix] : @"";
...

[tarrinneal]

It appears there could be a bug within the Objective-C generator in c55a91673d7b. Specifically, the issue involves the messageChannelSuffix being repeatedly modified in the generated code. Initially, it's changed to .messageChannelSuffix, but with subsequent generations, an additional dot is prepended each time, leading to ..messageChannelSuffix, then ...messageChannelSuffix, and so on, eventually resulting in .......messageChannelSuffix.

  {
      messageChannelSuffix = messageChannelSuffix.length > 0 ? [NSString stringWithFormat: @".%@", messageChannelSuffix] : @"";
    FlutterBasicMessageChannel *channel =
      [[FlutterBasicMessageChannel alloc]
        initWithName:[NSString stringWithFormat:@"%@%@", @"SDK.joinChannel", messageChannelSuffix]
        binaryMessenger:binaryMessenger
        codec:SDKGetCodec()];
   ...
  }
  {
      messageChannelSuffix = messageChannelSuffix.length > 0 ? [NSString stringWithFormat: @".%@", messageChannelSuffix] : @"";
...

I don't think this was an issue, but I was already planning on changing it anyway (and have).

[bparrishMines]

LGTM

[tarrinneal]

Not entirely sure why the format tests are failing like this. The code is formatted correctly. If go back and update the code to the "asked for" style, the formatter reverts it. @stuartmorgan

[stuartmorgan-g]

Could be a difference in local vs bot clang-format version. The real fix is to remove the stray semicolon from the ends of those two lines though, then it'll be both correct and consistent :)

[stuartmorgan-g]

LGTM