Fixes https://github.com/flutter/flutter/issues/112833
Most of the actual changes here are in [packages/flutter_tools/lib/src/version.dart](https://github.com/flutter/flutter/pull/124558/files#diff-092e00109d9e1589fbc7c6de750e29a6ae512b2dd44e85d60028953561201605), while the rest is largely just addressing changes to the constructor of `FlutterVersion` which now has different dependencies.
This change makes `FlutterVersion` an interface with two concrete implementations:
1. `_FlutterVersionGit` which is mostly the previous implementation, and
2. `_FlutterVersionFromFile` which will read a new `.version.json` file from the root of the repo
The [`FlutterVersion` constructor](https://github.com/flutter/flutter/pull/124558/files#diff-092e00109d9e1589fbc7c6de750e29a6ae512b2dd44e85d60028953561201605R70) is now a factory that first checks if `.version.json` exists, and if so returns an instance of `_FlutterVersionFromGit` else it returns the fallback `_FlutterVersionGit` which will end up writing `.version.json` so that we don't need to re-calculate the version on the next invocation.
`.version.json` will be deleted in the bash/batch entrypoints any time we need to rebuild he tool (this will usually be because the user did `flutter upgrade` or `flutter channel`, or manually changed the commit with git).
## How we determine the channel name
Historically, we used the current branch's upstream to figure out the current channel name. I have no idea why. I traced it back to https://github.com/flutter/flutter/pull/446/files where @abarth implement this and I reviewed that PR and left no comment on it at the time.
I think this is confusing. You can be on a branch and it tells you that your channel is different. That seems weird.
This PR changes the logic to uses the current branch as the channel name.
## How we display channels
The main reason this PR exists is to add channel descriptions to the `flutter channel` list:
```
ianh@burmese:~/dev/flutter/packages/flutter_tools$ flutter channel
Flutter channels:
master (tip of tree, for contributors)
main (tip of tree, follows master channel)
beta (updated monthly, recommended for experienced users)
stable (updated quarterly, for new users and for production app releases)
* foo_bar
Currently not on an official channel.
ianh@burmese:~/dev/flutter/packages/flutter_tools$
```
## Other changes
I made a few other changes while I was at it:
* If you're not on an official channel, we used to imply `--show-all`, but now we don't, we just show the official channels plus yours. This avoids flooding the screen in the case the user is on a weird channel and just wants to know what channel they're on.
* I made the tool more consistent about how it handles unofficial branches. Now it's always `[user branch]`.
* I slightly adjusted how unknown versions are rendered so it's clearer the version is unknown rather than just having the word "Unknown" floating in the output without context.
* Simplified some of the code.
* Made some of the tests more strict (checking all output rather than just some aspects of it).
* Changed the MockFlutterVersion to implement the FlutterVersion API more strictly.
* I made sure we escape the output to `.metadata` to avoid potential injection bugs (previously we just inlined the version and channel name verbatim with no escaping, which is super sketchy).
* Tweaked the help text for the `downgrade` command to be clearer.
* Removed some misleading text in some error messages.
* Made the `.metadata` generator consistent with the template file.
* Removed some obsolete code to do with the `dev` branch.
## Reviewer notes
I'm worried that there are implications to some of these changes that I am not aware of, so please don't assume I know what I'm doing when reviewing this code. :-)
There have been some more additional reports of a missing 'package:characters' import after upgrading flutter. This has me concerned that our pub caching logic is incorrect. Instead of the tool attempting to guess when pub should be run, always delegate to pub.
Also takes an opportunity to fix the kernel snapshot depending on the .packages or package_config. Due to the generated: date field this causes extra rebuilds. Instead when pub get is run, write out an additional file with just the package contents and version.
Fixes#66777Fixes#65723
There have been some more additional reports of a missing 'package:characters' import after upgrading flutter, as well as problems with detecting the correct language version. This has me concerned that our pub caching logic is incorrect. Instead of the tool attempting to guess when pub should be run, always delegate to pub.
Integration tests must only go through the real file system/process manager/platform. The global indirection makes this code harder to understand than if it directly referred to the concrete instances that are being used.
Update the integration shard to use a const instance of a LocalFIleSystem, LocalProcessManager, and LocalPlatform. Remove global usage and apply testWithoutContext.
