[flutter_tools] The UserMessages class should be deprecated

[andrewkolos]

The tool has a UserMessages class that houses some user messages displayed to the user by the flutter tool. However, many messages are not stored in this class (example).

Going back to the PR that introduced it, it's still unclear what the original intent was. See this comment from @Hixie on the PR.

The class does allow partial reimplementations of the flutter tool to override messages, and it sees very light use in g3. However, it is unclear if this is worth the confusion this class can cause.

Some possible ways to address this:

• Delete the class entirely, either removing the g3 message overrides entirely or finding some other way to enable g3 specific messages.
• Rename and document the class to better describe it's specific purpose. Perhaps the class should only contain messages that need to be overridden in g3.
• Be consistent and have all user messages stored in this class. This would probably result in more trouble than it's worth.

[andoriyaprashant]

hey @andrewkolos can you please review my pr #125192

[TzviPM]

I think the right way forward here, if we want to support building tooling on top of flutter_tools, may be to externalize all the strings. This could provide a path to i18n in the way GNU tools like ls support multiple languages.

[christopherfujino]

I think the right way forward here, if we want to support building tooling on top of flutter_tools, may be to externalize all the strings. This could provide a path to i18n in the way GNU tools like ls support multiple languages.

Do we want to support building additional tooling on top of flutter_tools? Or do you mean continuing to support the internal flutter tool?