Swift Build should provide task environment in the message stream in a better way

[jakepetroules]

Today in OperationDelegate.taskStarted, there is some complex logic to determine whether environment is shown:

let environmentToShow = (task.showEnvironment && !operation.request.hideShellScriptEnvironment) ? task.environment : nil

This sort of presentation-level logic doesn't seem like it belongs here. It also doesn't incorporate the operation.environment base environment given to the llbuild BuildSystem, so what's printed isn't entirely representative of what the subprocess sees.

This should be made better...

[shrudge]

@jakepetroules Hi, I might be wrong here but I think we can resolve this by combining operation.environment and task.environment inside OperationDelegate.taskStarted then pass the unfiltered environment dictionary downstream.
and Shift the showEnvironment checks to the console output layer.
lemme know if i can work on this one.

[jakepetroules]

There are some performance considerations to keep in mind with this, as we'd want to avoid bloating every IPC message with the same base environment, so we'd probably want some dedicated types like TaskEnvironment and BaseEnvironment, which can be threaded through at various points and re-combined on the client side as desired.

showEnvironment is also a task-specific property and that might be something that should change to some other semantic hint that clients can use to decide whether to show the environment.

[jakepetroules]

You're welcome to try experimenting in this area as no one's looking at this task right.

[shrudge]

got a bit sidetracked by some noise in BuildOperationTests, mostly unrelated visionOS and RealityAssets compile errors that were specific to my local environment :)

Refactored the task environment handling to move the presentation logic out of the server and into the client. Instead of the server baking environment strings into the command log, it now sends the base environment once at the start of the build and then sends structured deltas for each individual task.

To support this, i updated the serialization aggregate counts for BuildOperationStarted (1→2) and BuildOperationTaskInfo (7→9). anddd i used a semantic hint (.normal & .prominent) to give the client better control over rendering
i have verified the IPC stability with MessageSerializationTests and confirmed the client-side merging in BuildLogTests, both of which pass.