Provide plugin mechanism to cancel compilation

[luis-j-soares]

There's several scenarios in which a plugin could realistically ask the Program/ProgramBuilder to fail early and cancel a build during setup, like missing configuration/manifest entries, or incorrect entry parameters.

The plugin architecture currently does not support ending compilation early. The compiler will keep working to gather all diagnostics before stopping short of outputting a build, but by that point every file will have been parsed and validated, which can take a while on large projects. Additionally, diagnostics for non-parseable files (i.e. those that are not BrsFile or XmlFile, i.e. manifest or images) seem to be discarded.

I'm opening this issue so we can discuss how to approach a feature like this.

[luis-j-soares]

To elaborate on what some of these use-cases look like, my app uses a build workflow that relies entirely on bsc plugins. This workflow:

• Gathers environment variables to modify certain aspects of the project (environment, territory, app logging level, etc.)
• Applies dynamic rules (if certain flags are included, include/exclude certain files, or rewrite certain pieces of code before files are parsed, turn on other flags like bslibs and manifest entries, etc.)
• Prepares rooibos by assembling test suites based on filters (only for the test runner project)
• Enriches the final manifest file with all of the variables we need (collected from the build context above, but also management of secrets and whatnot)
• Includes other machinery (inline configs, debugging and proxying mechanisms, etc)

Some of these benefit from early cancellation where we have incorrect configuration (i.e. unsupported environment, missing secrets, wrong test filters, etc).

At the moment, the workaround we use is process.exit(1), to ensure we can fail early and save around 20 seconds of CI time for each build that is misconfigured.

[iBicha]

Another essential use case is when a plugin is doing a transformation (generating code or assets) but if it fails, the whole build is now considered broken, and it shouldn't even be pushed to device. We need plugins to push a clear error message so that devs can go deal with the issue.
This is not about saving compute time. This is about avoiding bad builds. Sometimes plugins can fail in subtle ways, the app would still work, but only some feature is now broken. The build must be prevented to avoid shipping broken software.