Log template errors as debug message

[JoannaaKL]

Background
When parsing a workflow template there are two objects at play: ExecutionContext and TemplateContext. ExecutionContext stores all errors (named issues) that are later sent as job results. TemplateContext on the other side is an object used, as the name suggests, during the template parsing. It also stores template errors together with field ids and names, to provide a meaningful message, which workflow line was invalid.

The duplication comes from the fact that during the template reading:

1. first we’re loading the template using TemplateReader.Read and here template errors are being written to the TemplateContext for the first time
2. after we’re done with loading all tokens we go through all TemplateContext errors and add them to the ExecutionContext errors list here (screenshot with more logs is at the bottom in expandable section)

All that would be fine if not the small fact, that in step 1 TemplateContext already added errors to the ExecutionContext: internally it is using TraceWriter.Error method that is…writing errors to the ExecutionContext:

internal void Error(TemplateValidationError error)
{
            Errors.Add(error); <——— add error to Template errors (we iterate over them in step 2) 
            TraceWriter.Error(error.Message); <—— TraceWriter writes errors to ExecutionContext directly causing duplication 
}

link

We could deduplicate issues in ExecutionContext based on error position and message, but that would not fix the underlying issue of logging two times the same error or fix the real issue, that is writing the same errors in multiple places.
Since the workflow parser code is used in other classes and there's a risk of regression, I have added a feature flag DistributedTask.LogTemplateErrorsToTraceWriter that will be passed from actions service. This way only one method in TemplateReader will stop duplicating errors. With time we can expand this logic and disable TraceWriter error logging in other places.
Long term solution would be code a refactoring, since TemplateContext has access to the TraceWriter, it can manipulate the state of ExecutionContext. These two should either be separated or merged into one object.

Closes https://github.com/github/c2c-actions-runtime/issues/2381
Follow-up: https://github.com/github/actions-dotnet/pull/15290

Before

After

Workflow run with more debug logs

Branch

[TingluoHuang]

Try to not change anything under src/Sdk within the runner, these files are shared with the service and they should be keep in sync. If you really plan to change this file, you will need to change it on the service first and rollout out to production, then copy the changed version to the runner.

[TingluoHuang]

Undo change in this file?