add simple tracing API

[guybedford]

The API works as:

  System.trace = true;
  System.execute = false; // optionally disable execution. Still executes wrappers.

  System.import('some/module').then(function() {
    // System.loads['some/module'] is the load record
    // System.loads['some/module'].dependencies == [{ name, value from unnormalized to normalized dependencies }]
    // System.loads['some/module'].metadata is metadata object
    // System.loads['some/module'].address is the resolved address
    // System.loads['some/module'].source is the translated source string
  });

The information above provides everything a build tool would need - translation, resolution, dependencies.

If this seems obscure, let me know - happy to consider other APIs too.

[guybedford]

/cc @justinbmeyer - is this very different to what you were doing?

[guybedford]

I've just updated and simplified this PR from the previous suggestions.

[briandipalma]

This should just output to the console?

I'm not seeing it in my simple tests in this webpage.

[guybedford]

It stores the trace at System.loads.

So you can read off the meta-information.

[briandipalma]

@guybedford Excellent thank you, very helpful debug information.

[briandipalma]

It seems like when there is a loading error System.loads isn't populated, it's left undefined, is that as expected?

[guybedford]

Yes this is correct. It is actually up to the trace implementation to
ensure the fetch function doesn't throw errors during tracing for example.
The goal would be for it to be completely resilient though certainly.

Perhaps try something like -

var systemFetch = System.fetch;
System.fetch = function(load) {
return Promise.resolve(systemFetch(load))
.catch(function(err) {
console.log(err); //just note the err
load.metadata.build = false; // tell trace tree consumer to ignore
this module
return ''; // becomes empty module
});
}

So it doesn't escalate the fetch error. Something along those lines...

If the error is in instantiate, a similar idea can apply I expect.

On Tuesday, May 27, 2014, Brian Di Palma notifications@github.com wrote:

It seems like when there is a loading error System.loads isn't populated,
it's left undefined, is that as expected?

Reply to this email directly or view it on GitHubhttps://github.com//pull/141#issuecomment-44266021
.