Basic runtime support for dynamic providers

[iwahbe]

This PR replaces the .Replace method with a sounder construct: XParameterizeResetProvider.

• To achieve a working result, it relaxes an assert in ProposeNew.
• To clarify how XParameterizeResetProvider works, a level of interface indirection was removed.

[codecov]

Codecov Report

Attention: Patch coverage is 13.51351% with 32 lines in your changes missing coverage. Please review.

Project coverage is 60.74%. Comparing base (2094289) to head (53ffefd).

Files	Patch %	Lines
pf/internal/pfutils/proposed_new.go	21.73%	18 Missing ⚠️
pf/tfbridge/provider.go	0.00%	13 Missing ⚠️
pf/tfbridge/main.go	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2102      +/-   ##
==========================================
- Coverage   60.76%   60.74%   -0.03%     
==========================================
  Files         350      350              
  Lines       45686    45711      +25     
==========================================
+ Hits        27762    27768       +6     
- Misses      16405    16425      +20     
+ Partials     1519     1518       -1     

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[VenelinMartinov]

Is this the variable which contains the lambda? Is it passed as a reference?

[iwahbe]

If your talking about the lambda introduced in provider.go:

pulumi-terraform-bridge/pf/tfbridge/provider.go

Lines 213 to 222 in 8c172bf

	ctx = context.WithValue(ctx, xResetProviderKey{},
	func(ctx context.Context, info tfbridge.ProviderInfo, meta ProviderMetadata) error {
	pp, err := newProviderWithContext(ctx, info, meta)
	if err != nil {
	return err
	}
	*p = *pp
	return nil
	})

Then ctx is the variable which contains the lambda. XParameterizeResetProvider unpacks the lambda from ctx and then calls it.

[VenelinMartinov]

The metadata used on this line comes from line 51, as far as I can see, right?

The same metadata also contains this function which captures it.

It looks a bit odd and I was wondering if it's passed as a reference for this to work.

[iwahbe]

Ah, I think I know what you mean. In Go, lambdas always have access to the location of variables in their scope. If your familiar with C++, then lambdas close over the lvalue of variables they reference.