[AutoDiff] Be able to parse linear argument in @differentiable attribute

[bartchr808]

This PR adds the ability to parse and handle a linear argument in the @differentiable attribute in parseDifferentiableAttributeArguments

This PR does not handle modifying the C++ attribute class such that it handles whether the linear attribute is being used.

[dan-zheng]

Could you please also create and add tests to test/AutoDiff/differentiating_attr_parse.swift?
You can:

• Copy differentiating_attr_type_checking.swift
• Change the RUN line to %target-swift-frontend -parse -verify %s
• Preserve just a few @differentiating examples - no need to keep "original" functions since Sema isn't tested.
• Add @differentiating(linear, ...) tests.

Thank you!

[rxwei]

Suggested change

	consumeIdentifier();
	consumeIdentifier(tok::identifier);

This makes an assertion about the identifier being consumed, preventing errors in future changes just in case.

[bartchr808]

consumeIdentifier() does the following assertion inside to check if it's identifier, but also does a couple more:

assert(Tok.isAny(tok::identifier, tok::kw_self, tok::kw_Self));

However, I think calling consumeToken(tok::identifier) could be a better option as it internally does the following assertion to specifically only check if it's an identifier:

SourceLoc consumeToken(tok K) {
  assert(Tok.is(K) && "Consuming wrong token kind");
  return consumeToken();
}

[rxwei]

Yes, it should be consumeToken(). I didn't notice that and thought you wrote consumeToken already :)

[bartchr808]

Could you please also create and add tests to test/AutoDiff/differentiating_attr_parse.swift?

@dan-zheng I'll do it in my next PR for the @differentiating attr 😄

[rxwei]

Could you please also create and add tests to test/AutoDiff/differentiating_attr_parse.swift?

@dan-zheng I'll do it in my next PR for the @differentiating attr 😄

For @differentiating, the linear symbol should appear after the original function name and a comma, e.g. @differentiating(orig(_:_:), linear), and @differentiating(orig(_:_:), linear, wrt: x).

[bartchr808]

For @differentiating, the linear symbol should appear after the original function name and a comma, e.g. @differentiating(orig(::), linear), and @differentiating(orig(::), linear, wrt: x).

Sounds good!

[bartchr808]

@swift-ci please test tensorflow

[bartchr808]

@swift-ci please test tensorflow

[bartchr808]

Hmm seems like CI got some weird issue:

'Build finished. No test results found.'

Will try again

[bartchr808]

@swift-ci please test tensorflow