Implement AST changes

[TimothyGu]

Implement AST changes according to:

• Make AST more consistent pug#2124 (AST PR at Update AST according to latest consensus pug-ast-spec#2)
• Rename escaped/escape to mustEscape pug-ast-spec#1

[ForbesLindesay]

I'm a little concerned someone might accidentally use this with a version of code-gen that has not been updated. We should update code-gen first and have it check explicitly for mustEscape === false so it fails into a safe state if paired with an out of date parser. Then I guess we could npm deprecate the old versions of jade-code-gen?

[TimothyGu]

My understanding is that because the versions of these modules are <1, added the fact that a version of jade that uses these features has not been released, we can break compat in whatever way we want. I guess we should npm deprecate earlier versions. Then, when the AST is stable, we can then deprecate all the <1 versions.

[ForbesLindesay]

I agree in principle, but given that this is such a security critical feature I want to be extra careful :)

[ForbesLindesay]

This looks good except for the filtered include. Once that's updated to match our discussion in pugjs/pug-ast-spec#3, please reassign this pull request to me and ping me to have another look.

[TimothyGu]

@ForbesLindesay, updated. Note that I left some commented-out errors in place, which we can use when pugjs/pug#2155 is implemented.

[jeromew]

the Use YieldBlock for yield keywords makes me wonder if we shouldn't change this keyword for 2.0 as yield is now a reserved keyword in javascript and people may get confused

[TimothyGu]

@jeromew I believe changing it is planned for the next release: pugjs/pug#2055

[ForbesLindesay]

I'd prefer just tok.mustEscape !== false here. That fails to safe. Alternatively (perhaps as well) we could add an assert(typeof tok.mustEscape === 'boolean') check before this. I want to ensure everyone is on a compatible version, and that if they aren't then it's not dangerous, rather than trying to necessarily just work.

[ForbesLindesay]

This is looking pretty good apart from those few minor points.

@jeromew yes, 3.0.0 will deprecate or remove the yield keyword and replace it with a more powerful model of blocks.

[TimothyGu]

@ForbesLindesay all fixed.

[ForbesLindesay]

Why not just make this a hard error? The block has always been ignored in the past so it seems fine to remove it as we release this major version.

[ForbesLindesay]

You can merge this once RawInclude + Block is a hard error.