Allow type predicates as return types only #5992
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Also remove now-unused "Type predicate is only allowed as a return type" diagnostic.
| return id; | ||
| } | ||
| }); | ||
| const t = parseType(); |
| @@ -2542,6 +2537,26 @@ namespace ts { | |||
| return false; | |||
| } | |||
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| function parseTypeOrTypePredicate(): TypeNode { | |||
| const typePredicateVariable = tryParse(() => { | |||
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Only call tryParse if a call to isIdentifier() is true. No point in incurring the tryParse overhead if it isn't. Also, don't pass an arrow function to tryParse. Instead, make a function called nextTokenIsIsKeyword or some such and pass that. Avoids creating a function object on every invocation.
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@ahejlsberg does this look good now? |
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You might want to wait on @weswigham's work as a heads up. |
Also: 1. Remove notes I wrote myself for merging. 2. Switch to pattern matching on properties in a few places.
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@DanielRosenwasser I merged to get Wesley's changes. The parser may need some work to forbid |
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I'd like to get this in for 1.8. @ahejlsberg, @weswigham, can you take another look? |
| case SyntaxKind.PropertySignature: | ||
| case SyntaxKind.GetAccessor: | ||
| return node === (node.parent as (PropertyDeclaration | GetAccessorDeclaration | PropertySignature)).type; | ||
| function checkBindingPatternForTypePredicateVariable( |
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Consider checkIfTypePredicateVariableIsDeclaredInBindingPattern
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what about isTypePredicateVariableDeclaredInBindingPattern
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I considered that, but it also reports errors. I think that would still be fine
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oh, I forgot about that -- check* is a better prefix. (This is just a move of the code, so I hadn't looked too closely at the contents.)
checkBindingPatternForTypeVariable -> checkIfTypeVariableIsDeclaredInBindingPattern
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@ahejlsberg can you take a look so I can merge this for 1.8? |
| let typePredicateVariable: Identifier; | ||
| if (isIdentifier()) { | ||
| typePredicateVariable = tryParse(parseTypePredicatePrefix); | ||
| } |
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const typePredicateVariable = isIdentifier() && tryParse(parseTypePredicatePrefix);
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👍 With my minor suggested change. |
…rn-types-only Allow type predicates as return types only
It does this in the parser instead of piecemeal in the checker. This means that the checker has some unused error checking code, so I took the opportunity to move the type predicate checking code into
checkTypePredicateinstead ofcheckSignatureDeclarationwhere it was previously.Fixed #5903 and #5731. Obsoletes PRs #5936 and #5977.
@ahejlsberg and @weswigham, can you take a look?