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More permissive parsing of instantiation expressions #48659

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Apr 13, 2022
Merged

More permissive parsing of instantiation expressions #48659

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46cab89
More permissive parsing of expressions with type arguments
ahejlsberg Apr 12, 2022
801c903
Add test
ahejlsberg Apr 12, 2022
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28 changes: 2 additions & 26 deletions src/compiler/parser.ts
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Expand Up @@ -5735,34 +5735,10 @@ namespace ts {
case SyntaxKind.OpenParenToken: // foo<x>(
case SyntaxKind.NoSubstitutionTemplateLiteral: // foo<T> `...`
case SyntaxKind.TemplateHead: // foo<T> `...${100}...`
// These tokens can't follow in a call expression, nor can they start an
// expression. So, consider the type argument list part of an instantiation
// expression.
// falls through
case SyntaxKind.CommaToken: // foo<x>,
case SyntaxKind.DotToken: // foo<x>.
case SyntaxKind.QuestionDotToken: // foo<x>?.
case SyntaxKind.CloseParenToken: // foo<x>)
case SyntaxKind.CloseBracketToken: // foo<x>]
case SyntaxKind.ColonToken: // foo<x>:
case SyntaxKind.SemicolonToken: // foo<x>;
case SyntaxKind.QuestionToken: // foo<x>?
case SyntaxKind.EqualsEqualsToken: // foo<x> ==
case SyntaxKind.EqualsEqualsEqualsToken: // foo<x> ===
case SyntaxKind.ExclamationEqualsToken: // foo<x> !=
case SyntaxKind.ExclamationEqualsEqualsToken: // foo<x> !==
case SyntaxKind.AmpersandAmpersandToken: // foo<x> &&
case SyntaxKind.BarBarToken: // foo<x> ||
case SyntaxKind.QuestionQuestionToken: // foo<x> ??
case SyntaxKind.CaretToken: // foo<x> ^
case SyntaxKind.AmpersandToken: // foo<x> &
case SyntaxKind.BarToken: // foo<x> |
case SyntaxKind.CloseBraceToken: // foo<x> }
case SyntaxKind.EndOfFileToken: // foo<x>
return true;
}
// Treat anything else as an expression.
return false;
// Consider something a type argument list only if the following token can't start an expression.
return !isStartOfExpression();
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I'm always surprised that this function exists and doesn't fall out of date in some catastrophic way.

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Oh, we'd know right away. For example, in when parsing argument lists or array literal elements, we require it to return true before each element (it's called from isListElement which is called from parseList).

}

function parsePrimaryExpression(): PrimaryExpression {
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5 changes: 5 additions & 0 deletions tests/baselines/reference/instantiationExpressionErrors.errors.txt
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Expand Up @@ -72,4 +72,9 @@ tests/cases/conformance/types/typeParameters/typeArgumentLists/instantiationExpr

const x3 = f<true>;
true;

// Parsed as instantiation expression

const x4 = f<true>
if (true) {}

12 changes: 12 additions & 0 deletions tests/baselines/reference/instantiationExpressionErrors.js
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Expand Up @@ -40,6 +40,11 @@ true;

const x3 = f<true>;
true;

// Parsed as instantiation expression

const x4 = f<true>
if (true) {}


//// [instantiationExpressionErrors.js]
Expand Down Expand Up @@ -70,6 +75,9 @@ var x2 = f < true >
// Parsed as instantiation expression
var x3 = (f);
true;
// Parsed as instantiation expression
var x4 = (f);
if (true) { }


//// [instantiationExpressionErrors.d.ts]
Expand Down Expand Up @@ -101,3 +109,7 @@ declare const x3: {
(): true;
g<U>(): U;
};
declare const x4: {
(): true;
g<U>(): U;
};
8 changes: 8 additions & 0 deletions tests/baselines/reference/instantiationExpressionErrors.symbols
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Expand Up @@ -99,3 +99,11 @@ const x3 = f<true>;

true;

// Parsed as instantiation expression

const x4 = f<true>
>x4 : Symbol(x4, Decl(instantiationExpressionErrors.ts, 44, 5))
>f : Symbol(f, Decl(instantiationExpressionErrors.ts, 0, 11))

if (true) {}

10 changes: 10 additions & 0 deletions tests/baselines/reference/instantiationExpressionErrors.types
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Expand Up @@ -122,3 +122,13 @@ const x3 = f<true>;
true;
>true : true

// Parsed as instantiation expression

const x4 = f<true>
>x4 : { (): true; g<U>(): U; }
>f : { <T>(): T; g<U>(): U; }
>true : true

if (true) {}
>true : true

5 changes: 5 additions & 0 deletions ...cases/conformance/types/typeParameters/typeArgumentLists/instantiationExpressionErrors.ts
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Expand Up @@ -42,3 +42,8 @@ true;

const x3 = f<true>;
true;

// Parsed as instantiation expression

const x4 = f<true>
if (true) {}