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Merge pull request microsoft#5992 from Microsoft/allow-type-predicates-as-return-types-only
Allow type predicates as return types only
2 parents 5f024a3 + a9f2cb6 commit 911d07a

8 files changed

Lines changed: 282 additions & 144 deletions

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‎src/compiler/checker.ts‎

Lines changed: 74 additions & 89 deletions
Original file line numberDiff line numberDiff line change
@@ -11187,7 +11187,53 @@ namespace ts {
1118711187
return -1;
1118811188
}
1118911189

11190-
function isInLegalParameterTypePredicatePosition(node: Node): boolean {
11190+
function checkTypePredicate(node: TypePredicateNode) {
11191+
const parent = getTypePredicateParent(node);
11192+
if (!parent) {
11193+
return;
11194+
}
11195+
const returnType = getReturnTypeOfSignature(getSignatureFromDeclaration(parent));
11196+
if (!returnType || !(returnType.flags & TypeFlags.PredicateType)) {
11197+
return;
11198+
}
11199+
const { parameterName } = node;
11200+
if (parameterName.kind === SyntaxKind.ThisType) {
11201+
getTypeFromThisTypeNode(parameterName as ThisTypeNode);
11202+
}
11203+
else {
11204+
const typePredicate = <IdentifierTypePredicate>(<PredicateType>returnType).predicate;
11205+
if (typePredicate.parameterIndex >= 0) {
11206+
if (parent.parameters[typePredicate.parameterIndex].dotDotDotToken) {
11207+
error(parameterName,
11208+
Diagnostics.A_type_predicate_cannot_reference_a_rest_parameter);
11209+
}
11210+
else {
11211+
checkTypeAssignableTo(typePredicate.type,
11212+
getTypeOfNode(parent.parameters[typePredicate.parameterIndex]),
11213+
node.type);
11214+
}
11215+
}
11216+
else if (parameterName) {
11217+
let hasReportedError = false;
11218+
for (const { name } of parent.parameters) {
11219+
if ((name.kind === SyntaxKind.ObjectBindingPattern ||
11220+
name.kind === SyntaxKind.ArrayBindingPattern) &&
11221+
checkIfTypePredicateVariableIsDeclaredInBindingPattern(
11222+
<BindingPattern>name,
11223+
parameterName,
11224+
typePredicate.parameterName)) {
11225+
hasReportedError = true;
11226+
break;
11227+
}
11228+
}
11229+
if (!hasReportedError) {
11230+
error(node.parameterName, Diagnostics.Cannot_find_parameter_0, typePredicate.parameterName);
11231+
}
11232+
}
11233+
}
11234+
}
11235+
11236+
function getTypePredicateParent(node: Node): SignatureDeclaration {
1119111237
switch (node.parent.kind) {
1119211238
case SyntaxKind.ArrowFunction:
1119311239
case SyntaxKind.CallSignature:
@@ -11196,22 +11242,35 @@ namespace ts {
1119611242
case SyntaxKind.FunctionType:
1119711243
case SyntaxKind.MethodDeclaration:
1119811244
case SyntaxKind.MethodSignature:
11199-
return node === (<SignatureDeclaration>node.parent).type;
11245+
const parent = <SignatureDeclaration>node.parent;
11246+
if (node === parent.type) {
11247+
return parent;
11248+
}
1120011249
}
11201-
return false;
1120211250
}
1120311251

11204-
function isInLegalThisTypePredicatePosition(node: Node): boolean {
11205-
if (isInLegalParameterTypePredicatePosition(node)) {
11206-
return true;
11207-
}
11208-
switch (node.parent.kind) {
11209-
case SyntaxKind.PropertyDeclaration:
11210-
case SyntaxKind.PropertySignature:
11211-
case SyntaxKind.GetAccessor:
11212-
return node === (node.parent as (PropertyDeclaration | GetAccessorDeclaration | PropertySignature)).type;
11252+
function checkIfTypePredicateVariableIsDeclaredInBindingPattern(
11253+
pattern: BindingPattern,
11254+
predicateVariableNode: Node,
11255+
predicateVariableName: string) {
11256+
for (const { name } of pattern.elements) {
11257+
if (name.kind === SyntaxKind.Identifier &&
11258+
(<Identifier>name).text === predicateVariableName) {
11259+
error(predicateVariableNode,
11260+
Diagnostics.A_type_predicate_cannot_reference_element_0_in_a_binding_pattern,
11261+
predicateVariableName);
11262+
return true;
11263+
}
11264+
else if (name.kind === SyntaxKind.ArrayBindingPattern ||
11265+
name.kind === SyntaxKind.ObjectBindingPattern) {
11266+
if (checkIfTypePredicateVariableIsDeclaredInBindingPattern(
11267+
<BindingPattern>name,
11268+
predicateVariableNode,
11269+
predicateVariableName)) {
11270+
return true;
11271+
}
11272+
}
1121311273
}
11214-
return false;
1121511274
}
1121611275

1121711276
function checkSignatureDeclaration(node: SignatureDeclaration) {
@@ -11230,68 +11289,8 @@ namespace ts {
1123011289

1123111290
forEach(node.parameters, checkParameter);
1123211291

11233-
if (node.type) {
11234-
if (node.type.kind === SyntaxKind.TypePredicate) {
11235-
const returnType = getReturnTypeOfSignature(getSignatureFromDeclaration(node));
11236-
if (!returnType || !(returnType.flags & TypeFlags.PredicateType)) {
11237-
return;
11238-
}
11239-
const typePredicate = (returnType as PredicateType).predicate;
11240-
const typePredicateNode = node.type as TypePredicateNode;
11241-
checkSourceElement(typePredicateNode);
11242-
if (isIdentifierTypePredicate(typePredicate)) {
11243-
if (typePredicate.parameterIndex >= 0) {
11244-
if (node.parameters[typePredicate.parameterIndex].dotDotDotToken) {
11245-
error(typePredicateNode.parameterName,
11246-
Diagnostics.A_type_predicate_cannot_reference_a_rest_parameter);
11247-
}
11248-
else {
11249-
checkTypeAssignableTo(typePredicate.type,
11250-
getTypeOfNode(node.parameters[typePredicate.parameterIndex]),
11251-
typePredicateNode.type);
11252-
}
11253-
}
11254-
else if (typePredicateNode.parameterName) {
11255-
let hasReportedError = false;
11256-
for (var param of node.parameters) {
11257-
if (hasReportedError) {
11258-
break;
11259-
}
11260-
if (param.name.kind === SyntaxKind.ObjectBindingPattern ||
11261-
param.name.kind === SyntaxKind.ArrayBindingPattern) {
11262-
11263-
(function checkBindingPattern(pattern: BindingPattern) {
11264-
for (const element of pattern.elements) {
11265-
if (element.name.kind === SyntaxKind.Identifier &&
11266-
(<Identifier>element.name).text === typePredicate.parameterName) {
11267-
11268-
error(typePredicateNode.parameterName,
11269-
Diagnostics.A_type_predicate_cannot_reference_element_0_in_a_binding_pattern,
11270-
typePredicate.parameterName);
11271-
hasReportedError = true;
11272-
break;
11273-
}
11274-
else if (element.name.kind === SyntaxKind.ArrayBindingPattern ||
11275-
element.name.kind === SyntaxKind.ObjectBindingPattern) {
11276-
11277-
checkBindingPattern(<BindingPattern>element.name);
11278-
}
11279-
}
11280-
})(<BindingPattern>param.name);
11281-
}
11282-
}
11283-
if (!hasReportedError) {
11284-
error(typePredicateNode.parameterName,
11285-
Diagnostics.Cannot_find_parameter_0,
11286-
typePredicate.parameterName);
11287-
}
11288-
}
11289-
}
11290-
}
11291-
else {
11292-
checkSourceElement(node.type);
11293-
}
11294-
}
11292+
checkSourceElement(node.type);
11293+
1129511294

1129611295
if (produceDiagnostics) {
1129711296
checkCollisionWithArgumentsInGeneratedCode(node);
@@ -14460,20 +14459,6 @@ namespace ts {
1446014459
}
1446114460
}
1446214461

14463-
function checkTypePredicate(node: TypePredicateNode) {
14464-
const { parameterName } = node;
14465-
if (parameterName.kind === SyntaxKind.Identifier && !isInLegalParameterTypePredicatePosition(node)) {
14466-
error(node, Diagnostics.A_type_predicate_is_only_allowed_in_return_type_position_for_functions_and_methods);
14467-
}
14468-
else if (parameterName.kind === SyntaxKind.ThisType) {
14469-
if (!isInLegalThisTypePredicatePosition(node)) {
14470-
error(node, Diagnostics.A_this_based_type_predicate_is_only_allowed_within_a_class_or_interface_s_members_get_accessors_or_return_type_positions_for_functions_and_methods);
14471-
}
14472-
else {
14473-
getTypeFromThisTypeNode(parameterName as ThisTypeNode);
14474-
}
14475-
}
14476-
}
1447714462

1447814463
function checkSourceElement(node: Node): void {
1447914464
if (!node) {

‎src/compiler/diagnosticMessages.json‎

Lines changed: 0 additions & 8 deletions
Original file line numberDiff line numberDiff line change
@@ -711,10 +711,6 @@
711711
"category": "Error",
712712
"code": 1227
713713
},
714-
"A type predicate is only allowed in return type position for functions and methods.": {
715-
"category": "Error",
716-
"code": 1228
717-
},
718714
"A type predicate cannot reference a rest parameter.": {
719715
"category": "Error",
720716
"code": 1229
@@ -1655,10 +1651,6 @@
16551651
"category": "Error",
16561652
"code": 2518
16571653
},
1658-
"A 'this'-based type predicate is only allowed within a class or interface's members, get accessors, or return type positions for functions and methods.": {
1659-
"category": "Error",
1660-
"code": 2519
1661-
},
16621654
"Duplicate identifier '{0}'. Compiler uses declaration '{1}' to support async functions.": {
16631655
"category": "Error",
16641656
"code": 2520

‎src/compiler/parser.ts‎

Lines changed: 36 additions & 15 deletions
Original file line numberDiff line numberDiff line change
@@ -896,17 +896,19 @@ namespace ts {
896896
return result;
897897
}
898898

899-
// Invokes the provided callback then unconditionally restores the parser to the state it
900-
// was in immediately prior to invoking the callback. The result of invoking the callback
901-
// is returned from this function.
899+
/** Invokes the provided callback then unconditionally restores the parser to the state it
900+
* was in immediately prior to invoking the callback. The result of invoking the callback
901+
* is returned from this function.
902+
*/
902903
function lookAhead<T>(callback: () => T): T {
903904
return speculationHelper(callback, /*isLookAhead*/ true);
904905
}
905906

906-
// Invokes the provided callback. If the callback returns something falsy, then it restores
907-
// the parser to the state it was in immediately prior to invoking the callback. If the
908-
// callback returns something truthy, then the parser state is not rolled back. The result
909-
// of invoking the callback is returned from this function.
907+
/** Invokes the provided callback. If the callback returns something falsy, then it restores
908+
* the parser to the state it was in immediately prior to invoking the callback. If the
909+
* callback returns something truthy, then the parser state is not rolled back. The result
910+
* of invoking the callback is returned from this function.
911+
*/
910912
function tryParse<T>(callback: () => T): T {
911913
return speculationHelper(callback, /*isLookAhead*/ false);
912914
}
@@ -1948,11 +1950,8 @@ namespace ts {
19481950

19491951
// TYPES
19501952

1951-
function parseTypeReferenceOrTypePredicate(): TypeReferenceNode | TypePredicateNode {
1953+
function parseTypeReference(): TypeReferenceNode {
19521954
const typeName = parseEntityName(/*allowReservedWords*/ false, Diagnostics.Type_expected);
1953-
if (typeName.kind === SyntaxKind.Identifier && token === SyntaxKind.IsKeyword && !scanner.hasPrecedingLineBreak()) {
1954-
return parseTypePredicate(typeName as Identifier);
1955-
}
19561955
const node = <TypeReferenceNode>createNode(SyntaxKind.TypeReference, typeName.pos);
19571956
node.typeName = typeName;
19581957
if (!scanner.hasPrecedingLineBreak() && token === SyntaxKind.LessThanToken) {
@@ -2092,10 +2091,10 @@ namespace ts {
20922091

20932092
if (returnTokenRequired) {
20942093
parseExpected(returnToken);
2095-
signature.type = parseType();
2094+
signature.type = parseTypeOrTypePredicate();
20962095
}
20972096
else if (parseOptional(returnToken)) {
2098-
signature.type = parseType();
2097+
signature.type = parseTypeOrTypePredicate();
20992098
}
21002099
}
21012100

@@ -2411,7 +2410,7 @@ namespace ts {
24112410
case SyntaxKind.SymbolKeyword:
24122411
// If these are followed by a dot, then parse these out as a dotted type reference instead.
24132412
const node = tryParse(parseKeywordAndNoDot);
2414-
return node || parseTypeReferenceOrTypePredicate();
2413+
return node || parseTypeReference();
24152414
case SyntaxKind.StringLiteral:
24162415
return parseStringLiteralTypeNode();
24172416
case SyntaxKind.VoidKeyword:
@@ -2434,7 +2433,7 @@ namespace ts {
24342433
case SyntaxKind.OpenParenToken:
24352434
return parseParenthesizedType();
24362435
default:
2437-
return parseTypeReferenceOrTypePredicate();
2436+
return parseTypeReference();
24382437
}
24392438
}
24402439

@@ -2541,6 +2540,28 @@ namespace ts {
25412540
return false;
25422541
}
25432542

2543+
function parseTypeOrTypePredicate(): TypeNode {
2544+
const typePredicateVariable = isIdentifier() && tryParse(parseTypePredicatePrefix);
2545+
const type = parseType();
2546+
if (typePredicateVariable) {
2547+
const node = <TypePredicateNode>createNode(SyntaxKind.TypePredicate, typePredicateVariable.pos);
2548+
node.parameterName = typePredicateVariable;
2549+
node.type = type;
2550+
return finishNode(node);
2551+
}
2552+
else {
2553+
return type;
2554+
}
2555+
}
2556+
2557+
function parseTypePredicatePrefix() {
2558+
const id = parseIdentifier();
2559+
if (token === SyntaxKind.IsKeyword && !scanner.hasPrecedingLineBreak()) {
2560+
nextToken();
2561+
return id;
2562+
}
2563+
}
2564+
25442565
function parseType(): TypeNode {
25452566
// The rules about 'yield' only apply to actual code/expression contexts. They don't
25462567
// apply to 'type' contexts. So we disable these parameters here before moving on.

‎tests/baselines/reference/typeAssertions.errors.txt‎

Lines changed: 51 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -7,9 +7,23 @@ tests/cases/conformance/expressions/typeAssertions/typeAssertions.ts(37,13): err
77
Property 'q' is missing in type 'SomeDerived'.
88
tests/cases/conformance/expressions/typeAssertions/typeAssertions.ts(38,13): error TS2352: Neither type 'SomeBase' nor type 'SomeOther' is assignable to the other.
99
Property 'q' is missing in type 'SomeBase'.
10+
tests/cases/conformance/expressions/typeAssertions/typeAssertions.ts(44,5): error TS2304: Cannot find name 'numOrStr'.
11+
tests/cases/conformance/expressions/typeAssertions/typeAssertions.ts(44,14): error TS1005: '>' expected.
12+
tests/cases/conformance/expressions/typeAssertions/typeAssertions.ts(44,14): error TS2304: Cannot find name 'is'.
13+
tests/cases/conformance/expressions/typeAssertions/typeAssertions.ts(44,17): error TS1005: ')' expected.
14+
tests/cases/conformance/expressions/typeAssertions/typeAssertions.ts(44,17): error TS2304: Cannot find name 'string'.
15+
tests/cases/conformance/expressions/typeAssertions/typeAssertions.ts(44,48): error TS1005: ';' expected.
16+
tests/cases/conformance/expressions/typeAssertions/typeAssertions.ts(45,2): error TS2322: Type 'number | string' is not assignable to type 'string'.
17+
Type 'number' is not assignable to type 'string'.
18+
tests/cases/conformance/expressions/typeAssertions/typeAssertions.ts(48,32): error TS2304: Cannot find name 'numOrStr'.
19+
tests/cases/conformance/expressions/typeAssertions/typeAssertions.ts(48,41): error TS1005: ')' expected.
20+
tests/cases/conformance/expressions/typeAssertions/typeAssertions.ts(48,41): error TS2304: Cannot find name 'is'.
21+
tests/cases/conformance/expressions/typeAssertions/typeAssertions.ts(48,44): error TS1005: ';' expected.
22+
tests/cases/conformance/expressions/typeAssertions/typeAssertions.ts(48,44): error TS2304: Cannot find name 'string'.
23+
tests/cases/conformance/expressions/typeAssertions/typeAssertions.ts(48,50): error TS1005: ';' expected.
1024

1125

12-
==== tests/cases/conformance/expressions/typeAssertions/typeAssertions.ts (5 errors) ====
26+
==== tests/cases/conformance/expressions/typeAssertions/typeAssertions.ts (18 errors) ====
1327
// Function call whose argument is a 1 arg generic function call with explicit type arguments
1428
function fn1<T>(t: T) { }
1529
function fn2(t: any) { }
@@ -64,5 +78,41 @@ tests/cases/conformance/expressions/typeAssertions/typeAssertions.ts(38,13): err
6478
!!! error TS2352: Property 'q' is missing in type 'SomeBase'.
6579
someOther = <SomeOther>someOther;
6680

81+
// Type assertion cannot be a type-predicate type
82+
var numOrStr: number | string;
83+
var str: string;
84+
if(<numOrStr is string>(numOrStr === undefined)) { // Error
85+
~~~~~~~~
86+
!!! error TS2304: Cannot find name 'numOrStr'.
87+
~~
88+
!!! error TS1005: '>' expected.
89+
~~
90+
!!! error TS2304: Cannot find name 'is'.
91+
~~~~~~
92+
!!! error TS1005: ')' expected.
93+
~~~~~~
94+
!!! error TS2304: Cannot find name 'string'.
95+
~
96+
!!! error TS1005: ';' expected.
97+
str = numOrStr; // Error, no narrowing occurred
98+
~~~
99+
!!! error TS2322: Type 'number | string' is not assignable to type 'string'.
100+
!!! error TS2322: Type 'number' is not assignable to type 'string'.
101+
}
102+
103+
if((numOrStr === undefined) as numOrStr is string) { // Error
104+
~~~~~~~~
105+
!!! error TS2304: Cannot find name 'numOrStr'.
106+
~~
107+
!!! error TS1005: ')' expected.
108+
~~
109+
!!! error TS2304: Cannot find name 'is'.
110+
~~~~~~
111+
!!! error TS1005: ';' expected.
112+
~~~~~~
113+
!!! error TS2304: Cannot find name 'string'.
114+
~
115+
!!! error TS1005: ';' expected.
116+
}
67117

68118

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