Consistently use len(x) != 0 checks for Signature.typeParameters

internal/checker/checker.go

@@ -6987,7 +6987,7 @@ func (c *Checker) getQuickTypeOfExpression(node *ast.Node) *Type {
 
 func (c *Checker) getReturnTypeOfSingleNonGenericCallSignature(funcType *Type) *Type {
 	signature := c.getSingleCallSignature(funcType)
-	if signature != nil && signature.typeParameters == nil {
+	if signature != nil && len(signature.typeParameters) == 0 {
 		return c.getReturnTypeOfSignature(signature)
 	}
 	return nil
@@ -9121,7 +9121,7 @@ func (c *Checker) inferTypeArguments(node *ast.Node, signature *Signature, args
 					// Above, the type of the 'value' parameter is inferred to be 'A'.
 					contextualSignature := c.getSingleCallSignature(instantiatedType)
 					var inferenceSourceType *Type
-					if contextualSignature != nil && contextualSignature.typeParameters != nil {
+					if contextualSignature != nil && len(contextualSignature.typeParameters) != 0 {
 						inferenceSourceType = c.getOrCreateTypeFromSignature(c.getSignatureInstantiationWithoutFillingInTypeArguments(contextualSignature, contextualSignature.typeParameters), nil)
 					} else {
 						inferenceSourceType = instantiatedType
@@ -9382,7 +9382,7 @@ func (c *Checker) addImplementationSuccessElaboration(s *CallState, failed *Sign
 				candidate := c.getSignatureFromDeclaration(implementation)
 				localState := *s
 				localState.candidates = []*Signature{candidate}
-				localState.isSingleNonGenericCandidate = candidate.typeParameters == nil
+				localState.isSingleNonGenericCandidate = len(candidate.typeParameters) == 0
 				if c.chooseOverload(&localState, c.assignableRelation) != nil {
 					diagnostic.AddRelatedInfo(NewDiagnosticForNode(implementation, diagnostics.The_call_would_have_succeeded_against_this_implementation_but_implementation_signatures_of_overloads_are_not_externally_visible))
 				}
@@ -9949,8 +9949,8 @@ func (c *Checker) isAritySmaller(signature *Signature, target *ast.Node) bool {
 }
 
 func (c *Checker) assignContextualParameterTypes(sig *Signature, context *Signature) {
-	if context.typeParameters != nil {
-		if sig.typeParameters != nil {
+	if len(context.typeParameters) != 0 {
+		if len(sig.typeParameters) != 0 {
 			// This signature has already has a contextual inference performed and cached on it
 			return
 		}
@@ -20201,8 +20201,8 @@ func (c *Checker) getUnionSignatures(signatureLists [][]*Signature) []*Signature
 			if !core.Same(signatures, masterList) {
 				signature := signatures[0]
 				// Debug.assert(signature, "getUnionSignatures bails early on empty signature lists and should not have empty lists on second pass")
-				if signature.typeParameters != nil && core.Some(results, func(s *Signature) bool {
-					return s.typeParameters != nil && !c.compareTypeParametersIdentical(signature.typeParameters, s.typeParameters)
+				if len(signature.typeParameters) != 0 && core.Some(results, func(s *Signature) bool {
+					return len(s.typeParameters) != 0 && !c.compareTypeParametersIdentical(signature.typeParameters, s.typeParameters)
 				}) {
 					results = nil
 				} else {

internal/checker/flow.go

@@ -2040,7 +2040,7 @@ func (c *Checker) getEffectsSignature(node *ast.Node) *Signature {
 		}
 		signatures := c.getSignaturesOfType(core.OrElse(apparentType, c.unknownType), SignatureKindCall)
 		switch {
-		case len(signatures) == 1 && signatures[0].typeParameters == nil:
+		case len(signatures) == 1 && len(signatures[0].typeParameters) == 0:
 			signature = signatures[0]
 		case core.Some(signatures, c.hasTypePredicateOrNeverReturnType):
 			signature = c.getResolvedSignature(node, nil, CheckModeNormal)

internal/checker/nodebuilderimpl.go

@@ -1690,11 +1690,11 @@ func (b *nodeBuilderImpl) signatureToSignatureDeclarationHelper(signature *Signa
 	b.ctx.approximateLength += 3
 	// Usually a signature contributes a few more characters than this, but 3 is the minimum
 
-	if b.ctx.flags&nodebuilder.FlagsWriteTypeArgumentsOfSignature != 0 && signature.target != nil && signature.mapper != nil && signature.target.typeParameters != nil {
+	if b.ctx.flags&nodebuilder.FlagsWriteTypeArgumentsOfSignature != 0 && signature.target != nil && signature.mapper != nil && len(signature.target.typeParameters) != 0 {
 		for _, parameter := range signature.target.typeParameters {
 			typeParameters = append(typeParameters, b.typeToTypeNode(b.ch.instantiateType(parameter, signature.mapper)))
 		}
-	} else if signature.typeParameters != nil {
+	} else {
 		for _, parameter := range signature.typeParameters {
 			typeParameters = append(typeParameters, b.typeParameterToDeclaration(parameter))
 		}

internal/checker/relater.go

@@ -1462,7 +1462,7 @@ func (c *Checker) compareSignaturesRelated(source *Signature, target *Signature,
 		}
 		return TernaryFalse
 	}
-	if source.typeParameters != nil && !core.Same(source.typeParameters, target.typeParameters) {
+	if len(source.typeParameters) != 0 && !core.Same(source.typeParameters, target.typeParameters) {
 		target = c.getCanonicalSignature(target)
 		source = c.instantiateSignatureInContextOf(source, target /*inferenceContext*/, nil, compareTypes)
 	}
@@ -1653,7 +1653,7 @@ func (c *Checker) compareTypePredicateRelatedTo(source *TypePredicate, target *T
 
 // Returns true if `s` is `(...args: A) => R` where `A` is `any`, `any[]`, `never`, or `never[]`, and `R` is `any` or `unknown`.
 func (c *Checker) isTopSignature(s *Signature) bool {
-	if s.typeParameters == nil && (s.thisParameter == nil || IsTypeAny(c.getTypeOfParameter(s.thisParameter))) && len(s.parameters) == 1 && signatureHasRestParameter(s) {
+	if len(s.typeParameters) == 0 && (s.thisParameter == nil || IsTypeAny(c.getTypeOfParameter(s.thisParameter))) && len(s.parameters) == 1 && signatureHasRestParameter(s) {
 		paramType := c.getTypeOfParameter(s.parameters[0])
 		var restType *Type
 		if c.isArrayType(paramType) {
@@ -2090,7 +2090,7 @@ func (c *Checker) isResolvingReturnTypeOfSignature(signature *Signature) bool {
 }
 
 func (c *Checker) findMatchingSignatures(signatureLists [][]*Signature, signature *Signature, listIndex int) []*Signature {
-	if signature.typeParameters != nil {
+	if len(signature.typeParameters) != 0 {
 		// We require an exact match for generic signatures, so we only return signatures from the first
 		// signature list and only if they have exact matches in the other signature lists.
 		if listIndex > 0 {
@@ -2150,7 +2150,7 @@ func (c *Checker) compareSignaturesIdentical(source *Signature, target *Signatur
 	}
 	// Check that type parameter constraints and defaults match. If they do, instantiate the source
 	// signature with the type parameters of the target signature and continue the comparison.
-	if target.typeParameters != nil {
+	if len(target.typeParameters) != 0 {
 		mapper := newTypeMapper(source.typeParameters, target.typeParameters)
 		for i := range len(target.typeParameters) {
 			s := source.typeParameters[i]

testdata/baselines/reference/submodule/compiler/abstractClassUnionInstantiation.types

@@ -46,7 +46,7 @@ new cls2(); // should error
 >cls2 : Abstracts
 
 new cls3(); // should work
->new cls3() : ConcreteA
+>new cls3() : ConcreteA | ConcreteB
 >cls3 : Concretes
 
 [ConcreteA, AbstractA, AbstractB].map(cls => new cls()); // should error

testdata/baselines/reference/submodule/compiler/abstractClassUnionInstantiation.types.diff

@@ -1,15 +1,6 @@
 --- old.abstractClassUnionInstantiation.types
 +++ new.abstractClassUnionInstantiation.types
-@@= skipped -45, +45 lines =@@
- >cls2 : Abstracts
-
- new cls3(); // should work
-->new cls3() : ConcreteA | ConcreteB
-+>new cls3() : ConcreteA
- >cls3 : Concretes
-
- [ConcreteA, AbstractA, AbstractB].map(cls => new cls()); // should error
-@@= skipped -31, +31 lines =@@
+@@= skipped -76, +76 lines =@@
 
  [ConcreteA, ConcreteB].map(cls => new cls()); // should work
  >[ConcreteA, ConcreteB].map(cls => new cls()) : ConcreteA[]

testdata/baselines/reference/submodule/compiler/jsxComponentTypeErrors.errors.txt

@@ -17,7 +17,13 @@ jsxComponentTypeErrors.tsx(27,16): error TS2786: 'ClassComponent' cannot be used
   Its instance type 'ClassComponent' is not a valid JSX element.
     Types of property 'type' are incompatible.
       Type 'string' is not assignable to type '"element-class"'.
-jsxComponentTypeErrors.tsx(28,16): error TS2604: JSX element type 'MixedComponent' does not have any construct or call signatures.
+jsxComponentTypeErrors.tsx(28,16): error TS2786: 'MixedComponent' cannot be used as a JSX component.
+  Its element type 'ClassComponent | { type: string | undefined; }' is not a valid JSX element.
+    Type 'ClassComponent' is not assignable to type 'Element | ElementClass | null'.
+      Type 'ClassComponent' is not assignable to type 'Element | ElementClass'.
+        Type 'ClassComponent' is not assignable to type 'ElementClass'.
+          Types of property 'type' are incompatible.
+            Type 'string' is not assignable to type '"element-class"'.
 jsxComponentTypeErrors.tsx(37,16): error TS2786: 'obj.MemberFunctionComponent' cannot be used as a JSX component.
   Property 'type' is missing in type '{}' but required in type 'Element'.
 jsxComponentTypeErrors.tsx(38,16): error TS2786: 'obj. MemberClassComponent' cannot be used as a JSX component.
@@ -77,7 +83,13 @@ jsxComponentTypeErrors.tsx(38,16): error TS2786: 'obj. MemberClassComponent' can
 !!! error TS2786:       Type 'string' is not assignable to type '"element-class"'.
     const elem4 = <MixedComponent />;
                    ~~~~~~~~~~~~~~
-!!! error TS2604: JSX element type 'MixedComponent' does not have any construct or call signatures.
+!!! error TS2786: 'MixedComponent' cannot be used as a JSX component.
+!!! error TS2786:   Its element type 'ClassComponent | { type: string | undefined; }' is not a valid JSX element.
+!!! error TS2786:     Type 'ClassComponent' is not assignable to type 'Element | ElementClass | null'.
+!!! error TS2786:       Type 'ClassComponent' is not assignable to type 'Element | ElementClass'.
+!!! error TS2786:         Type 'ClassComponent' is not assignable to type 'ElementClass'.
+!!! error TS2786:           Types of property 'type' are incompatible.
+!!! error TS2786:             Type 'string' is not assignable to type '"element-class"'.
 
     const obj = {
       MemberFunctionComponent() {

testdata/baselines/reference/submodule/compiler/jsxComponentTypeErrors.errors.txt.diff

@@ -1,17 +1,8 @@
 --- old.jsxComponentTypeErrors.errors.txt
 +++ new.jsxComponentTypeErrors.errors.txt
-@@= skipped -16, +16 lines =@@
-   Its instance type 'ClassComponent' is not a valid JSX element.
-     Types of property 'type' are incompatible.
-       Type 'string' is not assignable to type '"element-class"'.
--jsxComponentTypeErrors.tsx(28,16): error TS2786: 'MixedComponent' cannot be used as a JSX component.
--  Its element type 'ClassComponent | { type: string | undefined; }' is not a valid JSX element.
--    Type 'ClassComponent' is not assignable to type 'Element | ElementClass | null'.
--      Type 'ClassComponent' is not assignable to type 'Element | ElementClass'.
--        Type 'ClassComponent' is not assignable to type 'ElementClass'.
--          Types of property 'type' are incompatible.
--            Type 'string' is not assignable to type '"element-class"'.
-+jsxComponentTypeErrors.tsx(28,16): error TS2604: JSX element type 'MixedComponent' does not have any construct or call signatures.
+@@= skipped -24, +24 lines =@@
+           Types of property 'type' are incompatible.
+             Type 'string' is not assignable to type '"element-class"'.
  jsxComponentTypeErrors.tsx(37,16): error TS2786: 'obj.MemberFunctionComponent' cannot be used as a JSX component.
 -  Its return type '{}' is not a valid JSX element.
 -    Property 'type' is missing in type '{}' but required in type 'Element'.
@@ -23,22 +14,7 @@
 
 
  ==== jsxComponentTypeErrors.tsx (7 errors) ====
-@@= skipped -68, +60 lines =@@
- !!! error TS2786:       Type 'string' is not assignable to type '"element-class"'.
-     const elem4 = <MixedComponent />;
-                    ~~~~~~~~~~~~~~
--!!! error TS2786: 'MixedComponent' cannot be used as a JSX component.
--!!! error TS2786:   Its element type 'ClassComponent | { type: string | undefined; }' is not a valid JSX element.
--!!! error TS2786:     Type 'ClassComponent' is not assignable to type 'Element | ElementClass | null'.
--!!! error TS2786:       Type 'ClassComponent' is not assignable to type 'Element | ElementClass'.
--!!! error TS2786:         Type 'ClassComponent' is not assignable to type 'ElementClass'.
--!!! error TS2786:           Types of property 'type' are incompatible.
--!!! error TS2786:             Type 'string' is not assignable to type '"element-class"'.
-+!!! error TS2604: JSX element type 'MixedComponent' does not have any construct or call signatures.
-
-     const obj = {
-       MemberFunctionComponent() {
-@@= skipped -18, +12 lines =@@
+@@= skipped -78, +76 lines =@@
      const elem5 = <obj.MemberFunctionComponent />;
                     ~~~~~~~~~~~~~~~~~~~~~~~~~~~
  !!! error TS2786: 'obj.MemberFunctionComponent' cannot be used as a JSX component.