Fixed isVariadic handling when signature parameters are expanded for itemInfoForParameters

Author: Titian Cernicova-Dragomir

src/compiler/checker.ts

@@ -232,6 +232,7 @@ namespace ts {
             getResolvedSignatureForSignatureHelp: (node, candidatesOutArray, agumentCount) =>
                 getResolvedSignatureWorker(node, candidatesOutArray, agumentCount, CheckMode.IsForSignatureHelp),
             getExpandedParameters,
+            hasEffectiveRestParameter,
             getConstantValue: nodeIn => {
                 const node = getParseTreeNode(nodeIn, canHaveConstantValue);
                 return node ? getConstantValue(node) : undefined;

src/compiler/types.ts

@@ -3093,7 +3093,6 @@ namespace ts {
         /* @internal */
         getPromisedTypeOfPromise(promise: Type, errorNode?: Node): Type | undefined;
         getReturnTypeOfSignature(signature: Signature): Type;
-        /* @internal */ getExpandedParameters(sig: Signature): ReadonlyArray<Symbol>;
         /**
          * Gets the type of a parameter at a given position in a signature.
          * Returns `any` if the index is not valid.
@@ -3172,6 +3171,7 @@ namespace ts {
         getResolvedSignature(node: CallLikeExpression, candidatesOutArray?: Signature[], argumentCount?: number): Signature | undefined;
         /* @internal */ getResolvedSignatureForSignatureHelp(node: CallLikeExpression, candidatesOutArray?: Signature[], argumentCount?: number): Signature | undefined;
         /* @internal */ getExpandedParameters(sig: Signature): ReadonlyArray<Symbol>;
+        /* @internal */ hasEffectiveRestParameter(sig: Signature): boolean;
         getSignatureFromDeclaration(declaration: SignatureDeclaration): Signature | undefined;
         isImplementationOfOverload(node: SignatureDeclaration): boolean | undefined;
         isUndefinedSymbol(symbol: Symbol): boolean;

src/services/signatureHelp.ts

@@ -566,7 +566,7 @@ namespace ts.SignatureHelp {
     }
 
     function itemInfoForParameters(candidateSignature: Signature, checker: TypeChecker, enclosingDeclaration: Node, sourceFile: SourceFile): SignatureHelpItemInfo {
-        let isVariadic = candidateSignature.hasRestParameter;
+        const isVariadic = checker.hasEffectiveRestParameter(candidateSignature);
         const printer = createPrinter({ removeComments: true });
         const typeParameterParts = mapToDisplayParts(writer => {
             if (candidateSignature.typeParameters && candidateSignature.typeParameters.length) {