Show expanded parameter lists in signature help

Author: ahejlsberg

src/compiler/checker.ts

@@ -231,6 +231,7 @@ namespace ts {
                 getResolvedSignatureWorker(node, candidatesOutArray, agumentCount, CheckMode.Normal),
             getResolvedSignatureForSignatureHelp: (node, candidatesOutArray, agumentCount) =>
                 getResolvedSignatureWorker(node, candidatesOutArray, agumentCount, CheckMode.IsForSignatureHelp),
+            getExpandedParameters,
             getConstantValue: nodeIn => {
                 const node = getParseTreeNode(nodeIn, canHaveConstantValue);
                 return node ? getConstantValue(node) : undefined;

src/compiler/types.ts

@@ -3170,6 +3170,7 @@ 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>;
         getSignatureFromDeclaration(declaration: SignatureDeclaration): Signature | undefined;
         isImplementationOfOverload(node: SignatureDeclaration): boolean | undefined;
         isUndefinedSymbol(symbol: Symbol): boolean;

src/services/signatureHelp.ts

@@ -559,7 +559,7 @@ namespace ts.SignatureHelp {
         const parameters = (typeParameters || emptyArray).map(t => createSignatureHelpParameterForTypeParameter(t, checker, enclosingDeclaration, sourceFile, printer));
         const parameterParts = mapToDisplayParts(writer => {
             const thisParameter = candidateSignature.thisParameter ? [checker.symbolToParameterDeclaration(candidateSignature.thisParameter, enclosingDeclaration, signatureHelpNodeBuilderFlags)!] : [];
-            const params = createNodeArray([...thisParameter, ...candidateSignature.parameters.map(param => checker.symbolToParameterDeclaration(param, enclosingDeclaration, signatureHelpNodeBuilderFlags)!)]);
+            const params = createNodeArray([...thisParameter, ...checker.getExpandedParameters(candidateSignature).map(param => checker.symbolToParameterDeclaration(param, enclosingDeclaration, signatureHelpNodeBuilderFlags)!)]);
             printer.writeList(ListFormat.CallExpressionArguments, params, sourceFile, writer);
         });
         return { isVariadic: false, parameters, prefix: [punctuationPart(SyntaxKind.LessThanToken)], suffix: [punctuationPart(SyntaxKind.GreaterThanToken), ...parameterParts] };
@@ -574,7 +574,7 @@ namespace ts.SignatureHelp {
                 printer.writeList(ListFormat.TypeParameters, args, sourceFile, writer);
             }
         });
-        const parameters = candidateSignature.parameters.map(p => createSignatureHelpParameterForParameter(p, checker, enclosingDeclaration, sourceFile, printer));
+        const parameters = checker.getExpandedParameters(candidateSignature).map(p => createSignatureHelpParameterForParameter(p, checker, enclosingDeclaration, sourceFile, printer));
         return { isVariadic, parameters, prefix: [...typeParameterParts, punctuationPart(SyntaxKind.OpenParenToken)], suffix: [punctuationPart(SyntaxKind.CloseParenToken)] };
     }