use single, original tuple instead

Author: sandersn

src/services/signatureHelp.ts

@@ -540,15 +540,7 @@ namespace ts.SignatureHelp {
         }
 
         Debug.assert(selectedItemIndex !== -1); // If candidates is non-empty it should always include bestSignature. We check for an empty candidates before calling this function.
-        const help = { items: flatMapToMutable(items, identity), applicableSpan, selectedItemIndex, argumentIndex, argumentCount };
-        const selected = help.items[selectedItemIndex];
-        if (selected.isVariadic) {
-            const firstRest = findIndex(selected.parameters, p => !!p.isRest);
-            if (firstRest > -1 && help.argumentIndex > firstRest) {
-                help.argumentIndex = firstRest;
-            }
-        }
-        return help;
+        return { items: flatMapToMutable(items, identity), applicableSpan, selectedItemIndex, argumentIndex, argumentCount };
     }
 
     function createTypeHelpItems(
@@ -628,10 +620,12 @@ namespace ts.SignatureHelp {
                 printer.writeList(ListFormat.TypeParameters, args, sourceFile, writer);
             }
         });
-        const lists = checker.getExpandedParameters(candidateSignature);
-        return lists.map(parameterList => {
+        const expansions = checker.getExpandedParameters(candidateSignature);
+        const hasNonTrailingRest = expansions.some(e => e.some((p,i) => (p as TransientSymbol).checkFlags & CheckFlags.RestParameter && i !== e.length - 1));
+        const hasTupleExpansion = expansions.length > 1;
+        return (hasNonTrailingRest ? [candidateSignature.parameters] : expansions).map(parameterList => {
             return {
-                isVariadic: isVariadic && (lists.length === 1 || !!((parameterList[parameterList.length - 1] as TransientSymbol).checkFlags & CheckFlags.RestParameter)),
+                isVariadic: isVariadic && (!hasTupleExpansion || !!((parameterList[parameterList.length - 1] as TransientSymbol).checkFlags & CheckFlags.RestParameter)),
                 parameters: parameterList.map(p => createSignatureHelpParameterForParameter(p, checker, enclosingDeclaration, sourceFile, printer)),
                 prefix: [...typeParameterParts, punctuationPart(SyntaxKind.OpenParenToken)],
                 suffix: [punctuationPart(SyntaxKind.CloseParenToken)]
@@ -645,15 +639,14 @@ namespace ts.SignatureHelp {
             printer.writeNode(EmitHint.Unspecified, param, sourceFile, writer);
         });
         const isOptional = checker.isOptionalParameter(parameter.valueDeclaration as ParameterDeclaration);
-        const isRest = !!((parameter as TransientSymbol).checkFlags & CheckFlags.RestParameter);
-        return { name: parameter.name, documentation: parameter.getDocumentationComment(checker), displayParts, isOptional, isRest };
+        return { name: parameter.name, documentation: parameter.getDocumentationComment(checker), displayParts, isOptional };
     }
 
     function createSignatureHelpParameterForTypeParameter(typeParameter: TypeParameter, checker: TypeChecker, enclosingDeclaration: Node, sourceFile: SourceFile, printer: Printer): SignatureHelpParameter {
         const displayParts = mapToDisplayParts(writer => {
             const param = checker.typeParameterToDeclaration(typeParameter, enclosingDeclaration, signatureHelpNodeBuilderFlags)!;
             printer.writeNode(EmitHint.Unspecified, param, sourceFile, writer);
         });
-        return { name: typeParameter.symbol.name, documentation: typeParameter.symbol.getDocumentationComment(checker), displayParts, isOptional: false, isRest: false };
+        return { name: typeParameter.symbol.name, documentation: typeParameter.symbol.getDocumentationComment(checker), displayParts, isOptional: false };
     }
 }

src/services/types.ts

@@ -1078,7 +1078,6 @@ namespace ts {
         documentation: SymbolDisplayPart[];
         displayParts: SymbolDisplayPart[];
         isOptional: boolean;
-        isRest?: boolean;
     }
 
     export interface SelectionRange {

tests/cases/fourslash/signatureHelpLeadingRestTuple.ts

@@ -1,6 +1,6 @@
 /// <reference path='fourslash.ts' />
 
-////export function leading(...args: [...names: string[], allCaps: boolean]): void {
+////export function leading(...args: [...names: string[], x: boolean, y: number]): void {
 ////}
 ////
 ////leading(/*1*/);
@@ -10,29 +10,25 @@
 verify.signatureHelp(
     {
         marker: "1",
-        text: "leading(...names: string[], allCaps: boolean): void",
+        text: "leading(...args: [...names: string[], x: boolean, y: number]): void",
         overloadsCount: 1,
-        parameterCount: 2,
-        parameterName: "names",
-        parameterSpan: "...names: string[]",
+        parameterCount: 1,
+        parameterName: "args",
+        parameterSpan: "...args: [...names: string[], x: boolean, y: number]",
         isVariadic: true,
     },
     {
         marker: "2",
-        text: "leading(...names: string[], allCaps: boolean): void",
+        text: "leading(...args: [...names: string[], x: boolean, y: number]): void",
         overloadsCount: 1,
-        parameterCount: 2,
-        parameterName: "names",
-        parameterSpan: "...names: string[]",
+        parameterCount: 1,
         isVariadic: true,
     },
     {
         marker: "3",
-        text: "leading(...names: string[], allCaps: boolean): void",
+        text: "leading(...args: [...names: string[], x: boolean, y: number]): void",
         overloadsCount: 1,
-        parameterCount: 2,
-        parameterName: "names",
-        parameterSpan: "...names: string[]",
+        parameterCount: 1,
         isVariadic: true,
     },
 );