Use mapped rest type member when expanding rest parameter names (microsoft#39317)

* Use mapped rest type member when expanding rest parameter names

* Add test for microsoft#39228 which is also fixed by parameters having unique names

Author: weswigham

src/compiler/checker.ts

@@ -9781,7 +9781,7 @@ namespace ts {
                 const restParams = map(elementTypes, (t, i) => {
                     // Lookup the label from the individual tuple passed in before falling back to the signature `rest` parameter name
                     const tupleLabelName = !!associatedNames && getTupleElementLabel(associatedNames[i]);
-                    const name = tupleLabelName || getParameterNameAtPosition(sig, restIndex + i);
+                    const name = tupleLabelName || getParameterNameAtPosition(sig, restIndex + i, restType);
                     const flags = restType.target.elementFlags[i];
                     const checkFlags = flags & ElementFlags.Variable ? CheckFlags.RestParameter :
                         flags & ElementFlags.Optional ? CheckFlags.OptionalParameter : 0;
@@ -27708,13 +27708,13 @@ namespace ts {
             return d.name.escapedText;
         }
 
-        function getParameterNameAtPosition(signature: Signature, pos: number) {
+        function getParameterNameAtPosition(signature: Signature, pos: number, overrideRestType?: Type) {
             const paramCount = signature.parameters.length - (signatureHasRestParameter(signature) ? 1 : 0);
             if (pos < paramCount) {
                 return signature.parameters[pos].escapedName;
             }
             const restParameter = signature.parameters[paramCount] || unknownSymbol;
-            const restType = getTypeOfSymbol(restParameter);
+            const restType = overrideRestType || getTypeOfSymbol(restParameter);
             if (isTupleType(restType)) {
                 const associatedNames = (<TupleType>(<TypeReference>restType).target).labeledElementDeclarations;
                 const index = pos - paramCount;

src/harness/fourslashImpl.ts

@@ -1426,7 +1426,7 @@ namespace FourSlash {
                 this.raiseError("Could not get a help signature");
             }
 
-            const selectedItem = help.items[help.selectedItemIndex];
+            const selectedItem = help.items[options.overrideSelectedItemIndex ?? help.selectedItemIndex];
             // Argument index may exceed number of parameters
             const currentParameter = selectedItem.parameters[help.argumentIndex] as ts.SignatureHelpParameter | undefined;
 
@@ -1478,6 +1478,7 @@ namespace FourSlash {
                 "isVariadic",
                 "tags",
                 "argumentCount",
+                "overrideSelectedItemIndex"
             ];
             for (const key in options) {
                 if (!ts.contains(allKeys, key)) {

src/harness/fourslashInterfaceImpl.ts

@@ -1533,6 +1533,7 @@ namespace FourSlashInterface {
         /** @default ts.emptyArray */
         readonly tags?: readonly ts.JSDocTagInfo[];
         readonly triggerReason?: ts.SignatureHelpTriggerReason;
+        readonly overrideSelectedItemIndex?: number;
     }
 
     export interface VerifyNavigateToOptions {

tests/cases/fourslash/fourslash.ts

@@ -644,6 +644,7 @@ declare namespace FourSlashInterface {
         isVariadic?: boolean;
         tags?: ReadonlyArray<JSDocTagInfo>;
         triggerReason?: SignatureHelpTriggerReason;
+        overrideSelectedItemIndex?: number;
     }
 
     export type SignatureHelpTriggerReason =

tests/cases/fourslash/signatureHelpExpandedRestUnlabeledTuples.ts

@@ -0,0 +1,36 @@
+/// <reference path='fourslash.ts' />
+
+////export function complex(item: string, another: string, ...rest: [] | [object, (err: Error) => void] | [(err: Error) => void, ...object[]]) {
+////    
+////}
+////
+////complex(/*1*/);
+////complex("ok", "ok", /*2*/);
+////complex("ok", "ok", e => void e, {}, /*3*/);
+
+verify.signatureHelp(
+    {
+        marker: "1",
+        text: "complex(item: string, another: string): void",
+        overloadsCount: 3,
+        parameterCount: 2,
+        parameterName: "item",
+        parameterSpan: "item: string",
+        isVariadic: false,
+    },
+    {
+        marker: "2",
+        text: "complex(item: string, another: string, rest_0: object, rest_1: (err: Error) => void): void",
+        overloadsCount: 3,
+        parameterCount: 4,
+        parameterName: "rest_0",
+        parameterSpan: "rest_0: object",
+        isVariadic: false,
+    },
+    {
+        marker: "3",
+        text: "complex(item: string, another: string, rest_0: (err: Error) => void, ...rest_1: object[]): void",
+        overloadsCount: 3,
+        isVariadic: true,
+    },
+);

tests/cases/fourslash/signatureHelpExpandedTuplesArgumentIndex.ts

@@ -0,0 +1,94 @@
+/// <reference path='fourslash.ts' />
+
+////function foo(...args: [string, string] | [number, string, string]
+////) {
+////
+////}
+////
+////foo(123/*1*/,)
+////foo(""/*2*/, ""/*3*/)
+////foo(123/*4*/, ""/*5*/, )
+////foo(123/*6*/, ""/*7*/, ""/*8*/)
+
+verify.signatureHelp(
+    {
+        marker: "1",
+        text: "foo(args_0: number, args_1: string, args_2: string): void",
+        overloadsCount: 2,
+        parameterCount: 3,
+        parameterName: "args_0",
+        parameterSpan: "args_0: number",
+        isVariadic: false,
+        overrideSelectedItemIndex: 1
+    },
+    {
+        marker: "2",
+        text: "foo(args_0: string, args_1: string): void",
+        overloadsCount: 2,
+        parameterCount: 2,
+        parameterName: "args_0",
+        parameterSpan: "args_0: string",
+        isVariadic: false,
+        overrideSelectedItemIndex: 0
+    },
+    {
+        marker: "3",
+        text: "foo(args_0: string, args_1: string): void",
+        overloadsCount: 2,
+        parameterCount: 2,
+        parameterName: "args_1",
+        parameterSpan: "args_1: string",
+        isVariadic: false,
+        overrideSelectedItemIndex: 0
+    },
+    {
+        marker: "4",
+        text: "foo(args_0: number, args_1: string, args_2: string): void",
+        overloadsCount: 2,
+        parameterCount: 3,
+        parameterName: "args_0",
+        parameterSpan: "args_0: number",
+        isVariadic: false,
+        overrideSelectedItemIndex: 1
+    },
+    {
+        marker: "5",
+        text: "foo(args_0: number, args_1: string, args_2: string): void",
+        overloadsCount: 2,
+        parameterCount: 3,
+        parameterName: "args_1",
+        parameterSpan: "args_1: string",
+        isVariadic: false,
+        overrideSelectedItemIndex: 1
+    },
+    {
+        marker: "6",
+        text: "foo(args_0: number, args_1: string, args_2: string): void",
+        overloadsCount: 2,
+        parameterCount: 3,
+        parameterName: "args_0",
+        parameterSpan: "args_0: number",
+        isVariadic: false,
+        overrideSelectedItemIndex: 1
+    },
+    {
+        marker: "7",
+        text: "foo(args_0: number, args_1: string, args_2: string): void",
+        overloadsCount: 2,
+        parameterCount: 3,
+        parameterName: "args_1",
+        parameterSpan: "args_1: string",
+        isVariadic: false,
+        overrideSelectedItemIndex: 1
+    },
+    {
+        marker: "8",
+        text: "foo(args_0: number, args_1: string, args_2: string): void",
+        overloadsCount: 2,
+        parameterCount: 3,
+        parameterName: "args_2",
+        parameterSpan: "args_2: string",
+        isVariadic: false,
+        overrideSelectedItemIndex: 1
+    },
+);