(signature help) type parameter lists are never variadic (#12112)

Author: vladima

src/harness/fourslash.ts

@@ -1026,7 +1026,7 @@ namespace FourSlash {
                 ts.displayPartsToString(help.suffixDisplayParts), expected);
         }
 
-        public verifyCurrentParameterIsletiable(isVariable: boolean) {
+        public verifyCurrentParameterIsVariable(isVariable: boolean) {
             const signature = this.getActiveSignatureHelpItem();
             assert.isOk(signature);
             assert.equal(isVariable, signature.isVariadic);
@@ -1053,6 +1053,10 @@ namespace FourSlash {
             assert.equal(this.getActiveSignatureHelpItem().parameters.length, expectedCount);
         }
 
+        public verifyCurrentSignatureHelpIsVariadic(expected: boolean) {
+            assert.equal(this.getActiveSignatureHelpItem().isVariadic, expected);
+        }
+
         public verifyCurrentSignatureHelpDocComment(docComment: string) {
             const actualDocComment = this.getActiveSignatureHelpItem().documentation;
             assert.equal(ts.displayPartsToString(actualDocComment), docComment, this.assertionMessageAtLastKnownMarker("current signature help doc comment"));
@@ -3231,6 +3235,10 @@ namespace FourSlashInterface {
             this.state.verifySignatureHelpCount(expected);
         }
 
+        public signatureHelpCurrentArgumentListIsVariadic(expected: boolean) {
+            this.state.verifyCurrentSignatureHelpIsVariadic(expected);
+        }
+
         public signatureHelpArgumentCountIs(expected: number) {
             this.state.verifySignatureHelpArgumentCount(expected);
         }

src/services/signatureHelp.ts

@@ -557,7 +557,9 @@ namespace ts.SignatureHelp {
                 addRange(prefixDisplayParts, callTargetDisplayParts);
             }
 
+            let isVariadic: boolean;
             if (isTypeParameterList) {
+                isVariadic = false; // type parameter lists are not variadic
                 prefixDisplayParts.push(punctuationPart(SyntaxKind.LessThanToken));
                 const typeParameters = candidateSignature.typeParameters;
                 signatureHelpParameters = typeParameters && typeParameters.length > 0 ? map(typeParameters, createSignatureHelpParameterForTypeParameter) : emptyArray;
@@ -567,6 +569,7 @@ namespace ts.SignatureHelp {
                 addRange(suffixDisplayParts, parameterParts);
             }
             else {
+                isVariadic = candidateSignature.hasRestParameter;
                 const typeParameterParts = mapToDisplayParts(writer =>
                     typeChecker.getSymbolDisplayBuilder().buildDisplayForTypeParametersAndDelimiters(candidateSignature.typeParameters, writer, invocation));
                 addRange(prefixDisplayParts, typeParameterParts);
@@ -582,7 +585,7 @@ namespace ts.SignatureHelp {
             addRange(suffixDisplayParts, returnTypeParts);
 
             return {
-                isVariadic: candidateSignature.hasRestParameter,
+                isVariadic,
                 prefixDisplayParts,
                 suffixDisplayParts,
                 separatorDisplayParts: [punctuationPart(SyntaxKind.CommaToken), spacePart()],

tests/cases/fourslash/fourslash.ts

@@ -194,6 +194,7 @@ declare namespace FourSlashInterface {
         currentSignatureHelpDocCommentIs(docComment: string): void;
         signatureHelpCountIs(expected: number): void;
         signatureHelpArgumentCountIs(expected: number): void;
+        signatureHelpCurrentArgumentListIsVariadic(expected: boolean);
         currentSignatureParameterCountIs(expected: number): void;
         currentSignatureTypeParameterCountIs(expected: number): void;
         currentSignatureHelpIs(expected: string): void;

tests/cases/fourslash/signatureHelpTypeParametersNotVariadic.ts

@@ -0,0 +1,8 @@
+/// <reference path="fourslash.ts" />
+
+//// declare function f(a: any, ...b: any[]): any;
+//// f</*1*/>(1, 2);
+
+goTo.marker("1");
+verify.signatureHelpArgumentCountIs(0);
+verify.signatureHelpCurrentArgumentListIsVariadic(false);