Require all parameters in JS

src/compiler/checker.ts

@@ -10100,11 +10100,17 @@ namespace ts {
                 let hasThisParameter = false;
                 const iife = getImmediatelyInvokedFunctionExpression(declaration);
                 const isJSConstructSignature = isJSDocConstructSignature(declaration);
-                const isUntypedSignatureInJSFile = !iife &&
+                let isUntypedSignatureInJSFile = !iife &&
                     isInJSFile(declaration) &&
                     isValueSignatureDeclaration(declaration) &&
                     !hasJSDocParameterTags(declaration) &&
                     !getJSDocType(declaration);
+                if (isUntypedSignatureInJSFile && isFunctionExpressionOrArrowFunction(declaration) && isContextSensitiveFunctionLikeDeclaration(declaration)) {
+                    const t = getContextualType(declaration);
+                    if (t) {
+                        isUntypedSignatureInJSFile = t !== anyType;
+                    }
+                }
 
                 // If this is a JSDoc construct signature, then skip the first parameter in the
                 // parameter list.  The first parameter represents the return type of the construct

tests/baselines/reference/argumentsObjectCreatesRestForJs.symbols

@@ -15,7 +15,7 @@ function someRest(x, y) { arguments; }
 >y : Symbol(y, Decl(main.js, 3, 20))
 >arguments : Symbol(arguments)
 
-someRest(); // x and y are still optional because they are in a JS file
+someRest(); // x and y are still required even though they're in a JS file
 >someRest : Symbol(someRest, Decl(main.js, 2, 17))
 
 someRest(1, 2, 3);

tests/baselines/reference/argumentsObjectCreatesRestForJs.types

@@ -20,7 +20,7 @@ function someRest(x, y) { arguments; }
 >y : any
 >arguments : IArguments
 
-someRest(); // x and y are still optional because they are in a JS file
+someRest(); // x and y are still required even though they're in a JS file
 >someRest() : void
 >someRest : (x: any, y: any, ...args: any[]) => void
 

tests/cases/compiler/argumentsObjectCreatesRestForJs.ts

@@ -6,7 +6,7 @@ function allRest() { arguments; }
 allRest();
 allRest(1, 2, 3);
 function someRest(x, y) { arguments; }
-someRest(); // x and y are still optional because they are in a JS file
+someRest(); // x and y are still required even though they're in a JS file
 someRest(1, 2, 3);
 
 /**

tests/cases/fourslash/signatureHelpCallExpressionJs.ts

@@ -4,15 +4,15 @@
 // @allowJs: true
 
 // @Filename: main.js
-////function allOptional() { arguments; }
-////allOptional(/*1*/);
-////allOptional(1, 2, 3);
-////function someOptional(x, y) { arguments; }
-////someOptional(/*2*/);
-////someOptional(1, 2, 3);
-////someOptional(); // no error here; x and y are optional in JS
+//// function allOptional() { arguments; }
+//// allOptional(/*1*/);
+//// allOptional(1, 2, 3);
+//// function someOptional(x, y) { arguments; }
+//// someOptional(/*2*/);
+//// someOptional(1, 2, 3);
+//// /*missing*/someOptional(); // no error here; x and y are optional in JS
 
-verify.noErrors();
+verify.not.errorExistsAfterMarker("missing");
 verify.signatureHelp(
     {
         marker: "1",