Fix the quickInfo for rest parameters

Author: sheetalkamat

src/compiler/checker.ts

@@ -3876,9 +3876,21 @@ module ts {
             var func = <FunctionDeclaration>parameter.parent;
             if (func.kind === SyntaxKind.FunctionExpression || func.kind === SyntaxKind.ArrowFunction) {
                 if (isContextSensitiveExpression(func)) {
-                    var signature = getContextualSignature(func);
-                    if (signature) {
-                        return getTypeAtPosition(signature, indexOf(func.parameters, parameter));
+                    var contextualSignature = getContextualSignature(func);
+                    if (contextualSignature) {
+
+                        var funcHasRestParameters = hasRestParameters(func);
+                        var len = func.parameters.length - (funcHasRestParameters ? 1 : 0);
+                        var indexOfParameter = indexOf(func.parameters, parameter);
+                        if (indexOfParameter < len) {
+                            return getTypeAtPosition(contextualSignature, indexOfParameter);
+                        }
+
+                        // If last parameter is contextually rest parameter get its type
+                        if (indexOfParameter === (func.parameters.length - 1) && 
+                            funcHasRestParameters && contextualSignature.hasRestParameter && func.parameters.length >= contextualSignature.parameters.length) {
+                            return getTypeOfSymbol(contextualSignature.parameters[contextualSignature.parameters.length - 1]);
+                        }
                     }
                 }
             }

tests/cases/fourslash_old/restArgType.ts renamed to tests/cases/fourslash/restArgType.ts

@@ -19,7 +19,7 @@
 ////});
 ////var t1 :(a1: string, a2: string) => void = (.../*t1*/f1) => { }  // f1 => any[];
 ////var t2: (a1: string, ...a2: string[]) => void = (.../*t2*/f1) => { } // f1 => any[];
-////var t3: (a1: number, a2: boolean, ...c: string[]) => void  = (f1/*t31*/, .../*t32*/f2) => { }; // f1 => number, f2 => any[]
+////var t3: (a1: number, a2: boolean, ...c: string[]) => void  = (/*t31*/f1, .../*t32*/f2) => { }; // f1 => number, f2 => any[]
 ////var t4: (...a1: string[]) => void = (.../*t4*/f1) => { };      // f1 => string[]
 ////var t5: (...a1: string[]) => void = (/*t5*/f1) => { };         // f1 => string
 ////var t6: (...a1: string[]) => void = (/*t61*/f1, .../*t62*/f2) => { };  // f1 => string, f2 => string[]