Reduce rest parameter reduce if not referenced

Author: Kingwl

src/compiler/checker.ts

@@ -21693,6 +21693,18 @@ namespace ts {
                 return getTypeOfSymbol(symbol);
             }
 
+            if ((symbol.flags & SymbolFlags.Value) && symbol.valueDeclaration && isParameter(symbol.valueDeclaration) && isRestParameter(symbol.valueDeclaration)) {
+                const containerFunctionLikeDeclaration = findAncestor(symbol.valueDeclaration, isFunctionLikeDeclaration);
+                if (containerFunctionLikeDeclaration) {
+                    const topLevelStatementInContainer = findAncestor(node, n => {
+                        return n.parent && (isBlock(n.parent) ? n.parent.parent === containerFunctionLikeDeclaration : n.parent === containerFunctionLikeDeclaration);
+                    })
+                    if (topLevelStatementInContainer) {
+                        (<Mutable<Node>>topLevelStatementInContainer).flags |= NodeFlags.ContainsRestParameterReference;
+                    }
+                }
+            }
+
             // We should only mark aliases as referenced if there isn't a local value declaration
             // for the symbol. Also, don't mark any property access expression LHS - checkPropertyAccessExpression will handle that
             if (!(node.parent && isPropertyAccessExpression(node.parent) && node.parent.expression === node)) {
@@ -21787,7 +21799,7 @@ namespace ts {
             // The declaration container is the innermost function that encloses the declaration of the variable
             // or parameter. The flow container is the innermost function starting with which we analyze the control
             // flow graph to determine the control flow based type.
-            const isParameter = getRootDeclaration(declaration).kind === SyntaxKind.Parameter;
+            const isParameterDecl = getRootDeclaration(declaration).kind === SyntaxKind.Parameter;
             const declarationContainer = getControlFlowContainer(declaration);
             let flowContainer = getControlFlowContainer(node);
             const isOuterVariable = flowContainer !== declarationContainer;
@@ -21798,19 +21810,19 @@ namespace ts {
             // analysis to include the immediately enclosing function.
             while (flowContainer !== declarationContainer && (flowContainer.kind === SyntaxKind.FunctionExpression ||
                 flowContainer.kind === SyntaxKind.ArrowFunction || isObjectLiteralOrClassExpressionMethod(flowContainer)) &&
-                (isConstVariable(localOrExportSymbol) || isParameter && !isParameterAssigned(localOrExportSymbol))) {
+                (isConstVariable(localOrExportSymbol) || isParameterDecl && !isParameterAssigned(localOrExportSymbol))) {
                 flowContainer = getControlFlowContainer(flowContainer);
             }
             // We only look for uninitialized variables in strict null checking mode, and only when we can analyze
             // the entire control flow graph from the variable's declaration (i.e. when the flow container and
             // declaration container are the same).
-            const assumeInitialized = isParameter || isAlias || isOuterVariable || isSpreadDestructuringAssignmentTarget || isModuleExports || isBindingElement(declaration) ||
+            const assumeInitialized = isParameterDecl || isAlias || isOuterVariable || isSpreadDestructuringAssignmentTarget || isModuleExports || isBindingElement(declaration) ||
                 type !== autoType && type !== autoArrayType && (!strictNullChecks || (type.flags & (TypeFlags.AnyOrUnknown | TypeFlags.Void)) !== 0 ||
                 isInTypeQuery(node) || node.parent.kind === SyntaxKind.ExportSpecifier) ||
                 node.parent.kind === SyntaxKind.NonNullExpression ||
                 declaration.kind === SyntaxKind.VariableDeclaration && (<VariableDeclaration>declaration).exclamationToken ||
                 declaration.flags & NodeFlags.Ambient;
-            const initialType = assumeInitialized ? (isParameter ? removeOptionalityFromDeclaredType(type, declaration as VariableLikeDeclaration) : type) :
+            const initialType = assumeInitialized ? (isParameterDecl ? removeOptionalityFromDeclaredType(type, declaration as VariableLikeDeclaration) : type) :
                 type === autoType || type === autoArrayType ? undefinedType :
                 getOptionalType(type);
             const flowType = getFlowTypeOfReference(node, type, initialType, flowContainer, !assumeInitialized);

src/compiler/transformers/es2015.ts

@@ -1354,6 +1354,14 @@ namespace ts {
                 return false;
             }
 
+            const firstStatementContainsRestParameter = node.body && (isBlock(node.body) ?
+                find(node.body.statements, stmt => !!(stmt.flags & NodeFlags.ContainsRestParameterReference)) :
+                (node.body.flags & NodeFlags.ContainsRestParameterReference) ? node.body : undefined
+            );
+            if (!firstStatementContainsRestParameter) {
+                return false;
+            }
+
             // `declarationName` is the name of the local declaration for the parameter.
             // TODO(rbuckton): Does this need to be parented?
             const declarationName = parameter.name.kind === SyntaxKind.Identifier ? setParent(setTextRange(factory.cloneNode(parameter.name), parameter.name), parameter.name.parent) : factory.createTempVariable(/*recordTempVariable*/ undefined);

src/compiler/types.ts

@@ -746,15 +746,17 @@ namespace ts {
         // removal, it is likely that users will add the import anyway.
         // The advantage of this approach is its simplicity. For the case of batch compilation,
         // we guarantee that users won't have to pay the price of walking the tree if a dynamic import isn't used.
-        /* @internal */ PossiblyContainsDynamicImport = 1 << 20,
-        /* @internal */ PossiblyContainsImportMeta    = 1 << 21,
-
-        JSDoc                                         = 1 << 22, // If node was parsed inside jsdoc
-        /* @internal */ Ambient                       = 1 << 23, // If node was inside an ambient context -- a declaration file, or inside something with the `declare` modifier.
-        /* @internal */ InWithStatement               = 1 << 24, // If any ancestor of node was the `statement` of a WithStatement (not the `expression`)
-        JsonFile                                      = 1 << 25, // If node was parsed in a Json
-        /* @internal */ TypeCached                    = 1 << 26, // If a type was cached for node at any point
-        /* @internal */ Deprecated                    = 1 << 27, // If has '@deprecated' JSDoc tag
+        /* @internal */ PossiblyContainsDynamicImport   = 1 << 20,
+        /* @internal */ PossiblyContainsImportMeta      = 1 << 21,
+
+        JSDoc                                           = 1 << 22, // If node was parsed inside jsdoc
+        /* @internal */ Ambient                         = 1 << 23, // If node was inside an ambient context -- a declaration file, or inside something with the `declare` modifier.
+        /* @internal */ InWithStatement                 = 1 << 24, // If any ancestor of node was the `statement` of a WithStatement (not the `expression`)
+        JsonFile                                        = 1 << 25, // If node was parsed in a Json
+        /* @internal */ TypeCached                      = 1 << 26, // If a type was cached for node at any point
+        /* @internal */ Deprecated                      = 1 << 27, // If has '@deprecated' JSDoc tag
+
+        /* @internal */ ContainsRestParameterReference  = 1 << 28, // If contains rest parameter reference
 
         BlockScoped = Let | Const,
 

tests/baselines/reference/accessorWithRestParam.js

@@ -9,22 +9,12 @@ var C = /** @class */ (function () {
     function C() {
     }
     Object.defineProperty(C.prototype, "X", {
-        set: function () {
-            var v = [];
-            for (var _i = 0; _i < arguments.length; _i++) {
-                v[_i] = arguments[_i];
-            }
-        },
+        set: function () { },
         enumerable: false,
         configurable: true
     });
     Object.defineProperty(C, "X", {
-        set: function () {
-            var v2 = [];
-            for (var _i = 0; _i < arguments.length; _i++) {
-                v2[_i] = arguments[_i];
-            }
-        },
+        set: function () { },
         enumerable: false,
         configurable: true
     });

tests/baselines/reference/arrayLiteralInNonVarArgParameter.js

@@ -5,10 +5,5 @@ panic([], 'one', 'two');
 
 
 //// [arrayLiteralInNonVarArgParameter.js]
-function panic(val) {
-    var opt = [];
-    for (var _i = 1; _i < arguments.length; _i++) {
-        opt[_i - 1] = arguments[_i];
-    }
-}
+function panic(val) { }
 panic([], 'one', 'two');

tests/baselines/reference/assignmentCompatWithCallSignaturesWithRestParameters.js

@@ -49,49 +49,19 @@ var a4: (x?: number, y?: string, ...z: number[]) => number;
 // call signatures in derived types must have the same or fewer optional parameters as the target for assignment
 var a; // ok, same number of required params
 a = function () { return 1; }; // ok, same number of required params
-a = function () {
-    var args = [];
-    for (var _i = 0; _i < arguments.length; _i++) {
-        args[_i] = arguments[_i];
-    }
-    return 1;
-}; // ok, same number of required params
-a = function () {
-    var args = [];
-    for (var _i = 0; _i < arguments.length; _i++) {
-        args[_i] = arguments[_i];
-    }
-    return 1;
-}; // error, type mismatch
+a = function () { return 1; }; // ok, same number of required params
+a = function () { return 1; }; // error, type mismatch
 a = function (x) { return 1; }; // ok, same number of required params
 a = function (x, y, z) { return 1; }; // ok, same number of required params
 a = function (x) { return 1; }; // ok, rest param corresponds to infinite number of params
 a = function (x) { return 1; }; // error, incompatible type
 var a2;
 a2 = function () { return 1; }; // ok, fewer required params
-a2 = function () {
-    var args = [];
-    for (var _i = 0; _i < arguments.length; _i++) {
-        args[_i] = arguments[_i];
-    }
-    return 1;
-}; // ok, fewer required params
+a2 = function () { return 1; }; // ok, fewer required params
 a2 = function (x) { return 1; }; // ok, fewer required params
 a2 = function (x) { return 1; }; // ok, same number of required params
-a2 = function (x) {
-    var args = [];
-    for (var _i = 1; _i < arguments.length; _i++) {
-        args[_i - 1] = arguments[_i];
-    }
-    return 1;
-}; // ok, same number of required params
-a2 = function (x) {
-    var args = [];
-    for (var _i = 1; _i < arguments.length; _i++) {
-        args[_i - 1] = arguments[_i];
-    }
-    return 1;
-}; // should be type mismatch error
+a2 = function (x) { return 1; }; // ok, same number of required params
+a2 = function (x) { return 1; }; // should be type mismatch error
 a2 = function (x, y) { return 1; }; // ok, rest param corresponds to infinite number of params
 a2 = function (x, y) { return 1; }; // ok, same number of required params
 var a3;
@@ -100,24 +70,12 @@ a3 = function (x) { return 1; }; // ok, fewer required params
 a3 = function (x) { return 1; }; // ok, same number of required params
 a3 = function (x, y) { return 1; }; // ok, all present params match
 a3 = function (x, y, z) { return 1; }; // error
-a3 = function (x) {
-    var z = [];
-    for (var _i = 1; _i < arguments.length; _i++) {
-        z[_i - 1] = arguments[_i];
-    }
-    return 1;
-}; // error
+a3 = function (x) { return 1; }; // error
 a3 = function (x, y, z) { return 1; }; // error
 var a4;
 a4 = function () { return 1; }; // ok, fewer required params
 a4 = function (x, y) { return 1; }; // error, type mismatch
 a4 = function (x) { return 1; }; // ok, all present params match
 a4 = function (x, y) { return 1; }; // error, second param has type mismatch
 a4 = function (x, y) { return 1; }; // ok, same number of required params with matching types
-a4 = function (x) {
-    var args = [];
-    for (var _i = 1; _i < arguments.length; _i++) {
-        args[_i - 1] = arguments[_i];
-    }
-    return 1;
-}; // error, rest params have type mismatch
+a4 = function (x) { return 1; }; // error, rest params have type mismatch

tests/baselines/reference/asyncArrowFunction11_es5.js

@@ -48,26 +48,20 @@ var __generator = (this && this.__generator) || function (thisArg, body) {
 var A = /** @class */ (function () {
     function A() {
         var _this = this;
-        this.b = function () {
-            var args = [];
-            for (var _i = 0; _i < arguments.length; _i++) {
-                args[_i] = arguments[_i];
-            }
-            return __awaiter(_this, void 0, void 0, function () {
-                var obj;
-                var _a;
-                var _this = this;
-                return __generator(this, function (_b) {
-                    switch (_b.label) {
-                        case 0: return [4 /*yield*/, Promise.resolve()];
-                        case 1:
-                            _b.sent();
-                            obj = (_a = {}, _a["a"] = function () { return _this; }, _a);
-                            return [2 /*return*/];
-                    }
-                });
+        this.b = function () { return __awaiter(_this, void 0, void 0, function () {
+            var obj;
+            var _a;
+            var _this = this;
+            return __generator(this, function (_b) {
+                switch (_b.label) {
+                    case 0: return [4 /*yield*/, Promise.resolve()];
+                    case 1:
+                        _b.sent();
+                        obj = (_a = {}, _a["a"] = function () { return _this; }, _a);
+                        return [2 /*return*/];
+                }
             });
-        };
+        }); };
     }
     return A;
 }());

tests/baselines/reference/baseTypeAfterDerivedType.js

@@ -20,11 +20,6 @@ interface Base2 {
 var Derived2 = /** @class */ (function () {
     function Derived2() {
     }
-    Derived2.prototype.method = function () {
-        var args = [];
-        for (var _i = 0; _i < arguments.length; _i++) {
-            args[_i] = arguments[_i];
-        }
-    };
+    Derived2.prototype.method = function () { };
     return Derived2;
 }());

tests/baselines/reference/callWithSpread.js

@@ -81,10 +81,6 @@ var __spreadArrays = (this && this.__spreadArrays) || function () {
 };
 var _a, _b, _c, _d, _e, _f, _g;
 function foo(x, y) {
-    var z = [];
-    for (var _i = 2; _i < arguments.length; _i++) {
-        z[_i - 2] = arguments[_i];
-    }
 }
 var a;
 var z;
@@ -119,10 +115,6 @@ var C = /** @class */ (function () {
         this.foo.apply(this, __spreadArrays([x, y], z));
     }
     C.prototype.foo = function (x, y) {
-        var z = [];
-        for (var _i = 2; _i < arguments.length; _i++) {
-            z[_i - 2] = arguments[_i];
-        }
     };
     return C;
 }());

tests/baselines/reference/checkSuperCallBeforeThisAccessing5.js

@@ -23,10 +23,6 @@ var __extends = (this && this.__extends) || (function () {
 })();
 var Based = /** @class */ (function () {
     function Based() {
-        var arg = [];
-        for (var _i = 0; _i < arguments.length; _i++) {
-            arg[_i] = arguments[_i];
-        }
     }
     return Based;
 }());

tests/baselines/reference/checkSuperCallBeforeThisAccessing6.js

@@ -26,10 +26,6 @@ var __extends = (this && this.__extends) || (function () {
 })();
 var Base = /** @class */ (function () {
     function Base() {
-        var arg = [];
-        for (var _i = 0; _i < arguments.length; _i++) {
-            arg[_i] = arguments[_i];
-        }
     }
     return Base;
 }());

tests/baselines/reference/checkSuperCallBeforeThisAccessing8.js

@@ -26,10 +26,6 @@ var __extends = (this && this.__extends) || (function () {
 })();
 var Base = /** @class */ (function () {
     function Base() {
-        var arg = [];
-        for (var _i = 0; _i < arguments.length; _i++) {
-            arg[_i] = arguments[_i];
-        }
     }
     return Base;
 }());

tests/baselines/reference/collisionArgumentsArrowFunctions.js

@@ -18,27 +18,15 @@ var f2NoError = () => {
 
 //// [collisionArgumentsArrowFunctions.js]
 var f1 = function (i) {
-    var arguments = [];
-    for (var _i = 1; _i < arguments.length; _i++) {
-        arguments[_i - 1] = arguments[_i];
-    }
     var arguments; // no error
 };
 var f12 = function (arguments) {
-    var rest = [];
-    for (var _i = 1; _i < arguments.length; _i++) {
-        rest[_i - 1] = arguments[_i];
-    }
     var arguments = 10; // no error
 };
 var f1NoError = function (arguments) {
     var arguments = 10; // no error
 };
 var f2 = function () {
-    var restParameters = [];
-    for (var _i = 0; _i < arguments.length; _i++) {
-        restParameters[_i] = arguments[_i];
-    }
     var arguments = 10; // No Error
 };
 var f2NoError = function () {