add special check for parameter initializer lookup if targeting es2015+

src/compiler/checker.ts

@@ -1197,16 +1197,22 @@ namespace ts {
                                     : false;
                             }
                             if (meaning & SymbolFlags.Value && result.flags & SymbolFlags.FunctionScopedVariable) {
-                                // parameters are visible only inside function body, parameter list and return type
-                                // technically for parameter list case here we might mix parameters and variables declared in function,
-                                // however it is detected separately when checking initializers of parameters
-                                // to make sure that they reference no variables declared after them.
-                                useResult =
+                                // parameter initializer will lookup as normal variable scope when targeting es2015+
+                                if (compilerOptions.target && compilerOptions.target >= ScriptTarget.ES2015 && isParameter(lastLocation) && lastLocation.initializer === originalLocation && result.valueDeclaration !== lastLocation) {
+                                    useResult = false;
+                                }
+                                else {
+                                    // parameters are visible only inside function body, parameter list and return type
+                                    // technically for parameter list case here we might mix parameters and variables declared in function,
+                                    // however it is detected separately when checking initializers of parameters
+                                    // to make sure that they reference no variables declared after them.
+                                    useResult =
                                     lastLocation.kind === SyntaxKind.Parameter ||
                                     (
                                         lastLocation === (<FunctionLikeDeclaration>location).type &&
                                         !!findAncestor(result.valueDeclaration, isParameter)
                                     );
+                                }
                             }
                         }
                         else if (location.kind === SyntaxKind.ConditionalType) {

tests/baselines/reference/parameterInitializersForwardReferencing1.errors.txt

@@ -0,0 +1,45 @@
+tests/cases/conformance/functions/parameterInitializersForwardReferencing1.ts(3,20): error TS2373: Initializer of parameter 'bar' cannot reference identifier 'foo' declared after it.
+tests/cases/conformance/functions/parameterInitializersForwardReferencing1.ts(8,27): error TS2373: Initializer of parameter 'bar' cannot reference identifier 'foo' declared after it.
+tests/cases/conformance/functions/parameterInitializersForwardReferencing1.ts(13,20): error TS2373: Initializer of parameter 'bar' cannot reference identifier 'foo' declared after it.
+tests/cases/conformance/functions/parameterInitializersForwardReferencing1.ts(21,18): error TS2372: Parameter 'a' cannot be referenced in its initializer.
+tests/cases/conformance/functions/parameterInitializersForwardReferencing1.ts(25,22): error TS2372: Parameter 'async' cannot be referenced in its initializer.
+
+
+==== tests/cases/conformance/functions/parameterInitializersForwardReferencing1.ts (5 errors) ====
+    let foo: string = "";
+    
+    function f1 (bar = foo) { // unexpected compiler error; works at runtime
+                       ~~~
+!!! error TS2373: Initializer of parameter 'bar' cannot reference identifier 'foo' declared after it.
+        var foo: number = 2;
+        return bar; // returns 1
+    }
+    
+    function f2 (bar = (baz = foo) => baz) { // unexpected compiler error; works at runtime
+                              ~~~
+!!! error TS2373: Initializer of parameter 'bar' cannot reference identifier 'foo' declared after it.
+        var foo: number = 2;
+        return bar(); // returns 1
+    }
+    
+    function f3 (bar = foo, foo = 2) { // correct compiler error, error at runtime
+                       ~~~
+!!! error TS2373: Initializer of parameter 'bar' cannot reference identifier 'foo' declared after it.
+        return bar;
+    }
+    
+    function f4 (foo, bar = foo) {
+        return bar
+    }
+    
+    function f5 (a = a) {
+                     ~
+!!! error TS2372: Parameter 'a' cannot be referenced in its initializer.
+        return a
+    }
+    
+    function f6 (async = async) {
+                         ~~~~~
+!!! error TS2372: Parameter 'async' cannot be referenced in its initializer.
+        return async
+    }

tests/baselines/reference/parameterInitializersForwardReferencing1.js

@@ -0,0 +1,61 @@
+//// [parameterInitializersForwardReferencing1.ts]
+let foo: string = "";
+
+function f1 (bar = foo) { // unexpected compiler error; works at runtime
+    var foo: number = 2;
+    return bar; // returns 1
+}
+
+function f2 (bar = (baz = foo) => baz) { // unexpected compiler error; works at runtime
+    var foo: number = 2;
+    return bar(); // returns 1
+}
+
+function f3 (bar = foo, foo = 2) { // correct compiler error, error at runtime
+    return bar;
+}
+
+function f4 (foo, bar = foo) {
+    return bar
+}
+
+function f5 (a = a) {
+    return a
+}
+
+function f6 (async = async) {
+    return async
+}
+
+//// [parameterInitializersForwardReferencing1.js]
+var foo = "";
+function f1(bar) {
+    if (bar === void 0) { bar = foo; }
+    var foo = 2;
+    return bar; // returns 1
+}
+function f2(bar) {
+    if (bar === void 0) { bar = function (baz) {
+        if (baz === void 0) { baz = foo; }
+        return baz;
+    }; }
+    var foo = 2;
+    return bar(); // returns 1
+}
+function f3(bar, foo) {
+    if (bar === void 0) { bar = foo; }
+    if (foo === void 0) { foo = 2; }
+    return bar;
+}
+function f4(foo, bar) {
+    if (bar === void 0) { bar = foo; }
+    return bar;
+}
+function f5(a) {
+    if (a === void 0) { a = a; }
+    return a;
+}
+function f6(async) {
+    if (async === void 0) { async = async; }
+    return async;
+}

tests/baselines/reference/parameterInitializersForwardReferencing1.symbols

@@ -0,0 +1,67 @@
+=== tests/cases/conformance/functions/parameterInitializersForwardReferencing1.ts ===
+let foo: string = "";
+>foo : Symbol(foo, Decl(parameterInitializersForwardReferencing1.ts, 0, 3))
+
+function f1 (bar = foo) { // unexpected compiler error; works at runtime
+>f1 : Symbol(f1, Decl(parameterInitializersForwardReferencing1.ts, 0, 21))
+>bar : Symbol(bar, Decl(parameterInitializersForwardReferencing1.ts, 2, 13))
+>foo : Symbol(foo, Decl(parameterInitializersForwardReferencing1.ts, 3, 7))
+
+    var foo: number = 2;
+>foo : Symbol(foo, Decl(parameterInitializersForwardReferencing1.ts, 3, 7))
+
+    return bar; // returns 1
+>bar : Symbol(bar, Decl(parameterInitializersForwardReferencing1.ts, 2, 13))
+}
+
+function f2 (bar = (baz = foo) => baz) { // unexpected compiler error; works at runtime
+>f2 : Symbol(f2, Decl(parameterInitializersForwardReferencing1.ts, 5, 1))
+>bar : Symbol(bar, Decl(parameterInitializersForwardReferencing1.ts, 7, 13))
+>baz : Symbol(baz, Decl(parameterInitializersForwardReferencing1.ts, 7, 20))
+>foo : Symbol(foo, Decl(parameterInitializersForwardReferencing1.ts, 8, 7))
+>baz : Symbol(baz, Decl(parameterInitializersForwardReferencing1.ts, 7, 20))
+
+    var foo: number = 2;
+>foo : Symbol(foo, Decl(parameterInitializersForwardReferencing1.ts, 8, 7))
+
+    return bar(); // returns 1
+>bar : Symbol(bar, Decl(parameterInitializersForwardReferencing1.ts, 7, 13))
+}
+
+function f3 (bar = foo, foo = 2) { // correct compiler error, error at runtime
+>f3 : Symbol(f3, Decl(parameterInitializersForwardReferencing1.ts, 10, 1))
+>bar : Symbol(bar, Decl(parameterInitializersForwardReferencing1.ts, 12, 13))
+>foo : Symbol(foo, Decl(parameterInitializersForwardReferencing1.ts, 12, 23))
+>foo : Symbol(foo, Decl(parameterInitializersForwardReferencing1.ts, 12, 23))
+
+    return bar;
+>bar : Symbol(bar, Decl(parameterInitializersForwardReferencing1.ts, 12, 13))
+}
+
+function f4 (foo, bar = foo) {
+>f4 : Symbol(f4, Decl(parameterInitializersForwardReferencing1.ts, 14, 1))
+>foo : Symbol(foo, Decl(parameterInitializersForwardReferencing1.ts, 16, 13))
+>bar : Symbol(bar, Decl(parameterInitializersForwardReferencing1.ts, 16, 17))
+>foo : Symbol(foo, Decl(parameterInitializersForwardReferencing1.ts, 16, 13))
+
+    return bar
+>bar : Symbol(bar, Decl(parameterInitializersForwardReferencing1.ts, 16, 17))
+}
+
+function f5 (a = a) {
+>f5 : Symbol(f5, Decl(parameterInitializersForwardReferencing1.ts, 18, 1))
+>a : Symbol(a, Decl(parameterInitializersForwardReferencing1.ts, 20, 13))
+>a : Symbol(a, Decl(parameterInitializersForwardReferencing1.ts, 20, 13))
+
+    return a
+>a : Symbol(a, Decl(parameterInitializersForwardReferencing1.ts, 20, 13))
+}
+
+function f6 (async = async) {
+>f6 : Symbol(f6, Decl(parameterInitializersForwardReferencing1.ts, 22, 1))
+>async : Symbol(async, Decl(parameterInitializersForwardReferencing1.ts, 24, 13))
+>async : Symbol(async, Decl(parameterInitializersForwardReferencing1.ts, 24, 13))
+
+    return async
+>async : Symbol(async, Decl(parameterInitializersForwardReferencing1.ts, 24, 13))
+}

tests/baselines/reference/parameterInitializersForwardReferencing1.types

@@ -0,0 +1,73 @@
+=== tests/cases/conformance/functions/parameterInitializersForwardReferencing1.ts ===
+let foo: string = "";
+>foo : string
+>"" : ""
+
+function f1 (bar = foo) { // unexpected compiler error; works at runtime
+>f1 : (bar?: number) => number
+>bar : number
+>foo : number
+
+    var foo: number = 2;
+>foo : number
+>2 : 2
+
+    return bar; // returns 1
+>bar : number
+}
+
+function f2 (bar = (baz = foo) => baz) { // unexpected compiler error; works at runtime
+>f2 : (bar?: (baz?: number) => number) => number
+>bar : (baz?: number) => number
+>(baz = foo) => baz : (baz?: number) => number
+>baz : number
+>foo : number
+>baz : number
+
+    var foo: number = 2;
+>foo : number
+>2 : 2
+
+    return bar(); // returns 1
+>bar() : number
+>bar : (baz?: number) => number
+}
+
+function f3 (bar = foo, foo = 2) { // correct compiler error, error at runtime
+>f3 : (bar?: number, foo?: number) => number
+>bar : number
+>foo : number
+>foo : number
+>2 : 2
+
+    return bar;
+>bar : number
+}
+
+function f4 (foo, bar = foo) {
+>f4 : (foo: any, bar?: any) => any
+>foo : any
+>bar : any
+>foo : any
+
+    return bar
+>bar : any
+}
+
+function f5 (a = a) {
+>f5 : (a?: any) => any
+>a : any
+>a : any
+
+    return a
+>a : any
+}
+
+function f6 (async = async) {
+>f6 : (async?: any) => any
+>async : any
+>async : any
+
+    return async
+>async : any
+}

tests/baselines/reference/parameterInitializersForwardReferencing1_es6.errors.txt

@@ -0,0 +1,36 @@
+tests/cases/conformance/functions/parameterInitializersForwardReferencing1_es6.ts(21,18): error TS2372: Parameter 'a' cannot be referenced in its initializer.
+tests/cases/conformance/functions/parameterInitializersForwardReferencing1_es6.ts(25,22): error TS2372: Parameter 'async' cannot be referenced in its initializer.
+
+
+==== tests/cases/conformance/functions/parameterInitializersForwardReferencing1_es6.ts (2 errors) ====
+    let foo: string = "";
+    
+    function f1 (bar = foo) { // unexpected compiler error; works at runtime
+        var foo: number = 2;
+        return bar; // returns 1
+    }
+    
+    function f2 (bar = (baz = foo) => baz) { // unexpected compiler error; works at runtime
+        var fooo: number = 2;
+        return bar(); // returns 1
+    }
+    
+    function f3 (bar = foo, foo = 2) { // correct compiler error, error at runtime
+        return bar;
+    }
+    
+    function f4 (foo, bar = foo) {
+        return bar
+    }
+    
+    function f5 (a = a) {
+                     ~
+!!! error TS2372: Parameter 'a' cannot be referenced in its initializer.
+        return a
+    }
+    
+    function f6 (async = async) {
+                         ~~~~~
+!!! error TS2372: Parameter 'async' cannot be referenced in its initializer.
+        return async
+    }

tests/baselines/reference/parameterInitializersForwardReferencing1_es6.js

@@ -0,0 +1,51 @@
+//// [parameterInitializersForwardReferencing1_es6.ts]
+let foo: string = "";
+
+function f1 (bar = foo) { // unexpected compiler error; works at runtime
+    var foo: number = 2;
+    return bar; // returns 1
+}
+
+function f2 (bar = (baz = foo) => baz) { // unexpected compiler error; works at runtime
+    var fooo: number = 2;
+    return bar(); // returns 1
+}
+
+function f3 (bar = foo, foo = 2) { // correct compiler error, error at runtime
+    return bar;
+}
+
+function f4 (foo, bar = foo) {
+    return bar
+}
+
+function f5 (a = a) {
+    return a
+}
+
+function f6 (async = async) {
+    return async
+}
+
+//// [parameterInitializersForwardReferencing1_es6.js]
+let foo = "";
+function f1(bar = foo) {
+    var foo = 2;
+    return bar; // returns 1
+}
+function f2(bar = (baz = foo) => baz) {
+    var fooo = 2;
+    return bar(); // returns 1
+}
+function f3(bar = foo, foo = 2) {
+    return bar;
+}
+function f4(foo, bar = foo) {
+    return bar;
+}
+function f5(a = a) {
+    return a;
+}
+function f6(async = async) {
+    return async;
+}

tests/baselines/reference/parameterInitializersForwardReferencing1_es6.symbols

@@ -0,0 +1,67 @@
+=== tests/cases/conformance/functions/parameterInitializersForwardReferencing1_es6.ts ===
+let foo: string = "";
+>foo : Symbol(foo, Decl(parameterInitializersForwardReferencing1_es6.ts, 0, 3))
+
+function f1 (bar = foo) { // unexpected compiler error; works at runtime
+>f1 : Symbol(f1, Decl(parameterInitializersForwardReferencing1_es6.ts, 0, 21))
+>bar : Symbol(bar, Decl(parameterInitializersForwardReferencing1_es6.ts, 2, 13))
+>foo : Symbol(foo, Decl(parameterInitializersForwardReferencing1_es6.ts, 0, 3))
+
+    var foo: number = 2;
+>foo : Symbol(foo, Decl(parameterInitializersForwardReferencing1_es6.ts, 3, 7))
+
+    return bar; // returns 1
+>bar : Symbol(bar, Decl(parameterInitializersForwardReferencing1_es6.ts, 2, 13))
+}
+
+function f2 (bar = (baz = foo) => baz) { // unexpected compiler error; works at runtime
+>f2 : Symbol(f2, Decl(parameterInitializersForwardReferencing1_es6.ts, 5, 1))
+>bar : Symbol(bar, Decl(parameterInitializersForwardReferencing1_es6.ts, 7, 13))
+>baz : Symbol(baz, Decl(parameterInitializersForwardReferencing1_es6.ts, 7, 20))
+>foo : Symbol(foo, Decl(parameterInitializersForwardReferencing1_es6.ts, 0, 3))
+>baz : Symbol(baz, Decl(parameterInitializersForwardReferencing1_es6.ts, 7, 20))
+
+    var fooo: number = 2;
+>fooo : Symbol(fooo, Decl(parameterInitializersForwardReferencing1_es6.ts, 8, 7))
+
+    return bar(); // returns 1
+>bar : Symbol(bar, Decl(parameterInitializersForwardReferencing1_es6.ts, 7, 13))
+}
+
+function f3 (bar = foo, foo = 2) { // correct compiler error, error at runtime
+>f3 : Symbol(f3, Decl(parameterInitializersForwardReferencing1_es6.ts, 10, 1))
+>bar : Symbol(bar, Decl(parameterInitializersForwardReferencing1_es6.ts, 12, 13))
+>foo : Symbol(foo, Decl(parameterInitializersForwardReferencing1_es6.ts, 0, 3))
+>foo : Symbol(foo, Decl(parameterInitializersForwardReferencing1_es6.ts, 12, 23))
+
+    return bar;
+>bar : Symbol(bar, Decl(parameterInitializersForwardReferencing1_es6.ts, 12, 13))
+}
+
+function f4 (foo, bar = foo) {
+>f4 : Symbol(f4, Decl(parameterInitializersForwardReferencing1_es6.ts, 14, 1))
+>foo : Symbol(foo, Decl(parameterInitializersForwardReferencing1_es6.ts, 16, 13))
+>bar : Symbol(bar, Decl(parameterInitializersForwardReferencing1_es6.ts, 16, 17))
+>foo : Symbol(foo, Decl(parameterInitializersForwardReferencing1_es6.ts, 0, 3))
+
+    return bar
+>bar : Symbol(bar, Decl(parameterInitializersForwardReferencing1_es6.ts, 16, 17))
+}
+
+function f5 (a = a) {
+>f5 : Symbol(f5, Decl(parameterInitializersForwardReferencing1_es6.ts, 18, 1))
+>a : Symbol(a, Decl(parameterInitializersForwardReferencing1_es6.ts, 20, 13))
+>a : Symbol(a, Decl(parameterInitializersForwardReferencing1_es6.ts, 20, 13))
+
+    return a
+>a : Symbol(a, Decl(parameterInitializersForwardReferencing1_es6.ts, 20, 13))
+}
+
+function f6 (async = async) {
+>f6 : Symbol(f6, Decl(parameterInitializersForwardReferencing1_es6.ts, 22, 1))
+>async : Symbol(async, Decl(parameterInitializersForwardReferencing1_es6.ts, 24, 13))
+>async : Symbol(async, Decl(parameterInitializersForwardReferencing1_es6.ts, 24, 13))
+
+    return async
+>async : Symbol(async, Decl(parameterInitializersForwardReferencing1_es6.ts, 24, 13))
+}

tests/baselines/reference/parameterInitializersForwardReferencing1_es6.types

@@ -0,0 +1,73 @@
+=== tests/cases/conformance/functions/parameterInitializersForwardReferencing1_es6.ts ===
+let foo: string = "";
+>foo : string
+>"" : ""
+
+function f1 (bar = foo) { // unexpected compiler error; works at runtime
+>f1 : (bar?: string) => string
+>bar : string
+>foo : string
+
+    var foo: number = 2;
+>foo : number
+>2 : 2
+
+    return bar; // returns 1
+>bar : string
+}
+
+function f2 (bar = (baz = foo) => baz) { // unexpected compiler error; works at runtime
+>f2 : (bar?: (baz?: string) => string) => string
+>bar : (baz?: string) => string
+>(baz = foo) => baz : (baz?: string) => string
+>baz : string
+>foo : string
+>baz : string
+
+    var fooo: number = 2;
+>fooo : number
+>2 : 2
+
+    return bar(); // returns 1
+>bar() : string
+>bar : (baz?: string) => string
+}
+
+function f3 (bar = foo, foo = 2) { // correct compiler error, error at runtime
+>f3 : (bar?: string, foo?: number) => string
+>bar : string
+>foo : string
+>foo : number
+>2 : 2
+
+    return bar;
+>bar : string
+}
+
+function f4 (foo, bar = foo) {
+>f4 : (foo: any, bar?: string) => string
+>foo : any
+>bar : string
+>foo : string
+
+    return bar
+>bar : string
+}
+
+function f5 (a = a) {
+>f5 : (a?: any) => any
+>a : any
+>a : any
+
+    return a
+>a : any
+}
+
+function f6 (async = async) {
+>f6 : (async?: any) => any
+>async : any
+>async : any
+
+    return async
+>async : any
+}

tests/cases/conformance/functions/parameterInitializersForwardReferencing1.ts

@@ -0,0 +1,27 @@
+let foo: string = "";
+
+function f1 (bar = foo) { // unexpected compiler error; works at runtime
+    var foo: number = 2;
+    return bar; // returns 1
+}
+
+function f2 (bar = (baz = foo) => baz) { // unexpected compiler error; works at runtime
+    var foo: number = 2;
+    return bar(); // returns 1
+}
+
+function f3 (bar = foo, foo = 2) { // correct compiler error, error at runtime
+    return bar;
+}
+
+function f4 (foo, bar = foo) {
+    return bar
+}
+
+function f5 (a = a) {
+    return a
+}
+
+function f6 (async = async) {
+    return async
+}

tests/cases/conformance/functions/parameterInitializersForwardReferencing1_es6.ts

@@ -0,0 +1,29 @@
+// @target: es2015
+
+let foo: string = "";
+
+function f1 (bar = foo) { // unexpected compiler error; works at runtime
+    var foo: number = 2;
+    return bar; // returns 1
+}
+
+function f2 (bar = (baz = foo) => baz) { // unexpected compiler error; works at runtime
+    var fooo: number = 2;
+    return bar(); // returns 1
+}
+
+function f3 (bar = foo, foo = 2) { // correct compiler error, error at runtime
+    return bar;
+}
+
+function f4 (foo, bar = foo) {
+    return bar
+}
+
+function f5 (a = a) {
+    return a
+}
+
+function f6 (async = async) {
+    return async
+}