fix lookup regression again and again

src/compiler/checker.ts

@@ -1237,17 +1237,25 @@ namespace ts {
                                     // local types not visible outside the function body
                                     : false;
                             }
-                            if (meaning & 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 =
-                                    lastLocation.kind === SyntaxKind.Parameter ||
-                                    (
-                                        lastLocation === (<FunctionLikeDeclaration>location).type &&
-                                        !!findAncestor(result.valueDeclaration, isParameter)
-                                    );
+                            if (meaning & result.flags & SymbolFlags.Variable) {
+                                // expression inside parameter will lookup as normal variable scope when targeting es2015+
+                                const functionLocation = <FunctionLikeDeclaration>location;
+                                if (compilerOptions.target && compilerOptions.target >= ScriptTarget.ES2015 && isParameter(lastLocation) &&
+                                    functionLocation.body && result.valueDeclaration.pos >= functionLocation.body.pos && result.valueDeclaration.end <= functionLocation.body.end) {
+                                    useResult = false;
+                                }
+                                else if (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 =
+                                        lastLocation.kind === SyntaxKind.Parameter ||
+                                        (
+                                            lastLocation === (<FunctionLikeDeclaration>location).type &&
+                                            !!findAncestor(result.valueDeclaration, isParameter)
+                                        );
+                                }
                             }
                         }
                         else if (location.kind === SyntaxKind.ConditionalType) {

tests/baselines/reference/parameterInitializersForwardReferencing1_es6.errors.txt

@@ -1,24 +1,17 @@
-tests/cases/conformance/functions/parameterInitializersForwardReferencing1_es6.ts(3,20): error TS2373: Initializer of parameter 'bar' cannot reference identifier 'foo' declared after it.
-tests/cases/conformance/functions/parameterInitializersForwardReferencing1_es6.ts(8,27): error TS2373: Initializer of parameter 'bar' cannot reference identifier 'foo' declared after it.
 tests/cases/conformance/functions/parameterInitializersForwardReferencing1_es6.ts(13,20): error TS2373: Initializer of parameter 'bar' cannot reference identifier 'foo' declared after it.
 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(29,15): error TS2448: Block-scoped variable 'foo' used before its declaration.
 
 
-==== tests/cases/conformance/functions/parameterInitializersForwardReferencing1_es6.ts (6 errors) ====
+==== tests/cases/conformance/functions/parameterInitializersForwardReferencing1_es6.ts (3 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
     }
@@ -46,9 +39,6 @@ tests/cases/conformance/functions/parameterInitializersForwardReferencing1_es6.t
     }
 
     function f7({[foo]: bar}: any[]) {
-                  ~~~
-!!! error TS2448: Block-scoped variable 'foo' used before its declaration.
-!!! related TS2728 tests/cases/conformance/functions/parameterInitializersForwardReferencing1_es6.ts:30:9: 'foo' is declared here.
         let foo: number = 2;
     }
 

tests/baselines/reference/parameterInitializersForwardReferencing1_es6.symbols

@@ -5,7 +5,7 @@ let foo: string = "";
 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, 3, 7))
+>foo : Symbol(foo, Decl(parameterInitializersForwardReferencing1_es6.ts, 0, 3))
 
     var foo: number = 2;
 >foo : Symbol(foo, Decl(parameterInitializersForwardReferencing1_es6.ts, 3, 7))
@@ -18,7 +18,7 @@ function f2 (bar = (baz = foo) => baz) { // unexpected compiler error; works at
 >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, 8, 7))
+>foo : Symbol(foo, Decl(parameterInitializersForwardReferencing1_es6.ts, 0, 3))
 >baz : Symbol(baz, Decl(parameterInitializersForwardReferencing1_es6.ts, 7, 20))
 
     var foo: number = 2;
@@ -68,7 +68,7 @@ function f6 (async = async) {
 
 function f7({[foo]: bar}: any[]) {
 >f7 : Symbol(f7, Decl(parameterInitializersForwardReferencing1_es6.ts, 26, 1))
->foo : Symbol(foo, Decl(parameterInitializersForwardReferencing1_es6.ts, 29, 7))
+>foo : Symbol(foo, Decl(parameterInitializersForwardReferencing1_es6.ts, 0, 3))
 >bar : Symbol(bar, Decl(parameterInitializersForwardReferencing1_es6.ts, 28, 13))
 
     let foo: number = 2;

tests/baselines/reference/parameterInitializersForwardReferencing1_es6.types

@@ -4,33 +4,33 @@ let foo: string = "";
 >"" : ""
 
 function f1 (bar = foo) { // unexpected compiler error; works at runtime
->f1 : (bar?: number) => number
->bar : number
->foo : number
+>f1 : (bar?: string) => string
+>bar : string
+>foo : string
 
     var foo: number = 2;
 >foo : number
 >2 : 2
 
     return bar; // returns 1
->bar : number
+>bar : string
 }
 
 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
+>f2 : (bar?: (baz?: string) => string) => string
+>bar : (baz?: string) => string
+>(baz = foo) => baz : (baz?: string) => string
+>baz : string
+>foo : string
+>baz : string
 
     var foo: number = 2;
 >foo : number
 >2 : 2
 
     return bar(); // returns 1
->bar() : number
->bar : (baz?: number) => number
+>bar() : string
+>bar : (baz?: string) => string
 }
 
 function f3 (bar = foo, foo = 2) { // correct compiler error, error at runtime
@@ -74,7 +74,7 @@ function f6 (async = async) {
 
 function f7({[foo]: bar}: any[]) {
 >f7 : ({ [foo]: bar }: any[]) => void
->foo : number
+>foo : string
 >bar : any
 
     let foo: number = 2;