Type this in more constructor functions

Previously,  `this: this` in constructor functions only when there was
an explicit `@constructor` tag on the function. Now, `this: this` for
any function that's known to be a constructor function.

This improves completions inside constructor functions; also note that
previously the compiler *did* type `this: this` inside methods of constructor
functions, so this fix makes us more consistent. This is reflected in
the large number of baselines that improve.

The fix is a simple switch to `isJSConstructor`, which is the standard
way to detect constructor functions. I'm not sure why the original PR
didn't use this method.

I remember discussing this limitation in the original bug, #25979, and
I guess I decided that it made sense. But I was heavily primed by the bug's
framing of the problem in terms of `noImplicitThis`, which *should*
require an explicit `@constructor` tag.

With better typing comes better detection of `@readonly` assignment; I
had to fix the readonly detection code to use `isJSConstructor` as well.

Author: sandersn

src/compiler/checker.ts

@@ -22416,30 +22416,21 @@ namespace ts {
             const isInJS = isInJSFile(node);
             if (isFunctionLike(container) &&
                 (!isInParameterInitializerBeforeContainingFunction(node) || getThisParameter(container))) {
+                let thisType: Type | undefined;
                 // Note: a parameter initializer should refer to class-this unless function-this is explicitly annotated.
                 // If this is a function in a JS file, it might be a class method.
                 const className = getClassNameFromPrototypeMethod(container);
                 if (isInJS && className) {
                     const classSymbol = checkExpression(className).symbol;
                     if (classSymbol && classSymbol.members && (classSymbol.flags & SymbolFlags.Function)) {
-                        const classType = (getDeclaredTypeOfSymbol(classSymbol) as InterfaceType).thisType;
-                        if (classType) {
-                            return getFlowTypeOfReference(node, classType);
-                        }
+                        thisType = (getDeclaredTypeOfSymbol(classSymbol) as InterfaceType).thisType;
                     }
                 }
-                // Check if it's a constructor definition, can be either a variable decl or function decl
-                // i.e.
-                //   * /** @constructor */ function [name]() { ... }
-                //   * /** @constructor */ var x = function() { ... }
-                else if (isInJS &&
-                         (container.kind === SyntaxKind.FunctionExpression || container.kind === SyntaxKind.FunctionDeclaration) &&
-                         getJSDocClassTag(container)) {
-                    const classType = (getDeclaredTypeOfSymbol(getMergedSymbol(container.symbol)) as InterfaceType).thisType!;
-                    return getFlowTypeOfReference(node, classType);
+                else if (isJSConstructor(container)) {
+                    thisType = (getDeclaredTypeOfSymbol(getMergedSymbol(container.symbol)) as InterfaceType).thisType;
                 }
 
-                const thisType = getThisTypeOfDeclaration(container) || getContextualThisParameterType(container);
+                thisType ||= getThisTypeOfDeclaration(container) || getContextualThisParameterType(container);
                 if (thisType) {
                     return getFlowTypeOfReference(node, thisType);
                 }
@@ -28543,7 +28534,7 @@ namespace ts {
                     expr.expression.kind === SyntaxKind.ThisKeyword) {
                     // Look for if this is the constructor for the class that `symbol` is a property of.
                     const ctor = getContainingFunction(expr);
-                    if (!(ctor && ctor.kind === SyntaxKind.Constructor)) {
+                    if (!(ctor && (ctor.kind === SyntaxKind.Constructor || isJSConstructor(ctor)))) {
                         return true;
                     }
                     if (symbol.valueDeclaration) {

tests/baselines/reference/callbackCrossModule.symbols

@@ -13,6 +13,8 @@ function C() {
 >C : Symbol(C, Decl(mod1.js, 4, 18))
 
     this.p = 1
+>this.p : Symbol(C.p, Decl(mod1.js, 5, 14))
+>this : Symbol(C, Decl(mod1.js, 4, 18))
 >p : Symbol(C.p, Decl(mod1.js, 5, 14))
 }
 

tests/baselines/reference/callbackCrossModule.types

@@ -16,7 +16,7 @@ function C() {
     this.p = 1
 >this.p = 1 : 1
 >this.p : any
->this : any
+>this : this
 >p : any
 >1 : 1
 }

tests/baselines/reference/chainedPrototypeAssignment.symbols

@@ -42,13 +42,17 @@ var A = function A() {
 >A : Symbol(A, Decl(mod.js, 1, 7))
 
     this.a = 1
+>this.a : Symbol(A.a, Decl(mod.js, 1, 22))
+>this : Symbol(A, Decl(mod.js, 1, 7))
 >a : Symbol(A.a, Decl(mod.js, 1, 22))
 }
 var B = function B() {
 >B : Symbol(B, Decl(mod.js, 4, 3), Decl(mod.js, 9, 13))
 >B : Symbol(B, Decl(mod.js, 4, 7))
 
     this.b = 2
+>this.b : Symbol(B.b, Decl(mod.js, 4, 22))
+>this : Symbol(B, Decl(mod.js, 4, 7))
 >b : Symbol(B.b, Decl(mod.js, 4, 22))
 }
 exports.A = A

tests/baselines/reference/chainedPrototypeAssignment.types

@@ -52,7 +52,7 @@ var A = function A() {
     this.a = 1
 >this.a = 1 : 1
 >this.a : any
->this : any
+>this : this
 >a : any
 >1 : 1
 }
@@ -64,7 +64,7 @@ var B = function B() {
     this.b = 2
 >this.b = 2 : 2
 >this.b : any
->this : any
+>this : this
 >b : any
 >2 : 2
 }

tests/baselines/reference/classCanExtendConstructorFunction.symbols

@@ -193,6 +193,8 @@ function Soup(flavour) {
 >flavour : Symbol(flavour, Decl(generic.js, 4, 14))
 
     this.flavour = flavour
+>this.flavour : Symbol(Soup.flavour, Decl(generic.js, 4, 24))
+>this : Symbol(Soup, Decl(generic.js, 0, 0))
 >flavour : Symbol(Soup.flavour, Decl(generic.js, 4, 24))
 >flavour : Symbol(flavour, Decl(generic.js, 4, 14))
 }

tests/baselines/reference/classCanExtendConstructorFunction.types

@@ -238,7 +238,7 @@ function Soup(flavour) {
     this.flavour = flavour
 >this.flavour = flavour : T
 >this.flavour : any
->this : any
+>this : this
 >flavour : any
 >flavour : T
 }

tests/baselines/reference/commonjsAccessExports.symbols

@@ -18,6 +18,8 @@ exports.x;
 >Cls : Symbol(Cls, Decl(a.js, 4, 1))
 
         this.x = 0;
+>this.x : Symbol(Cls.x, Decl(a.js, 6, 30))
+>this : Symbol(Cls, Decl(a.js, 6, 17))
 >x : Symbol(Cls.x, Decl(a.js, 6, 30))
     }
 }

tests/baselines/reference/commonjsAccessExports.types

@@ -24,7 +24,7 @@ exports.x;
         this.x = 0;
 >this.x = 0 : 0
 >this.x : any
->this : any
+>this : this
 >x : any
 >0 : 0
     }

tests/baselines/reference/constructorFunctionMergeWithClass.symbols

@@ -3,6 +3,8 @@ var SomeClass = function () {
 >SomeClass : Symbol(SomeClass, Decl(file1.js, 0, 3), Decl(file2.js, 0, 0), Decl(file2.js, 0, 19))
 
     this.otherProp = 0;
+>this.otherProp : Symbol(SomeClass.otherProp, Decl(file1.js, 0, 29))
+>this : Symbol(SomeClass, Decl(file1.js, 0, 15))
 >otherProp : Symbol(SomeClass.otherProp, Decl(file1.js, 0, 29))
 
 };

tests/baselines/reference/constructorFunctionMergeWithClass.types

@@ -6,7 +6,7 @@ var SomeClass = function () {
     this.otherProp = 0;
 >this.otherProp = 0 : 0
 >this.otherProp : any
->this : any
+>this : this
 >otherProp : any
 >0 : 0
 

tests/baselines/reference/constructorFunctions.symbols

@@ -3,10 +3,13 @@ function C1() {
 >C1 : Symbol(C1, Decl(index.js, 0, 0))
 
     if (!(this instanceof C1)) return new C1();
+>this : Symbol(C1, Decl(index.js, 0, 0))
 >C1 : Symbol(C1, Decl(index.js, 0, 0))
 >C1 : Symbol(C1, Decl(index.js, 0, 0))
 
     this.x = 1;
+>this.x : Symbol(C1.x, Decl(index.js, 1, 47))
+>this : Symbol(C1, Decl(index.js, 0, 0))
 >x : Symbol(C1.x, Decl(index.js, 1, 47))
 }
 
@@ -22,10 +25,13 @@ var C2 = function () {
 >C2 : Symbol(C2, Decl(index.js, 8, 3))
 
     if (!(this instanceof C2)) return new C2();
+>this : Symbol(C2, Decl(index.js, 8, 8))
 >C2 : Symbol(C2, Decl(index.js, 8, 3))
 >C2 : Symbol(C2, Decl(index.js, 8, 3))
 
     this.x = 1;
+>this.x : Symbol(C2.x, Decl(index.js, 9, 47))
+>this : Symbol(C2, Decl(index.js, 8, 8))
 >x : Symbol(C2.x, Decl(index.js, 9, 47))
 
 };

tests/baselines/reference/constructorFunctions.types

@@ -6,15 +6,15 @@ function C1() {
 >!(this instanceof C1) : boolean
 >(this instanceof C1) : boolean
 >this instanceof C1 : boolean
->this : any
+>this : this
 >C1 : typeof C1
 >new C1() : C1
 >C1 : typeof C1
 
     this.x = 1;
 >this.x = 1 : 1
 >this.x : any
->this : any
+>this : this
 >x : any
 >1 : 1
 }
@@ -37,15 +37,15 @@ var C2 = function () {
 >!(this instanceof C2) : boolean
 >(this instanceof C2) : boolean
 >this instanceof C2 : boolean
->this : any
+>this : this
 >C2 : typeof C2
 >new C2() : C2
 >C2 : typeof C2
 
     this.x = 1;
 >this.x = 1 : 1
 >this.x : any
->this : any
+>this : this
 >x : any
 >1 : 1
 

tests/baselines/reference/constructorFunctions2.symbols

@@ -21,6 +21,8 @@ const a = new A().id;
 
 const B = function() { this.id = 1; }
 >B : Symbol(B, Decl(index.js, 3, 5))
+>this.id : Symbol(B.id, Decl(index.js, 3, 22))
+>this : Symbol(B, Decl(index.js, 3, 9))
 >id : Symbol(B.id, Decl(index.js, 3, 22))
 
 B.prototype.m = function() { this.x = 2; }
@@ -49,6 +51,8 @@ b.x;
 === tests/cases/conformance/salsa/other.js ===
 function A() { this.id = 1; }
 >A : Symbol(A, Decl(other.js, 0, 0))
+>this.id : Symbol(A.id, Decl(other.js, 0, 14))
+>this : Symbol(A, Decl(other.js, 0, 0))
 >id : Symbol(A.id, Decl(other.js, 0, 14))
 
 module.exports = A;

tests/baselines/reference/constructorFunctions2.types

@@ -26,7 +26,7 @@ const B = function() { this.id = 1; }
 >function() { this.id = 1; } : typeof B
 >this.id = 1 : 1
 >this.id : any
->this : any
+>this : this
 >id : any
 >1 : 1
 
@@ -64,7 +64,7 @@ function A() { this.id = 1; }
 >A : typeof A
 >this.id = 1 : 1
 >this.id : any
->this : any
+>this : this
 >id : any
 >1 : 1
 

tests/baselines/reference/constructorFunctions3.symbols

@@ -3,6 +3,8 @@ function Instance() {
 >Instance : Symbol(Instance, Decl(a.js, 0, 0))
 
     this.i = 'simple'
+>this.i : Symbol(Instance.i, Decl(a.js, 0, 21))
+>this : Symbol(Instance, Decl(a.js, 0, 0))
 >i : Symbol(Instance.i, Decl(a.js, 0, 21))
 }
 var i = new Instance();
@@ -19,6 +21,8 @@ function StaticToo() {
 >StaticToo : Symbol(StaticToo, Decl(a.js, 5, 2), Decl(a.js, 9, 1))
 
     this.i = 'more complex'
+>this.i : Symbol(StaticToo.i, Decl(a.js, 7, 22))
+>this : Symbol(StaticToo, Decl(a.js, 5, 2), Decl(a.js, 9, 1))
 >i : Symbol(StaticToo.i, Decl(a.js, 7, 22))
 }
 StaticToo.property = 'yep'
@@ -41,10 +45,14 @@ function A () {
 >A : Symbol(A, Decl(a.js, 13, 10), Decl(a.js, 24, 1))
 
     this.x = 1
+>this.x : Symbol(A.x, Decl(a.js, 16, 15))
+>this : Symbol(A, Decl(a.js, 13, 10), Decl(a.js, 24, 1))
 >x : Symbol(A.x, Decl(a.js, 16, 15))
 
     /** @type {1} */
     this.second = 1
+>this.second : Symbol(A.second, Decl(a.js, 17, 14))
+>this : Symbol(A, Decl(a.js, 13, 10), Decl(a.js, 24, 1))
 >second : Symbol(A.second, Decl(a.js, 17, 14))
 }
 /** @param {number} n */

tests/baselines/reference/constructorFunctions3.types

@@ -5,7 +5,7 @@ function Instance() {
     this.i = 'simple'
 >this.i = 'simple' : "simple"
 >this.i : any
->this : any
+>this : this
 >i : any
 >'simple' : "simple"
 }
@@ -26,7 +26,7 @@ function StaticToo() {
     this.i = 'more complex'
 >this.i = 'more complex' : "more complex"
 >this.i : any
->this : any
+>this : this
 >i : any
 >'more complex' : "more complex"
 }
@@ -55,16 +55,16 @@ function A () {
     this.x = 1
 >this.x = 1 : 1
 >this.x : any
->this : any
+>this : this
 >x : any
 >1 : 1
 
     /** @type {1} */
     this.second = 1
 >this.second = 1 : 1
->this.second : any
->this : any
->second : any
+>this.second : 1
+>this : this
+>second : 1
 >1 : 1
 }
 /** @param {number} n */

tests/baselines/reference/constructorFunctionsStrict.symbols

@@ -5,6 +5,8 @@ function C(x) {
 >x : Symbol(x, Decl(a.js, 1, 11))
 
     this.x = x
+>this.x : Symbol(C.x, Decl(a.js, 1, 15))
+>this : Symbol(C, Decl(a.js, 0, 0))
 >x : Symbol(C.x, Decl(a.js, 1, 15))
 >x : Symbol(x, Decl(a.js, 1, 11))
 }
@@ -41,13 +43,16 @@ function A(x) {
 >x : Symbol(x, Decl(a.js, 12, 11))
 
     if (!(this instanceof A)) {
+>this : Symbol(A, Decl(a.js, 9, 15))
 >A : Symbol(A, Decl(a.js, 9, 15))
 
         return new A(x)
 >A : Symbol(A, Decl(a.js, 9, 15))
 >x : Symbol(x, Decl(a.js, 12, 11))
     }
     this.x = x
+>this.x : Symbol(A.x, Decl(a.js, 15, 5))
+>this : Symbol(A, Decl(a.js, 9, 15))
 >x : Symbol(A.x, Decl(a.js, 15, 5))
 >x : Symbol(x, Decl(a.js, 12, 11))
 }

tests/baselines/reference/constructorFunctionsStrict.types

@@ -7,7 +7,7 @@ function C(x) {
     this.x = x
 >this.x = x : number
 >this.x : any
->this : any
+>this : this
 >x : any
 >x : number
 }
@@ -56,7 +56,7 @@ function A(x) {
 >!(this instanceof A) : boolean
 >(this instanceof A) : boolean
 >this instanceof A : boolean
->this : any
+>this : this
 >A : typeof A
 
         return new A(x)
@@ -67,7 +67,7 @@ function A(x) {
     this.x = x
 >this.x = x : number
 >this.x : any
->this : any
+>this : this
 >x : any
 >x : number
 }

tests/baselines/reference/expandoFunctionContextualTypesJs.symbols

@@ -58,11 +58,14 @@ function foo() {
      * @type {MyComponentProps}
      */
     this.props = { color: "red" };
+>this.props : Symbol(foo.props, Decl(input.js, 35, 16))
+>this : Symbol(foo, Decl(input.js, 33, 28))
 >props : Symbol(foo.props, Decl(input.js, 35, 16))
 >color : Symbol(color, Decl(input.js, 39, 18))
 
     expectLiteral(this);
 >expectLiteral : Symbol(expectLiteral, Decl(input.js, 27, 27))
+>this : Symbol(foo, Decl(input.js, 33, 28))
 }
 
 /**