Allow private symbols to be control flow narrowed (microsoft#39978)

* Allow private symbols to be control flow narrowed

* Add test with narrowing of inferred control flow type for completeness

* Reformat long line

Author: weswigham

Diff for: src/compiler/binder.ts

@@ -831,6 +831,7 @@ namespace ts {
         function isNarrowingExpression(expr: Expression): boolean {
             switch (expr.kind) {
                 case SyntaxKind.Identifier:
+                case SyntaxKind.PrivateIdentifier:
                 case SyntaxKind.ThisKeyword:
                 case SyntaxKind.PropertyAccessExpression:
                 case SyntaxKind.ElementAccessExpression:
@@ -850,7 +851,7 @@ namespace ts {
         }
 
         function isNarrowableReference(expr: Expression): boolean {
-            return expr.kind === SyntaxKind.Identifier || expr.kind === SyntaxKind.ThisKeyword || expr.kind === SyntaxKind.SuperKeyword ||
+            return expr.kind === SyntaxKind.Identifier || expr.kind === SyntaxKind.PrivateIdentifier || expr.kind === SyntaxKind.ThisKeyword || expr.kind === SyntaxKind.SuperKeyword ||
                 (isPropertyAccessExpression(expr) || isNonNullExpression(expr) || isParenthesizedExpression(expr)) && isNarrowableReference(expr.expression) ||
                 isElementAccessExpression(expr) && isStringOrNumericLiteralLike(expr.argumentExpression) && isNarrowableReference(expr.expression) ||
                 isAssignmentExpression(expr) && isNarrowableReference(expr.left);

Diff for: src/compiler/checker.ts

@@ -8023,7 +8023,10 @@ namespace ts {
         }
 
         function getFlowTypeInConstructor(symbol: Symbol, constructor: ConstructorDeclaration) {
-            const reference = factory.createPropertyAccessExpression(factory.createThis(), unescapeLeadingUnderscores(symbol.escapedName));
+            const accessName = startsWith(symbol.escapedName as string, "__#")
+                ? factory.createPrivateIdentifier((symbol.escapedName as string).split("@")[1])
+                : unescapeLeadingUnderscores(symbol.escapedName);
+            const reference = factory.createPropertyAccessExpression(factory.createThis(), accessName);
             setParent(reference.expression, reference);
             setParent(reference, constructor);
             reference.flowNode = constructor.returnFlowNode;
@@ -20232,6 +20235,7 @@ namespace ts {
             }
             switch (source.kind) {
                 case SyntaxKind.Identifier:
+                case SyntaxKind.PrivateIdentifier:
                     return target.kind === SyntaxKind.Identifier && getResolvedSymbol(<Identifier>source) === getResolvedSymbol(<Identifier>target) ||
                         (target.kind === SyntaxKind.VariableDeclaration || target.kind === SyntaxKind.BindingElement) &&
                         getExportSymbolOfValueSymbolIfExported(getResolvedSymbol(<Identifier>source)) === getSymbolOfNode(target);

Diff for: tests/baselines/reference/controlFlowPrivateClassField.js

@@ -0,0 +1,51 @@
+//// [controlFlowPrivateClassField.ts]
+class Example {
+    #test;
+
+    constructor(test: number) {
+        this.#test = test;
+    }
+
+    get test() {
+        return this.#test
+    }
+}
+
+class Example2 {
+    #test;
+
+    constructor(test: number | undefined) {
+        this.#test = test;
+    }
+
+    get test() {
+        if (this.#test) {
+            return this.#test
+        }
+        return 0;
+    }
+}
+
+//// [controlFlowPrivateClassField.js]
+"use strict";
+class Example {
+    constructor(test) {
+        this.#test = test;
+    }
+    #test;
+    get test() {
+        return this.#test;
+    }
+}
+class Example2 {
+    constructor(test) {
+        this.#test = test;
+    }
+    #test;
+    get test() {
+        if (this.#test) {
+            return this.#test;
+        }
+        return 0;
+    }
+}

Diff for: tests/baselines/reference/controlFlowPrivateClassField.symbols

@@ -0,0 +1,54 @@
+=== tests/cases/compiler/controlFlowPrivateClassField.ts ===
+class Example {
+>Example : Symbol(Example, Decl(controlFlowPrivateClassField.ts, 0, 0))
+
+    #test;
+>#test : Symbol(Example.#test, Decl(controlFlowPrivateClassField.ts, 0, 15))
+
+    constructor(test: number) {
+>test : Symbol(test, Decl(controlFlowPrivateClassField.ts, 3, 16))
+
+        this.#test = test;
+>this.#test : Symbol(Example.#test, Decl(controlFlowPrivateClassField.ts, 0, 15))
+>this : Symbol(Example, Decl(controlFlowPrivateClassField.ts, 0, 0))
+>test : Symbol(test, Decl(controlFlowPrivateClassField.ts, 3, 16))
+    }
+
+    get test() {
+>test : Symbol(Example.test, Decl(controlFlowPrivateClassField.ts, 5, 5))
+
+        return this.#test
+>this.#test : Symbol(Example.#test, Decl(controlFlowPrivateClassField.ts, 0, 15))
+>this : Symbol(Example, Decl(controlFlowPrivateClassField.ts, 0, 0))
+    }
+}
+
+class Example2 {
+>Example2 : Symbol(Example2, Decl(controlFlowPrivateClassField.ts, 10, 1))
+
+    #test;
+>#test : Symbol(Example2.#test, Decl(controlFlowPrivateClassField.ts, 12, 16))
+
+    constructor(test: number | undefined) {
+>test : Symbol(test, Decl(controlFlowPrivateClassField.ts, 15, 16))
+
+        this.#test = test;
+>this.#test : Symbol(Example2.#test, Decl(controlFlowPrivateClassField.ts, 12, 16))
+>this : Symbol(Example2, Decl(controlFlowPrivateClassField.ts, 10, 1))
+>test : Symbol(test, Decl(controlFlowPrivateClassField.ts, 15, 16))
+    }
+
+    get test() {
+>test : Symbol(Example2.test, Decl(controlFlowPrivateClassField.ts, 17, 5))
+
+        if (this.#test) {
+>this.#test : Symbol(Example2.#test, Decl(controlFlowPrivateClassField.ts, 12, 16))
+>this : Symbol(Example2, Decl(controlFlowPrivateClassField.ts, 10, 1))
+
+            return this.#test
+>this.#test : Symbol(Example2.#test, Decl(controlFlowPrivateClassField.ts, 12, 16))
+>this : Symbol(Example2, Decl(controlFlowPrivateClassField.ts, 10, 1))
+        }
+        return 0;
+    }
+}

Diff for: tests/baselines/reference/controlFlowPrivateClassField.types

@@ -0,0 +1,57 @@
+=== tests/cases/compiler/controlFlowPrivateClassField.ts ===
+class Example {
+>Example : Example
+
+    #test;
+>#test : number
+
+    constructor(test: number) {
+>test : number
+
+        this.#test = test;
+>this.#test = test : number
+>this.#test : number
+>this : this
+>test : number
+    }
+
+    get test() {
+>test : number
+
+        return this.#test
+>this.#test : number
+>this : this
+    }
+}
+
+class Example2 {
+>Example2 : Example2
+
+    #test;
+>#test : number | undefined
+
+    constructor(test: number | undefined) {
+>test : number | undefined
+
+        this.#test = test;
+>this.#test = test : number | undefined
+>this.#test : number | undefined
+>this : this
+>test : number | undefined
+    }
+
+    get test() {
+>test : number
+
+        if (this.#test) {
+>this.#test : number | undefined
+>this : this
+
+            return this.#test
+>this.#test : number
+>this : this
+        }
+        return 0;
+>0 : 0
+    }
+}

Diff for: tests/cases/compiler/controlFlowPrivateClassField.ts

@@ -0,0 +1,28 @@
+// @strict: true
+// @target: esnext
+class Example {
+    #test;
+
+    constructor(test: number) {
+        this.#test = test;
+    }
+
+    get test() {
+        return this.#test
+    }
+}
+
+class Example2 {
+    #test;
+
+    constructor(test: number | undefined) {
+        this.#test = test;
+    }
+
+    get test() {
+        if (this.#test) {
+            return this.#test
+        }
+        return 0;
+    }
+}