Narrowed consts flow through object literal or class expression method

src/compiler/binder.ts

@@ -84,6 +84,7 @@ namespace ts {
         IsFunctionExpression = 1 << 4,
         HasLocals = 1 << 5,
         IsInterface = 1 << 6,
+        IsObjectLiteralOrClassExpressionMethod = 1 << 7,
     }
 
     const binder = createBinder();
@@ -486,8 +487,8 @@ namespace ts {
                 }
                 else {
                     currentFlow = { flags: FlowFlags.Start };
-                    if (containerFlags & ContainerFlags.IsFunctionExpression) {
-                        (<FlowStart>currentFlow).container = <FunctionExpression | ArrowFunction>node;
+                    if (containerFlags & (ContainerFlags.IsFunctionExpression | ContainerFlags.IsObjectLiteralOrClassExpressionMethod)) {
+                        (<FlowStart>currentFlow).container = <FunctionExpression | ArrowFunction | MethodDeclaration>node;
                     }
                     currentReturnTarget = undefined;
                 }
@@ -1237,9 +1238,12 @@ namespace ts {
                 case SyntaxKind.SourceFile:
                     return ContainerFlags.IsContainer | ContainerFlags.IsControlFlowContainer | ContainerFlags.HasLocals;
 
+                case SyntaxKind.MethodDeclaration:
+                    if (isObjectLiteralOrClassExpressionMethod(node)) {
+                        return ContainerFlags.IsContainer | ContainerFlags.IsControlFlowContainer | ContainerFlags.HasLocals | ContainerFlags.IsFunctionLike | ContainerFlags.IsObjectLiteralOrClassExpressionMethod;
+                    }
                 case SyntaxKind.Constructor:
                 case SyntaxKind.FunctionDeclaration:
-                case SyntaxKind.MethodDeclaration:
                 case SyntaxKind.MethodSignature:
                 case SyntaxKind.GetAccessor:
                 case SyntaxKind.SetAccessor:
@@ -2238,6 +2242,10 @@ namespace ts {
                 }
             }
 
+            if (currentFlow && isObjectLiteralOrClassExpressionMethod(node)) {
+                node.flowNode = currentFlow;
+            }
+
             return hasDynamicName(node)
                 ? bindAnonymousDeclaration(node, symbolFlags, "__computed")
                 : declareSymbolAndAddToSymbolTable(node, symbolFlags, symbolExcludes);

src/compiler/checker.ts

@@ -9163,7 +9163,9 @@ namespace ts {
             // a const variable or parameter from an outer function, we extend the origin of the control flow
             // analysis to include the immediately enclosing function.
             while (flowContainer !== declarationContainer &&
-                (flowContainer.kind === SyntaxKind.FunctionExpression || flowContainer.kind === SyntaxKind.ArrowFunction) &&
+                (flowContainer.kind === SyntaxKind.FunctionExpression ||
+                    flowContainer.kind === SyntaxKind.ArrowFunction ||
+                    isObjectLiteralOrClassExpressionMethod(flowContainer)) &&
                 (isReadonlySymbol(localOrExportSymbol) || isParameter && !isParameterAssigned(localOrExportSymbol))) {
                 flowContainer = getControlFlowContainer(flowContainer);
             }

src/compiler/types.ts

@@ -1922,7 +1922,7 @@ namespace ts {
     // function, the container property references the function (which in turn has a flowNode
     // property for the containing control flow).
     export interface FlowStart extends FlowNode {
-        container?: FunctionExpression | ArrowFunction;
+        container?: FunctionExpression | ArrowFunction | MethodDeclaration;
     }
 
     // FlowLabel represents a junction with multiple possible preceding control flows.

src/compiler/utilities.ts

@@ -895,6 +895,12 @@ namespace ts {
         return node && node.kind === SyntaxKind.MethodDeclaration && node.parent.kind === SyntaxKind.ObjectLiteralExpression;
     }
 
+    export function isObjectLiteralOrClassExpressionMethod(node: Node): node is MethodDeclaration {
+        return node.kind === SyntaxKind.MethodDeclaration &&
+            (node.parent.kind === SyntaxKind.ObjectLiteralExpression ||
+            node.parent.kind === SyntaxKind.ClassExpression);
+    }
+
     export function isIdentifierTypePredicate(predicate: TypePredicate): predicate is IdentifierTypePredicate {
         return predicate && predicate.kind === TypePredicateKind.Identifier;
     }

tests/baselines/reference/narrowedConstInMethod.js

@@ -0,0 +1,40 @@
+//// [narrowedConstInMethod.ts]
+
+function f() {
+    const x: string | null = <any>{};
+    if (x !== null) {
+        return {
+            bar() { return x.length; }  // Error: possibly null x
+        };
+    }
+}
+
+function f2() {
+    const x: string | null = <any>{};
+    if (x !== null) {
+        return class {
+            bar() { return x.length; }  // Error: possibly null x
+        };
+    }
+}
+
+//// [narrowedConstInMethod.js]
+function f() {
+    var x = {};
+    if (x !== null) {
+        return {
+            bar: function () { return x.length; } // Error: possibly null x
+        };
+    }
+}
+function f2() {
+    var x = {};
+    if (x !== null) {
+        return (function () {
+            function class_1() {
+            }
+            class_1.prototype.bar = function () { return x.length; }; // Error: possibly null x
+            return class_1;
+        }());
+    }
+}

tests/baselines/reference/narrowedConstInMethod.symbols

@@ -0,0 +1,41 @@
+=== tests/cases/compiler/narrowedConstInMethod.ts ===
+
+function f() {
+>f : Symbol(f, Decl(narrowedConstInMethod.ts, 0, 0))
+
+    const x: string | null = <any>{};
+>x : Symbol(x, Decl(narrowedConstInMethod.ts, 2, 9))
+
+    if (x !== null) {
+>x : Symbol(x, Decl(narrowedConstInMethod.ts, 2, 9))
+
+        return {
+            bar() { return x.length; }  // Error: possibly null x
+>bar : Symbol(bar, Decl(narrowedConstInMethod.ts, 4, 16))
+>x.length : Symbol(String.length, Decl(lib.d.ts, --, --))
+>x : Symbol(x, Decl(narrowedConstInMethod.ts, 2, 9))
+>length : Symbol(String.length, Decl(lib.d.ts, --, --))
+
+        };
+    }
+}
+
+function f2() {
+>f2 : Symbol(f2, Decl(narrowedConstInMethod.ts, 8, 1))
+
+    const x: string | null = <any>{};
+>x : Symbol(x, Decl(narrowedConstInMethod.ts, 11, 9))
+
+    if (x !== null) {
+>x : Symbol(x, Decl(narrowedConstInMethod.ts, 11, 9))
+
+        return class {
+            bar() { return x.length; }  // Error: possibly null x
+>bar : Symbol((Anonymous class).bar, Decl(narrowedConstInMethod.ts, 13, 22))
+>x.length : Symbol(String.length, Decl(lib.d.ts, --, --))
+>x : Symbol(x, Decl(narrowedConstInMethod.ts, 11, 9))
+>length : Symbol(String.length, Decl(lib.d.ts, --, --))
+
+        };
+    }
+}

tests/baselines/reference/narrowedConstInMethod.types

@@ -0,0 +1,55 @@
+=== tests/cases/compiler/narrowedConstInMethod.ts ===
+
+function f() {
+>f : () => { bar(): number; } | undefined
+
+    const x: string | null = <any>{};
+>x : string | null
+>null : null
+><any>{} : any
+>{} : {}
+
+    if (x !== null) {
+>x !== null : boolean
+>x : string | null
+>null : null
+
+        return {
+>{            bar() { return x.length; }  // Error: possibly null x        } : { bar(): number; }
+
+            bar() { return x.length; }  // Error: possibly null x
+>bar : () => number
+>x.length : number
+>x : string
+>length : number
+
+        };
+    }
+}
+
+function f2() {
+>f2 : () => typeof (Anonymous class) | undefined
+
+    const x: string | null = <any>{};
+>x : string | null
+>null : null
+><any>{} : any
+>{} : {}
+
+    if (x !== null) {
+>x !== null : boolean
+>x : string | null
+>null : null
+
+        return class {
+>class {            bar() { return x.length; }  // Error: possibly null x        } : typeof (Anonymous class)
+
+            bar() { return x.length; }  // Error: possibly null x
+>bar : () => number
+>x.length : number
+>x : string
+>length : number
+
+        };
+    }
+}

tests/cases/compiler/narrowedConstInMethod.ts

@@ -0,0 +1,19 @@
+// @strictNullChecks: true
+
+function f() {
+    const x: string | null = <any>{};
+    if (x !== null) {
+        return {
+            bar() { return x.length; }  // Error: possibly null x
+        };
+    }
+}
+
+function f2() {
+    const x: string | null = <any>{};
+    if (x !== null) {
+        return class {
+            bar() { return x.length; }  // Error: possibly null x
+        };
+    }
+}