Merge pull request #33821 from microsoft/fix33806

Reflect control flow effects of optional chains in equality checks

Author: ahejlsberg

src/compiler/binder.ts

@@ -856,9 +856,8 @@ namespace ts {
         function isNarrowableReference(expr: Expression): boolean {
             return expr.kind === SyntaxKind.Identifier || 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);
+                isElementAccessExpression(expr) && isStringOrNumericLiteralLike(expr.argumentExpression) && isNarrowableReference(expr.expression) ||
+                isOptionalChain(expr);
         }
 
         function hasNarrowableArgument(expr: CallExpression) {

src/compiler/checker.ts

@@ -18124,6 +18124,16 @@ namespace ts {
             return false;
         }
 
+        function optionalChainContainsReference(source: Node, target: Node) {
+            while (isOptionalChain(source)) {
+                source = source.expression;
+                if (isMatchingReference(source, target)) {
+                    return true;
+                }
+            }
+            return false;
+        }
+
         // Return true if target is a property access xxx.yyy, source is a property access xxx.zzz, the declared
         // type of xxx is a union type, and yyy is a property that is possibly a discriminant. We consider a property
         // a possible discriminant if its type differs in the constituents of containing union type, and if every
@@ -19350,6 +19360,14 @@ namespace ts {
                         if (isMatchingReference(reference, right)) {
                             return narrowTypeByEquality(type, operator, left, assumeTrue);
                         }
+                        if (assumeTrue && strictNullChecks) {
+                            if (optionalChainContainsReference(left, reference)) {
+                                type = narrowTypeByOptionalChainContainment(type, operator, right);
+                            }
+                            else if (optionalChainContainsReference(right, reference)) {
+                                type = narrowTypeByOptionalChainContainment(type, operator, left);
+                            }
+                        }
                         if (isMatchingReferenceDiscriminant(left, declaredType)) {
                             return narrowTypeByDiscriminant(type, <AccessExpression>left, t => narrowTypeByEquality(t, operator, right, assumeTrue));
                         }
@@ -19374,6 +19392,18 @@ namespace ts {
                 return type;
             }
 
+            function narrowTypeByOptionalChainContainment(type: Type, operator: SyntaxKind, value: Expression): Type {
+                // We are in the true branch of obj?.foo === value or obj?.foo !== value. We remove undefined and null from
+                // the type of obj if (a) the operator is === and the type of value doesn't include undefined or (b) the
+                // operator is !== and the type of value is undefined.
+                const valueType = getTypeOfExpression(value);
+                return operator === SyntaxKind.EqualsEqualsToken && !(getTypeFacts(valueType) & TypeFacts.EQUndefinedOrNull) ||
+                    operator === SyntaxKind.EqualsEqualsEqualsToken && !(getTypeFacts(valueType) & TypeFacts.EQUndefined) ||
+                    operator === SyntaxKind.ExclamationEqualsToken && valueType.flags & TypeFlags.Nullable ||
+                    operator === SyntaxKind.ExclamationEqualsEqualsToken && valueType.flags & TypeFlags.Undefined ?
+                    getTypeWithFacts(type, TypeFacts.NEUndefinedOrNull) : type;
+            }
+
             function narrowTypeByEquality(type: Type, operator: SyntaxKind, value: Expression, assumeTrue: boolean): Type {
                 if (type.flags & TypeFlags.Any) {
                     return type;
@@ -19424,6 +19454,10 @@ namespace ts {
                 // We have '==', '!=', '===', or !==' operator with 'typeof xxx' and string literal operands
                 const target = getReferenceCandidate(typeOfExpr.expression);
                 if (!isMatchingReference(reference, target)) {
+                    if (assumeTrue && (operator === SyntaxKind.EqualsEqualsToken || operator === SyntaxKind.EqualsEqualsEqualsToken) &&
+                        strictNullChecks && optionalChainContainsReference(target, reference)) {
+                        return getTypeWithFacts(type, TypeFacts.NEUndefinedOrNull);
+                    }
                     // For a reference of the form 'x.y', a 'typeof x === ...' type guard resets the
                     // narrowed type of 'y' to its declared type.
                     if (containsMatchingReference(reference, target)) {
@@ -19605,6 +19639,9 @@ namespace ts {
             function narrowTypeByInstanceof(type: Type, expr: BinaryExpression, assumeTrue: boolean): Type {
                 const left = getReferenceCandidate(expr.left);
                 if (!isMatchingReference(reference, left)) {
+                    if (assumeTrue && strictNullChecks && optionalChainContainsReference(left, reference)) {
+                        return getTypeWithFacts(type, TypeFacts.NEUndefinedOrNull);
+                    }
                     // For a reference of the form 'x.y', an 'x instanceof T' type guard resets the
                     // narrowed type of 'y' to its declared type. We do this because preceding 'x.y'
                     // references might reference a different 'y' property. However, we make an exception

tests/baselines/reference/controlFlowOptionalChain.errors.txt

@@ -6,7 +6,6 @@ tests/cases/conformance/controlFlow/controlFlowOptionalChain.ts(35,5): error TS2
 tests/cases/conformance/controlFlow/controlFlowOptionalChain.ts(39,1): error TS2722: Cannot invoke an object which is possibly 'undefined'.
 tests/cases/conformance/controlFlow/controlFlowOptionalChain.ts(52,5): error TS2532: Object is possibly 'undefined'.
 tests/cases/conformance/controlFlow/controlFlowOptionalChain.ts(57,1): error TS2532: Object is possibly 'undefined'.
-tests/cases/conformance/controlFlow/controlFlowOptionalChain.ts(62,5): error TS2532: Object is possibly 'undefined'.
 tests/cases/conformance/controlFlow/controlFlowOptionalChain.ts(68,5): error TS2532: Object is possibly 'undefined'.
 tests/cases/conformance/controlFlow/controlFlowOptionalChain.ts(72,1): error TS2532: Object is possibly 'undefined'.
 tests/cases/conformance/controlFlow/controlFlowOptionalChain.ts(83,5): error TS2532: Object is possibly 'undefined'.
@@ -20,9 +19,21 @@ tests/cases/conformance/controlFlow/controlFlowOptionalChain.ts(112,1): error TS
 tests/cases/conformance/controlFlow/controlFlowOptionalChain.ts(130,5): error TS2532: Object is possibly 'undefined'.
 tests/cases/conformance/controlFlow/controlFlowOptionalChain.ts(134,1): error TS2532: Object is possibly 'undefined'.
 tests/cases/conformance/controlFlow/controlFlowOptionalChain.ts(153,9): error TS2775: Assertions require every name in the call target to be declared with an explicit type annotation.
+tests/cases/conformance/controlFlow/controlFlowOptionalChain.ts(208,9): error TS2532: Object is possibly 'undefined'.
+tests/cases/conformance/controlFlow/controlFlowOptionalChain.ts(211,9): error TS2532: Object is possibly 'undefined'.
+tests/cases/conformance/controlFlow/controlFlowOptionalChain.ts(214,9): error TS2532: Object is possibly 'undefined'.
+tests/cases/conformance/controlFlow/controlFlowOptionalChain.ts(217,9): error TS2532: Object is possibly 'undefined'.
+tests/cases/conformance/controlFlow/controlFlowOptionalChain.ts(220,9): error TS2532: Object is possibly 'undefined'.
+tests/cases/conformance/controlFlow/controlFlowOptionalChain.ts(223,9): error TS2532: Object is possibly 'undefined'.
+tests/cases/conformance/controlFlow/controlFlowOptionalChain.ts(238,9): error TS2532: Object is possibly 'undefined'.
+tests/cases/conformance/controlFlow/controlFlowOptionalChain.ts(241,9): error TS2532: Object is possibly 'undefined'.
+tests/cases/conformance/controlFlow/controlFlowOptionalChain.ts(244,9): error TS2532: Object is possibly 'undefined'.
+tests/cases/conformance/controlFlow/controlFlowOptionalChain.ts(271,9): error TS2532: Object is possibly 'undefined'.
+tests/cases/conformance/controlFlow/controlFlowOptionalChain.ts(274,9): error TS2532: Object is possibly 'undefined'.
+tests/cases/conformance/controlFlow/controlFlowOptionalChain.ts(277,9): error TS2532: Object is possibly 'undefined'.
 
 
-==== tests/cases/conformance/controlFlow/controlFlowOptionalChain.ts (22 errors) ====
+==== tests/cases/conformance/controlFlow/controlFlowOptionalChain.ts (33 errors) ====
     // assignments in shortcutting chain
     declare const o: undefined | {
         [key: string]: any;
@@ -99,10 +110,8 @@ tests/cases/conformance/controlFlow/controlFlowOptionalChain.ts(153,9): error TS
 
     declare const o3: { x: 1, y: string } | { x: 2, y: number } | undefined;
     if (o3?.x === 1) {
-        o3; // TODO: should be `{ x: y, y: string }`
-        o3.x; // TODO: should not be an error.
-        ~~
-!!! error TS2532: Object is possibly 'undefined'.
+        o3;
+        o3.x;
         o3?.x;
     }
     else {
@@ -227,4 +236,198 @@ tests/cases/conformance/controlFlow/controlFlowOptionalChain.ts(153,9): error TS
             x;
         }
     }
+    
+    type Thing = { foo: string | number, bar(): number, baz: object };
+    
+    function f10(o: Thing | undefined, value: number) {
+        if (o?.foo === value) {
+            o.foo;
+        }
+        if (o?.["foo"] === value) {
+            o["foo"];
+        }
+        if (o?.bar() === value) {
+            o.bar;
+        }
+        if (o?.foo == value) {
+            o.foo;
+        }
+        if (o?.["foo"] == value) {
+            o["foo"];
+        }
+        if (o?.bar() == value) {
+            o.bar;
+        }
+    }
+    
+    function f11(o: Thing | null, value: number) {
+        if (o?.foo === value) {
+            o.foo;
+        }
+        if (o?.["foo"] === value) {
+            o["foo"];
+        }
+        if (o?.bar() === value) {
+            o.bar;
+        }
+        if (o?.foo == value) {
+            o.foo;
+        }
+        if (o?.["foo"] == value) {
+            o["foo"];
+        }
+        if (o?.bar() == value) {
+            o.bar;
+        }
+    }
+    
+    function f12(o: Thing | undefined, value: number | undefined) {
+        if (o?.foo === value) {
+            o.foo;  // Error
+            ~
+!!! error TS2532: Object is possibly 'undefined'.
+        }
+        if (o?.["foo"] === value) {
+            o["foo"];  // Error
+            ~
+!!! error TS2532: Object is possibly 'undefined'.
+        }
+        if (o?.bar() === value) {
+            o.bar;  // Error
+            ~
+!!! error TS2532: Object is possibly 'undefined'.
+        }
+        if (o?.foo == value) {
+            o.foo;  // Error
+            ~
+!!! error TS2532: Object is possibly 'undefined'.
+        }
+        if (o?.["foo"] == value) {
+            o["foo"];  // Error
+            ~
+!!! error TS2532: Object is possibly 'undefined'.
+        }
+        if (o?.bar() == value) {
+            o.bar;  // Error
+            ~
+!!! error TS2532: Object is possibly 'undefined'.
+        }
+    }
+    
+    function f12a(o: Thing | undefined, value: number | null) {
+        if (o?.foo === value) {
+            o.foo;
+        }
+        if (o?.["foo"] === value) {
+            o["foo"];
+        }
+        if (o?.bar() === value) {
+            o.bar;
+        }
+        if (o?.foo == value) {
+            o.foo;  // Error
+            ~
+!!! error TS2532: Object is possibly 'undefined'.
+        }
+        if (o?.["foo"] == value) {
+            o["foo"];  // Error
+            ~
+!!! error TS2532: Object is possibly 'undefined'.
+        }
+        if (o?.bar() == value) {
+            o.bar;  // Error
+            ~
+!!! error TS2532: Object is possibly 'undefined'.
+        }
+    }
+    
+    function f13(o: Thing | undefined) {
+        if (o?.foo !== undefined) {
+            o.foo;
+        }
+        if (o?.["foo"] !== undefined) {
+            o["foo"];
+        }
+        if (o?.bar() !== undefined) {
+            o.bar;
+        }
+        if (o?.foo != undefined) {
+            o.foo;
+        }
+        if (o?.["foo"] != undefined) {
+            o["foo"];
+        }
+        if (o?.bar() != undefined) {
+            o.bar;
+        }
+    }
+    
+    function f13a(o: Thing | undefined) {
+        if (o?.foo !== null) {
+            o.foo;  // Error
+            ~
+!!! error TS2532: Object is possibly 'undefined'.
+        }
+        if (o?.["foo"] !== null) {
+            o["foo"];  // Error
+            ~
+!!! error TS2532: Object is possibly 'undefined'.
+        }
+        if (o?.bar() !== null) {
+            o.bar;  // Error
+            ~
+!!! error TS2532: Object is possibly 'undefined'.
+        }
+        if (o?.foo != null) {
+            o.foo;
+        }
+        if (o?.["foo"] != null) {
+            o["foo"];
+        }
+        if (o?.bar() != null) {
+            o.bar;
+        }
+    }
+    
+    function f14(o: Thing | null) {
+        if (o?.foo !== undefined) {
+            o.foo;
+        }
+        if (o?.["foo"] !== undefined) {
+            o["foo"];
+        }
+        if (o?.bar() !== undefined) {
+            o.bar;
+        }
+    }
+    
+    function f20(o: Thing | undefined) {
+        if (typeof o?.foo === "number") {
+            o.foo;
+        }
+        if (typeof o?.["foo"] === "number") {
+            o["foo"];
+        }
+        if (typeof o?.bar() === "number") {
+            o.bar;
+        }
+        if (o?.baz instanceof Error) {
+            o.baz;
+        }
+    }
+    
+    function f21(o: Thing | null) {
+        if (typeof o?.foo === "number") {
+            o.foo;
+        }
+        if (typeof o?.["foo"] === "number") {
+            o["foo"];
+        }
+        if (typeof o?.bar() === "number") {
+            o.bar;
+        }
+        if (o?.baz instanceof Error) {
+            o.baz;
+        }
+    }