Narrowing from truthy unknown to object (#37507)

* For x && typeof x === 'object', narrow x to just type object * Add tests * Allow arbitrary nesting / add comments * Add additional tests
2026-06-30 04:16:48 -05:00 · 2020-03-20 17:09:24 -07:00
parent e3ec7b18b8
commit fde9c7f555
6 changed files with 379 additions and 3 deletions
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -19013,6 +19013,13 @@ namespace ts {
            return false;
        }

+        // Given a source x, check if target matches x or is an && operation with an operand that matches x.
+        function containsTruthyCheck(source: Node, target: Node): boolean {
+            return isMatchingReference(source, target) ||
+                (target.kind === SyntaxKind.BinaryExpression && (<BinaryExpression>target).operatorToken.kind === SyntaxKind.AmpersandAmpersandToken &&
+                (containsTruthyCheck(source, (<BinaryExpression>target).left) || containsTruthyCheck(source, (<BinaryExpression>target).right)));
+        }
+
        function getAccessedPropertyName(access: AccessExpression): __String | undefined {
            return access.kind === SyntaxKind.PropertyAccessExpression ? access.name.escapedText :
                isStringOrNumericLiteralLike(access.argumentExpression) ? escapeLeadingUnderscores(access.argumentExpression.text) :
@@ -20409,15 +20416,23 @@ namespace ts {
                if (type.flags & TypeFlags.Any && literal.text === "function") {
                    return type;
                }
+                if (assumeTrue && type.flags & TypeFlags.Unknown && literal.text === "object") {
+                    // The pattern x && typeof x === 'object', where x is of type unknown, narrows x to type object. We don't
+                    // need to check for the reverse typeof x === 'object' && x since that already narrows correctly.
+                    if (typeOfExpr.parent.parent.kind === SyntaxKind.BinaryExpression) {
+                        const expr = <BinaryExpression>typeOfExpr.parent.parent;
+                        if (expr.operatorToken.kind === SyntaxKind.AmpersandAmpersandToken && expr.right === typeOfExpr.parent && containsTruthyCheck(reference, expr.left)) {
+                            return nonPrimitiveType;
+                        }
+                    }
+                    return getUnionType([nonPrimitiveType, nullType]);
+                }
                const facts = assumeTrue ?
                    typeofEQFacts.get(literal.text) || TypeFacts.TypeofEQHostObject :
                    typeofNEFacts.get(literal.text) || TypeFacts.TypeofNEHostObject;
                return getTypeWithFacts(assumeTrue ? mapType(type, narrowTypeForTypeof) : type, facts);

                function narrowTypeForTypeof(type: Type) {
-                    if (type.flags & TypeFlags.Unknown && literal.text === "object") {
-                        return getUnionType([nonPrimitiveType, nullType]);
-                    }
                    // We narrow a non-union type to an exact primitive type if the non-union type
                    // is a supertype of that primitive type. For example, type 'any' can be narrowed
                    // to one of the primitive types.
--- a/tests/baselines/reference/narrowingTruthyObject.errors.txt
+++ b/tests/baselines/reference/narrowingTruthyObject.errors.txt
@@ -0,0 +1,36 @@
+tests/cases/compiler/narrowingTruthyObject.ts(3,9): error TS2531: Object is possibly 'null'.
+
+
+==== tests/cases/compiler/narrowingTruthyObject.ts (1 errors) ====
+    function foo(x: unknown, b: boolean) {
+        if (typeof x === 'object') {
+            x.toString();
+            ~
+!!! error TS2531: Object is possibly 'null'.
+        }
+        if (typeof x === 'object' && x) {
+            x.toString();
+        }
+        if (x && typeof x === 'object') {
+            x.toString();
+        }
+        if (b && x && typeof x === 'object') {
+            x.toString();
+        }
+        if (x && b && typeof x === 'object') {
+            x.toString();
+        }
+        if (x && b && b && typeof x === 'object') {
+            x.toString();
+        }
+        if (b && b && x && b && b && typeof x === 'object') {
+            x.toString();
+        }
+    }
+    
+    // Repro from #36870
+    
+    function f1(x: unknown): any {
+        return x && typeof x === 'object' && x.hasOwnProperty('x');
+    }
+    
--- a/tests/baselines/reference/narrowingTruthyObject.js
+++ b/tests/baselines/reference/narrowingTruthyObject.js
@@ -0,0 +1,61 @@
+//// [narrowingTruthyObject.ts]
+function foo(x: unknown, b: boolean) {
+    if (typeof x === 'object') {
+        x.toString();
+    }
+    if (typeof x === 'object' && x) {
+        x.toString();
+    }
+    if (x && typeof x === 'object') {
+        x.toString();
+    }
+    if (b && x && typeof x === 'object') {
+        x.toString();
+    }
+    if (x && b && typeof x === 'object') {
+        x.toString();
+    }
+    if (x && b && b && typeof x === 'object') {
+        x.toString();
+    }
+    if (b && b && x && b && b && typeof x === 'object') {
+        x.toString();
+    }
+}
+
+// Repro from #36870
+
+function f1(x: unknown): any {
+    return x && typeof x === 'object' && x.hasOwnProperty('x');
+}
+
+
+//// [narrowingTruthyObject.js]
+"use strict";
+function foo(x, b) {
+    if (typeof x === 'object') {
+        x.toString();
+    }
+    if (typeof x === 'object' && x) {
+        x.toString();
+    }
+    if (x && typeof x === 'object') {
+        x.toString();
+    }
+    if (b && x && typeof x === 'object') {
+        x.toString();
+    }
+    if (x && b && typeof x === 'object') {
+        x.toString();
+    }
+    if (x && b && b && typeof x === 'object') {
+        x.toString();
+    }
+    if (b && b && x && b && b && typeof x === 'object') {
+        x.toString();
+    }
+}
+// Repro from #36870
+function f1(x) {
+    return x && typeof x === 'object' && x.hasOwnProperty('x');
+}
--- a/tests/baselines/reference/narrowingTruthyObject.symbols
+++ b/tests/baselines/reference/narrowingTruthyObject.symbols
@@ -0,0 +1,92 @@
+=== tests/cases/compiler/narrowingTruthyObject.ts ===
+function foo(x: unknown, b: boolean) {
+>foo : Symbol(foo, Decl(narrowingTruthyObject.ts, 0, 0))
+>x : Symbol(x, Decl(narrowingTruthyObject.ts, 0, 13))
+>b : Symbol(b, Decl(narrowingTruthyObject.ts, 0, 24))
+
+    if (typeof x === 'object') {
+>x : Symbol(x, Decl(narrowingTruthyObject.ts, 0, 13))
+
+        x.toString();
+>x.toString : Symbol(Object.toString, Decl(lib.es5.d.ts, --, --))
+>x : Symbol(x, Decl(narrowingTruthyObject.ts, 0, 13))
+>toString : Symbol(Object.toString, Decl(lib.es5.d.ts, --, --))
+    }
+    if (typeof x === 'object' && x) {
+>x : Symbol(x, Decl(narrowingTruthyObject.ts, 0, 13))
+>x : Symbol(x, Decl(narrowingTruthyObject.ts, 0, 13))
+
+        x.toString();
+>x.toString : Symbol(Object.toString, Decl(lib.es5.d.ts, --, --))
+>x : Symbol(x, Decl(narrowingTruthyObject.ts, 0, 13))
+>toString : Symbol(Object.toString, Decl(lib.es5.d.ts, --, --))
+    }
+    if (x && typeof x === 'object') {
+>x : Symbol(x, Decl(narrowingTruthyObject.ts, 0, 13))
+>x : Symbol(x, Decl(narrowingTruthyObject.ts, 0, 13))
+
+        x.toString();
+>x.toString : Symbol(Object.toString, Decl(lib.es5.d.ts, --, --))
+>x : Symbol(x, Decl(narrowingTruthyObject.ts, 0, 13))
+>toString : Symbol(Object.toString, Decl(lib.es5.d.ts, --, --))
+    }
+    if (b && x && typeof x === 'object') {
+>b : Symbol(b, Decl(narrowingTruthyObject.ts, 0, 24))
+>x : Symbol(x, Decl(narrowingTruthyObject.ts, 0, 13))
+>x : Symbol(x, Decl(narrowingTruthyObject.ts, 0, 13))
+
+        x.toString();
+>x.toString : Symbol(Object.toString, Decl(lib.es5.d.ts, --, --))
+>x : Symbol(x, Decl(narrowingTruthyObject.ts, 0, 13))
+>toString : Symbol(Object.toString, Decl(lib.es5.d.ts, --, --))
+    }
+    if (x && b && typeof x === 'object') {
+>x : Symbol(x, Decl(narrowingTruthyObject.ts, 0, 13))
+>b : Symbol(b, Decl(narrowingTruthyObject.ts, 0, 24))
+>x : Symbol(x, Decl(narrowingTruthyObject.ts, 0, 13))
+
+        x.toString();
+>x.toString : Symbol(Object.toString, Decl(lib.es5.d.ts, --, --))
+>x : Symbol(x, Decl(narrowingTruthyObject.ts, 0, 13))
+>toString : Symbol(Object.toString, Decl(lib.es5.d.ts, --, --))
+    }
+    if (x && b && b && typeof x === 'object') {
+>x : Symbol(x, Decl(narrowingTruthyObject.ts, 0, 13))
+>b : Symbol(b, Decl(narrowingTruthyObject.ts, 0, 24))
+>b : Symbol(b, Decl(narrowingTruthyObject.ts, 0, 24))
+>x : Symbol(x, Decl(narrowingTruthyObject.ts, 0, 13))
+
+        x.toString();
+>x.toString : Symbol(Object.toString, Decl(lib.es5.d.ts, --, --))
+>x : Symbol(x, Decl(narrowingTruthyObject.ts, 0, 13))
+>toString : Symbol(Object.toString, Decl(lib.es5.d.ts, --, --))
+    }
+    if (b && b && x && b && b && typeof x === 'object') {
+>b : Symbol(b, Decl(narrowingTruthyObject.ts, 0, 24))
+>b : Symbol(b, Decl(narrowingTruthyObject.ts, 0, 24))
+>x : Symbol(x, Decl(narrowingTruthyObject.ts, 0, 13))
+>b : Symbol(b, Decl(narrowingTruthyObject.ts, 0, 24))
+>b : Symbol(b, Decl(narrowingTruthyObject.ts, 0, 24))
+>x : Symbol(x, Decl(narrowingTruthyObject.ts, 0, 13))
+
+        x.toString();
+>x.toString : Symbol(Object.toString, Decl(lib.es5.d.ts, --, --))
+>x : Symbol(x, Decl(narrowingTruthyObject.ts, 0, 13))
+>toString : Symbol(Object.toString, Decl(lib.es5.d.ts, --, --))
+    }
+}
+
+// Repro from #36870
+
+function f1(x: unknown): any {
+>f1 : Symbol(f1, Decl(narrowingTruthyObject.ts, 22, 1))
+>x : Symbol(x, Decl(narrowingTruthyObject.ts, 26, 12))
+
+    return x && typeof x === 'object' && x.hasOwnProperty('x');
+>x : Symbol(x, Decl(narrowingTruthyObject.ts, 26, 12))
+>x : Symbol(x, Decl(narrowingTruthyObject.ts, 26, 12))
+>x.hasOwnProperty : Symbol(Object.hasOwnProperty, Decl(lib.es5.d.ts, --, --))
+>x : Symbol(x, Decl(narrowingTruthyObject.ts, 26, 12))
+>hasOwnProperty : Symbol(Object.hasOwnProperty, Decl(lib.es5.d.ts, --, --))
+}
+
--- a/tests/baselines/reference/narrowingTruthyObject.types
+++ b/tests/baselines/reference/narrowingTruthyObject.types
@@ -0,0 +1,141 @@
+=== tests/cases/compiler/narrowingTruthyObject.ts ===
+function foo(x: unknown, b: boolean) {
+>foo : (x: unknown, b: boolean) => void
+>x : unknown
+>b : boolean
+
+    if (typeof x === 'object') {
+>typeof x === 'object' : boolean
+>typeof x : "string" | "number" | "bigint" | "boolean" | "symbol" | "undefined" | "object" | "function"
+>x : unknown
+>'object' : "object"
+
+        x.toString();
+>x.toString() : string
+>x.toString : () => string
+>x : object | null
+>toString : () => string
+    }
+    if (typeof x === 'object' && x) {
+>typeof x === 'object' && x : false | object | null
+>typeof x === 'object' : boolean
+>typeof x : "string" | "number" | "bigint" | "boolean" | "symbol" | "undefined" | "object" | "function"
+>x : unknown
+>'object' : "object"
+>x : object | null
+
+        x.toString();
+>x.toString() : string
+>x.toString : () => string
+>x : object
+>toString : () => string
+    }
+    if (x && typeof x === 'object') {
+>x && typeof x === 'object' : boolean
+>x : unknown
+>typeof x === 'object' : boolean
+>typeof x : "string" | "number" | "bigint" | "boolean" | "symbol" | "undefined" | "object" | "function"
+>x : unknown
+>'object' : "object"
+
+        x.toString();
+>x.toString() : string
+>x.toString : () => string
+>x : object
+>toString : () => string
+    }
+    if (b && x && typeof x === 'object') {
+>b && x && typeof x === 'object' : boolean
+>b && x : unknown
+>b : boolean
+>x : unknown
+>typeof x === 'object' : boolean
+>typeof x : "string" | "number" | "bigint" | "boolean" | "symbol" | "undefined" | "object" | "function"
+>x : unknown
+>'object' : "object"
+
+        x.toString();
+>x.toString() : string
+>x.toString : () => string
+>x : object
+>toString : () => string
+    }
+    if (x && b && typeof x === 'object') {
+>x && b && typeof x === 'object' : boolean
+>x && b : boolean
+>x : unknown
+>b : boolean
+>typeof x === 'object' : boolean
+>typeof x : "string" | "number" | "bigint" | "boolean" | "symbol" | "undefined" | "object" | "function"
+>x : unknown
+>'object' : "object"
+
+        x.toString();
+>x.toString() : string
+>x.toString : () => string
+>x : object
+>toString : () => string
+    }
+    if (x && b && b && typeof x === 'object') {
+>x && b && b && typeof x === 'object' : boolean
+>x && b && b : boolean
+>x && b : boolean
+>x : unknown
+>b : boolean
+>b : true
+>typeof x === 'object' : boolean
+>typeof x : "string" | "number" | "bigint" | "boolean" | "symbol" | "undefined" | "object" | "function"
+>x : unknown
+>'object' : "object"
+
+        x.toString();
+>x.toString() : string
+>x.toString : () => string
+>x : object
+>toString : () => string
+    }
+    if (b && b && x && b && b && typeof x === 'object') {
+>b && b && x && b && b && typeof x === 'object' : boolean
+>b && b && x && b && b : true
+>b && b && x && b : true
+>b && b && x : unknown
+>b && b : boolean
+>b : boolean
+>b : true
+>x : unknown
+>b : true
+>b : true
+>typeof x === 'object' : boolean
+>typeof x : "string" | "number" | "bigint" | "boolean" | "symbol" | "undefined" | "object" | "function"
+>x : unknown
+>'object' : "object"
+
+        x.toString();
+>x.toString() : string
+>x.toString : () => string
+>x : object
+>toString : () => string
+    }
+}
+
+// Repro from #36870
+
+function f1(x: unknown): any {
+>f1 : (x: unknown) => any
+>x : unknown
+
+    return x && typeof x === 'object' && x.hasOwnProperty('x');
+>x && typeof x === 'object' && x.hasOwnProperty('x') : boolean
+>x && typeof x === 'object' : boolean
+>x : unknown
+>typeof x === 'object' : boolean
+>typeof x : "string" | "number" | "bigint" | "boolean" | "symbol" | "undefined" | "object" | "function"
+>x : unknown
+>'object' : "object"
+>x.hasOwnProperty('x') : boolean
+>x.hasOwnProperty : (v: string | number | symbol) => boolean
+>x : object
+>hasOwnProperty : (v: string | number | symbol) => boolean
+>'x' : "x"
+}
+
--- a/tests/cases/compiler/narrowingTruthyObject.ts
+++ b/tests/cases/compiler/narrowingTruthyObject.ts
@@ -0,0 +1,31 @@
+// @strict: true
+
+function foo(x: unknown, b: boolean) {
+    if (typeof x === 'object') {
+        x.toString();
+    }
+    if (typeof x === 'object' && x) {
+        x.toString();
+    }
+    if (x && typeof x === 'object') {
+        x.toString();
+    }
+    if (b && x && typeof x === 'object') {
+        x.toString();
+    }
+    if (x && b && typeof x === 'object') {
+        x.toString();
+    }
+    if (x && b && b && typeof x === 'object') {
+        x.toString();
+    }
+    if (b && b && x && b && b && typeof x === 'object') {
+        x.toString();
+    }
+}
+
+// Repro from #36870
+
+function f1(x: unknown): any {
+    return x && typeof x === 'object' && x.hasOwnProperty('x');
+}