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Merged
ahejlsberg merged 4 commits into from
Mar 21, 2020
Merged

Narrowing from truthy unknown to object #37507

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14cee1f
For x && typeof x === 'object', narrow x to just type object
ahejlsberg Mar 20, 2020
1380811
Add tests
ahejlsberg Mar 20, 2020
092a805
Allow arbitrary nesting / add comments
ahejlsberg Mar 20, 2020
b5ef182
Add additional tests
ahejlsberg Mar 20, 2020
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19 changes: 16 additions & 3 deletions src/compiler/checker.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -18947,6 +18947,12 @@ namespace ts {
return false;
}

function containsTruthyCheck(source: Node, target: Node) {
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@DanielRosenwasser DanielRosenwasser Mar 20, 2020

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A comment here that this specifically deals the binary operator precedence. would also be useful. The implementation looks good here, but this function is named something much more general than it actually is and that's going to be confusing in the future.

return isMatchingReference(source, target) ||
(target.kind === SyntaxKind.BinaryExpression && (<BinaryExpression>target).operatorToken.kind === SyntaxKind.AmpersandAmpersandToken &&
(isMatchingReference(source, (<BinaryExpression>target).left) || isMatchingReference(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) :
Expand Down Expand Up @@ -20343,15 +20349,22 @@ 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.
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@DanielRosenwasser DanielRosenwasser Mar 20, 2020

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Would be nice to note here that you don't need to check both directions because the typeof x === "object" && x is narrowed as two separate steps. I don't think that would be obvious to a casual reader.

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.
Expand Down
30 changes: 30 additions & 0 deletions tests/baselines/reference/narrowingTruthyObject.errors.txt
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@@ -0,0 +1,30 @@
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();
}
}

// Repro from #36870

function f1(x: unknown): any {
return x && typeof x === 'object' && x.hasOwnProperty('x');
}

49 changes: 49 additions & 0 deletions tests/baselines/reference/narrowingTruthyObject.js
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@@ -0,0 +1,49 @@
//// [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();
}
}

// 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();
}
}
// Repro from #36870
function f1(x) {
return x && typeof x === 'object' && x.hasOwnProperty('x');
}
68 changes: 68 additions & 0 deletions tests/baselines/reference/narrowingTruthyObject.symbols
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@@ -0,0 +1,68 @@
=== 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, --, --))
}
}

// Repro from #36870

function f1(x: unknown): any {
>f1 : Symbol(f1, Decl(narrowingTruthyObject.ts, 16, 1))
>x : Symbol(x, Decl(narrowingTruthyObject.ts, 20, 12))

return x && typeof x === 'object' && x.hasOwnProperty('x');
>x : Symbol(x, Decl(narrowingTruthyObject.ts, 20, 12))
>x : Symbol(x, Decl(narrowingTruthyObject.ts, 20, 12))
>x.hasOwnProperty : Symbol(Object.hasOwnProperty, Decl(lib.es5.d.ts, --, --))
>x : Symbol(x, Decl(narrowingTruthyObject.ts, 20, 12))
>hasOwnProperty : Symbol(Object.hasOwnProperty, Decl(lib.es5.d.ts, --, --))
}

101 changes: 101 additions & 0 deletions tests/baselines/reference/narrowingTruthyObject.types
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@@ -0,0 +1,101 @@
=== 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
}
}

// 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"
}

25 changes: 25 additions & 0 deletions tests/cases/compiler/narrowingTruthyObject.ts
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@@ -0,0 +1,25 @@
// @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();
}
}

// Repro from #36870

function f1(x: unknown): any {
return x && typeof x === 'object' && x.hasOwnProperty('x');
}