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Merged
merged 2 commits into from
Jun 8, 2016
Merged

Allow nested assignments in type guards #9013

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6a243e3
Allow nested assignments in type guards
ahejlsberg Jun 8, 2016
cdf5b7a
Add tests
ahejlsberg Jun 8, 2016
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28 changes: 22 additions & 6 deletions src/compiler/checker.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -7662,6 +7662,21 @@ namespace ts {
getInitialTypeOfBindingElement(<BindingElement>node);
}

function getReferenceFromExpression(node: Expression): Expression {
switch (node.kind) {
case SyntaxKind.ParenthesizedExpression:
return getReferenceFromExpression((<ParenthesizedExpression>node).expression);
case SyntaxKind.BinaryExpression:
switch ((<BinaryExpression>node).operatorToken.kind) {
case SyntaxKind.EqualsToken:
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Technically you should consider the compound assignment operators here as well (e.g. +=, -= etc)

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Compound operators aren't included in control flow analysis in our current design, so that would be a separate issue. But as I see it they wouldn't affect the type because they both a read and a write operation (you're basically storing a value of the same type back into the variable). Did you have something in mind?

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@DanielRosenwasser DanielRosenwasser Jun 8, 2016 •
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Nothing other than odd cases like this:

var x: number | string = getNumberOrString();
x += "hello";
x; // currently has type 'string | number'

whereas in this case you get a different result

var x: number | string = getNumberOrString();
x = x + "hello";
x; // currently has type 'string'

I don't know how often something like that comes up in practice though.

return getReferenceFromExpression((<BinaryExpression>node).left);
case SyntaxKind.CommaToken:
return getReferenceFromExpression((<BinaryExpression>node).right);
}
}
return node;
}

function getFlowTypeOfReference(reference: Node, declaredType: Type, assumeInitialized: boolean, includeOuterFunctions: boolean) {
let key: string;
if (!reference.flowNode || assumeInitialized && !(declaredType.flags & TypeFlags.Narrowable)) {
Expand Down Expand Up @@ -7882,7 +7897,7 @@ namespace ts {
if (operator === SyntaxKind.ExclamationEqualsToken || operator === SyntaxKind.ExclamationEqualsEqualsToken) {
assumeTrue = !assumeTrue;
}
if (!strictNullChecks || !isMatchingReference(reference, expr.left)) {
if (!strictNullChecks || !isMatchingReference(reference, getReferenceFromExpression(expr.left))) {
return type;
}
const doubleEquals = operator === SyntaxKind.EqualsEqualsToken || operator === SyntaxKind.ExclamationEqualsToken;
Expand All @@ -7897,12 +7912,12 @@ namespace ts {
function narrowTypeByTypeof(type: Type, expr: BinaryExpression, assumeTrue: boolean): Type {
// We have '==', '!=', '====', or !==' operator with 'typeof xxx' on the left
// and string literal on the right
const left = <TypeOfExpression>expr.left;
const left = getReferenceFromExpression((<TypeOfExpression>expr.left).expression);
const right = <LiteralExpression>expr.right;
if (!isMatchingReference(reference, left.expression)) {
if (!isMatchingReference(reference, left)) {
// 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, left.expression)) {
if (containsMatchingReference(reference, left)) {
return declaredType;
}
return type;
Expand All @@ -7927,10 +7942,11 @@ namespace ts {
}

function narrowTypeByInstanceof(type: Type, expr: BinaryExpression, assumeTrue: boolean): Type {
if (!isMatchingReference(reference, expr.left)) {
const left = getReferenceFromExpression(expr.left);
if (!isMatchingReference(reference, left)) {
// For a reference of the form 'x.y', an 'x instanceof T' type guard resets the
// narrowed type of 'y' to its declared type.
if (containsMatchingReference(reference, expr.left)) {
if (containsMatchingReference(reference, left)) {
return declaredType;
}
return type;
Expand Down
86 changes: 86 additions & 0 deletions tests/baselines/reference/typeGuardsNestedAssignments.js
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@@ -0,0 +1,86 @@
//// [typeGuardsNestedAssignments.ts]

class Foo {
x: string;
}

declare function getFooOrNull(): Foo | null;
declare function getStringOrNumberOrNull(): string | number | null;

function f1() {
let foo: Foo | null;
if ((foo = getFooOrNull()) !== null) {
foo; // Foo
}
}

function f2() {
let foo1: Foo | null;
let foo2: Foo | null;
if ((foo1 = getFooOrNull(), foo2 = foo1) !== null) {
foo1; // Foo | null
foo2; // Foo
}
}

function f3() {
let obj: Object | null;
if ((obj = getFooOrNull()) instanceof Foo) {
obj;
}
}

function f4() {
let x: string | number | null;
if (typeof (x = getStringOrNumberOrNull()) === "number") {
x;
}
}

// Repro from #8851

const re = /./g
let match: RegExpExecArray | null

while ((match = re.exec("xxx")) != null) {
const length = match[1].length + match[2].length
}

//// [typeGuardsNestedAssignments.js]
var Foo = (function () {
function Foo() {
}
return Foo;
}());
function f1() {
var foo;
if ((foo = getFooOrNull()) !== null) {
foo; // Foo
}
}
function f2() {
var foo1;
var foo2;
if ((foo1 = getFooOrNull(), foo2 = foo1) !== null) {
foo1; // Foo | null
foo2; // Foo
}
}
function f3() {
var obj;
if ((obj = getFooOrNull()) instanceof Foo) {
obj;
}
}
function f4() {
var x;
if (typeof (x = getStringOrNumberOrNull()) === "number") {
x;
}
}
// Repro from #8851
var re = /./g;
var match;
while ((match = re.exec("xxx")) != null) {
var length = match[1].length + match[2].length;
}
113 changes: 113 additions & 0 deletions tests/baselines/reference/typeGuardsNestedAssignments.symbols
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@@ -0,0 +1,113 @@
=== tests/cases/conformance/controlFlow/typeGuardsNestedAssignments.ts ===

class Foo {
>Foo : Symbol(Foo, Decl(typeGuardsNestedAssignments.ts, 0, 0))

x: string;
>x : Symbol(Foo.x, Decl(typeGuardsNestedAssignments.ts, 1, 11))
}

declare function getFooOrNull(): Foo | null;
>getFooOrNull : Symbol(getFooOrNull, Decl(typeGuardsNestedAssignments.ts, 3, 1))
>Foo : Symbol(Foo, Decl(typeGuardsNestedAssignments.ts, 0, 0))

declare function getStringOrNumberOrNull(): string | number | null;
>getStringOrNumberOrNull : Symbol(getStringOrNumberOrNull, Decl(typeGuardsNestedAssignments.ts, 5, 44))

function f1() {
>f1 : Symbol(f1, Decl(typeGuardsNestedAssignments.ts, 6, 67))

let foo: Foo | null;
>foo : Symbol(foo, Decl(typeGuardsNestedAssignments.ts, 9, 7))
>Foo : Symbol(Foo, Decl(typeGuardsNestedAssignments.ts, 0, 0))

if ((foo = getFooOrNull()) !== null) {
>foo : Symbol(foo, Decl(typeGuardsNestedAssignments.ts, 9, 7))
>getFooOrNull : Symbol(getFooOrNull, Decl(typeGuardsNestedAssignments.ts, 3, 1))

foo; // Foo
>foo : Symbol(foo, Decl(typeGuardsNestedAssignments.ts, 9, 7))
}
}

function f2() {
>f2 : Symbol(f2, Decl(typeGuardsNestedAssignments.ts, 13, 1))

let foo1: Foo | null;
>foo1 : Symbol(foo1, Decl(typeGuardsNestedAssignments.ts, 16, 7))
>Foo : Symbol(Foo, Decl(typeGuardsNestedAssignments.ts, 0, 0))

let foo2: Foo | null;
>foo2 : Symbol(foo2, Decl(typeGuardsNestedAssignments.ts, 17, 7))
>Foo : Symbol(Foo, Decl(typeGuardsNestedAssignments.ts, 0, 0))

if ((foo1 = getFooOrNull(), foo2 = foo1) !== null) {
>foo1 : Symbol(foo1, Decl(typeGuardsNestedAssignments.ts, 16, 7))
>getFooOrNull : Symbol(getFooOrNull, Decl(typeGuardsNestedAssignments.ts, 3, 1))
>foo2 : Symbol(foo2, Decl(typeGuardsNestedAssignments.ts, 17, 7))
>foo1 : Symbol(foo1, Decl(typeGuardsNestedAssignments.ts, 16, 7))

foo1; // Foo | null
>foo1 : Symbol(foo1, Decl(typeGuardsNestedAssignments.ts, 16, 7))

foo2; // Foo
>foo2 : Symbol(foo2, Decl(typeGuardsNestedAssignments.ts, 17, 7))
}
}

function f3() {
>f3 : Symbol(f3, Decl(typeGuardsNestedAssignments.ts, 22, 1))

let obj: Object | null;
>obj : Symbol(obj, Decl(typeGuardsNestedAssignments.ts, 25, 7))
>Object : Symbol(Object, Decl(lib.d.ts, --, --), Decl(lib.d.ts, --, --))

if ((obj = getFooOrNull()) instanceof Foo) {
>obj : Symbol(obj, Decl(typeGuardsNestedAssignments.ts, 25, 7))
>getFooOrNull : Symbol(getFooOrNull, Decl(typeGuardsNestedAssignments.ts, 3, 1))
>Foo : Symbol(Foo, Decl(typeGuardsNestedAssignments.ts, 0, 0))

obj;
>obj : Symbol(obj, Decl(typeGuardsNestedAssignments.ts, 25, 7))
}
}

function f4() {
>f4 : Symbol(f4, Decl(typeGuardsNestedAssignments.ts, 29, 1))

let x: string | number | null;
>x : Symbol(x, Decl(typeGuardsNestedAssignments.ts, 32, 7))

if (typeof (x = getStringOrNumberOrNull()) === "number") {
>x : Symbol(x, Decl(typeGuardsNestedAssignments.ts, 32, 7))
>getStringOrNumberOrNull : Symbol(getStringOrNumberOrNull, Decl(typeGuardsNestedAssignments.ts, 5, 44))

x;
>x : Symbol(x, Decl(typeGuardsNestedAssignments.ts, 32, 7))
}
}

// Repro from #8851

const re = /./g
>re : Symbol(re, Decl(typeGuardsNestedAssignments.ts, 40, 5))

let match: RegExpExecArray | null
>match : Symbol(match, Decl(typeGuardsNestedAssignments.ts, 41, 3))
>RegExpExecArray : Symbol(RegExpExecArray, Decl(lib.d.ts, --, --))

while ((match = re.exec("xxx")) != null) {
>match : Symbol(match, Decl(typeGuardsNestedAssignments.ts, 41, 3))
>re.exec : Symbol(RegExp.exec, Decl(lib.d.ts, --, --))
>re : Symbol(re, Decl(typeGuardsNestedAssignments.ts, 40, 5))
>exec : Symbol(RegExp.exec, Decl(lib.d.ts, --, --))

const length = match[1].length + match[2].length
>length : Symbol(length, Decl(typeGuardsNestedAssignments.ts, 44, 9))
>match[1].length : Symbol(String.length, Decl(lib.d.ts, --, --))
>match : Symbol(match, Decl(typeGuardsNestedAssignments.ts, 41, 3))
>length : Symbol(String.length, Decl(lib.d.ts, --, --))
>match[2].length : Symbol(String.length, Decl(lib.d.ts, --, --))
>match : Symbol(match, Decl(typeGuardsNestedAssignments.ts, 41, 3))
>length : Symbol(String.length, Decl(lib.d.ts, --, --))
}
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