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Bug 1685482 - Part 2: Disallow identifiers named "async" in for-of lo…
…ops. r=yulia
`for-of` loops mustn't start with the token sequence `async of`, because that
leads to a shift-reduce conflict when parsing `for (async of => {};;)` or
`for (async of [])`. This restriction doesn't apply to `for-await-of` loops,
because `async` in `for await (async of ...)` is always parsed as an identifier.
Parsing `for (async of ...)` already results in a SyntaxError, but that happens
because `assignExpr()` always tries to parse the sequence `async [no LineTerminator] of`
as the start of an async arrow function. That means `forHeadStart()` still needs
to handle the case when `async` and `of` are separated by a line terminator.
Part 3 will update the parser to allow `for await (async of ...)`.
Spec change: tc39/ecma262#2256
Depends on D100994
Differential Revision: https://phabricator.services.mozilla.com/D100995- Loading branch information
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116 changes: 116 additions & 0 deletions
116
js/src/tests/non262/statements/for-of-async-of-starting-lhs.js
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,116 @@ | ||
| if (typeof getRealmConfiguration === "undefined") { | ||
| var getRealmConfiguration = SpecialPowers.Cu.getJSTestingFunctions().getRealmConfiguration; | ||
| } | ||
|
|
||
| const IsTopLevelAwaitEnabled = getRealmConfiguration().topLevelAwait; | ||
|
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| const AsyncFunction = async function(){}.constructor; | ||
|
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| function assertNoError(f, msg) { | ||
| try { | ||
| f(); | ||
| } catch (e) { | ||
| assertEq(true, false, `${msg}: ${e}`); | ||
| } | ||
| } | ||
|
|
||
| function assertSyntaxError(code) { | ||
| assertThrowsInstanceOf(function () { Function(code); }, SyntaxError, "Function:" + code); | ||
| assertThrowsInstanceOf(function () { AsyncFunction(code); }, SyntaxError, "AsyncFunction:" + code); | ||
|
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||
| if (typeof parseModule === "function") { | ||
| assertThrowsInstanceOf(function () { parseModule(code); }, SyntaxError, "Module:" + code); | ||
| } | ||
| } | ||
|
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||
| function assertNoSyntaxError(code) { | ||
| assertNoError(function () { Function(code); }, "Function:" + code); | ||
| assertNoError(function () { AsyncFunction(code); }, "AsyncFunction:" + code); | ||
|
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||
| if (typeof parseModule === "function") { | ||
| assertNoError(function () { parseModule(code); }, "Module:" + code); | ||
| } | ||
| } | ||
|
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| function assertNoSyntaxErrorAsyncContext(code) { | ||
| assertNoError(function () { AsyncFunction(code); }, "AsyncFunction:" + code); | ||
|
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| if (typeof parseModule === "function" && IsTopLevelAwaitEnabled) { | ||
| assertNoError(function () { parseModule(code); }, "Module:" + code); | ||
| } | ||
| } | ||
|
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||
| const invalidTestCases = [ | ||
| // for-in loop: LHS can't start with an async arrow function. | ||
| "for ( async of => {} in [] ) ;", | ||
| "for ( async o\\u0066 => {} in [] ) ;", | ||
|
|
||
| // for-of loop: LHS can't start with an async arrow function. | ||
| "for ( async of => {} of [] ) ;", | ||
| "for ( async o\\u0066 => {} of [] ) ;", | ||
|
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| // for-of loop: LHS can't start with an identifier named "async". | ||
| "for ( async of [] ) ;", | ||
|
|
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| // for-await-of loop: LHS can't start with an async arrow function. | ||
| "for await ( async of => {} of [] ) ;", | ||
| "for await ( async o\\u0066 => {} of [] ) ;", | ||
| ]; | ||
|
|
||
| for (let source of invalidTestCases) { | ||
| assertSyntaxError(source); | ||
|
|
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| // Also test when the tokens are separated by newline characters. | ||
| assertSyntaxError(source.split(" ").join("\n")); | ||
| } | ||
|
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| // for-loop: async arrow functions are allowed in C-style for-loops. | ||
| assertNoSyntaxError("for ( async of => {} ; ; ) ;") | ||
|
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| const validTestCases = [ | ||
| // for-loop: LHS can start with an identifier named "async". | ||
| "for ( async ; ; ) ;", | ||
| "for ( \\u0061sync ; ; ) ;", | ||
|
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| // for-in loop: LHS can start with an identifier named "async". | ||
| "for ( async in [] ) ;", | ||
| "for ( \\u0061sync in [] ) ;", | ||
|
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| // for-in loop: LHS can start with an property assignment starting with "async". | ||
| "for ( async . prop in [] ) ;", | ||
| "for ( async [ 0 ] in [] ) ;", | ||
|
|
||
| // for-of loop: LHS can start with an identifier named "async" when escape characters are used. | ||
| "for ( \\u0061sync of [] ) ;", | ||
|
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| // for-of loop: LHS can start with an property assignment starting with "async". | ||
| "for ( async . prop of [] ) ;", | ||
| "for ( async [ 0 ] of [] ) ;", | ||
| ]; | ||
|
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| for (let source of validTestCases) { | ||
| assertNoSyntaxError(source); | ||
|
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| // Also test when the tokens are separated by newline characters. | ||
| assertNoSyntaxError(source.split(" ").join("\n")); | ||
| } | ||
|
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| const validTestCasesAsync = [ | ||
| // for-await-of loop: LHS can start with an identifier named "async". | ||
| // "for await ( async of [] ) ;", | ||
| "for await ( \\u0061sync of [] ) ;", | ||
|
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| // for-await-of loop: LHS can start with an property assignment starting with "async". | ||
| "for await ( async . prop of [] ) ;", | ||
| "for await ( async [ 0 ] of [] ) ;", | ||
| ]; | ||
|
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| for (let source of validTestCasesAsync) { | ||
| assertNoSyntaxErrorAsyncContext(source); | ||
|
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| // Also test when the tokens are separated by newline characters. | ||
| assertNoSyntaxErrorAsyncContext(source.split(" ").join("\n")); | ||
| } | ||
|
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| if (typeof reportCompare === "function") | ||
| reportCompare(true, true); |