Missing early error for duplicate lexically-bound variable declarations #487
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not-an-aardvark
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Dec 7, 2016
Due to acornjs/acorn#487, espree does not throw a syntax error for duplicate `let` or `const` declarations. Previously, the `prefer-const` rule assumed that a `let` variable would always have exactly one declaration. This adds a sanity check to avoid reporting (and possibly creating incorrect autofixes) a `let` variable if it has more than one declaration.
not-an-aardvark
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Dec 8, 2016
Due to acornjs/acorn#487, espree does not throw a syntax error for duplicate `let` or `const` declarations. Previously, the `prefer-const` rule assumed that a `let` variable would always have exactly one declaration. This adds a sanity check to avoid reporting (and possibly creating incorrect autofixes) a `let` variable if it has more than one declaration.
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Bump |
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This needs to be fixed in Acorn for it to flow through here, although, I'm not sure this check is feasible implementation-wise. @oliverwoodings please don't do that. We are all very busy and sometimes it takes longer for us to get around to less critical issues. |
I'm confused -- this is Acorn. |
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@nzakas apologies, I wouldn't normally, but given this was posted a month ago and has had zero responses, what else should I do? Whilst it may not seem critical, it is causing myself and others issues downstream. |
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@not-an-aardvark sorry, some reason I thought this was in Espree. @oliverwoodings something like, "I'm affected by this, is there anything I can do to help address it?" is much nicer. "Bump" is a bit rude as it triggers notifications without providing any additional information. |
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Will do next time 👍 |
not-an-aardvark
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Feb 14, 2017
This implements the static errors specified [here](https://tc39.github.io/ecma262/#sec-block-static-semantics-early-errors): > It is a Syntax Error if the LexicallyDeclaredNames of StatementList contains any duplicate entries. > It is a Syntax Error if any element of the LexicallyDeclaredNames of StatementList also occurs in the VarDeclaredNames of StatementList. In other words, if a `let`/`const` variable is declared in the same scope as another variable with the same name, a parsing error should be thrown. This is implemented with the following steps: * When entering a function scope, create an empty set of var-declared names * When entering a block scope, create a new empty set of lexically-declared names. Additionally, push the current set of var-declared names, and work with a new empty set. * When exiting a block scope, merge the set of var-declared names from the block with the set of var-declared names from the parent scope. * When parsing a binding pattern (e.g. a variable declaration or function parameters), check if the bound identifier clashes with any lexically-declared names (if the bound identifier is non-lexical), or any variable names at all (if the bound identifier is lexical). If so, raise a parsing error. Otherwise, add it to the current lexically-declared name set or var-declared name set as appropriate. The merging behavior for var-declared names in the third bullet-point is necessary due to how `var` scoping works. For example, this should be a syntax error: ```js { var foo = 1; } let foo = 1; ``` But this should not be a syntax error: ```js { var foo = 1; { let foo = 1; } } ```
not-an-aardvark
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Feb 17, 2017
This implements the static errors specified [here](https://tc39.github.io/ecma262/#sec-block-static-semantics-early-errors): > It is a Syntax Error if the LexicallyDeclaredNames of StatementList contains any duplicate entries. > It is a Syntax Error if any element of the LexicallyDeclaredNames of StatementList also occurs in the VarDeclaredNames of StatementList. In other words, if a `let`/`const` variable is declared in the same scope as another variable with the same name, a parsing error should be thrown. This is implemented with the following steps: * When entering a function scope, create an empty set of var-declared names * When entering a block scope, create a new empty set of lexically-declared names. Additionally, push the current set of var-declared names, and work with a new empty set. * When exiting a block scope, merge the set of var-declared names from the block with the set of var-declared names from the parent scope. * When parsing a binding pattern (e.g. a variable declaration or function parameters), check if the bound identifier clashes with any lexically-declared names (if the bound identifier is non-lexical), or any variable names at all (if the bound identifier is lexical). If so, raise a parsing error. Otherwise, add it to the current lexically-declared name set or var-declared name set as appropriate. The merging behavior for var-declared names in the third bullet-point is necessary due to how `var` scoping works. For example, this should be a syntax error: ```js { var foo = 1; } let foo = 1; ``` But this should not be a syntax error: ```js { var foo = 1; { let foo = 1; } } ```
not-an-aardvark
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Jun 3, 2017
This code was added to work around a bug in acorn (acornjs/acorn#487), which has since been fixed.
not-an-aardvark
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Jun 3, 2017
This code was added to work around a bug in acorn (acornjs/acorn#487), which has since been fixed.
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Using Acorn 4.0.3:
I expected a syntax error to get thrown, because this code is invalid syntax according to the spec. However, acorn parsed it without any errors.
Relevant portion of the spec:
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