From 5ddd8593615c8884ecda34befbb3053427491dd3 Mon Sep 17 00:00:00 2001 From: Michael Dyck Date: Fri, 24 Nov 2023 11:03:33 -0500 Subject: [PATCH] Bring together all the prose about ObjectLiteral being a cover for ObjectAssignmentPattern. --- spec.html | 25 +++++++++++++------------ 1 file changed, 13 insertions(+), 12 deletions(-) diff --git a/spec.html b/spec.html index 974e33b47e..cabb4ec84c 100644 --- a/spec.html +++ b/spec.html @@ -18401,17 +18401,7 @@

Syntax

|MethodDefinition| is defined in .

-

In certain contexts, |ObjectLiteral| is used as a cover grammar for a more restricted secondary grammar. The |CoverInitializedName| production is necessary to fully cover these secondary grammars. However, use of this production results in an early Syntax Error in normal contexts where an actual |ObjectLiteral| is expected.

-

For example, consider:

- 

-          let o = {f = 1};
-
-

`{f = 1}` is parsed as an |ObjectLiteral| with a |CoverInitializedName|, which results in a Syntax Error via one of the early error rules in the next section.

-

In contrast, consider:

- 

-          ({f = 1} = {f: 2});
-
-

Here, `{f = 1}` is again initially parsed as an |ObjectLiteral| with a |CoverInitializedName|, but since it's the |LeftHandSideExpression| of an |AssignmentExpression|, it must cover an |AssignmentPattern|, so the |ObjectLiteral| and |CoverInitializedName| are not subject to early error rules. Instead, `{f = 1}` is reparsed as an |ObjectAssignmentPattern| with an |AssignmentProperty|, and there is no Syntax Error.

+

See the next section for the significance of |CoverInitializedName|.

 @@ -18445,7 +18435,18 @@

Static Semantics: Early Errors

-

This production exists so that |ObjectLiteral| can serve as a cover grammar for |ObjectAssignmentPattern|. It cannot occur in an actual object initializer.

+

Elsewhere in this specification, there are early error rules that, under certain circumstances, require that a |LeftHandSideExpression| must cover an |AssignmentPattern|. Consequently, |ObjectLiteral| serves as a cover grammar for |ObjectAssignmentPattern|. The |CoverInitializedName| production is necessary to fully cover |AssignmentProperty|, but is not valid within an actual object initializer.

+

Specifically, in a context where an actual |ObjectLiteral| is expected, the above early error rule prevents the use of |CoverInitializedName|. But in cases where |ObjectLiteral| is used as a cover grammar, the semantics of "must cover" state that the Parse Nodes within the |ObjectLiteral| are not subject to early error rules, and so |CoverInitializedName| is allowed.

+

For example, consider:

+ 

+            let o = {f = 1};
+
+

`{f = 1}` is parsed as an |ObjectLiteral| with a |CoverInitializedName|, which results in a Syntax Error via this early error rule.

+

In contrast, consider:

+ 

+            ({f = 1} = {f: 2});
+
+

Here, `{f = 1}` is again initially parsed as an |ObjectLiteral| with a |CoverInitializedName|, but since it's the |LeftHandSideExpression| of an |AssignmentExpression|, it must cover an |AssignmentPattern|, so the |ObjectLiteral| and |CoverInitializedName| are not subject to early error rules. Instead, `{f = 1}` is reparsed as an |ObjectAssignmentPattern| with an |AssignmentProperty|, and there is no Syntax Error.