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Specify the grammar formulations for attributes #65

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Specify the grammar formulations for attributes #65

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61 changes: 61 additions & 0 deletions proposals/0002-cxx-attributes.md
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Expand Up @@ -124,4 +124,65 @@ Below are a few more examples of C++ attributes that we could support:
}
}
```
## Detailed design

The simplest explanation of this feature is supporting C++11 attribute syntax on
all shared grammar elements between HLSL and C++. This spec attempts to detail
some of the grammar and parsing implications and will specify the process by
which existing attributes will convert to C++ attributes.
### Attribute Parsing
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Best to add a blank line before the section header for the benefit of those reading the markdown directly (I don't think it makes a difference in the rendered doc)


This proposal introduces new grammar formulations for parsing attributes
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I'd probably drop the word "new" - "introduces grammar formulations" is clear

matching some formulations from C++ `dcl.attr.grammar`. Specifically:

```ebnf
attribute-specifier-seq: [ attribute-specifier-seq ], attribute-specifier
attribute-specifier: "[" , "[" , attribute-list , "]" , "]"
attribute-list: [ attribute ] ||
attribute-list , "," , [attribute] ||
{ attribute } ||
attribute-list , "," , { attribute }
attribute: attribute-token , [attribute-argument-clause]
attribute-token: identifier ||
attribute-scoped-token
attribute-scoped-token: attribute-namespace , "::" , identifier
attribute-namespace: identifier
attribute-argument-clause: "(" , balanced-token-seq , ")"
balanced-token-seq: [ balanced-token ] ||
balanced-token-seq , balanced-token
balanced-token: "(" , balanced-token-seq , ")"
"[" , balanced-token-seq , "]"
"{" , balanced-token-seq , "}"
```

In contrast to existing HLSL annotations and Microsoft-style attributes, these
attribute identifiers are case-sensitive `identifier` tokens.
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This is probably clear enough from context and I'm just being pedantic, but "attribute identifiers are case-sensitive identifier tokens" isn't strictly true (there's also the attribute-scoped-token formulation).

Maybe:

In contrast to existing HLSL annotations and Microsoft-style attributes, these formulations use case-sensitive identifier tokens



#### Statements

```ebnf
statement: [ attribute-specifier-seq ] , expression-statement ||
[ attribute-specifier-seq ] , compound-statement ||
[ attribute-specifier-seq ] , selection-statement ||
[ attribute-specifier-seq ] , iteration-statement ||
[ attribute-specifier-seq ] , jump-statement ||
declaration-statement
labeled-statement
labeled-statement: [ attribute-specifier-seq ] , "case" , constant-expression , ":" , statement
[ attribute-specifier-seq ] , "default" , ":" , statement
```

#### Declarations

The `attribute-specifier-seq` element supports annotating type declarations. The
following grammar formulations are valid:

```ebnf
class-key: "class" || "struct"
class-declaration: class-key , attribute-specifier-seq , identifier

alias-declaration: "using" , identifier , [ attribute-specifier-seq ] , "=" , type-id , ";"
```

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