Adjusted spec to outlaw built-in identifiers in type annotations.

docs/language/dartLangSpec.tex

 \documentclass{article}
 \usepackage{epsfig}
 \usepackage{color}
 \usepackage{dart}
 \usepackage{bnf}
 \usepackage{hyperref}
 \usepackage{lmodern}
 \usepackage[T1]{fontenc}
 \newcommand{\code}[1]{{\sf #1}}
 \title{Dart Programming Language  Specification  \\
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     .
 
 
 
 {\bf qualified:}
       identifier (`{\escapegrammar .}' identifier)?
       .
 \end{grammar}
 
 \LMHash{}
-A built-in identifier is one of the identifiers produced by the production {\em BUILT\_IN\_IDENTIFIER}. It is a compile-time error if a built-in identifier is used as the declared name of a prefix, class, type parameter or type alias. It is a compile-time error to use a built-in identifier other than \DYNAMIC{} as a type annotation or type parameter.
+A built-in identifier is one of the identifiers produced by the production {\em BUILT\_IN\_IDENTIFIER}.
+It is a compile-time error if a built-in identifier is used as the declared name of a prefix, class, type parameter or type alias.
+It is a compile-time error to use a built-in identifier other than \DYNAMIC{} in a type annotation or type parameter.

[Lasse Reichstein Nielsen, 2017/02/19 11:43:53]

The "in" is somewhat vague, but I think it works. We should just be careful in
the future (good thing "extends" is a reserved word).

If we make Function a built-in identifier, it needs to be added here as an
exception too.

[eernst, 2017/02/20 08:25:12]

Acknowledged!

 
 \rationale{
 Built-in identifiers are identifiers that are used as keywords in Dart, but are not reserved words in Javascript. To minimize incompatibilities when porting Javascript code to Dart, we do not make these into reserved words. A built-in identifier may not be used to name a class or type. In other words, they are treated as reserved words when used as types.  This eliminates many confusing situations without causing compatibility problems. After all, a Javascript program has no type declarations or annotations so no clash can occur.  Furthermore, types should begin with an uppercase letter (see the appendix) and so no clash should occur in any Dart user program anyway.
 }
 
 \LMHash{}
 It is a compile-time error if any of the identifiers \ASYNC, \AWAIT{} or \YIELD{} is used as an identifier in a function body marked with either \ASYNC{}, \ASYNC* or \SYNC*.
 
 \rationale{
 For compatibility reasons, new constructs cannot  rely upon new reserved words or even built-in identifiers. However, the constructs above are only usable in contexts that require special markers introduced concurrently with these constructs, so no old code could use them. Hence the restriction, which treats these names as reserved words in a limited context.
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 The invariant that each normative paragraph is associated with a line
 containing the text \LMHash{} should be maintained.  Extra occurrences
 of \LMHash{} can be added if needed, e.g., in order to make
 individual \item{}s in itemized lists addressable.  Each \LM.. command
 must occur on a separate line.  \LMHash{} must occur immediately
 before the associated paragraph, and \LMLabel must occur immediately
 after the associated \section{}, \subsection{} etc.
 
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