Change classMemberDeclaration to memberDeclaration

The grammar in the language specification used to have a non-terminal `<classMemberDeclaration>`, and the spec parser had special variants like `<mixinMemberDeclaration>` and `<extensionTypeMemberDeclaration>`. This would be useful if different membered declarations have different syntax, and that was once the plan.

However, we never actually got around to make this kind of distinction, and it's a more useful approach to report disallowed kinds of member declarations using ad-hoc compile-time checks (which is also what the implementations do already).

This PR changes all references to these non-terminals to the plain name `<memberDeclaration>` and adjusts the accompanying explanations accordingly.

Author: eernstg

specification/dartLangSpec.tex

@@ -41,6 +41,11 @@
 % version of the language which will actually be specified by the next stable
 % release of this document.
 %
+% Oct 2025
+% - Simplify the member declaration grammar by using a single `memberDeclaration`
+%   to derive all kinds of member declarations (for a class, a mixin, etc),
+%   rather than having a dedicated `classMemberDeclaration`.
+%
 % Sep 2025
 % - Remove the rules about DartDoc comments. This topic is now handled by each
 %   of the tools that process those comments in any way.
@@ -2831,12 +2836,12 @@ \section{Classes}
 <classDeclaration> ::=
   \ABSTRACT? \CLASS{} <typeIdentifier> <typeParameters>?
   \gnewline{} <superclass>? <interfaces>?
-  \gnewline{} `{' (<metadata> <classMemberDeclaration>)* `}'
+  \gnewline{} `{' (<metadata> <memberDeclaration>)* `}'
   \alt \ABSTRACT? \CLASS{} <mixinApplicationClass>
 
 <typeNotVoidList> ::= <typeNotVoid> (`,' <typeNotVoid>)*
 
-<classMemberDeclaration> ::= <declaration> `;'
+<memberDeclaration> ::= <declaration> `;'
   \alt <methodSignature> <functionBody>
 
 <methodSignature> ::= <constructorSignature> <initializers>?
@@ -2879,6 +2884,8 @@ \section{Classes}
 
 \LMHash{}%
 A class has constructors, instance members and static members.
+The members are declared by
+\IndexCustom{member declarations}{member declaration}.
 The \IndexCustom{instance members}{members!instance} of a class
 are its instance methods, getters, setters and instance variables.
 The \IndexCustom{static members}{members!static} of a class
@@ -5963,7 +5970,7 @@ \subsection{Mixin Declaration}
 
 \LMHash{}%
 A mixin defines zero or more
-\IndexCustom{mixin member declarations}{mixin!member declaration},
+\IndexCustom{member declarations}{member declaration},
 zero or more
 \IndexCustom{required superinterfaces}{mixin!required superinterface},
 one
@@ -5994,7 +6001,7 @@ \subsection{Mixin Declaration}
 \begin{grammar}
 <mixinDeclaration> ::= \MIXIN{} <typeIdentifier> <typeParameters>?
   \gnewline{} (\ON{} <typeNotVoidList>)? <interfaces>?
-  \gnewline{} `\{' (<metadata> <classMemberDeclaration>)* `\}'
+  \gnewline{} `\{' (<metadata> <memberDeclaration>)* `\}'
 \end{grammar}
 
 \LMHash{}%
@@ -6081,7 +6088,7 @@ \subsection{Mixin Declaration}
 with the \NoIndex{required superinterface}s $T_1$, \ldots, $T_n$,
 the \NoIndex{combined superinterface} $M_S$,
 \NoIndex{implemented interface}s $I_1$, \ldots, $I_k$
-and the instance members declared in $M$ as \Index{mixin member declarations}.
+and the instance members declared in $M$ as \Index{member declarations}.
 
 
 \subsection{Mixin Application}
@@ -6095,7 +6102,7 @@ \subsection{Mixin Application}
 $M$ be a mixin with \NoIndex{required superinterface}s $T_1$, \ldots, $T_n$,
 \NoIndex{combined superinterface} $M_S$,
 \NoIndex{implemented interfaces} $I_1$, \ldots, $I_k$ and
-\metavar{members} as \NoIndex{mixin member declarations},
+\metavar{members} as \NoIndex{member declarations},
 and let $N$ be a name.
 
 \LMHash{}%
@@ -6224,7 +6231,7 @@ \section{Extensions}
 \begin{grammar}
 <extensionDeclaration> ::= \gnewline{}
   \EXTENSION{} <typeIdentifierNotType>? <typeParameters>? \ON{} <type>
-  \gnewline{} `\{' (<metadata> <classMemberDeclaration>)* `\}'
+  \gnewline{} `\{' (<metadata> <memberDeclaration>)* `\}'
 \end{grammar}
 
 \LMHash{}%