Addresses issue #1283.

Updates §6.2.5 as per issue and also changes the descriptive style to the proscriptive requirement of the Standard

Author: Nigel-Ecma

standard/expressions.md

@@ -4161,7 +4161,7 @@ equality_expression
     ;
 ```
 
-> *Note*: Lookup for the right operand of the `is` operator must first test as a *type*, then as an *expression* which may span multiple tokens. In the case where the operand is an *expreesion*, the pattern expression must have precedence at least as high as *shift_expression*. *end note*
+> *Note*: Lookup for the right operand of the `is` operator must first test as a *type*, then as an *expression* which may span multiple tokens. In the case where the operand is an *expression*, the pattern expression must have precedence at least as high as *shift_expression*. *end note*
 
 The `is` operator is described in [§12.12.12](expressions.md#121212-the-is-operator) and the `as` operator is described in [§12.12.13](expressions.md#121213-the-as-operator).
 

standard/lexical-structure.md

@@ -52,7 +52,18 @@ Every compilation unit in a C# program shall conform to the *compilation_unit*
 
 ### 6.2.5 Grammar ambiguities
 
-The productions for *simple_name* ([§12.8.4](expressions.md#1284-simple-names)) and *member_access* ([§12.8.7](expressions.md#1287-member-access)) can give rise to ambiguities in the grammar for expressions.
+The productions for:
+
+- *simple_name* ([§12.8.4](expressions.md#1284-simple-names)),
+- *member_access* ([§12.8.7](expressions.md#1287-member-access)),
+- *null_conditional_member_access* ([§12.8.8](expressions.md#1288-null-conditional-member-access)),
+- *dependent_access* ([§12.8.8](expressions.md#1288-dependent-access)),
+- *base_access* ([§12.8.15](expressions.md#12815-base-access)) and
+- *pointer_member_access* ([§23.6.3](unsafe-code.md#2363-pointer-member-access));
+
+(the “disambiguated productions”) can give rise to ambiguities in the grammar for expressions.
+
+These productions occur in contexts where a value can occur in an expression, and have one or more alternatives that end with the grammar “`identifier type_argument_list?`”. It is the optional *type_argument_list* which results in the possible ambiguity.
 
 > *Example*: The statement:
 >
@@ -65,16 +76,17 @@ The productions for *simple_name* ([§12.8.4](expressions.md#1284-simple-names))
 >
 > *end example*
 
-If a sequence of tokens can be parsed (in context) as a *simple_name* ([§12.8.4](expressions.md#1284-simple-names)), *member_access* ([§12.8.7](expressions.md#1287-member-access)), or *pointer_member_access* ([§23.6.3](unsafe-code.md#2363-pointer-member-access)) ending with a *type_argument_list* ([§8.4.2](types.md#842-type-arguments)), the token immediately following the closing `>` token is examined, to see if it is
+If a sequence of tokens can be parsed, in context, as one of the disambiguated productions
+including an optional *type_argument_list* ([§8.4.2](types.md#842-type-arguments)), then
+the token immediately following the closing `>` token shall be examined and if it is:
 
-- One of `(  )  ]  }  :  ;  ,  .  ?  ==  !=  |  ^  &&  ||  &  [`; or
-- One of the relational operators `<  <=  >=  is as`; or
-- A contextual query keyword appearing inside a query expression; or
-- In certain contexts, *identifier* is treated as a disambiguating token. Those contexts are where the sequence of tokens being disambiguated is immediately preceded by one of the keywords `is`, `case` or `out`, or arises while parsing the first element of a tuple literal (in which case the tokens are preceded by `(` or `:` and the identifier is followed by a `,`) or a subsequent element of a tuple literal.
+- one of `(  )  ]  }  :  ;  ,  .  ?  ==  !=  |  ^  &&  ||  &  [`; or
+- one of the relational operators `<  <=  >=  is as`; or
+- a contextual query keyword appearing inside a query expression.
 
-If the following token is among this list, or an identifier in such a context, then the *type_argument_list* is retained as part of the *simple_name*, *member_access* or  *pointer_member-access* and any other possible parse of the sequence of tokens is discarded. Otherwise, the *type_argument_list* is not considered to be part of the *simple_name*, *member_access* or *pointer_member_access*, even if there is no other possible parse of the sequence of tokens.
+then the *type_argument_list* shall be retained as part of the disambiguated production and any other possible parse of the sequence of tokens discarded. Otherwise, the tokens parsed as a *type_argument_list* shall not be considered to be part of the disambiguated production, even if there is no other possible parse of those tokens.
 
-> *Note*: These rules are not applied when parsing a *type_argument_list* in a *namespace_or_type_name* ([§7.8](basic-concepts.md#78-namespace-and-type-names)). *end note*
+> *Note*: These disambiguation rules shall not be applied when parsing other productions even if they similarly end in “`identifier type_argument_list?`”; such productions shall be parsed as normal. Examples include: *namespace_or_type_name* ([§7.8](basic-concepts.md#78-namespace-and-type-names)); *named_entity* ([§12.8.23](expressions.md#12823-named-entity)); *null_conditional_projection_initializer* ([§12.8.8](expressions.md#§1288-null_conditional-projection-initializer)); and *qualified_alias_member* ([§14.8.1](namespaces.md#1481-qualified-alias-member)). *end note*
 <!-- markdownlint-disable MD028 -->
 
 <!-- markdownlint-enable MD028 -->
@@ -124,7 +136,7 @@ If the following token is among this list, or an identifier in such a context, t
 >
 > *end example*
 
-When recognising a *relational_expression* ([§12.12.1](expressions.md#12121-general)) if both the “*relational_expression* `is` *type*” and “*relational_expression* `is` *constant_pattern*” alternatives are applicable, and *type* resolves to an accessible type, then the “*relational_expression* `is` *type*” alternative shall be chosen.
+When recognising a *relational_expression* ([§12.12.1](expressions.md#12121-general)) if both the “*relational_expression* `is` *type*” and “*relational_expression* `is` *pattern*” alternatives are applicable, and *type* resolves to an accessible type, then the “*relational_expression* `is` *type*” alternative shall be chosen.
 
 ## 6.3 Lexical analysis
 
@@ -189,7 +201,7 @@ Line terminators divide the characters of a C# compilation unit into lines.
 ```ANTLR
 New_Line
     : New_Line_Character
-    | '\u000D\u000A'    // carriage return, line feed 
+    | '\u000D\u000A'    // carriage return, line feed
     ;
 ```
 
@@ -262,19 +274,19 @@ fragment Input_Character
     // anything but New_Line_Character
     : ~('\u000D' | '\u000A'   | '\u0085' | '\u2028' | '\u2029')
     ;
-    
+
 fragment New_Line_Character
     : '\u000D'  // carriage return
     | '\u000A'  // line feed
     | '\u0085'  // next line
     | '\u2028'  // line separator
     | '\u2029'  // paragraph separator
     ;
-    
+
 fragment Delimited_Comment
     : '/*' Delimited_Comment_Section* ASTERISK+ '/'
     ;
-    
+
 fragment Delimited_Comment_Section
     : SLASH
     | ASTERISK* Not_Slash_Or_Asterisk
@@ -428,7 +440,7 @@ fragment Available_Identifier
 fragment Escaped_Identifier
     // Includes keywords and contextual keywords prefixed by '@'.
     // See note below.
-    : '@' Basic_Identifier 
+    : '@' Basic_Identifier
     ;
 
 fragment Basic_Identifier
@@ -664,36 +676,36 @@ fragment Decimal_Integer_Literal
 fragment Decorated_Decimal_Digit
     : '_'* Decimal_Digit
     ;
-       
+
 fragment Decimal_Digit
     : '0'..'9'
     ;
-    
+
 fragment Integer_Type_Suffix
     : 'U' | 'u' | 'L' | 'l' |
       'UL' | 'Ul' | 'uL' | 'ul' | 'LU' | 'Lu' | 'lU' | 'lu'
     ;
-    
+
 fragment Hexadecimal_Integer_Literal
     : ('0x' | '0X') Decorated_Hex_Digit+ Integer_Type_Suffix?
     ;
 
 fragment Decorated_Hex_Digit
     : '_'* Hex_Digit
     ;
-       
+
 fragment Hex_Digit
     : '0'..'9' | 'A'..'F' | 'a'..'f'
     ;
-   
+
 fragment Binary_Integer_Literal
     : ('0b' | '0B') Decorated_Binary_Digit+ Integer_Type_Suffix?
     ;
 
 fragment Decorated_Binary_Digit
     : '_'* Binary_Digit
     ;
-       
+
 fragment Binary_Digit
     : '0' | '1'
     ;
@@ -723,14 +735,14 @@ To permit the smallest possible `int` and `long` values to be written as integer
 > 1_2__3___4____5      // decimal, int
 > _123                 // not a numeric literal; identifier due to leading _
 > 123_                 // invalid; no trailing _allowed
-> 
+>
 > 0xFf                 // hex, int
 > 0X1b_a0_44_fEL       // hex, long
 > 0x1ade_3FE1_29AaUL   // hex, ulong
 > 0x_abc               // hex, int
 > _0x123               // not a numeric literal; identifier due to leading _
 > 0xabc_               // invalid; no trailing _ allowed
-> 
+>
 > 0b101                // binary, int
 > 0B1001_1010u         // binary, uint
 > 0b1111_1111_0000UL   // binary, ulong
@@ -774,7 +786,7 @@ If no *Real_Type_Suffix* is specified, the type of the *Real_Literal* is `double
 - A real literal suffixed by `D` or `d` is of type `double`.
   > *Example*: The literals `1d`, `1.5d`, `1e10d`, and `123.456D` are all of type `double`. *end example*
 - A real literal suffixed by `M` or `m` is of type `decimal`.
-  > *Example*: The literals `1m`, `1.5m`, `1e10m`, and `123.456M` are all of type `decimal`. *end example*  
+  > *Example*: The literals `1m`, `1.5m`, `1e10m`, and `123.456M` are all of type `decimal`. *end example*
   This literal is converted to a `decimal` value by taking the exact value, and, if necessary, rounding to the nearest representable value using banker’s rounding ([§8.3.8](types.md#838-the-decimal-type)). Any scale apparent in the literal is preserved unless the value is rounded.
   > *Note*: Hence, the literal `2.900m` will be parsed to form the `decimal` with sign `0`, coefficient `2900`, and scale `3`. *end note*
 
@@ -812,24 +824,24 @@ A character literal represents a single character, and consists of a character i
 Character_Literal
     : '\'' Character '\''
     ;
-    
+
 fragment Character
     : Single_Character
     | Simple_Escape_Sequence
     | Hexadecimal_Escape_Sequence
     | Unicode_Escape_Sequence
     ;
-    
+
 fragment Single_Character
     // anything but ', \, and New_Line_Character
     : ~['\\\u000D\u000A\u0085\u2028\u2029]
     ;
-    
+
 fragment Simple_Escape_Sequence
     : '\\\'' | '\\"' | '\\\\' | '\\0' | '\\a' | '\\b' |
       '\\f' | '\\n' | '\\r' | '\\t' | '\\v'
     ;
-    
+
 fragment Hexadecimal_Escape_Sequence
     : '\\x' Hex_Digit Hex_Digit? Hex_Digit? Hex_Digit?
     ;
@@ -890,11 +902,11 @@ String_Literal
     : Regular_String_Literal
     | Verbatim_String_Literal
     ;
-    
+
 fragment Regular_String_Literal
     : '"' Regular_String_Literal_Character* '"'
     ;
-    
+
 fragment Regular_String_Literal_Character
     : Single_Regular_String_Literal_Character
     | Simple_Escape_Sequence
@@ -910,16 +922,16 @@ fragment Single_Regular_String_Literal_Character
 fragment Verbatim_String_Literal
     : '@"' Verbatim_String_Literal_Character* '"'
     ;
-    
+
 fragment Verbatim_String_Literal_Character
     : Single_Verbatim_String_Literal_Character
     | Quote_Escape_Sequence
     ;
-    
+
 fragment Single_Verbatim_String_Literal_Character
     : ~["]     // anything but quotation mark (U+0022)
     ;
-    
+
 fragment Quote_Escape_Sequence
     : '""'
     ;
@@ -1102,7 +1114,7 @@ Pre-processing directives are not part of the syntactic grammar of C#. However,
 > #endif
 > #if B
 >     void H() {}
-> #else    
+> #else
 >     void I() {}
 > #endif
 > }
@@ -1155,11 +1167,11 @@ Pre-processing expressions can occur in `#if` and `#elif` directives. The operat
 fragment PP_Expression
     : PP_Whitespace? PP_Or_Expression PP_Whitespace?
     ;
-    
+
 fragment PP_Or_Expression
     : PP_And_Expression (PP_Whitespace? '||' PP_Whitespace? PP_And_Expression)*
     ;
-    
+
 fragment PP_And_Expression
     : PP_Equality_Expression (PP_Whitespace? '&&' PP_Whitespace?
       PP_Equality_Expression)*
@@ -1169,12 +1181,12 @@ fragment PP_Equality_Expression
     : PP_Unary_Expression (PP_Whitespace? ('==' | '!=') PP_Whitespace?
       PP_Unary_Expression)*
     ;
-    
+
 fragment PP_Unary_Expression
     : PP_Primary_Expression
     | '!' PP_Whitespace? PP_Unary_Expression
     ;
-    
+
 fragment PP_Primary_Expression
     : TRUE
     | FALSE
@@ -1282,15 +1294,15 @@ fragment PP_Conditional
 fragment PP_If_Section
     : 'if' PP_Whitespace PP_Expression
     ;
-    
+
 fragment PP_Elif_Section
     : 'elif' PP_Whitespace PP_Expression
     ;
-    
+
 fragment PP_Else_Section
     : 'else'
     ;
-    
+
 fragment PP_Endif
     : 'endif'
     ;
@@ -1488,11 +1500,11 @@ fragment PP_Line_Indicator
     | DEFAULT
     | 'hidden'
     ;
-    
+
 fragment PP_Compilation_Unit_Name
     : '"' PP_Compilation_Unit_Name_Character* '"'
     ;
-    
+
 fragment PP_Compilation_Unit_Name_Character
     // Any Input_Character except "
     : ~('\u000D' | '\u000A'   | '\u0085' | '\u2028' | '\u2029' | '"')