Add other grammar compactions

Using a number of strategies, there are some other grammar compactions
and regularizations that stand out as similarly possible, so let's do
those.

In doing these, we prefer to pick a factoring of the grammar that
calls for the least lookahead or backtracking.

Author: traviscross

src/comments.md

@@ -4,8 +4,7 @@ r[comments]
 r[comments.syntax]
 ```grammar,lexer
 @root LINE_COMMENT ->
-      `//` (~[`/` `!` LF] | `//`) ~LF*
-    | `//`
+    `//` ( ( ~[`/` `!` LF] | `//` ) ~LF* )?
 
 BLOCK_COMMENT ->
       `/*`

src/expressions/operator-expr.md

@@ -256,8 +256,7 @@ r[expr.negate]
 r[expr.negate.syntax]
 ```grammar,expressions
 NegationExpression ->
-      `-` Expression
-    | `!` Expression
+    ( `-` | `!`)  Expression
 ```
 
 r[expr.negate.intro]

src/items/functions.md

@@ -16,15 +16,17 @@ ItemSafety -> `safe`[^extern-safe] | `unsafe`
 Abi -> STRING_LITERAL | RAW_STRING_LITERAL
 
 FunctionParameters ->
-      SelfParam `,`?
-    | (SelfParam `,`)? FunctionParam (`,` FunctionParam)* `,`?
+      SelfParam ( `,` FunctionParams? )?
+    | FunctionParams
 
 SelfParam -> OuterAttribute* ( ShorthandSelf | TypedSelf )
 
 ShorthandSelf -> ( `&` Lifetime? )? `mut`? `self`
 
 TypedSelf -> `mut`? `self` `:` Type
 
+FunctionParams -> FunctionParam ( `,` FunctionParam )* `,`?
+
 FunctionParam -> OuterAttribute* ( FunctionParamPattern | `...` | Type[^fn-param-2015] )
 
 FunctionParamPattern -> PatternNoTopAlt `:` ( Type | `...` )

src/statements.md

@@ -61,8 +61,11 @@ r[statement.let.syntax]
 LetStatement ->
     OuterAttribute* `let` PatternNoTopAlt ( `:` Type )?
     (
-          `=` Expression
-        | `=` Expression _except [LazyBooleanExpression] or end with a `}`_ `else` BlockExpression
+        `=` (
+            Expression _except [LazyBooleanExpression] or end with a `}`_
+            `else` BlockExpression
+          | Expression
+        )
     )? `;`
 ```
 

src/tokens.md

@@ -659,8 +659,8 @@ r[lex.token.literal.float.syntax]
 FLOAT_LITERAL ->
     DEC_LITERAL (
         `.` _not immediately followed by `.`, `_` or an XID_Start character_
-      | `.` DEC_LITERAL SUFFIX_NO_E?
-      | ( `.` DEC_LITERAL )? FLOAT_EXPONENT SUFFIX?
+      | `.` DEC_LITERAL ( SUFFIX_NO_E? | FLOAT_EXPONENT SUFFIX? )
+      | FLOAT_EXPONENT SUFFIX?
     )
 
 FLOAT_EXPONENT ->
@@ -716,8 +716,11 @@ r[lex.token.literal.reserved.syntax]
 RESERVED_NUMBER ->
       BIN_LITERAL [`2`-`9`]
     | OCT_LITERAL [`8`-`9`]
-    | ( BIN_LITERAL | OCT_LITERAL | HEX_LITERAL ) `.` _not immediately followed by `.`, `_` or an XID_Start character_
-    | ( BIN_LITERAL | OCT_LITERAL ) (`e`|`E`)
+    | ( BIN_LITERAL | OCT_LITERAL ) (
+          `.` _not immediately followed by `.`, `_` or an XID_Start character_
+        | (`e`|`E`)
+      )
+    | HEX_LITERAL `.` _not immediately followed by `.`, `_` or an XID_Start character_
     | `0b` `_`* <end of input or not BIN_DIGIT>
     | `0o` `_`* <end of input or not OCT_DIGIT>
     | `0x` `_`* <end of input or not HEX_DIGIT>

src/trait-bounds.md

@@ -7,9 +7,9 @@ TypeParamBounds -> TypeParamBound ( `+` TypeParamBound )* `+`?
 
 TypeParamBound -> Lifetime | TraitBound | UseBound
 
-TraitBound ->
-      ( `?` | ForLifetimes )? TypePath
-    | `(` ( `?` | ForLifetimes )? TypePath `)`
+TraitBound -> `(` TraitBoundNoParens `)` | TraitBoundNoParens
+
+TraitBoundNoParens ->  ( `?` | ForLifetimes )? TypePath
 
 LifetimeBounds -> ( Lifetime `+` )* Lifetime?
 

src/types/function-pointer.md

@@ -21,7 +21,7 @@ MaybeNamedParam ->
     OuterAttribute* ( ( IDENTIFIER | `_` ) `:` )? Type
 
 MaybeNamedFunctionParametersVariadic ->
-    ( MaybeNamedParam `,` )* MaybeNamedParam `,` OuterAttribute* `...`
+    MaybeNamedParam ( `,` MaybeNamedParam )* `,` OuterAttribute* `...`
 ```
 
 r[type.fn-pointer.intro]