Expose internal CustomToken trait only through __private module

This trait is marked not public API and can only be implemented through
the public macros (custom_keyword and custom_punctuation).

src/custom_keyword.rs

@@ -128,7 +128,7 @@ macro_rules! custom_keyword {
 macro_rules! impl_parse_for_custom_keyword {
     ($ident:ident) => {
         // For peek.
-        impl $crate::token::CustomToken for $ident {
+        impl $crate::__private::CustomToken for $ident {
             fn peek(cursor: $crate::buffer::Cursor) -> $crate::__private::bool {
                 if let $crate::__private::Some((ident, _rest)) = cursor.ident() {
                     ident == $crate::__private::stringify!($ident)

src/custom_punctuation.rs

@@ -113,7 +113,7 @@ macro_rules! custom_punctuation {
 #[macro_export]
 macro_rules! impl_parse_for_custom_punctuation {
     ($ident:ident, $($tt:tt)+) => {
-        impl $crate::token::CustomToken for $ident {
+        impl $crate::__private::CustomToken for $ident {
             fn peek(cursor: $crate::buffer::Cursor) -> $crate::__private::bool {
                 $crate::__private::peek_punct(cursor, $crate::stringify_punct!($($tt)+))
             }

src/export.rs

@@ -57,6 +57,10 @@ pub use crate::token::parsing::{peek_punct, punct as parse_punct};
 #[doc(hidden)]
 pub use crate::token::printing::punct as print_punct;
 
+#[cfg(feature = "parsing")]
+#[doc(hidden)]
+pub use crate::token::private::CustomToken;
+
 #[cfg(feature = "proc-macro")]
 #[doc(hidden)]
 pub type TokenStream = proc_macro::TokenStream;

src/token.rs

@@ -88,6 +88,8 @@
 //! [Printing]: https://docs.rs/quote/1.0/quote/trait.ToTokens.html
 //! [`Span`]: https://docs.rs/proc-macro2/1.0/proc_macro2/struct.Span.html
 
+#[cfg(feature = "parsing")]
+pub(crate) use self::private::CustomToken;
 use self::private::WithSpan;
 #[cfg(feature = "parsing")]
 use crate::buffer::Cursor;
@@ -134,7 +136,9 @@ pub trait Token: private::Sealed {
     fn display() -> &'static str;
 }
 
-mod private {
+pub(crate) mod private {
+    #[cfg(feature = "parsing")]
+    use crate::buffer::Cursor;
     use proc_macro2::Span;
 
     #[cfg(feature = "parsing")]
@@ -147,6 +151,14 @@ mod private {
     pub struct WithSpan {
         pub span: Span,
     }
+
+    // Not public API.
+    #[doc(hidden)]
+    #[cfg(feature = "parsing")]
+    pub trait CustomToken {
+        fn peek(cursor: Cursor) -> bool;
+        fn display() -> &'static str;
+    }
 }
 
 #[cfg(feature = "parsing")]
@@ -218,14 +230,6 @@ impl_low_level_token!("punctuation token" Punct punct);
 impl_low_level_token!("literal" Literal literal);
 impl_low_level_token!("token" TokenTree token_tree);
 
-// Not public API.
-#[doc(hidden)]
-#[cfg(feature = "parsing")]
-pub trait CustomToken {
-    fn peek(cursor: Cursor) -> bool;
-    fn display() -> &'static str;
-}
-
 #[cfg(feature = "parsing")]
 impl<T: CustomToken> private::Sealed for T {}