Alternative approach with private types

dtolnay · Mar 13, 2023 · 76b38b2 · 76b38b2
1 parent 3eb1954
commit 76b38b2
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Showing 3 changed files with 37 additions and 30 deletions.
diff --git a/src/lib.rs b/src/lib.rs
@@ -619,28 +619,28 @@ macro_rules! quote_spanned {
 #[macro_export]
 macro_rules! quote_spanned {
     ($span:expr=>) => {{
-        let _ = $crate::__private::GetSpan($span).__into_span();
+        let _ = $crate::__private::get_span($span).__into_span();
         $crate::__private::TokenStream::new()
     }};
 
     // Special case rule for a single tt, for performance.
     ($span:expr=> $tt:tt) => {{
         let mut _s = $crate::__private::TokenStream::new();
-        let _span = $crate::__private::GetSpan($span).__into_span();
+        let _span = $crate::__private::get_span($span).__into_span();
         $crate::quote_token_spanned!{$tt _s _span}
         _s
     }};
 
     // Special case rules for two tts, for performance.
     ($span:expr=> # $var:ident) => {{
         let mut _s = $crate::__private::TokenStream::new();
-        let _ = $crate::__private::GetSpan($span).__into_span();
+        let _ = $crate::__private::get_span($span).__into_span();
         $crate::ToTokens::to_tokens(&$var, &mut _s);
         _s
     }};
     ($span:expr=> $tt1:tt $tt2:tt) => {{
         let mut _s = $crate::__private::TokenStream::new();
-        let _span = $crate::__private::GetSpan($span).__into_span();
+        let _span = $crate::__private::get_span($span).__into_span();
         $crate::quote_token_spanned!{$tt1 _s _span}
         $crate::quote_token_spanned!{$tt2 _s _span}
         _s
@@ -649,7 +649,7 @@ macro_rules! quote_spanned {
     // Rule for any other number of tokens.
     ($span:expr=> $($tt:tt)*) => {{
         let mut _s = $crate::__private::TokenStream::new();
-        let _span = $crate::__private::GetSpan($span).__into_span();
+        let _span = $crate::__private::get_span($span).__into_span();
         $crate::quote_each_token_spanned!{_s _span $($tt)*}
         _s
     }};

diff --git a/src/runtime.rs b/src/runtime.rs
@@ -1,8 +1,8 @@
+use self::get_span::{GetSpanInner, GetSpan};
 use crate::{IdentFragment, ToTokens, TokenStreamExt};
 use core::fmt;
 use core::iter;
-use core::ops::{BitOr, Deref};
-use proc_macro2::extra::DelimSpan;
+use core::ops::BitOr;
 use proc_macro2::{Group, Ident, Punct, Spacing, TokenTree};
 
 pub use core::option::Option;
@@ -166,34 +166,41 @@ impl<T: ToTokens> ToTokens for RepInterp<T> {
     }
 }
 
-#[repr(transparent)]
-pub struct GetSpan<T>(pub T);
-
-#[repr(transparent)]
-pub struct WrapperDelimSpan {
-    span: DelimSpan,
+#[inline]
+pub fn get_span<T>(span: T) -> GetSpan<T> {
+    GetSpan(GetSpanInner(span))
 }
 
-impl GetSpan<Span> {
-    #[inline]
-    pub fn __into_span(self) -> Span {
-        self.0
+mod get_span {
+    use core::ops::Deref;
+    use proc_macro2::extra::DelimSpan;
+    use proc_macro2::Span;
+
+    pub struct GetSpan<T>(pub(crate) GetSpanInner<T>);
+
+    pub struct GetSpanInner<T>(pub(crate) T);
+
+    impl GetSpan<Span> {
+        #[inline]
+        pub fn __into_span(self) -> Span {
+            self.0.0
+        }
     }
-}
 
-impl WrapperDelimSpan {
-    #[inline]
-    pub fn __into_span(&self) -> Span {
-        self.span.join()
+    impl GetSpanInner<DelimSpan> {
+        #[inline]
+        pub fn __into_span(&self) -> Span {
+            self.0.join()
+        }
     }
-}
 
-impl Deref for GetSpan<DelimSpan> {
-    type Target = WrapperDelimSpan;
+    impl Deref for GetSpan<DelimSpan> {
+        type Target = GetSpanInner<DelimSpan>;
 
-    #[inline]
-    fn deref(&self) -> &Self::Target {
-        unsafe { &*(self as *const GetSpan<DelimSpan> as *const WrapperDelimSpan) }
+        #[inline]
+        fn deref(&self) -> &Self::Target {
+            &self.0
+        }
     }
 }
 

diff --git a/tests/ui/wrong-type-span.stderr b/tests/ui/wrong-type-span.stderr
@@ -1,9 +1,9 @@
-error[E0599]: no method named `__into_span` found for struct `GetSpan<&str>` in the current scope
+error[E0599]: no method named `__into_span` found for struct `__private::get_span::GetSpan<&str>` in the current scope
  --> tests/ui/wrong-type-span.rs:6:5
   |
 6 |     quote_spanned!(span=> #x);
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^ method not found in `GetSpan<&str>`
   |
   = note: the method was found for
-          - `GetSpan<Span>`
+          - `__private::get_span::GetSpan<Span>`
   = note: this error originates in the macro `quote_spanned` (in Nightly builds, run with -Z macro-backtrace for more info)