Use Var wrapper only for Pointer formatting

Author: dtolnay

impl/src/fmt.rs

@@ -3,7 +3,7 @@ use crate::attr::{Display, Trait};
 use crate::scan_expr::scan_expr;
 use crate::unraw::{IdentUnraw, MemberUnraw};
 use proc_macro2::{Delimiter, TokenStream, TokenTree};
-use quote::{format_ident, quote, quote_spanned};
+use quote::{format_ident, quote, quote_spanned, ToTokens as _};
 use std::collections::{BTreeSet, HashMap};
 use std::iter;
 use syn::ext::IdentExt;
@@ -114,6 +114,8 @@ impl Display<'_> {
             }
             let formatvar_prefix = if bonus_display {
                 "__display"
+            } else if bound == Trait::Pointer {
+                "__pointer"
             } else {
                 "__field"
             };
@@ -137,8 +139,10 @@ impl Display<'_> {
             };
             let wrapped_binding_value = if bonus_display {
                 quote_spanned!(span=> #binding_value.as_display())
-            } else {
+            } else if bound == Trait::Pointer {
                 quote!(::thiserror::__private::Var(#binding_value))
+            } else {
+                binding_value.into_token_stream()
             };
             has_bonus_display |= bonus_display;
             bindings.push((formatvar.to_local(), wrapped_binding_value));

src/var.rs

@@ -1,61 +1,9 @@
-use core::fmt::{
-    self, Binary, Debug, Display, LowerExp, LowerHex, Octal, Pointer, UpperExp, UpperHex,
-};
+use core::fmt::{self, Pointer};
 
 pub struct Var<'a, T: ?Sized>(pub &'a T);
 
-/// Pointer is the only one for which there is a difference in behavior between
-/// `Var<'a, T>` vs `&'a T`.
 impl<'a, T: Pointer + ?Sized> Pointer for Var<'a, T> {
     fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
         Pointer::fmt(self.0, formatter)
     }
 }
-
-impl<'a, T: Binary + ?Sized> Binary for Var<'a, T> {
-    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
-        Binary::fmt(self.0, formatter)
-    }
-}
-
-impl<'a, T: Debug + ?Sized> Debug for Var<'a, T> {
-    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
-        Debug::fmt(self.0, formatter)
-    }
-}
-
-impl<'a, T: Display + ?Sized> Display for Var<'a, T> {
-    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
-        Display::fmt(self.0, formatter)
-    }
-}
-
-impl<'a, T: LowerExp + ?Sized> LowerExp for Var<'a, T> {
-    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
-        LowerExp::fmt(self.0, formatter)
-    }
-}
-
-impl<'a, T: LowerHex + ?Sized> LowerHex for Var<'a, T> {
-    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
-        LowerHex::fmt(self.0, formatter)
-    }
-}
-
-impl<'a, T: Octal + ?Sized> Octal for Var<'a, T> {
-    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
-        Octal::fmt(self.0, formatter)
-    }
-}
-
-impl<'a, T: UpperExp + ?Sized> UpperExp for Var<'a, T> {
-    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
-        UpperExp::fmt(self.0, formatter)
-    }
-}
-
-impl<'a, T: UpperHex + ?Sized> UpperHex for Var<'a, T> {
-    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
-        UpperHex::fmt(self.0, formatter)
-    }
-}

tests/ui/no-display.stderr

@@ -32,12 +32,12 @@ error[E0277]: the trait bound `NoDisplay: Octal` is not satisfied
              &mut T
              NonZero<T>
              Saturating<T>
-             Var<'a, T>
              Wrapping<T>
              i128
              i16
+             i32
            and $N others
-   = note: required for `Var<'_, NoDisplay>` to implement `Octal`
+   = note: required for `&NoDisplay` to implement `Octal`
 note: required by a bound in `core::fmt::rt::Argument::<'_>::new_octal`
   --> $RUST/core/src/fmt/rt.rs
    |