Merge pull request #384 from dtolnay/nowrap

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.rs

@@ -9,4 +9,10 @@ pub struct Error {
     thread: NoDisplay,
 }
 
+#[derive(Error, Debug)]
+#[error("thread: {thread:o}")]
+pub struct ErrorOctal {
+    thread: NoDisplay,
+}
+
 fn main() {}

tests/ui/no-display.stderr

@@ -18,3 +18,29 @@ note: the trait `std::fmt::Display` must be implemented
   = help: items from traits can only be used if the trait is implemented and in scope
   = note: the following trait defines an item `as_display`, perhaps you need to implement it:
           candidate #1: `AsDisplay`
+
+error[E0277]: the trait bound `NoDisplay: Octal` is not satisfied
+  --> tests/ui/no-display.rs:13:9
+   |
+12 | #[derive(Error, Debug)]
+   |          ----- in this derive macro expansion
+13 | #[error("thread: {thread:o}")]
+   |         ^^^^^^^^^^^^^^^^^^^^ the trait `Octal` is not implemented for `NoDisplay`
+   |
+   = help: the following other types implement trait `Octal`:
+             &T
+             &mut T
+             NonZero<T>
+             Saturating<T>
+             Wrapping<T>
+             i128
+             i16
+             i32
+           and $N others
+   = note: required for `&NoDisplay` to implement `Octal`
+note: required by a bound in `core::fmt::rt::Argument::<'_>::new_octal`
+  --> $RUST/core/src/fmt/rt.rs
+   |
+   |     pub fn new_octal<T: Octal>(x: &T) -> Argument<'_> {
+   |                         ^^^^^ required by this bound in `Argument::<'_>::new_octal`
+   = note: this error originates in the macro `$crate::format_args` which comes from the expansion of the derive macro `Error` (in Nightly builds, run with -Z macro-backtrace for more info)