Reject negative inherent impls

src/item.rs

@@ -2593,7 +2593,6 @@ pub(crate) mod parsing {
             input.parse::<Token![const]>()?;
         }
 
-        let begin = input.fork();
         let polarity = if input.peek(Token![!]) && !input.peek2(token::Brace) {
             Some(input.parse::<Token![!]>()?)
         } else {
@@ -2631,13 +2630,14 @@ pub(crate) mod parsing {
                 trait_ = None;
             }
             self_ty = input.parse()?;
+        } else if let Some(polarity) = polarity {
+            return Err(Error::new(
+                polarity.span,
+                "inherent impls cannot be negative",
+            ));
         } else {
             trait_ = None;
-            self_ty = if polarity.is_none() {
-                first_ty
-            } else {
-                Type::Verbatim(verbatim::between(&begin, input))
-            };
+            self_ty = first_ty;
         }
 
         generics.where_clause = input.parse()?;

tests/common/eq.rs

@@ -143,6 +143,7 @@ use rustc_ast::ast::StructRest;
 use rustc_ast::ast::Term;
 use rustc_ast::ast::Trait;
 use rustc_ast::ast::TraitBoundModifiers;
+use rustc_ast::ast::TraitImplHeader;
 use rustc_ast::ast::TraitObjectSyntax;
 use rustc_ast::ast::TraitRef;
 use rustc_ast::ast::Ty;
@@ -508,7 +509,7 @@ spanless_eq_struct!(FormatOptions; width precision alignment fill sign alternate
 spanless_eq_struct!(FormatPlaceholder; argument span format_trait format_options);
 spanless_eq_struct!(GenericParam; id ident attrs bounds is_placeholder kind !colon_span);
 spanless_eq_struct!(Generics; params where_clause span);
-spanless_eq_struct!(Impl; defaultness safety generics constness polarity of_trait self_ty items);
+spanless_eq_struct!(Impl; generics of_trait self_ty items);
 spanless_eq_struct!(InlineAsm; asm_macro template template_strs operands clobber_abis options line_spans);
 spanless_eq_struct!(InlineAsmSym; id qself path);
 spanless_eq_struct!(Item<K>; attrs id span vis kind !tokens);
@@ -539,6 +540,7 @@ spanless_eq_struct!(StructExpr; qself path fields rest);
 spanless_eq_struct!(Token; kind span);
 spanless_eq_struct!(Trait; constness safety is_auto ident generics bounds items);
 spanless_eq_struct!(TraitBoundModifiers; constness asyncness polarity);
+spanless_eq_struct!(TraitImplHeader; defaultness safety constness polarity trait_ref);
 spanless_eq_struct!(TraitRef; path ref_id);
 spanless_eq_struct!(Ty; id kind span tokens);
 spanless_eq_struct!(TyAlias; defaultness ident generics where_clauses bounds ty);

tests/repo/mod.rs

@@ -222,7 +222,11 @@ static EXCLUDE_FILES: &[&str] = &[
     // Rustc bug: https://github.com/rust-lang/rust/issues/132080
     "src/tools/rust-analyzer/crates/parser/test_data/parser/ok/0073_safe_declarations_in_extern_blocks.rs",
 
-    // Compile-fail expr parameter in const generic position: f::<1 + 2>()
+    // Negative inherent impl: `impl !Box<JoinHandle> {}`
+    "src/tools/rustfmt/tests/source/negative-impl.rs",
+    "src/tools/rustfmt/tests/target/negative-impl.rs",
+
+    // Compile-fail expr parameter in const generic position: `f::<1 + 2>()`
     "tests/ui/const-generics/early/closing-args-token.rs",
     "tests/ui/const-generics/early/const-expression-parameter.rs",
 

tests/test_item.rs

@@ -53,8 +53,6 @@ fn test_macro_variable_attr() {
 
 #[test]
 fn test_negative_impl() {
-    // Rustc parses all of the following.
-
     #[cfg(any())]
     impl ! {}
     let tokens = quote! {
@@ -67,18 +65,11 @@ fn test_negative_impl() {
     }
     "#);
 
-    #[cfg(any())]
-    #[rustfmt::skip]
-    impl !Trait {}
     let tokens = quote! {
         impl !Trait {}
     };
-    snapshot!(tokens as Item, @r#"
-    Item::Impl {
-        generics: Generics,
-        self_ty: Type::Verbatim(`! Trait`),
-    }
-    "#);
+    let err = syn::parse2::<Item>(tokens).unwrap_err();
+    assert_eq!(err.to_string(), "inherent impls cannot be negative");
 
     #[cfg(any())]
     impl !Trait for T {}
@@ -109,19 +100,6 @@ fn test_negative_impl() {
         },
     }
     "#);
-
-    #[cfg(any())]
-    #[rustfmt::skip]
-    impl !! {}
-    let tokens = quote! {
-        impl !! {}
-    };
-    snapshot!(tokens as Item, @r#"
-    Item::Impl {
-        generics: Generics,
-        self_ty: Type::Verbatim(`! !`),
-    }
-    "#);
 }
 
 #[test]