Auto merge of #57321 - petrochenkov:atokens, r=nikomatsakis

Implement basic input validation for built-in attributes

Correct top-level shape (`#[attr]` vs `#[attr(...)]` vs `#[attr = ...]`) is enforced for built-in attributes, built-in attributes must also fit into the "meta-item" syntax (aka the "classic attribute syntax").

For some subset of attributes (found by crater run), errors are lowered to deprecation warnings.

NOTE: This PR previously included #57367 as well.

Author: bors

src/librustc/diagnostics.rs

@@ -1180,27 +1180,6 @@ fn main() {
 ```
 "##,
 
-E0296: r##"
-This error indicates that the given recursion limit could not be parsed. Ensure
-that the value provided is a positive integer between quotes.
-
-Erroneous code example:
-
-```compile_fail,E0296
-#![recursion_limit]
-
-fn main() {}
-```
-
-And a working example:
-
-```
-#![recursion_limit="1000"]
-
-fn main() {}
-```
-"##,
-
 E0308: r##"
 This error occurs when the compiler was unable to infer the concrete type of a
 variable. It can occur for several cases, the most common of which is a
@@ -2093,20 +2072,6 @@ trait Foo { }
 ```
 "##,
 
-E0702: r##"
-This error indicates that a `#[non_exhaustive]` attribute had a value. The
-`#[non_exhaustive]` should be empty.
-
-Examples of erroneous code:
-
-```compile_fail,E0702
-# #![feature(non_exhaustive)]
-
-#[non_exhaustive(anything)]
-struct Foo;
-```
-"##,
-
 E0718: r##"
 This error indicates that a `#[lang = ".."]` attribute was placed
 on the wrong type of item.
@@ -2138,6 +2103,7 @@ register_diagnostics! {
     E0280, // requirement is not satisfied
     E0284, // cannot resolve type
 //  E0285, // overflow evaluation builtin bounds
+//  E0296, // replaced with a generic attribute input check
 //  E0300, // unexpanded macro
 //  E0304, // expected signed integer constant
 //  E0305, // expected constant
@@ -2180,4 +2146,5 @@ register_diagnostics! {
     E0709, // multiple different lifetimes used in arguments of `async fn`
     E0710, // an unknown tool name found in scoped lint
     E0711, // a feature has been declared with conflicting stability attributes
+//  E0702, // replaced with a generic attribute input check
 }

src/librustc/hir/check_attr.rs

@@ -142,15 +142,6 @@ impl<'a, 'tcx> CheckAttrVisitor<'a, 'tcx> {
                 return;
             }
         }
-
-        if attr.meta_item_list().is_some() || attr.value_str().is_some() {
-            struct_span_err!(self.tcx.sess,
-                             attr.span,
-                             E0702,
-                             "attribute should be empty")
-                .span_label(item.span, "not empty")
-                .emit();
-        }
     }
 
     /// Check if the `#[marker]` attribute on an `item` is valid.
@@ -165,12 +156,6 @@ impl<'a, 'tcx> CheckAttrVisitor<'a, 'tcx> {
                 return;
             }
         }
-
-        if !attr.is_word() {
-            self.tcx.sess
-                .struct_span_err(attr.span, "attribute should be empty")
-                .emit();
-        }
     }
 
     /// Check if the `#[repr]` attributes on `item` are valid.