Extend `proc_macro_back_compat` lint to `procedural-masquerade`

We now lint on *any* use of `procedural-masquerade` crate. While this
crate still exists, its main reverse dependency (`cssparser`) no longer
depends on it. Any crates still depending off should stop doing so, as
it only exists to support very old Rust versions.

If a crate actually needs to support old versions of rustc via
`procedural-masquerade`, then they'll just need to accept the warning
until we remove it entirely (at the same time as the back-compat hack).
The latest version of `procedural-masquerade` does not work with the
latest rustc, but trying to check for the version seems like more
trouble than it's worth.

While working on this, I realized that the `proc-macro-hack` check was
never actually doing anything. The corresponding enum variant in
`proc-macro-hack` is named `Value` or `Nested` - it has never been
called `Input`. Due to a strange Crater issue, the Crater run that
tested adding this did *not* end up testing it - some of the crates that
would have failed did not actually have their tests checked, making it
seem as though the `proc-macro-hack` check was working.

The Crater issue is being discussed at
https://rust-lang.zulipchat.com/#narrow/stream/242791-t-infra/topic/Nearly.20identical.20Crater.20runs.20processed.20a.20crate.20differently/near/230406661

Despite the `proc-macro-hack` check not actually doing anything, we
haven't gotten any reports from users about their build being broken.
I went ahead and removed it entirely, since it's clear that no one is
being affected by the `proc-macro-hack` regression in practice.

1 files changed, 0 insertions, 27 deletions

diff --git a/compiler/rustc_ast/src/token.rs b/compiler/rustc_ast/src/token.rs
index 093f7f2668c..7e58426d27d 100644
--- a/compiler/rustc_ast/src/token.rs
+++ b/compiler/rustc_ast/src/token.rs
@@ -784,33 +784,6 @@ impl Nonterminal {
             NtTT(tt) => tt.span(),
         }
     }
-
-    /// This nonterminal looks like some specific enums from
-    /// `proc-macro-hack` and `procedural-masquerade` crates.
-    /// We need to maintain some special pretty-printing behavior for them due to incorrect
-    /// asserts in old versions of those crates and their wide use in the ecosystem.
-    /// See issue #73345 for more details.
-    /// FIXME(#73933): Remove this eventually.
-    pub fn pretty_printing_compatibility_hack(&self) -> bool {
-        let item = match self {
-            NtItem(item) => item,
-            NtStmt(stmt) => match &stmt.kind {
-                ast::StmtKind::Item(item) => item,
-                _ => return false,
-            },
-            _ => return false,
-        };
-
-        let name = item.ident.name;
-        if name == sym::ProceduralMasqueradeDummyType || name == sym::ProcMacroHack {
-            if let ast::ItemKind::Enum(enum_def, _) = &item.kind {
-                if let [variant] = &*enum_def.variants {
-                    return variant.ident.name == sym::Input;
-                }
-            }
-        }
-        false
-    }
 }
 
 impl PartialEq for Nonterminal {