Add backwards-compat hack for certain '$name' tokens

See issue rust-lang#74616

src/librustc_ast/token.rs

@@ -11,9 +11,11 @@ use crate::tokenstream::TokenTree;
 use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
 use rustc_data_structures::sync::Lrc;
 use rustc_macros::HashStable_Generic;
+use rustc_span::hygiene::ExpnKind;
+use rustc_span::source_map::SourceMap;
 use rustc_span::symbol::{kw, sym};
 use rustc_span::symbol::{Ident, Symbol};
-use rustc_span::{self, Span, DUMMY_SP};
+use rustc_span::{self, FileName, RealFileName, Span, DUMMY_SP};
 use std::borrow::Cow;
 use std::{fmt, mem};
 
@@ -808,6 +810,31 @@ impl Nonterminal {
         }
         false
     }
+
+    // See issue #74616 for details
+    pub fn ident_name_compatibility_hack(
+        &self,
+        orig_span: Span,
+        source_map: &SourceMap,
+    ) -> Option<(Ident, bool)> {
+        if let NtIdent(ident, is_raw) = self {
+            if let ExpnKind::Macro(_, macro_name) = orig_span.ctxt().outer_expn_data().kind {
+                let filename = source_map.span_to_filename(orig_span);
+                if let FileName::Real(RealFileName::Named(path)) = filename {
+                    if (path.ends_with("time-macros-impl/src/lib.rs")
+                        && macro_name == sym::impl_macros)
+                        || (path.ends_with("js-sys/src/lib.rs") && macro_name == sym::arrays)
+                    {
+                        let snippet = source_map.span_to_snippet(orig_span);
+                        if snippet.as_deref() == Ok("$name") {
+                            return Some((*ident, *is_raw));
+                        }
+                    }
+                }
+            }
+        }
+        None
+    }
 }
 
 impl PartialEq for Nonterminal {

src/librustc_expand/proc_macro_server.rs

@@ -173,13 +173,19 @@ impl FromInternal<(TreeAndJoint, &'_ ParseSess, &'_ mut Vec<Self>)>
             }
 
             Interpolated(nt) => {
-                let stream = nt_to_tokenstream(&nt, sess, span);
-                TokenTree::Group(Group {
-                    delimiter: Delimiter::None,
-                    stream,
-                    span: DelimSpan::from_single(span),
-                    flatten: nt.pretty_printing_compatibility_hack(),
-                })
+                if let Some((name, is_raw)) =
+                    nt.ident_name_compatibility_hack(span, sess.source_map())
+                {
+                    TokenTree::Ident(Ident::new(sess, name.name, is_raw, name.span))
+                } else {
+                    let stream = nt_to_tokenstream(&nt, sess, span);
+                    TokenTree::Group(Group {
+                        delimiter: Delimiter::None,
+                        stream,
+                        span: DelimSpan::from_single(span),
+                        flatten: nt.pretty_printing_compatibility_hack(),
+                    })
+                }
             }
 
             OpenDelim(..) | CloseDelim(..) => unreachable!(),

src/librustc_span/symbol.rs

@@ -258,6 +258,7 @@ symbols! {
         arith_offset,
         arm_target_feature,
         array,
+        arrays,
         as_str,
         asm,
         assert,
@@ -571,6 +572,7 @@ symbols! {
         ignore,
         impl_header_lifetime_elision,
         impl_lint_pass,
+        impl_macros,
         impl_trait_in_bindings,
         import_shadowing,
         in_band_lifetimes,

src/test/ui/proc-macro/group-compat-hack/auxiliary/group-compat-hack.rs

@@ -0,0 +1,13 @@
+// force-host
+// no-prefer-dynamic
+
+#![crate_type = "proc-macro"]
+
+extern crate proc_macro;
+use proc_macro::TokenStream;
+
+#[proc_macro_attribute]
+pub fn my_macro(_attr: TokenStream, input: TokenStream) -> TokenStream {
+    println!("Called proc_macro_hack with {:?}", input);
+    input
+}

src/test/ui/proc-macro/group-compat-hack/group-compat-hack.rs

@@ -0,0 +1,30 @@
+// check-pass
+// aux-build:group-compat-hack.rs
+// compile-flags: -Z span-debug
+
+#![no_std] // Don't load unnecessary hygiene information from std
+extern crate std;
+
+#[macro_use] extern crate group_compat_hack;
+
+// Tests the backwards compatibility hack added for certain macros
+// When an attribute macro named `proc_macro_hack` or `wasm_bindgen`
+// has an `NtIdent` named `$name`, we pass a plain `Ident` token in
+// place of a `None`-delimited group. This allows us to maintain
+// backwards compatibility for older versions of these crates.
+
+include!("js-sys/src/lib.rs");
+include!("time-macros-impl/src/lib.rs");
+
+macro_rules! other {
+    ($name:ident) => {
+        #[my_macro] struct Three($name);
+    }
+}
+
+fn main() {
+    struct Foo;
+    impl_macros!(Foo);
+    arrays!(Foo);
+    other!(Foo);
+}

src/test/ui/proc-macro/group-compat-hack/group-compat-hack.stdout

@@ -0,0 +1,3 @@
+Called proc_macro_hack with TokenStream [Ident { ident: "struct", span: $DIR/time-macros-impl/src/lib.rs:5:21: 5:27 (#5) }, Ident { ident: "One", span: $DIR/time-macros-impl/src/lib.rs:5:28: 5:31 (#5) }, Group { delimiter: Parenthesis, stream: TokenStream [Ident { ident: "Foo", span: $DIR/group-compat-hack.rs:27:18: 27:21 (#0) }], span: $DIR/time-macros-impl/src/lib.rs:5:31: 5:38 (#5) }, Punct { ch: ';', spacing: Alone, span: $DIR/time-macros-impl/src/lib.rs:5:38: 5:39 (#5) }]
+Called proc_macro_hack with TokenStream [Ident { ident: "struct", span: $DIR/js-sys/src/lib.rs:5:21: 5:27 (#9) }, Ident { ident: "Two", span: $DIR/js-sys/src/lib.rs:5:28: 5:31 (#9) }, Group { delimiter: Parenthesis, stream: TokenStream [Ident { ident: "Foo", span: $DIR/group-compat-hack.rs:28:13: 28:16 (#0) }], span: $DIR/js-sys/src/lib.rs:5:31: 5:38 (#9) }, Punct { ch: ';', spacing: Alone, span: $DIR/js-sys/src/lib.rs:5:38: 5:39 (#9) }]
+Called proc_macro_hack with TokenStream [Ident { ident: "struct", span: $DIR/group-compat-hack.rs:21:21: 21:27 (#13) }, Ident { ident: "Three", span: $DIR/group-compat-hack.rs:21:28: 21:33 (#13) }, Group { delimiter: Parenthesis, stream: TokenStream [Group { delimiter: None, stream: TokenStream [Ident { ident: "Foo", span: $DIR/group-compat-hack.rs:29:12: 29:15 (#0) }], span: $DIR/group-compat-hack.rs:21:34: 21:39 (#13) }], span: $DIR/group-compat-hack.rs:21:33: 21:40 (#13) }, Punct { ch: ';', spacing: Alone, span: $DIR/group-compat-hack.rs:21:40: 21:41 (#13) }]

src/test/ui/proc-macro/group-compat-hack/js-sys/src/lib.rs

@@ -0,0 +1,7 @@
+// ignore-test this is not a test
+
+macro_rules! arrays {
+    ($name:ident) => {
+        #[my_macro] struct Two($name);
+    }
+}

src/test/ui/proc-macro/group-compat-hack/time-macros-impl/src/lib.rs

@@ -0,0 +1,7 @@
+// ignore-test this is not a test
+
+macro_rules! impl_macros {
+    ($name:ident) => {
+        #[my_macro] struct One($name);
+    }
+}