Manually cleanup token stream when macro expansion aborts.

compiler/rustc_builtin_macros/src/cfg_eval.rs

@@ -7,6 +7,7 @@ use rustc_ast::visit::Visitor;
 use rustc_ast::NodeId;
 use rustc_ast::{mut_visit, visit};
 use rustc_ast::{Attribute, HasAttrs, HasTokens};
+use rustc_errors::PResult;
 use rustc_expand::base::{Annotatable, ExtCtxt};
 use rustc_expand::config::StripUnconfigured;
 use rustc_expand::configure;
@@ -144,33 +145,34 @@ impl CfgEval<'_, '_> {
         // the location of `#[cfg]` and `#[cfg_attr]` in the token stream. The tokenization
         // process is lossless, so this process is invisible to proc-macros.
 
-        let parse_annotatable_with: fn(&mut Parser<'_>) -> _ = match annotatable {
-            Annotatable::Item(_) => {
-                |parser| Annotatable::Item(parser.parse_item(ForceCollect::Yes).unwrap().unwrap())
-            }
-            Annotatable::TraitItem(_) => |parser| {
-                Annotatable::TraitItem(
-                    parser.parse_trait_item(ForceCollect::Yes).unwrap().unwrap().unwrap(),
-                )
-            },
-            Annotatable::ImplItem(_) => |parser| {
-                Annotatable::ImplItem(
-                    parser.parse_impl_item(ForceCollect::Yes).unwrap().unwrap().unwrap(),
-                )
-            },
-            Annotatable::ForeignItem(_) => |parser| {
-                Annotatable::ForeignItem(
-                    parser.parse_foreign_item(ForceCollect::Yes).unwrap().unwrap().unwrap(),
-                )
-            },
-            Annotatable::Stmt(_) => |parser| {
-                Annotatable::Stmt(P(parser.parse_stmt(ForceCollect::Yes).unwrap().unwrap()))
-            },
-            Annotatable::Expr(_) => {
-                |parser| Annotatable::Expr(parser.parse_expr_force_collect().unwrap())
-            }
-            _ => unreachable!(),
-        };
+        let parse_annotatable_with: for<'a> fn(&mut Parser<'a>) -> PResult<'a, _> =
+            match annotatable {
+                Annotatable::Item(_) => {
+                    |parser| Ok(Annotatable::Item(parser.parse_item(ForceCollect::Yes)?.unwrap()))
+                }
+                Annotatable::TraitItem(_) => |parser| {
+                    Ok(Annotatable::TraitItem(
+                        parser.parse_trait_item(ForceCollect::Yes)?.unwrap().unwrap(),
+                    ))
+                },
+                Annotatable::ImplItem(_) => |parser| {
+                    Ok(Annotatable::ImplItem(
+                        parser.parse_impl_item(ForceCollect::Yes)?.unwrap().unwrap(),
+                    ))
+                },
+                Annotatable::ForeignItem(_) => |parser| {
+                    Ok(Annotatable::ForeignItem(
+                        parser.parse_foreign_item(ForceCollect::Yes)?.unwrap().unwrap(),
+                    ))
+                },
+                Annotatable::Stmt(_) => |parser| {
+                    Ok(Annotatable::Stmt(P(parser.parse_stmt(ForceCollect::Yes)?.unwrap())))
+                },
+                Annotatable::Expr(_) => {
+                    |parser| Ok(Annotatable::Expr(parser.parse_expr_force_collect()?))
+                }
+                _ => unreachable!(),
+            };
 
         // 'Flatten' all nonterminals (i.e. `TokenKind::Interpolated`)
         // to `None`-delimited groups containing the corresponding tokens. This
@@ -193,7 +195,13 @@ impl CfgEval<'_, '_> {
         let mut parser =
             rustc_parse::stream_to_parser(&self.cfg.sess.parse_sess, orig_tokens, None);
         parser.capture_cfg = true;
-        annotatable = parse_annotatable_with(&mut parser);
+        match parse_annotatable_with(&mut parser) {
+            Ok(a) => annotatable = a,
+            Err(mut err) => {
+                err.emit();
+                return Some(annotatable);
+            }
+        }
 
         // Now that we have our re-parsed `AttrTokenStream`, recursively configuring
         // our attribute target will correctly the tokens as well.

compiler/rustc_parse/src/parser/attr_wrapper.rs

@@ -459,6 +459,5 @@ fn make_token_stream(
             panic!("Unexpected last token {:?}", last_token)
         }
     }
-    assert!(stack.is_empty(), "Stack should be empty: final_buf={:?} stack={:?}", final_buf, stack);
     AttrTokenStream::new(final_buf.inner)
 }

src/test/ui/macros/syntax-error-recovery.rs

@@ -0,0 +1,18 @@
+macro_rules! values {
+    ($($token:ident($value:literal) $(as $inner:ty)? => $attr:meta,)*) => {
+        #[derive(Debug)]
+        pub enum TokenKind {
+            $(
+                #[$attr]
+                $token $($inner)? = $value,
+            )*
+        }
+    };
+}
+//~^^^^^ ERROR expected one of `(`, `,`, `=`, `{`, or `}`, found `(String)`
+//~| ERROR macro expansion ignores token `(String)` and any following
+
+values!(STRING(1) as (String) => cfg(test),);
+//~^ ERROR expected one of `!` or `::`, found `<eof>`
+
+fn main() {}

src/test/ui/macros/syntax-error-recovery.stderr

@@ -0,0 +1,30 @@
+error: expected one of `(`, `,`, `=`, `{`, or `}`, found `(String)`
+  --> $DIR/syntax-error-recovery.rs:7:26
+   |
+LL |                 $token $($inner)? = $value,
+   |                          ^^^^^^ expected one of `(`, `,`, `=`, `{`, or `}`
+...
+LL | values!(STRING(1) as (String) => cfg(test),);
+   | -------------------------------------------- in this macro invocation
+   |
+   = note: this error originates in the macro `values` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error: macro expansion ignores token `(String)` and any following
+  --> $DIR/syntax-error-recovery.rs:7:26
+   |
+LL |                 $token $($inner)? = $value,
+   |                          ^^^^^^
+...
+LL | values!(STRING(1) as (String) => cfg(test),);
+   | -------------------------------------------- caused by the macro expansion here
+   |
+   = note: the usage of `values!` is likely invalid in item context
+
+error: expected one of `!` or `::`, found `<eof>`
+  --> $DIR/syntax-error-recovery.rs:15:9
+   |
+LL | values!(STRING(1) as (String) => cfg(test),);
+   |         ^^^^^^ expected one of `!` or `::`
+
+error: aborting due to 3 previous errors
+