Some Nonterminal removal precursors

compiler/rustc_ast/src/attr/mod.rs

@@ -327,7 +327,8 @@ impl MetaItem {
         I: Iterator<Item = &'a TokenTree>,
     {
         // FIXME: Share code with `parse_path`.
-        let path = match tokens.next().map(|tt| TokenTree::uninterpolate(tt)).as_deref() {
+        let tt = tokens.next().map(|tt| TokenTree::uninterpolate(tt));
+        let path = match tt.as_deref() {
             Some(&TokenTree::Token(
                 Token { kind: ref kind @ (token::Ident(..) | token::PathSep), span },
                 _,
@@ -368,6 +369,12 @@ impl MetaItem {
                 token::Nonterminal::NtPath(path) => (**path).clone(),
                 _ => return None,
             },
+            Some(TokenTree::Token(
+                Token { kind: token::OpenDelim(_) | token::CloseDelim(_), .. },
+                _,
+            )) => {
+                panic!("Should be `AttrTokenTree::Delimited`, not delim tokens: {:?}", tt);
+            }
             _ => return None,
         };
         let list_closing_paren_pos = tokens.peek().map(|tt| tt.span().hi());

compiler/rustc_ast/src/tokenstream.rs

@@ -224,7 +224,7 @@ impl AttrTokenStream {
                                 // Inner attributes are only supported on extern blocks, functions,
                                 // impls, and modules. All of these have their inner attributes
                                 // placed at the beginning of the rightmost outermost braced group:
-                                // e.g. fn foo() { #![my_attr} }
+                                // e.g. fn foo() { #![my_attr] }
                                 //
                                 // Therefore, we can insert them back into the right location
                                 // without needing to do any extra position tracking.

compiler/rustc_expand/src/config.rs

@@ -214,6 +214,12 @@ impl<'a> StripUnconfigured<'a> {
                 ) => {
                     panic!("Nonterminal should have been flattened: {:?}", tree);
                 }
+                AttrTokenTree::Token(
+                    Token { kind: TokenKind::OpenDelim(_) | TokenKind::CloseDelim(_), .. },
+                    _,
+                ) => {
+                    panic!("Should be `AttrTokenTree::Delimited`, not delim tokens: {:?}", tree);
+                }
                 AttrTokenTree::Token(token, spacing) => {
                     Some(AttrTokenTree::Token(token, spacing)).into_iter()
                 }

tests/ui/macros/nonterminal-matching.rs

@@ -23,4 +23,34 @@ simple_nonterminal!(a, 'a, (x, y, z)); // OK
 
 complex_nonterminal!(enum E {});
 
+// `ident`, `lifetime`, and `tt` all work. Other fragments do not. See
+// https://doc.rust-lang.org/nightly/reference/macros-by-example.html#forwarding-a-matched-fragment
+macro_rules! foo {
+    (ident $x:ident) => { bar!(ident $x); };
+    (lifetime $x:lifetime) => { bar!(lifetime $x); };
+    (tt $x:tt) => { bar!(tt $x); };
+    (expr $x:expr) => { bar!(expr $x); }; //~ ERROR: no rules expected the token `3`
+    (literal $x:literal) => { bar!(literal $x); }; //~ ERROR: no rules expected the token `4`
+    (path $x:path) => { bar!(path $x); }; //~ ERROR: no rules expected the token `a::b::c`
+    (stmt $x:stmt) => { bar!(stmt $x); }; //~ ERROR: no rules expected the token `let abc = 0`
+}
+
+macro_rules! bar {
+    (ident abc) => {};
+    (lifetime 'abc) => {};
+    (tt 2) => {};
+    (expr 3) => {};
+    (literal 4) => {};
+    (path a::b::c) => {};
+    (stmt let abc = 0) => {};
+}
+
+foo!(ident abc);
+foo!(lifetime 'abc);
+foo!(tt 2);
+foo!(expr 3);
+foo!(literal 4);
+foo!(path a::b::c);
+foo!(stmt let abc = 0);
+
 fn main() {}

tests/ui/macros/nonterminal-matching.stderr

@@ -23,5 +23,93 @@ LL | complex_nonterminal!(enum E {});
    = help: try using `:tt` instead in the macro definition
    = note: this error originates in the macro `complex_nonterminal` (in Nightly builds, run with -Z macro-backtrace for more info)
 
-error: aborting due to 1 previous error
+error: no rules expected the token `3`
+  --> $DIR/nonterminal-matching.rs:32:35
+   |
+LL |     (expr $x:expr) => { bar!(expr $x); };
+   |                                   ^^ no rules expected this token in macro call
+...
+LL | macro_rules! bar {
+   | ---------------- when calling this macro
+...
+LL | foo!(expr 3);
+   | ------------ in this macro invocation
+   |
+note: while trying to match `3`
+  --> $DIR/nonterminal-matching.rs:42:11
+   |
+LL |     (expr 3) => {};
+   |           ^
+   = note: captured metavariables except for `:tt`, `:ident` and `:lifetime` cannot be compared to other tokens
+   = note: see <https://doc.rust-lang.org/nightly/reference/macros-by-example.html#forwarding-a-matched-fragment> for more information
+   = help: try using `:tt` instead in the macro definition
+   = note: this error originates in the macro `foo` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error: no rules expected the token `4`
+  --> $DIR/nonterminal-matching.rs:33:44
+   |
+LL |     (literal $x:literal) => { bar!(literal $x); };
+   |                                            ^^ no rules expected this token in macro call
+...
+LL | macro_rules! bar {
+   | ---------------- when calling this macro
+...
+LL | foo!(literal 4);
+   | --------------- in this macro invocation
+   |
+note: while trying to match `4`
+  --> $DIR/nonterminal-matching.rs:43:14
+   |
+LL |     (literal 4) => {};
+   |              ^
+   = note: captured metavariables except for `:tt`, `:ident` and `:lifetime` cannot be compared to other tokens
+   = note: see <https://doc.rust-lang.org/nightly/reference/macros-by-example.html#forwarding-a-matched-fragment> for more information
+   = help: try using `:tt` instead in the macro definition
+   = note: this error originates in the macro `foo` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error: no rules expected the token `a::b::c`
+  --> $DIR/nonterminal-matching.rs:34:35
+   |
+LL |     (path $x:path) => { bar!(path $x); };
+   |                                   ^^ no rules expected this token in macro call
+...
+LL | macro_rules! bar {
+   | ---------------- when calling this macro
+...
+LL | foo!(path a::b::c);
+   | ------------------ in this macro invocation
+   |
+note: while trying to match `a`
+  --> $DIR/nonterminal-matching.rs:44:11
+   |
+LL |     (path a::b::c) => {};
+   |           ^
+   = note: captured metavariables except for `:tt`, `:ident` and `:lifetime` cannot be compared to other tokens
+   = note: see <https://doc.rust-lang.org/nightly/reference/macros-by-example.html#forwarding-a-matched-fragment> for more information
+   = help: try using `:tt` instead in the macro definition
+   = note: this error originates in the macro `foo` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error: no rules expected the token `let abc = 0`
+  --> $DIR/nonterminal-matching.rs:35:35
+   |
+LL |     (stmt $x:stmt) => { bar!(stmt $x); };
+   |                                   ^^ no rules expected this token in macro call
+...
+LL | macro_rules! bar {
+   | ---------------- when calling this macro
+...
+LL | foo!(stmt let abc = 0);
+   | ---------------------- in this macro invocation
+   |
+note: while trying to match `let`
+  --> $DIR/nonterminal-matching.rs:45:11
+   |
+LL |     (stmt let abc = 0) => {};
+   |           ^^^
+   = note: captured metavariables except for `:tt`, `:ident` and `:lifetime` cannot be compared to other tokens
+   = note: see <https://doc.rust-lang.org/nightly/reference/macros-by-example.html#forwarding-a-matched-fragment> for more information
+   = help: try using `:tt` instead in the macro definition
+   = note: this error originates in the macro `foo` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error: aborting due to 5 previous errors