Rollup merge of #66935 - petrochenkov:attrtok2, r=Centril

syntax: Unify macro and attribute arguments in AST

The unified form (`ast::MacArgs`) represents parsed arguments instead of an unstructured token stream that was previously used for attributes.
It also tracks some spans and delimiter kinds better for fn-like macros and macro definitions.

I've been talking about implementing this with @nnethercote in https://github.com/rust-lang/rust/pull/65750#issuecomment-546517322.
The parsed representation is closer to `MetaItem` and requires less token juggling during conversions, so it potentially may be faster.

r? @Centril

src/test/ui/issues/issue-10536.rs

@@ -11,9 +11,9 @@ macro_rules! foo{
 pub fn main() {
     foo!();
 
-    assert!({one! two()}); //~ ERROR expected open delimiter
+    assert!({one! two()}); //~ ERROR expected one of `(`, `[`, or `{`, found `two`
 
     // regardless of whether nested macro_rules works, the following should at
     // least throw a conventional error.
-    assert!({one! two}); //~ ERROR expected open delimiter
+    assert!({one! two}); //~ ERROR expected one of `(`, `[`, or `{`, found `two`
 }

src/test/ui/issues/issue-10536.stderr

@@ -1,14 +1,14 @@
-error: expected open delimiter
+error: expected one of `(`, `[`, or `{`, found `two`
   --> $DIR/issue-10536.rs:14:19
    |
 LL |     assert!({one! two()});
-   |                   ^^^ expected open delimiter
+   |                   ^^^ expected one of `(`, `[`, or `{`
 
-error: expected open delimiter
+error: expected one of `(`, `[`, or `{`, found `two`
   --> $DIR/issue-10536.rs:18:19
    |
 LL |     assert!({one! two});
-   |                   ^^^ expected open delimiter
+   |                   ^^^ expected one of `(`, `[`, or `{`
 
 error: aborting due to 2 previous errors
 

src/test/ui/parser/macro-bad-delimiter-ident.rs

@@ -1,3 +1,3 @@
 fn main() {
-    foo! bar < //~ ERROR expected open delimiter
+    foo! bar < //~ ERROR expected one of `(`, `[`, or `{`, found `bar`
 }

src/test/ui/parser/macro-bad-delimiter-ident.stderr

@@ -1,8 +1,8 @@
-error: expected open delimiter
+error: expected one of `(`, `[`, or `{`, found `bar`
   --> $DIR/macro-bad-delimiter-ident.rs:2:10
    |
 LL |     foo! bar <
-   |          ^^^ expected open delimiter
+   |          ^^^ expected one of `(`, `[`, or `{`
 
 error: aborting due to previous error
 

src/test/ui/proc-macro/proc-macro-gates.rs

@@ -18,7 +18,7 @@ mod _test2_inner {
           //~| ERROR: non-builtin inner attributes are unstable
 }
 
-#[empty_attr = "y"] //~ ERROR: must only be followed by a delimiter token
+#[empty_attr = "y"] //~ ERROR: key-value macro attributes are not supported
 fn _test3() {}
 
 fn attrs() {

src/test/ui/proc-macro/proc-macro-gates.stderr

@@ -34,7 +34,7 @@ LL |     #![empty_attr]
    = note: for more information, see https://github.com/rust-lang/rust/issues/54727
    = help: add `#![feature(proc_macro_hygiene)]` to the crate attributes to enable
 
-error: custom attribute invocations must be of the form `#[foo]` or `#[foo(..)]`, the macro name must only be followed by a delimiter token
+error: key-value macro attributes are not supported
   --> $DIR/proc-macro-gates.rs:21:1
    |
 LL | #[empty_attr = "y"]