Permit token trees, identifiers, and blocks to be following by sequences.

[nikomatsakis]

Permit token trees, identifiers, and blocks to be following by sequences.

Fixes #25436.

r? @pnkfelix

[pnkfelix]

@nikomatsakis the PR looks good. Could you add a compile-fail test for two sequences with no delimiter between them, e.g.:

macro_rules! foo {
    ( $($a:tt)* $($b:tt)* ) => { }; //~ ERROR sequence repetition followed by another sequence repetition
    ( $($a:item)* $($b:item)* ) => { }; //~ ERROR sequence repetition followed by another sequence repetition
}

[pnkfelix]

(r=me after adding above test; or if you point me at a pre-existing test that does it -- i just didn't see one in my own grepping.)

[nikomatsakis]

@bors r=pnkfelix

[bors]

📌 Commit 7a5d748 has been approved by pnkfelix

[bors]

⌛ Testing commit 7a5d748 with merge 63b000b...

[bors]

☀️ Test successful - auto-linux-32-nopt-t, auto-linux-32-opt, auto-linux-64-nopt-t, auto-linux-64-opt, auto-linux-64-x-android-t, auto-mac-32-opt, auto-mac-64-nopt-t, auto-mac-64-opt, auto-win-32-nopt-t, auto-win-32-opt, auto-win-64-nopt-t, auto-win-64-opt