Auto merge of #70261 - Centril:angle-args-partition, r=varkor

Move arg/constraint partition check to validation & improve recovery

- In the first commit, we move the check rejecting e.g., `<'a, Item = u8, String>` from the parser into AST validation.
- We then use this to improve the code for parsing generic arguments.
- And we add recovery for e.g., `<Item = >` (missing), `<Item = 42>` (constant), and `<Item = 'a>` (lifetime).

This is also preparatory work for supporting https://github.com/rust-lang/rust/issues/70256.

r? @varkor

1 files changed, 2 insertions, 1 deletions

diff --git a/src/librustc_expand/build.rs b/src/librustc_expand/build.rs
index 48ceaf5fccd..4d89bf79e7c 100644
--- a/src/librustc_expand/build.rs
+++ b/src/librustc_expand/build.rs
@@ -36,7 +36,8 @@ impl<'a> ExtCtxt<'a> {
             idents.into_iter().map(|ident| ast::PathSegment::from_ident(ident.with_span_pos(span))),
         );
         let args = if !args.is_empty() {
-            ast::AngleBracketedArgs { args, constraints: Vec::new(), span }.into()
+            let args = args.into_iter().map(ast::AngleBracketedArg::Arg).collect();
+            ast::AngleBracketedArgs { args, span }.into()
         } else {
             None
         };