Auto merge of #66994 - Centril:stmt-polish, r=estebank

refactor expr & stmt parsing + improve recovery

Summary of important changes (best read commit-by-commit, ignoring whitespace changes):

- `AttrVec` is introduces as an alias for `ThinVec<Attribute>`
- `parse_expr_bottom` and `parse_stmt` are thoroughly refactored.
- Extract diagnostics logic for `vec![...]` in a pattern context.
- Recovery is added for `do catch { ... }`
- Recovery is added for `'label: non_block_expr`
- Recovery is added for `var $local`, `auto $local`, and `mut $local`. Fixes #65257.
- Recovery is added for `e1 and e2` and `e1 or e2`.
- ~~`macro_legacy_warnings` is turned into an error (has been a warning for 3 years!)~~
- Fixes #63396 by forward-porting #64105 which now works thanks to added recovery.
- `ui-fulldeps/ast_stmt_expr_attr.rs` is turned into UI and pretty tests.
- Recovery is fixed for `#[attr] if expr {}`

r? @estebank

1 files changed, 7 insertions, 16 deletions

diff --git a/src/librustc_parse/parser/attr.rs b/src/librustc_parse/parser/attr.rs
index 00fd6b8a25b..51310fb88f6 100644
--- a/src/librustc_parse/parser/attr.rs
+++ b/src/librustc_parse/parser/attr.rs
@@ -1,4 +1,4 @@
-use super::{SeqSep, Parser, TokenType, PathStyle};
+use super::{Parser, TokenType, PathStyle};
 use rustc_errors::PResult;
 use syntax::attr;
 use syntax::ast;
@@ -301,8 +301,10 @@ impl<'a> Parser<'a> {
     crate fn parse_meta_item_kind(&mut self) -> PResult<'a, ast::MetaItemKind> {
         Ok(if self.eat(&token::Eq) {
             ast::MetaItemKind::NameValue(self.parse_unsuffixed_lit()?)
-        } else if self.eat(&token::OpenDelim(token::Paren)) {
-            ast::MetaItemKind::List(self.parse_meta_seq()?)
+        } else if self.check(&token::OpenDelim(token::Paren)) {
+            // Matches `meta_seq = ( COMMASEP(meta_item_inner) )`.
+            let (list, _) = self.parse_paren_comma_seq(|p| p.parse_meta_item_inner())?;
+            ast::MetaItemKind::List(list)
         } else {
             ast::MetaItemKind::Word
         })
@@ -311,16 +313,12 @@ impl<'a> Parser<'a> {
     /// Matches `meta_item_inner : (meta_item | UNSUFFIXED_LIT) ;`.
     fn parse_meta_item_inner(&mut self) -> PResult<'a, ast::NestedMetaItem> {
         match self.parse_unsuffixed_lit() {
-            Ok(lit) => {
-                return Ok(ast::NestedMetaItem::Literal(lit))
-            }
+            Ok(lit) => return Ok(ast::NestedMetaItem::Literal(lit)),
             Err(ref mut err) => err.cancel(),
         }
 
         match self.parse_meta_item() {
-            Ok(mi) => {
-                return Ok(ast::NestedMetaItem::MetaItem(mi))
-            }
+            Ok(mi) => return Ok(ast::NestedMetaItem::MetaItem(mi)),
             Err(ref mut err) => err.cancel(),
         }
 
@@ -328,11 +326,4 @@ impl<'a> Parser<'a> {
         let msg = format!("expected unsuffixed literal or identifier, found `{}`", found);
         Err(self.diagnostic().struct_span_err(self.token.span, &msg))
     }
-
-    /// Matches `meta_seq = ( COMMASEP(meta_item_inner) )`.
-    fn parse_meta_seq(&mut self) -> PResult<'a, Vec<ast::NestedMetaItem>> {
-        self.parse_seq_to_end(&token::CloseDelim(token::Paren),
-                              SeqSep::trailing_allowed(token::Comma),
-                              |p: &mut Parser<'a>| p.parse_meta_item_inner())
-    }
 }