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

4 files changed, 5 insertions, 11 deletions

diff --git a/src/libsyntax_ext/asm.rs b/src/libsyntax_ext/asm.rs
index bd345a9a7da..5ec24b7a7ac 100644
--- a/src/libsyntax_ext/asm.rs
+++ b/src/libsyntax_ext/asm.rs
@@ -3,7 +3,6 @@
 use State::*;
 
 use errors::{DiagnosticBuilder, PResult};
-use rustc_data_structures::thin_vec::ThinVec;
 use rustc_parse::parser::Parser;
 use syntax_expand::base::*;
 use syntax_pos::Span;
@@ -63,7 +62,7 @@ pub fn expand_asm<'cx>(cx: &'cx mut ExtCtxt<'_>,
         id: ast::DUMMY_NODE_ID,
         kind: ast::ExprKind::InlineAsm(P(inline_asm)),
         span: cx.with_def_site_ctxt(sp),
-        attrs: ThinVec::new(),
+        attrs: ast::AttrVec::new(),
     }))
 }
 
diff --git a/src/libsyntax_ext/concat_idents.rs b/src/libsyntax_ext/concat_idents.rs
index 8a1bc56cf1c..7d8bc8b87bc 100644
--- a/src/libsyntax_ext/concat_idents.rs
+++ b/src/libsyntax_ext/concat_idents.rs
@@ -1,5 +1,3 @@
-use rustc_data_structures::thin_vec::ThinVec;
-
 use syntax::ast;
 use syntax_expand::base::{self, *};
 use syntax::token::{self, Token};
@@ -49,7 +47,7 @@ pub fn expand_concat_idents<'cx>(cx: &'cx mut ExtCtxt<'_>,
                 id: ast::DUMMY_NODE_ID,
                 kind: ast::ExprKind::Path(None, ast::Path::from_ident(self.ident)),
                 span: self.ident.span,
-                attrs: ThinVec::new(),
+                attrs: ast::AttrVec::new(),
             }))
         }
 
diff --git a/src/libsyntax_ext/deriving/debug.rs b/src/libsyntax_ext/deriving/debug.rs
index 35298211e4d..132ce76e1bb 100644
--- a/src/libsyntax_ext/deriving/debug.rs
+++ b/src/libsyntax_ext/deriving/debug.rs
@@ -2,8 +2,6 @@ use crate::deriving::path_std;
 use crate::deriving::generic::*;
 use crate::deriving::generic::ty::*;
 
-use rustc_data_structures::thin_vec::ThinVec;
-
 use syntax::ast::{self, Ident};
 use syntax::ast::{Expr, MetaItem};
 use syntax_expand::base::{Annotatable, ExtCtxt};
@@ -127,7 +125,7 @@ fn stmt_let_undescore(cx: &mut ExtCtxt<'_>, sp: Span, expr: P<ast::Expr>) -> ast
         init: Some(expr),
         id: ast::DUMMY_NODE_ID,
         span: sp,
-        attrs: ThinVec::new(),
+        attrs: ast::AttrVec::new(),
     });
     ast::Stmt {
         id: ast::DUMMY_NODE_ID,
diff --git a/src/libsyntax_ext/deriving/generic/mod.rs b/src/libsyntax_ext/deriving/generic/mod.rs
index b7707bfb8e5..5158a5b3da2 100644
--- a/src/libsyntax_ext/deriving/generic/mod.rs
+++ b/src/libsyntax_ext/deriving/generic/mod.rs
@@ -181,7 +181,6 @@ use std::cell::RefCell;
 use std::iter;
 use std::vec;
 
-use rustc_data_structures::thin_vec::ThinVec;
 use syntax::ast::{self, BinOpKind, EnumDef, Expr, Generics, Ident, PatKind};
 use syntax::ast::{VariantData, GenericParamKind, GenericArg};
 use syntax::attr;
@@ -919,7 +918,7 @@ impl<'a> MethodDef<'a> {
         let args = {
             let self_args = explicit_self.map(|explicit_self| {
                 let ident = Ident::with_dummy_span(kw::SelfLower).with_span_pos(trait_.span);
-                ast::Param::from_self(ThinVec::default(), explicit_self, ident)
+                ast::Param::from_self(ast::AttrVec::default(), explicit_self, ident)
             });
             let nonself_args = arg_types.into_iter()
                 .map(|(name, ty)| cx.param(trait_.span, name, ty));
@@ -1608,7 +1607,7 @@ impl<'a> TraitDef<'a> {
                         ast::FieldPat {
                             ident: ident.unwrap(),
                             is_shorthand: false,
-                            attrs: ThinVec::new(),
+                            attrs: ast::AttrVec::new(),
                             id: ast::DUMMY_NODE_ID,
                             span: pat.span.with_ctxt(self.span.ctxt()),
                             pat,