Rollup merge of #133021 - nnethercote:refactor-configure_annotatable, r=petrochenkov

Refactor `configure_annotatable`

This PR streamlines `configure_annotatable` and nearby code considerably.

r? `@petrochenkov`

Author: matthiaskrgr

compiler/rustc_builtin_macros/src/cfg_eval.rs

@@ -39,50 +39,10 @@ pub(crate) fn cfg_eval(
     let features = Some(features);
     CfgEval(StripUnconfigured { sess, features, config_tokens: true, lint_node_id })
         .configure_annotatable(annotatable)
-        // Since the item itself has already been configured by the `InvocationCollector`,
-        // we know that fold result vector will contain exactly one element.
-        .unwrap()
 }
 
 struct CfgEval<'a>(StripUnconfigured<'a>);
 
-fn flat_map_annotatable(
-    vis: &mut impl MutVisitor,
-    annotatable: Annotatable,
-) -> Option<Annotatable> {
-    match annotatable {
-        Annotatable::Item(item) => vis.flat_map_item(item).pop().map(Annotatable::Item),
-        Annotatable::AssocItem(item, ctxt) => {
-            Some(Annotatable::AssocItem(vis.flat_map_assoc_item(item, ctxt).pop()?, ctxt))
-        }
-        Annotatable::ForeignItem(item) => {
-            vis.flat_map_foreign_item(item).pop().map(Annotatable::ForeignItem)
-        }
-        Annotatable::Stmt(stmt) => {
-            vis.flat_map_stmt(stmt.into_inner()).pop().map(P).map(Annotatable::Stmt)
-        }
-        Annotatable::Expr(mut expr) => {
-            vis.visit_expr(&mut expr);
-            Some(Annotatable::Expr(expr))
-        }
-        Annotatable::Arm(arm) => vis.flat_map_arm(arm).pop().map(Annotatable::Arm),
-        Annotatable::ExprField(field) => {
-            vis.flat_map_expr_field(field).pop().map(Annotatable::ExprField)
-        }
-        Annotatable::PatField(fp) => vis.flat_map_pat_field(fp).pop().map(Annotatable::PatField),
-        Annotatable::GenericParam(param) => {
-            vis.flat_map_generic_param(param).pop().map(Annotatable::GenericParam)
-        }
-        Annotatable::Param(param) => vis.flat_map_param(param).pop().map(Annotatable::Param),
-        Annotatable::FieldDef(sf) => vis.flat_map_field_def(sf).pop().map(Annotatable::FieldDef),
-        Annotatable::Variant(v) => vis.flat_map_variant(v).pop().map(Annotatable::Variant),
-        Annotatable::Crate(mut krate) => {
-            vis.visit_crate(&mut krate);
-            Some(Annotatable::Crate(krate))
-        }
-    }
-}
-
 fn has_cfg_or_cfg_attr(annotatable: &Annotatable) -> bool {
     struct CfgFinder;
 
@@ -106,14 +66,7 @@ fn has_cfg_or_cfg_attr(annotatable: &Annotatable) -> bool {
         Annotatable::ForeignItem(item) => CfgFinder.visit_foreign_item(item),
         Annotatable::Stmt(stmt) => CfgFinder.visit_stmt(stmt),
         Annotatable::Expr(expr) => CfgFinder.visit_expr(expr),
-        Annotatable::Arm(arm) => CfgFinder.visit_arm(arm),
-        Annotatable::ExprField(field) => CfgFinder.visit_expr_field(field),
-        Annotatable::PatField(field) => CfgFinder.visit_pat_field(field),
-        Annotatable::GenericParam(param) => CfgFinder.visit_generic_param(param),
-        Annotatable::Param(param) => CfgFinder.visit_param(param),
-        Annotatable::FieldDef(field) => CfgFinder.visit_field_def(field),
-        Annotatable::Variant(variant) => CfgFinder.visit_variant(variant),
-        Annotatable::Crate(krate) => CfgFinder.visit_crate(krate),
+        _ => unreachable!(),
     };
     res.is_break()
 }
@@ -123,11 +76,11 @@ impl CfgEval<'_> {
         self.0.configure(node)
     }
 
-    fn configure_annotatable(&mut self, mut annotatable: Annotatable) -> Option<Annotatable> {
+    fn configure_annotatable(mut self, annotatable: Annotatable) -> Annotatable {
         // Tokenizing and re-parsing the `Annotatable` can have a significant
         // performance impact, so try to avoid it if possible
         if !has_cfg_or_cfg_attr(&annotatable) {
-            return Some(annotatable);
+            return annotatable;
         }
 
         // The majority of parsed attribute targets will never need to have early cfg-expansion
@@ -140,39 +93,6 @@ impl CfgEval<'_> {
         // the location of `#[cfg]` and `#[cfg_attr]` in the token stream. The tokenization
         // process is lossless, so this process is invisible to proc-macros.
 
-        let parse_annotatable_with: for<'a> fn(&mut Parser<'a>) -> PResult<'a, _> =
-            match annotatable {
-                Annotatable::Item(_) => {
-                    |parser| Ok(Annotatable::Item(parser.parse_item(ForceCollect::Yes)?.unwrap()))
-                }
-                Annotatable::AssocItem(_, AssocCtxt::Trait) => |parser| {
-                    Ok(Annotatable::AssocItem(
-                        parser.parse_trait_item(ForceCollect::Yes)?.unwrap().unwrap(),
-                        AssocCtxt::Trait,
-                    ))
-                },
-                Annotatable::AssocItem(_, AssocCtxt::Impl) => |parser| {
-                    Ok(Annotatable::AssocItem(
-                        parser.parse_impl_item(ForceCollect::Yes)?.unwrap().unwrap(),
-                        AssocCtxt::Impl,
-                    ))
-                },
-                Annotatable::ForeignItem(_) => |parser| {
-                    Ok(Annotatable::ForeignItem(
-                        parser.parse_foreign_item(ForceCollect::Yes)?.unwrap().unwrap(),
-                    ))
-                },
-                Annotatable::Stmt(_) => |parser| {
-                    Ok(Annotatable::Stmt(P(parser
-                        .parse_stmt_without_recovery(false, ForceCollect::Yes)?
-                        .unwrap())))
-                },
-                Annotatable::Expr(_) => {
-                    |parser| Ok(Annotatable::Expr(parser.parse_expr_force_collect()?))
-                }
-                _ => unreachable!(),
-            };
-
         // 'Flatten' all nonterminals (i.e. `TokenKind::Interpolated`)
         // to `None`-delimited groups containing the corresponding tokens. This
         // is normally delayed until the proc-macro server actually needs to
@@ -191,19 +111,56 @@ impl CfgEval<'_> {
         // Re-parse the tokens, setting the `capture_cfg` flag to save extra information
         // to the captured `AttrTokenStream` (specifically, we capture
         // `AttrTokenTree::AttrsTarget` for all occurrences of `#[cfg]` and `#[cfg_attr]`)
+        //
+        // After that we have our re-parsed `AttrTokenStream`, recursively configuring
+        // our attribute target will correctly configure the tokens as well.
         let mut parser = Parser::new(&self.0.sess.psess, orig_tokens, None);
         parser.capture_cfg = true;
-        match parse_annotatable_with(&mut parser) {
-            Ok(a) => annotatable = a,
+        let res: PResult<'_, Annotatable> = try {
+            match annotatable {
+                Annotatable::Item(_) => {
+                    let item = parser.parse_item(ForceCollect::Yes)?.unwrap();
+                    Annotatable::Item(self.flat_map_item(item).pop().unwrap())
+                }
+                Annotatable::AssocItem(_, AssocCtxt::Trait) => {
+                    let item = parser.parse_trait_item(ForceCollect::Yes)?.unwrap().unwrap();
+                    Annotatable::AssocItem(
+                        self.flat_map_assoc_item(item, AssocCtxt::Trait).pop().unwrap(),
+                        AssocCtxt::Trait,
+                    )
+                }
+                Annotatable::AssocItem(_, AssocCtxt::Impl) => {
+                    let item = parser.parse_impl_item(ForceCollect::Yes)?.unwrap().unwrap();
+                    Annotatable::AssocItem(
+                        self.flat_map_assoc_item(item, AssocCtxt::Impl).pop().unwrap(),
+                        AssocCtxt::Impl,
+                    )
+                }
+                Annotatable::ForeignItem(_) => {
+                    let item = parser.parse_foreign_item(ForceCollect::Yes)?.unwrap().unwrap();
+                    Annotatable::ForeignItem(self.flat_map_foreign_item(item).pop().unwrap())
+                }
+                Annotatable::Stmt(_) => {
+                    let stmt =
+                        parser.parse_stmt_without_recovery(false, ForceCollect::Yes)?.unwrap();
+                    Annotatable::Stmt(P(self.flat_map_stmt(stmt).pop().unwrap()))
+                }
+                Annotatable::Expr(_) => {
+                    let mut expr = parser.parse_expr_force_collect()?;
+                    self.visit_expr(&mut expr);
+                    Annotatable::Expr(expr)
+                }
+                _ => unreachable!(),
+            }
+        };
+
+        match res {
+            Ok(ann) => ann,
             Err(err) => {
                 err.emit();
-                return Some(annotatable);
+                annotatable
             }
         }
-
-        // Now that we have our re-parsed `AttrTokenStream`, recursively configuring
-        // our attribute target will correctly configure the tokens as well.
-        flat_map_annotatable(self, annotatable)
     }
 }