Rollup merge of rust-lang#79185 - petrochenkov:derattr2, r=Aaron1011

expand/resolve: Pre-requisites to "Turn `#[derive]` into a regular macro attribute"

Miscellaneous refactorings and error reporting changes extracted from rust-lang#79078.

Unlike rust-lang#79078 this PR doesn't make any observable changes to the language or library.
r? ```@Aaron1011```

Author: Dylan-DPC

Diff for: compiler/rustc_builtin_macros/src/cfg_accessible.rs

@@ -1,7 +1,7 @@
 //! Implementation of the `#[cfg_accessible(path)]` attribute macro.
 
 use rustc_ast as ast;
-use rustc_expand::base::{Annotatable, ExpandResult, ExtCtxt, MultiItemModifier};
+use rustc_expand::base::{Annotatable, ExpandResult, ExtCtxt, Indeterminate, MultiItemModifier};
 use rustc_feature::AttributeTemplate;
 use rustc_parse::validate_attr;
 use rustc_span::symbol::sym;
@@ -31,7 +31,7 @@ impl MultiItemModifier for Expander {
     fn expand(
         &self,
         ecx: &mut ExtCtxt<'_>,
-        _span: Span,
+        span: Span,
         meta_item: &ast::MetaItem,
         item: Annotatable,
     ) -> ExpandResult<Vec<Annotatable>, Annotatable> {
@@ -49,11 +49,14 @@ impl MultiItemModifier for Expander {
             None => return ExpandResult::Ready(Vec::new()),
         };
 
-        let failure_msg = "cannot determine whether the path is accessible or not";
         match ecx.resolver.cfg_accessible(ecx.current_expansion.id, path) {
             Ok(true) => ExpandResult::Ready(vec![item]),
             Ok(false) => ExpandResult::Ready(Vec::new()),
-            Err(_) => ExpandResult::Retry(item, failure_msg.into()),
+            Err(Indeterminate) if ecx.force_mode => {
+                ecx.span_err(span, "cannot determine whether the path is accessible or not");
+                ExpandResult::Ready(vec![item])
+            }
+            Err(Indeterminate) => ExpandResult::Retry(item),
         }
     }
 }

Diff for: compiler/rustc_builtin_macros/src/deriving/generic/mod.rs

@@ -407,13 +407,7 @@ impl<'a> TraitDef<'a> {
                             _ => false,
                         })
                     }
-                    _ => {
-                        // Non-ADT derive is an error, but it should have been
-                        // set earlier; see
-                        // librustc_expand/expand.rs:MacroExpander::fully_expand_fragment()
-                        // librustc_expand/base.rs:Annotatable::derive_allowed()
-                        return;
-                    }
+                    _ => unreachable!(),
                 };
                 let container_id = cx.current_expansion.id.expn_data().parent;
                 let always_copy = has_no_type_params && cx.resolver.has_derive_copy(container_id);
@@ -475,12 +469,7 @@ impl<'a> TraitDef<'a> {
                 );
                 push(Annotatable::Item(P(ast::Item { attrs, ..(*newitem).clone() })))
             }
-            _ => {
-                // Non-Item derive is an error, but it should have been
-                // set earlier; see
-                // librustc_expand/expand.rs:MacroExpander::fully_expand_fragment()
-                // librustc_expand/base.rs:Annotatable::derive_allowed()
-            }
+            _ => unreachable!(),
         }
     }
 

Diff for: compiler/rustc_builtin_macros/src/deriving/mod.rs

@@ -98,13 +98,7 @@ fn inject_impl_of_structural_trait(
 ) {
     let item = match *item {
         Annotatable::Item(ref item) => item,
-        _ => {
-            // Non-Item derive is an error, but it should have been
-            // set earlier; see
-            // librustc_expand/expand.rs:MacroExpander::fully_expand_fragment()
-            // librustc_expand/base.rs:Annotatable::derive_allowed()
-            return;
-        }
+        _ => unreachable!(),
     };
 
     let generics = match item.kind {

Diff for: compiler/rustc_expand/src/base.rs

@@ -251,8 +251,7 @@ pub enum ExpandResult<T, U> {
     /// Expansion produced a result (possibly dummy).
     Ready(T),
     /// Expansion could not produce a result and needs to be retried.
-    /// The string is an explanation that will be printed if we are stuck in an infinite retry loop.
-    Retry(U, String),
+    Retry(U),
 }
 
 // `meta_item` is the attribute, and `item` is the item being modified.
@@ -889,8 +888,10 @@ pub trait ResolverExpand {
     /// Some parent node that is close enough to the given macro call.
     fn lint_node_id(&mut self, expn_id: ExpnId) -> NodeId;
 
+    // Resolver interfaces for specific built-in macros.
+    /// Does `#[derive(...)]` attribute with the given `ExpnId` have built-in `Copy` inside it?
     fn has_derive_copy(&self, expn_id: ExpnId) -> bool;
-    fn add_derive_copy(&mut self, expn_id: ExpnId);
+    /// Path resolution logic for `#[cfg_accessible(path)]`.
     fn cfg_accessible(&mut self, expn_id: ExpnId, path: &ast::Path) -> Result<bool, Indeterminate>;
 }
 
@@ -919,6 +920,9 @@ pub struct ExtCtxt<'a> {
     pub root_path: PathBuf,
     pub resolver: &'a mut dyn ResolverExpand,
     pub current_expansion: ExpansionData,
+    /// Error recovery mode entered when expansion is stuck
+    /// (or during eager expansion, but that's a hack).
+    pub force_mode: bool,
     pub expansions: FxHashMap<Span, Vec<String>>,
     /// Called directly after having parsed an external `mod foo;` in expansion.
     pub(super) extern_mod_loaded: Option<&'a dyn Fn(&ast::Crate)>,
@@ -945,6 +949,7 @@ impl<'a> ExtCtxt<'a> {
                 directory_ownership: DirectoryOwnership::Owned { relative: None },
                 prior_type_ascription: None,
             },
+            force_mode: false,
             expansions: FxHashMap::default(),
         }
     }

Diff for: compiler/rustc_expand/src/config.rs

@@ -1,5 +1,7 @@
 //! Conditional compilation stripping.
 
+use crate::base::Annotatable;
+
 use rustc_ast::attr::HasAttrs;
 use rustc_ast::mut_visit::*;
 use rustc_ast::ptr::P;
@@ -496,6 +498,49 @@ impl<'a> StripUnconfigured<'a> {
     pub fn configure_fn_decl(&mut self, fn_decl: &mut ast::FnDecl) {
         fn_decl.inputs.flat_map_in_place(|arg| self.configure(arg));
     }
+
+    pub fn fully_configure(&mut self, item: Annotatable) -> Annotatable {
+        // Since the item itself has already been configured by the InvocationCollector,
+        // we know that fold result vector will contain exactly one element
+        match item {
+            Annotatable::Item(item) => Annotatable::Item(self.flat_map_item(item).pop().unwrap()),
+            Annotatable::TraitItem(item) => {
+                Annotatable::TraitItem(self.flat_map_trait_item(item).pop().unwrap())
+            }
+            Annotatable::ImplItem(item) => {
+                Annotatable::ImplItem(self.flat_map_impl_item(item).pop().unwrap())
+            }
+            Annotatable::ForeignItem(item) => {
+                Annotatable::ForeignItem(self.flat_map_foreign_item(item).pop().unwrap())
+            }
+            Annotatable::Stmt(stmt) => {
+                Annotatable::Stmt(stmt.map(|stmt| self.flat_map_stmt(stmt).pop().unwrap()))
+            }
+            Annotatable::Expr(mut expr) => Annotatable::Expr({
+                self.visit_expr(&mut expr);
+                expr
+            }),
+            Annotatable::Arm(arm) => Annotatable::Arm(self.flat_map_arm(arm).pop().unwrap()),
+            Annotatable::Field(field) => {
+                Annotatable::Field(self.flat_map_field(field).pop().unwrap())
+            }
+            Annotatable::FieldPat(fp) => {
+                Annotatable::FieldPat(self.flat_map_field_pattern(fp).pop().unwrap())
+            }
+            Annotatable::GenericParam(param) => {
+                Annotatable::GenericParam(self.flat_map_generic_param(param).pop().unwrap())
+            }
+            Annotatable::Param(param) => {
+                Annotatable::Param(self.flat_map_param(param).pop().unwrap())
+            }
+            Annotatable::StructField(sf) => {
+                Annotatable::StructField(self.flat_map_struct_field(sf).pop().unwrap())
+            }
+            Annotatable::Variant(v) => {
+                Annotatable::Variant(self.flat_map_variant(v).pop().unwrap())
+            }
+        }
+    }
 }
 
 impl<'a> MutVisitor for StripUnconfigured<'a> {