resolve: Remove `Scope::CrateRoot`

Use `Scope::Module` with the crate root module inside instead, which should be identical.

4 files changed, 39 insertions, 57 deletions

diff --git a/compiler/rustc_resolve/src/diagnostics.rs b/compiler/rustc_resolve/src/diagnostics.rs
index d72fbc189e7..75eed1e9ad3 100644
--- a/compiler/rustc_resolve/src/diagnostics.rs
+++ b/compiler/rustc_resolve/src/diagnostics.rs
@@ -1076,11 +1076,6 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                         }
                     }
                 }
-                Scope::CrateRoot => {
-                    let root_ident = Ident::new(kw::PathRoot, ident.span);
-                    let root_module = this.resolve_crate_root(root_ident);
-                    this.add_module_candidates(root_module, &mut suggestions, filter_fn, None);
-                }
                 Scope::Module(module, _) => {
                     this.add_module_candidates(module, &mut suggestions, filter_fn, None);
                 }
diff --git a/compiler/rustc_resolve/src/ident.rs b/compiler/rustc_resolve/src/ident.rs
index 34941398a2b..71cc68af499 100644
--- a/compiler/rustc_resolve/src/ident.rs
+++ b/compiler/rustc_resolve/src/ident.rs
@@ -93,20 +93,21 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
         // 6. Language prelude: builtin attributes (closed, controlled).
 
         let rust_2015 = ctxt.edition().is_rust_2015();
-        let (ns, macro_kind, is_absolute_path) = match scope_set {
-            ScopeSet::All(ns) => (ns, None, false),
-            ScopeSet::AbsolutePath(ns) => (ns, None, true),
-            ScopeSet::Macro(macro_kind) => (MacroNS, Some(macro_kind), false),
-            ScopeSet::Late(ns, ..) => (ns, None, false),
+        let (ns, macro_kind) = match scope_set {
+            ScopeSet::All(ns)
+            | ScopeSet::ModuleAndExternPrelude(ns, _)
+            | ScopeSet::Late(ns, ..) => (ns, None),
+            ScopeSet::Macro(macro_kind) => (MacroNS, Some(macro_kind)),
         };
         let module = match scope_set {
             // Start with the specified module.
-            ScopeSet::Late(_, module, _) => module,
+            ScopeSet::Late(_, module, _) | ScopeSet::ModuleAndExternPrelude(_, module) => module,
             // Jump out of trait or enum modules, they do not act as scopes.
             _ => parent_scope.module.nearest_item_scope(),
         };
+        let module_and_extern_prelude = matches!(scope_set, ScopeSet::ModuleAndExternPrelude(..));
         let mut scope = match ns {
-            _ if is_absolute_path => Scope::CrateRoot,
+            _ if module_and_extern_prelude => Scope::Module(module, None),
             TypeNS | ValueNS => Scope::Module(module, None),
             MacroNS => Scope::DeriveHelpers(parent_scope.expansion),
         };
@@ -134,11 +135,10 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                     }
                     true
                 }
-                Scope::CrateRoot => true,
                 Scope::Module(..) => true,
                 Scope::MacroUsePrelude => use_prelude || rust_2015,
                 Scope::BuiltinAttrs => true,
-                Scope::ExternPrelude => use_prelude || is_absolute_path,
+                Scope::ExternPrelude => use_prelude || module_and_extern_prelude,
                 Scope::ToolPrelude => use_prelude,
                 Scope::StdLibPrelude => use_prelude || ns == MacroNS,
                 Scope::BuiltinTypes => true,
@@ -174,7 +174,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                     }
                     MacroRulesScope::Empty => Scope::Module(module, None),
                 },
-                Scope::CrateRoot => match ns {
+                Scope::Module(..) if module_and_extern_prelude => match ns {
                     TypeNS => {
                         ctxt.adjust(ExpnId::root());
                         Scope::ExternPrelude
@@ -203,7 +203,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                 }
                 Scope::MacroUsePrelude => Scope::StdLibPrelude,
                 Scope::BuiltinAttrs => break, // nowhere else to search
-                Scope::ExternPrelude if is_absolute_path => break,
+                Scope::ExternPrelude if module_and_extern_prelude => break,
                 Scope::ExternPrelude => Scope::ToolPrelude,
                 Scope::ToolPrelude => Scope::StdLibPrelude,
                 Scope::StdLibPrelude => match ns {
@@ -404,10 +404,10 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
         }
 
         let (ns, macro_kind) = match scope_set {
-            ScopeSet::All(ns) => (ns, None),
-            ScopeSet::AbsolutePath(ns) => (ns, None),
+            ScopeSet::All(ns)
+            | ScopeSet::ModuleAndExternPrelude(ns, _)
+            | ScopeSet::Late(ns, ..) => (ns, None),
             ScopeSet::Macro(macro_kind) => (MacroNS, Some(macro_kind)),
-            ScopeSet::Late(ns, ..) => (ns, None),
         };
 
         // This is *the* result, resolution from the scope closest to the resolved identifier.
@@ -487,31 +487,16 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                         MacroRulesScope::Invocation(_) => Err(Determinacy::Undetermined),
                         _ => Err(Determinacy::Determined),
                     },
-                    Scope::CrateRoot => {
-                        let root_ident = Ident::new(kw::PathRoot, ident.span);
-                        let root_module = this.resolve_crate_root(root_ident);
-                        let binding = this.resolve_ident_in_module(
-                            ModuleOrUniformRoot::Module(root_module),
-                            ident,
-                            ns,
-                            parent_scope,
-                            finalize,
-                            ignore_binding,
-                            ignore_import,
-                        );
-                        match binding {
-                            Ok(binding) => Ok((binding, Flags::MODULE | Flags::MISC_SUGGEST_CRATE)),
-                            Err((Determinacy::Undetermined, Weak::No)) => {
-                                return Some(Err(Determinacy::determined(force)));
-                            }
-                            Err((Determinacy::Undetermined, Weak::Yes)) => {
-                                Err(Determinacy::Undetermined)
-                            }
-                            Err((Determinacy::Determined, _)) => Err(Determinacy::Determined),
-                        }
-                    }
                     Scope::Module(module, derive_fallback_lint_id) => {
-                        let adjusted_parent_scope = &ParentScope { module, ..*parent_scope };
+                        let (adjusted_parent_scope, finalize) =
+                            if matches!(scope_set, ScopeSet::ModuleAndExternPrelude(..)) {
+                                (parent_scope, finalize)
+                            } else {
+                                (
+                                    &ParentScope { module, ..*parent_scope },
+                                    finalize.map(|f| Finalize { used: Used::Scope, ..f }),
+                                )
+                            };
                         let binding = this.resolve_ident_in_module_unadjusted(
                             ModuleOrUniformRoot::Module(module),
                             ident,
@@ -522,7 +507,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                             } else {
                                 Shadowing::Restricted
                             },
-                            finalize.map(|finalize| Finalize { used: Used::Scope, ..finalize }),
+                            finalize,
                             ignore_binding,
                             ignore_import,
                         );
@@ -776,7 +761,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
             ModuleOrUniformRoot::ExternPrelude => {
                 ident.span.normalize_to_macros_2_0_and_adjust(ExpnId::root());
             }
-            ModuleOrUniformRoot::CrateRootAndExternPrelude | ModuleOrUniformRoot::CurrentScope => {
+            ModuleOrUniformRoot::ModuleAndExternPrelude(..) | ModuleOrUniformRoot::CurrentScope => {
                 // No adjustments
             }
         }
@@ -810,11 +795,11 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
     ) -> Result<NameBinding<'ra>, (Determinacy, Weak)> {
         let module = match module {
             ModuleOrUniformRoot::Module(module) => module,
-            ModuleOrUniformRoot::CrateRootAndExternPrelude => {
+            ModuleOrUniformRoot::ModuleAndExternPrelude(module) => {
                 assert_eq!(shadowing, Shadowing::Unrestricted);
                 let binding = self.early_resolve_ident_in_lexical_scope(
                     ident,
-                    ScopeSet::AbsolutePath(ns),
+                    ScopeSet::ModuleAndExternPrelude(ns, module),
                     parent_scope,
                     finalize,
                     finalize.is_some(),
@@ -1531,7 +1516,8 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                         && self.tcx.sess.at_least_rust_2018()
                     {
                         // `::a::b` from 2015 macro on 2018 global edition
-                        module = Some(ModuleOrUniformRoot::CrateRootAndExternPrelude);
+                        let crate_root = self.resolve_crate_root(ident);
+                        module = Some(ModuleOrUniformRoot::ModuleAndExternPrelude(crate_root));
                         continue;
                     }
                     if name == kw::PathRoot || name == kw::Crate || name == kw::DollarCrate {
diff --git a/compiler/rustc_resolve/src/imports.rs b/compiler/rustc_resolve/src/imports.rs
index 783c5005cca..986e703c0d2 100644
--- a/compiler/rustc_resolve/src/imports.rs
+++ b/compiler/rustc_resolve/src/imports.rs
@@ -181,10 +181,10 @@ pub(crate) struct ImportData<'ra> {
     ///
     /// | `module_path` | `imported_module` | remark |
     /// |-|-|-|
-    /// |`use prefix::foo`| `ModuleOrUniformRoot::Module(prefix)`               | - |
-    /// |`use ::foo`      | `ModuleOrUniformRoot::ExternPrelude`                | 2018+ editions |
-    /// |`use ::foo`      | `ModuleOrUniformRoot::CrateRootAndExternPrelude`    | a special case in 2015 edition |
-    /// |`use foo`        | `ModuleOrUniformRoot::CurrentScope`                 | - |
+    /// |`use prefix::foo`| `ModuleOrUniformRoot::Module(prefix)`         | - |
+    /// |`use ::foo`      | `ModuleOrUniformRoot::ExternPrelude`          | 2018+ editions |
+    /// |`use ::foo`      | `ModuleOrUniformRoot::ModuleAndExternPrelude` | a special case in 2015 edition |
+    /// |`use foo`        | `ModuleOrUniformRoot::CurrentScope`           | - |
     pub imported_module: Cell<Option<ModuleOrUniformRoot<'ra>>>,
     pub vis: Visibility,
 }
diff --git a/compiler/rustc_resolve/src/lib.rs b/compiler/rustc_resolve/src/lib.rs
index 08f1f61ea86..27e14e0e62b 100644
--- a/compiler/rustc_resolve/src/lib.rs
+++ b/compiler/rustc_resolve/src/lib.rs
@@ -119,7 +119,6 @@ enum Scope<'ra> {
     DeriveHelpers(LocalExpnId),
     DeriveHelpersCompat,
     MacroRules(MacroRulesScopeRef<'ra>),
-    CrateRoot,
     // The node ID is for reporting the `PROC_MACRO_DERIVE_RESOLUTION_FALLBACK`
     // lint if it should be reported.
     Module(Module<'ra>, Option<NodeId>),
@@ -139,8 +138,8 @@ enum Scope<'ra> {
 enum ScopeSet<'ra> {
     /// All scopes with the given namespace.
     All(Namespace),
-    /// Crate root, then extern prelude (used for mixed 2015-2018 mode in macros).
-    AbsolutePath(Namespace),
+    /// A module, then extern prelude (used for mixed 2015-2018 mode in macros).
+    ModuleAndExternPrelude(Namespace, Module<'ra>),
     /// All scopes with macro namespace and the given macro kind restriction.
     Macro(MacroKind),
     /// All scopes with the given namespace, used for partially performing late resolution.
@@ -419,8 +418,10 @@ enum ModuleOrUniformRoot<'ra> {
     /// Regular module.
     Module(Module<'ra>),
 
-    /// Virtual module that denotes resolution in crate root with fallback to extern prelude.
-    CrateRootAndExternPrelude,
+    /// Virtual module that denotes resolution in a module with fallback to extern prelude.
+    /// Used for paths starting with `::` coming from 2015 edition macros
+    /// used in 2018+ edition crates.
+    ModuleAndExternPrelude(Module<'ra>),
 
     /// Virtual module that denotes resolution in extern prelude.
     /// Used for paths starting with `::` on 2018 edition.