Auto merge of #52841 - petrochenkov:premacro, r=alexcrichton

resolve: Implement prelude search for macro paths, implement tool attributes

When identifier is macro path is resolved in scopes (i.e. the first path segment - `foo` in `foo::mac!()` or `foo!()`), scopes are searched in the same order as for non-macro paths - items in modules, extern prelude, tool prelude (see later), standard library prelude, language prelude, but with some extra shadowing restrictions (names from globs and macro expansions cannot shadow names from outer scopes). See the comment in `fn resolve_lexical_macro_path_segment` for more details.

"Tool prelude" currently contains two "tool modules" `rustfmt` and `clippy`, and is searched immediately after extern prelude.
This makes the [possible long-term solution](https://github.com/rust-lang/rfcs/blob/master/text/2103-tool-attributes.md#long-term-solution) for tool attributes exactly equivalent to the existing extern prelude scheme, except that `--extern=my_crate` making crate names available in scope is replaced with something like `--tool=my_tool` making tool names available in scope.

The `tool_attributes` feature is still unstable and `#![feature(tool_attributes)]` now implicitly enables `#![feature(use_extern_macros)]`. `use_extern_macros` is a prerequisite for `tool_attributes`, so their stabilization will happen in the same order.
If `use_extern_macros` is not enabled, then tool attributes are treated as custom attributes (this is temporary, anyway).

Fixes #52576
Fixes #52512
Fixes #51277
cc #52269

src/librustc/hir/def.rs

@@ -49,6 +49,7 @@ pub enum Def {
     PrimTy(hir::PrimTy),
     TyParam(DefId),
     SelfTy(Option<DefId> /* trait */, Option<DefId> /* impl */),
+    ToolMod, // e.g. `rustfmt` in `#[rustfmt::skip]`
 
     // Value namespace
     Fn(DefId),
@@ -67,6 +68,7 @@ pub enum Def {
 
     // Macro namespace
     Macro(DefId, MacroKind),
+    NonMacroAttr, // e.g. `#[inline]` or `#[rustfmt::skip]`
 
     GlobalAsm(DefId),
 
@@ -259,6 +261,8 @@ impl Def {
             Def::Label(..)  |
             Def::PrimTy(..) |
             Def::SelfTy(..) |
+            Def::ToolMod |
+            Def::NonMacroAttr |
             Def::Err => {
                 bug!("attempted .def_id() on invalid def: {:?}", self)
             }
@@ -299,6 +303,8 @@ impl Def {
             Def::SelfTy(..) => "self type",
             Def::Macro(.., macro_kind) => macro_kind.descr(),
             Def::GlobalAsm(..) => "global asm",
+            Def::ToolMod => "tool module",
+            Def::NonMacroAttr => "non-macro attribute",
             Def::Err => "unresolved item",
         }
     }

src/librustc/ich/impls_hir.rs

@@ -1016,6 +1016,8 @@ impl_stable_hash_for!(enum hir::def::Def {
     Label(node_id),
     Macro(def_id, macro_kind),
     GlobalAsm(def_id),
+    ToolMod,
+    NonMacroAttr,
     Err
 });
 

src/librustc_resolve/build_reduced_graph.rs

@@ -629,7 +629,8 @@ impl<'a> Resolver<'a> {
     pub fn get_macro(&mut self, def: Def) -> Lrc<SyntaxExtension> {
         let def_id = match def {
             Def::Macro(def_id, ..) => def_id,
-            _ => panic!("Expected Def::Macro(..)"),
+            Def::NonMacroAttr => return Lrc::new(SyntaxExtension::NonMacroAttr),
+            _ => panic!("Expected Def::Macro(..) or Def::NonMacroAttr"),
         };
         if let Some(ext) = self.macro_map.get(&def_id) {
             return ext.clone();

src/librustc_resolve/check_unused.rs

@@ -131,8 +131,7 @@ pub fn check_crate(resolver: &mut Resolver, krate: &ast::Crate) {
                  directive.vis.get() == ty::Visibility::Public ||
                  directive.span.is_dummy() => {
                 if let ImportDirectiveSubclass::MacroUse = directive.subclass {
-                    if resolver.session.features_untracked().use_extern_macros &&
-                        !directive.span.is_dummy() {
+                    if resolver.use_extern_macros && !directive.span.is_dummy() {
                         resolver.session.buffer_lint(
                             lint::builtin::MACRO_USE_EXTERN_CRATE,
                             directive.id,

src/librustc_resolve/lib.rs

@@ -86,6 +86,10 @@ mod check_unused;
 mod build_reduced_graph;
 mod resolve_imports;
 
+fn is_known_tool(name: Name) -> bool {
+    ["clippy", "rustfmt"].contains(&&*name.as_str())
+}
+
 /// A free importable items suggested in case of resolution failure.
 struct ImportSuggestion {
     path: Path,
@@ -200,15 +204,10 @@ fn resolve_struct_error<'sess, 'a>(resolver: &'sess Resolver,
                         err.span_label(typaram_span, "type variable from outer function");
                     }
                 },
-                Def::Mod(..) | Def::Struct(..) | Def::Union(..) | Def::Enum(..) | Def::Variant(..) |
-                Def::Trait(..) | Def::TyAlias(..) | Def::TyForeign(..) | Def::TraitAlias(..) |
-                Def::AssociatedTy(..) | Def::PrimTy(..) | Def::Fn(..) | Def::Const(..) |
-                Def::Static(..) | Def::StructCtor(..) | Def::VariantCtor(..) | Def::Method(..) |
-                Def::AssociatedConst(..) | Def::Local(..) | Def::Upvar(..) | Def::Label(..) |
-                Def::Existential(..) | Def::AssociatedExistential(..) |
-                Def::Macro(..) | Def::GlobalAsm(..) | Def::Err =>
+                _ => {
                     bug!("TypeParametersFromOuterFunction should only be used with Def::SelfTy or \
                          Def::TyParam")
+                }
             }
 
             // Try to retrieve the span of the function signature and generate a new message with
@@ -1711,9 +1710,7 @@ impl<'a> Resolver<'a> {
                 vis: ty::Visibility::Public,
             }),
 
-            // The `proc_macro` and `decl_macro` features imply `use_extern_macros`
-            use_extern_macros:
-                features.use_extern_macros || features.decl_macro,
+            use_extern_macros: features.use_extern_macros(),
 
             crate_loader,
             macro_names: FxHashSet(),
@@ -1846,6 +1843,7 @@ impl<'a> Resolver<'a> {
                                       path_span: Span)
                                       -> Option<LexicalScopeBinding<'a>> {
         let record_used = record_used_id.is_some();
+        assert!(ns == TypeNS  || ns == ValueNS);
         if ns == TypeNS {
             ident.span = if ident.name == keywords::SelfType.name() {
                 // FIXME(jseyfried) improve `Self` hygiene
@@ -1922,8 +1920,9 @@ impl<'a> Resolver<'a> {
                     return Some(LexicalScopeBinding::Item(binding))
                 }
                 _ if poisoned.is_some() => break,
-                Err(Undetermined) => return None,
-                Err(Determined) => {}
+                Err(Determined) => continue,
+                Err(Undetermined) =>
+                    span_bug!(ident.span, "undetermined resolution during main resolution pass"),
             }
         }
 
@@ -1945,6 +1944,11 @@ impl<'a> Resolver<'a> {
                                ident.span, Mark::root()).to_name_binding(self.arenas);
                 return Some(LexicalScopeBinding::Item(binding));
             }
+            if ns == TypeNS && is_known_tool(ident.name) {
+                let binding = (Def::ToolMod, ty::Visibility::Public,
+                               ident.span, Mark::root()).to_name_binding(self.arenas);
+                return Some(LexicalScopeBinding::Item(binding));
+            }
             if let Some(prelude) = self.prelude {
                 if let Ok(binding) = self.resolve_ident_in_module_unadjusted(prelude, ident, ns,
                                                                         false, false, path_span) {
@@ -3505,6 +3509,8 @@ impl<'a> Resolver<'a> {
                     let maybe_assoc = opt_ns != Some(MacroNS) && PathSource::Type.is_expected(def);
                     if let Some(next_module) = binding.module() {
                         module = Some(next_module);
+                    } else if def == Def::ToolMod && i + 1 != path.len() {
+                        return PathResult::NonModule(PathResolution::new(Def::NonMacroAttr))
                     } else if def == Def::Err {
                         return PathResult::NonModule(err_path_resolution());
                     } else if opt_ns.is_some() && (is_last || maybe_assoc) {