Auto merge of #53053 - petrochenkov:custattr, r=alexcrichton

resolve:  Support custom attributes when macro modularization is enabled

Basically, if resolution of a single-segment attribute is a determined error, then we interpret it as a custom attribute.

Since custom attributes are integrated into general macro resolution, `feature(custom_attribute)` now requires and implicitly enables macro modularization (`feature(use_extern_macros)`).
Actually, a few other "advanced" macro features now implicitly enable macro modularization too (and one bug was found and fixed in process of enabling it).

The first two commits are preliminary cleanups/refactorings.

src/librustc/hir/def.rs

@@ -28,6 +28,18 @@ pub enum CtorKind {
     Fictive,
 }
 
+#[derive(Clone, Copy, PartialEq, Eq, RustcEncodable, RustcDecodable, Hash, Debug)]
+pub enum NonMacroAttrKind {
+    /// Single-segment attribute defined by the language (`#[inline]`)
+    Builtin,
+    /// Multi-segment custom attribute living in a "tool module" (`#[rustfmt::skip]`).
+    Tool,
+    /// Single-segment custom attribute registered by a derive macro (`#[serde(default)]`).
+    DeriveHelper,
+    /// Single-segment custom attribute not registered in any way (`#[my_attr]`).
+    Custom,
+}
+
 #[derive(Clone, Copy, PartialEq, Eq, RustcEncodable, RustcDecodable, Hash, Debug)]
 pub enum Def {
     // Type namespace
@@ -68,7 +80,7 @@ pub enum Def {
 
     // Macro namespace
     Macro(DefId, MacroKind),
-    NonMacroAttr, // e.g. `#[inline]` or `#[rustfmt::skip]`
+    NonMacroAttr(NonMacroAttrKind), // e.g. `#[inline]` or `#[rustfmt::skip]`
 
     // Both namespaces
     Err,
@@ -240,6 +252,17 @@ impl CtorKind {
     }
 }
 
+impl NonMacroAttrKind {
+    fn descr(self) -> &'static str {
+        match self {
+            NonMacroAttrKind::Builtin => "built-in attribute",
+            NonMacroAttrKind::Tool => "tool attribute",
+            NonMacroAttrKind::DeriveHelper => "derive helper attribute",
+            NonMacroAttrKind::Custom => "custom attribute",
+        }
+    }
+}
+
 impl Def {
     pub fn def_id(&self) -> DefId {
         match *self {
@@ -259,7 +282,7 @@ impl Def {
             Def::PrimTy(..) |
             Def::SelfTy(..) |
             Def::ToolMod |
-            Def::NonMacroAttr |
+            Def::NonMacroAttr(..) |
             Def::Err => {
                 bug!("attempted .def_id() on invalid def: {:?}", self)
             }
@@ -300,7 +323,7 @@ impl Def {
             Def::SelfTy(..) => "self type",
             Def::Macro(.., macro_kind) => macro_kind.descr(),
             Def::ToolMod => "tool module",
-            Def::NonMacroAttr => "non-macro attribute",
+            Def::NonMacroAttr(attr_kind) => attr_kind.descr(),
             Def::Err => "unresolved item",
         }
     }

src/librustc/ich/impls_hir.rs

@@ -990,6 +990,13 @@ impl_stable_hash_for!(enum hir::def::CtorKind {
     Fictive
 });
 
+impl_stable_hash_for!(enum hir::def::NonMacroAttrKind {
+    Builtin,
+    Tool,
+    DeriveHelper,
+    Custom,
+});
+
 impl_stable_hash_for!(enum hir::def::Def {
     Mod(def_id),
     Struct(def_id),
@@ -1018,7 +1025,7 @@ impl_stable_hash_for!(enum hir::def::Def {
     Label(node_id),
     Macro(def_id, macro_kind),
     ToolMod,
-    NonMacroAttr,
+    NonMacroAttr(attr_kind),
     Err
 });
 

src/librustc_resolve/build_reduced_graph.rs

@@ -630,8 +630,10 @@ impl<'a, 'cl> Resolver<'a, 'cl> {
     pub fn get_macro(&mut self, def: Def) -> Lrc<SyntaxExtension> {
         let def_id = match def {
             Def::Macro(def_id, ..) => def_id,
-            Def::NonMacroAttr => return Lrc::new(SyntaxExtension::NonMacroAttr),
-            _ => panic!("Expected Def::Macro(..) or Def::NonMacroAttr"),
+            Def::NonMacroAttr(attr_kind) => return Lrc::new(SyntaxExtension::NonMacroAttr {
+                mark_used: attr_kind == NonMacroAttrKind::Tool,
+            }),
+            _ => panic!("expected `Def::Macro` or `Def::NonMacroAttr`"),
         };
         if let Some(ext) = self.macro_map.get(&def_id) {
             return ext.clone();

src/librustc_resolve/lib.rs

@@ -3485,8 +3485,9 @@ impl<'a, 'crateloader: 'a> Resolver<'a, 'crateloader> {
             let binding = if let Some(module) = module {
                 self.resolve_ident_in_module(module, ident, ns, record_used, path_span)
             } else if opt_ns == Some(MacroNS) {
-                self.resolve_lexical_macro_path_segment(ident, ns, record_used, path_span)
-                    .map(MacroBinding::binding)
+                assert!(ns == TypeNS);
+                self.resolve_lexical_macro_path_segment(ident, ns, record_used, record_used,
+                                                        false, path_span).map(MacroBinding::binding)
             } else {
                 let record_used_id =
                     if record_used { crate_lint.node_id().or(Some(CRATE_NODE_ID)) } else { None };
@@ -3514,7 +3515,8 @@ impl<'a, 'crateloader: 'a> Resolver<'a, 'crateloader> {
                     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))
+                        let def = Def::NonMacroAttr(NonMacroAttrKind::Tool);
+                        return PathResult::NonModule(PathResolution::new(def));
                     } else if def == Def::Err {
                         return PathResult::NonModule(err_path_resolution());
                     } else if opt_ns.is_some() && (is_last || maybe_assoc) {
@@ -4548,6 +4550,8 @@ impl<'a, 'crateloader: 'a> Resolver<'a, 'crateloader> {
             let result = self.resolve_lexical_macro_path_segment(ident,
                                                                  MacroNS,
                                                                  false,
+                                                                 false,
+                                                                 true,
                                                                  attr.path.span);
             if let Ok(binding) = result {
                 if let SyntaxExtension::AttrProcMacro(..) = *binding.binding().get_macro(self) {