Remove fallback to parent modules from lexical resolution

Author: petrochenkov

src/librustc/hir/def.rs

@@ -129,6 +129,16 @@ pub enum Namespace {
     MacroNS,
 }
 
+impl Namespace {
+    pub fn descr(self) -> &'static str {
+        match self {
+            TypeNS => "type",
+            ValueNS => "value",
+            MacroNS => "macro",
+        }
+    }
+}
+
 /// Just a helper ‒ separate structure for each namespace.
 #[derive(Copy, Clone, Default, Debug)]
 pub struct PerNS<T> {

src/librustc/hir/map/definitions.rs

@@ -153,6 +153,7 @@ impl Decodable for DefPathTable {
 /// The definition table containing node definitions.
 /// It holds the DefPathTable for local DefIds/DefPaths and it also stores a
 /// mapping from NodeIds to local DefIds.
+#[derive(Clone)]
 pub struct Definitions {
     table: DefPathTable,
     node_to_def_index: NodeMap<DefIndex>,
@@ -161,34 +162,12 @@ pub struct Definitions {
     /// If `Mark` is an ID of some macro expansion,
     /// then `DefId` is the normal module (`mod`) in which the expanded macro was defined.
     parent_modules_of_macro_defs: FxHashMap<Mark, DefId>,
-    /// Item with a given `DefIndex` was defined during opaque macro expansion with ID `Mark`.
-    /// It can actually be defined during transparent macro expansions inside that opaque expansion,
-    /// but transparent expansions are ignored here.
-    opaque_expansions_that_defined: FxHashMap<DefIndex, Mark>,
+    /// Item with a given `DefIndex` was defined during macro expansion with ID `Mark`.
+    expansions_that_defined: FxHashMap<DefIndex, Mark>,
     next_disambiguator: FxHashMap<(DefIndex, DefPathData), u32>,
     def_index_to_span: FxHashMap<DefIndex, Span>,
 }
 
-// Unfortunately we have to provide a manual impl of Clone because of the
-// fixed-sized array field.
-impl Clone for Definitions {
-    fn clone(&self) -> Self {
-        Definitions {
-            table: self.table.clone(),
-            node_to_def_index: self.node_to_def_index.clone(),
-            def_index_to_node: [
-                self.def_index_to_node[0].clone(),
-                self.def_index_to_node[1].clone(),
-            ],
-            node_to_hir_id: self.node_to_hir_id.clone(),
-            parent_modules_of_macro_defs: self.parent_modules_of_macro_defs.clone(),
-            opaque_expansions_that_defined: self.opaque_expansions_that_defined.clone(),
-            next_disambiguator: self.next_disambiguator.clone(),
-            def_index_to_span: self.def_index_to_span.clone(),
-        }
-    }
-}
-
 /// A unique identifier that we can use to lookup a definition
 /// precisely. It combines the index of the definition's parent (if
 /// any) with a `DisambiguatedDefPathData`.
@@ -409,7 +388,7 @@ impl Definitions {
             def_index_to_node: [vec![], vec![]],
             node_to_hir_id: IndexVec::new(),
             parent_modules_of_macro_defs: FxHashMap(),
-            opaque_expansions_that_defined: FxHashMap(),
+            expansions_that_defined: FxHashMap(),
             next_disambiguator: FxHashMap(),
             def_index_to_span: FxHashMap(),
         }
@@ -584,9 +563,8 @@ impl Definitions {
             self.node_to_def_index.insert(node_id, index);
         }
 
-        let expansion = expansion.modern();
         if expansion != Mark::root() {
-            self.opaque_expansions_that_defined.insert(index, expansion);
+            self.expansions_that_defined.insert(index, expansion);
         }
 
         // The span is added if it isn't dummy
@@ -606,8 +584,8 @@ impl Definitions {
         self.node_to_hir_id = mapping;
     }
 
-    pub fn opaque_expansion_that_defined(&self, index: DefIndex) -> Mark {
-        self.opaque_expansions_that_defined.get(&index).cloned().unwrap_or(Mark::root())
+    pub fn expansion_that_defined(&self, index: DefIndex) -> Mark {
+        self.expansions_that_defined.get(&index).cloned().unwrap_or(Mark::root())
     }
 
     pub fn parent_module_of_macro_def(&self, mark: Mark) -> DefId {

src/librustc/lint/builtin.rs

@@ -316,6 +316,12 @@ declare_lint! {
     "checks the object safety of where clauses"
 }
 
+declare_lint! {
+    pub PROC_MACRO_DERIVE_RESOLUTION_FALLBACK,
+    Warn,
+    "detects proc macro derives using inaccessible names from parent modules"
+}
+
 /// Does nothing as a lint pass, but registers some `Lint`s
 /// which are used by other parts of the compiler.
 #[derive(Copy, Clone)]
@@ -372,6 +378,7 @@ impl LintPass for HardwiredLints {
             DUPLICATE_MACRO_EXPORTS,
             INTRA_DOC_LINK_RESOLUTION_FAILURE,
             WHERE_CLAUSES_OBJECT_SAFETY,
+            PROC_MACRO_DERIVE_RESOLUTION_FALLBACK,
         )
     }
 }
@@ -384,6 +391,7 @@ pub enum BuiltinLintDiagnostics {
     BareTraitObject(Span, /* is_global */ bool),
     AbsPathWithModule(Span),
     DuplicatedMacroExports(ast::Ident, Span, Span),
+    ProcMacroDeriveResolutionFallback(Span),
 }
 
 impl BuiltinLintDiagnostics {
@@ -420,6 +428,10 @@ impl BuiltinLintDiagnostics {
                 db.span_label(later_span, format!("`{}` already exported", ident));
                 db.span_note(earlier_span, "previous macro export is now shadowed");
             }
+            BuiltinLintDiagnostics::ProcMacroDeriveResolutionFallback(span) => {
+                db.span_label(span, "names from parent modules are not \
+                                     accessible without an explicit import");
+            }
         }
     }
 }

src/librustc/ty/mod.rs

@@ -2724,7 +2724,7 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
     pub fn adjust_ident(self, mut ident: Ident, scope: DefId, block: NodeId) -> (Ident, DefId) {
         ident = ident.modern();
         let target_expansion = match scope.krate {
-            LOCAL_CRATE => self.hir.definitions().opaque_expansion_that_defined(scope.index),
+            LOCAL_CRATE => self.hir.definitions().expansion_that_defined(scope.index),
             _ => Mark::root(),
         };
         let scope = match ident.span.adjust(target_expansion) {

src/librustc_lint/lib.rs

@@ -293,6 +293,11 @@ pub fn register_builtins(store: &mut lint::LintStore, sess: Option<&Session>) {
             reference: "issue #50589 <https://github.com/rust-lang/rust/issues/50589>",
             edition: None,
         },
+        FutureIncompatibleInfo {
+            id: LintId::of(PROC_MACRO_DERIVE_RESOLUTION_FALLBACK),
+            reference: "issue #50504 <https://github.com/rust-lang/rust/issues/50504>",
+            edition: None,
+        },
         ]);
 
     // Register renamed and removed lints

src/librustc_resolve/lib.rs

@@ -55,7 +55,7 @@ use syntax::util::lev_distance::find_best_match_for_name;
 
 use syntax::visit::{self, FnKind, Visitor};
 use syntax::attr;
-use syntax::ast::{Arm, IsAsync, BindingMode, Block, Crate, Expr, ExprKind};
+use syntax::ast::{CRATE_NODE_ID, Arm, IsAsync, BindingMode, Block, Crate, Expr, ExprKind};
 use syntax::ast::{FnDecl, ForeignItem, ForeignItemKind, GenericParamKind, Generics};
 use syntax::ast::{Item, ItemKind, ImplItem, ImplItemKind};
 use syntax::ast::{Label, Local, Mutability, Pat, PatKind, Path};
@@ -1891,7 +1891,12 @@ impl<'a> Resolver<'a> {
 
         ident.span = ident.span.modern();
         loop {
-            module = unwrap_or!(self.hygienic_lexical_parent(module, &mut ident.span), break);
+            let (opt_module, poisoned) = if record_used {
+                self.hygienic_lexical_parent_with_compatibility_fallback(module, &mut ident.span)
+            } else {
+                (self.hygienic_lexical_parent(module, &mut ident.span), false)
+            };
+            module = unwrap_or!(opt_module, break);
             let orig_current_module = self.current_module;
             self.current_module = module; // Lexical resolutions can never be a privacy error.
             let result = self.resolve_ident_in_module_unadjusted(
@@ -1900,7 +1905,19 @@ impl<'a> Resolver<'a> {
             self.current_module = orig_current_module;
 
             match result {
-                Ok(binding) => return Some(LexicalScopeBinding::Item(binding)),
+                Ok(binding) => {
+                    if poisoned {
+                        self.session.buffer_lint_with_diagnostic(
+                            lint::builtin::PROC_MACRO_DERIVE_RESOLUTION_FALLBACK,
+                            CRATE_NODE_ID, ident.span,
+                            &format!("cannot find {} `{}` in this scope", ns.descr(), ident),
+                            lint::builtin::BuiltinLintDiagnostics::
+                                ProcMacroDeriveResolutionFallback(ident.span),
+                        );
+                    }
+                    return Some(LexicalScopeBinding::Item(binding))
+                }
+                _ if poisoned => break,
                 Err(Undetermined) => return None,
                 Err(Determined) => {}
             }
@@ -1935,7 +1952,7 @@ impl<'a> Resolver<'a> {
         None
     }
 
-    fn hygienic_lexical_parent(&mut self, mut module: Module<'a>, span: &mut Span)
+    fn hygienic_lexical_parent(&mut self, module: Module<'a>, span: &mut Span)
                                -> Option<Module<'a>> {
         if !module.expansion.is_descendant_of(span.ctxt().outer()) {
             return Some(self.macro_def_scope(span.remove_mark()));
@@ -1945,22 +1962,41 @@ impl<'a> Resolver<'a> {
             return Some(module.parent.unwrap());
         }
 
-        let mut module_expansion = module.expansion.modern(); // for backward compatibility
-        while let Some(parent) = module.parent {
-            let parent_expansion = parent.expansion.modern();
-            if module_expansion.is_descendant_of(parent_expansion) &&
-               parent_expansion != module_expansion {
-                return if parent_expansion.is_descendant_of(span.ctxt().outer()) {
-                    Some(parent)
-                } else {
-                    None
-                };
+        None
+    }
+
+    fn hygienic_lexical_parent_with_compatibility_fallback(
+        &mut self, module: Module<'a>, span: &mut Span) -> (Option<Module<'a>>, /* poisoned */ bool
+    ) {
+        if let module @ Some(..) = self.hygienic_lexical_parent(module, span) {
+            return (module, false);
+        }
+
+        // We need to support the next case under a deprecation warning
+        // ```
+        // struct MyStruct;
+        // ---- begin: this comes from a proc macro derive
+        // mod implementation_details {
+        //     // Note that `MyStruct` is not in scope here.
+        //     impl SomeTrait for MyStruct { ... }
+        // }
+        // ---- end
+        // ```
+        // So we have to fall back to the module's parent during lexical resolution in this case.
+        if let Some(parent) = module.parent {
+            // Inner module is inside the macro, parent module is outside of the macro.
+            if module.expansion != parent.expansion &&
+            module.expansion.is_descendant_of(parent.expansion) {
+                // The macro is a proc macro derive
+                if module.expansion.looks_like_proc_macro_derive() {
+                    if parent.expansion.is_descendant_of(span.ctxt().outer()) {
+                        return (module.parent, true);
+                    }
+                }
             }
-            module = parent;
-            module_expansion = parent_expansion;
         }
 
-        None
+        (None, false)
     }
 
     fn resolve_ident_in_module(&mut self,
@@ -4037,8 +4073,9 @@ impl<'a> Resolver<'a> {
         let mut search_module = self.current_module;
         loop {
             self.get_traits_in_module_containing_item(ident, ns, search_module, &mut found_traits);
-            search_module =
-                unwrap_or!(self.hygienic_lexical_parent(search_module, &mut ident.span), break);
+            search_module = unwrap_or!(
+                self.hygienic_lexical_parent(search_module, &mut ident.span), break
+            );
         }
 
         if let Some(prelude) = self.prelude {
@@ -4395,12 +4432,6 @@ impl<'a> Resolver<'a> {
             (TypeNS, _) => "type",
         };
 
-        let namespace = match ns {
-            ValueNS => "value",
-            MacroNS => "macro",
-            TypeNS => "type",
-        };
-
         let msg = format!("the name `{}` is defined multiple times", name);
 
         let mut err = match (old_binding.is_extern_crate(), new_binding.is_extern_crate()) {
@@ -4418,7 +4449,7 @@ impl<'a> Resolver<'a> {
 
         err.note(&format!("`{}` must be defined only once in the {} namespace of this {}",
                           name,
-                          namespace,
+                          ns.descr(),
                           container));
 
         err.span_label(span, format!("`{}` re{} here", name, new_participle));

src/libsyntax_pos/hygiene.rs

@@ -72,26 +72,16 @@ pub enum Transparency {
 }
 
 impl Mark {
-    fn fresh_with_data(mark_data: MarkData, data: &mut HygieneData) -> Self {
-        data.marks.push(mark_data);
-        Mark(data.marks.len() as u32 - 1)
-    }
-
     pub fn fresh(parent: Mark) -> Self {
         HygieneData::with(|data| {
-            Mark::fresh_with_data(MarkData {
+            data.marks.push(MarkData {
                 parent,
                 // By default expansions behave like `macro_rules`.
                 default_transparency: Transparency::SemiTransparent,
                 is_builtin: false,
                 expn_info: None,
-            }, data)
-        })
-    }
-
-    pub fn fresh_cloned(clone_from: Mark) -> Self {
-        HygieneData::with(|data| {
-            Mark::fresh_with_data(data.marks[clone_from.0 as usize].clone(), data)
+            });
+            Mark(data.marks.len() as u32 - 1)
         })
     }
 
@@ -128,17 +118,6 @@ impl Mark {
         })
     }
 
-    // FIXME: This operation doesn't really make sense when single macro expansion
-    // can produce tokens with different transparencies. Figure out how to avoid it.
-    pub fn modern(mut self) -> Mark {
-        HygieneData::with(|data| {
-            while data.marks[self.0 as usize].default_transparency != Transparency::Opaque {
-                self = data.marks[self.0 as usize].parent;
-            }
-            self
-        })
-    }
-
     #[inline]
     pub fn set_default_transparency(self, transparency: Transparency) {
         assert_ne!(self, Mark::root());
@@ -194,6 +173,24 @@ impl Mark {
             b
         })
     }
+
+    // Used for enabling some compatibility fallback in resolve.
+    #[inline]
+    pub fn looks_like_proc_macro_derive(self) -> bool {
+        HygieneData::with(|data| {
+            let mark_data = &data.marks[self.0 as usize];
+            if mark_data.default_transparency == Transparency::Opaque {
+                if let Some(expn_info) = &mark_data.expn_info {
+                    if let ExpnFormat::MacroAttribute(name) = expn_info.format {
+                        if name.as_str().starts_with("derive(") {
+                            return true;
+                        }
+                    }
+                }
+            }
+            false
+        })
+    }
 }
 
 #[derive(Debug)]
@@ -285,6 +282,7 @@ impl SyntaxContext {
         })
     }
 
+    /// Extend a syntax context with a given mark and default transparency for that mark.
     pub fn apply_mark(self, mark: Mark) -> SyntaxContext {
         assert_ne!(mark, Mark::root());
         self.apply_mark_with_transparency(