[SE-0491] Implement lookup and diagnostics for module selectors (MyMod::someName)

include/swift/AST/ASTBridging.h

@@ -164,10 +164,13 @@ BridgedDeclNameRef_createParsed(BridgedASTContext cContext,
 
 class BridgedDeclNameLoc {
   const void *_Nullable LocationInfo;
-  size_t NumArgumentLabels;
+  uint32_t NumArgumentLabels;
+  bool HasModuleSelectorLoc;
 
 public:
-  BridgedDeclNameLoc() : LocationInfo(nullptr), NumArgumentLabels(0) {}
+  BridgedDeclNameLoc()
+    : LocationInfo(nullptr), NumArgumentLabels(0), HasModuleSelectorLoc(false)
+  {}
 
   BRIDGED_INLINE BridgedDeclNameLoc(swift::DeclNameLoc loc);
 

include/swift/AST/ASTBridgingImpl.h

@@ -60,10 +60,12 @@ swift::DeclNameRef BridgedDeclNameRef::unbridged() const {
 
 BridgedDeclNameLoc::BridgedDeclNameLoc(swift::DeclNameLoc loc)
     : LocationInfo(loc.LocationInfo),
-      NumArgumentLabels(loc.NumArgumentLabels) {}
+      NumArgumentLabels(loc.NumArgumentLabels),
+      HasModuleSelectorLoc(loc.HasModuleSelectorLoc) {}
 
 swift::DeclNameLoc BridgedDeclNameLoc::unbridged() const {
-  return swift::DeclNameLoc(LocationInfo, NumArgumentLabels);
+  return swift::DeclNameLoc(LocationInfo, NumArgumentLabels,
+                            HasModuleSelectorLoc);
 }
 
 //===----------------------------------------------------------------------===//

include/swift/AST/Decl.h

@@ -3072,11 +3072,10 @@ class ValueDecl : public Decl {
     return Name.getBaseIdentifier();
   }
 
-  /// Generates a DeclNameRef referring to this declaration with as much
-  /// specificity as possible.
-  DeclNameRef createNameRef() const {
-    return DeclNameRef(Name);
-  }
+  /// Generates a DeclNameRef referring to this declaration.
+  ///
+  /// \param moduleSelector If true, the name ref includes the module name.
+  DeclNameRef createNameRef(bool moduleSelector = false) const;
 
   /// Retrieve the C declaration name that names this function, or empty
   /// string if it has none.

include/swift/AST/DeclNameLoc.h

@@ -35,61 +35,69 @@ class DeclNameLoc {
 
   /// Source location information.
   ///
-  /// If \c NumArgumentLabels == 0, this is the SourceLoc for the base name.
-  /// Otherwise, it points to an array of SourceLocs, which contains:
+  /// If \c NumArgumentLabels == 0 and \c !HasModuleSelectorLoc, this is the
+  /// SourceLoc for the base name. Otherwise, it points to an array of
+  /// SourceLocs, which contains:
   /// * The base name location
+  /// * The module selector location
   /// * The left parentheses location
   /// * The right parentheses location
   /// * The locations of each of the argument labels.
   const void *LocationInfo;
 
   /// The number of argument labels stored in the name.
-  unsigned NumArgumentLabels;
+  uint32_t NumArgumentLabels;
+  bool HasModuleSelectorLoc;
 
   enum {
     BaseNameIndex = 0,
-    LParenIndex = 1,
-    RParenIndex = 2,
-    FirstArgumentLabelIndex = 3,
+    ModuleSelectorIndex = 1,
+    LParenIndex = 2,
+    RParenIndex = 3,
+    FirstArgumentLabelIndex = 4,
   };
 
   /// Retrieve a pointer to either the only source location that was
   /// stored or to the array of source locations that was stored.
   SourceLoc const * getSourceLocs() const {
-    if (NumArgumentLabels == 0) 
+    if (NumArgumentLabels == 0 && !HasModuleSelectorLoc)
       return reinterpret_cast<SourceLoc const *>(&LocationInfo);
 
     return reinterpret_cast<SourceLoc const *>(LocationInfo);
   }
 
-  DeclNameLoc(const void *LocationInfo, unsigned NumArgumentLabels)
-      : LocationInfo(LocationInfo), NumArgumentLabels(NumArgumentLabels) {}
+  DeclNameLoc(const void *LocationInfo, unsigned NumArgumentLabels,
+              bool HasModuleSelectorLoc)
+      : LocationInfo(LocationInfo), NumArgumentLabels(NumArgumentLabels),
+        HasModuleSelectorLoc(HasModuleSelectorLoc) {}
 
 public:
   /// Create an invalid declaration name location.
-  DeclNameLoc() : DeclNameLoc(nullptr, 0) {}
+  DeclNameLoc() : DeclNameLoc(nullptr, 0, false) {}
 
   /// Create declaration name location information for a base name.
   explicit DeclNameLoc(SourceLoc baseNameLoc)
-      : DeclNameLoc(baseNameLoc.getOpaquePointerValue(), 0) {}
+      : DeclNameLoc(baseNameLoc.getOpaquePointerValue(), 0, false) {}
 
   explicit DeclNameLoc(ASTContext &ctx, SourceLoc moduleSelectorLoc,
                        SourceLoc baseNameLoc)
-    : DeclNameLoc(baseNameLoc) { }
+    : DeclNameLoc(ctx, moduleSelectorLoc, baseNameLoc,
+                  SourceLoc(), {}, SourceLoc()) { }
 
   /// Create declaration name location information for a compound
   /// name.
   DeclNameLoc(ASTContext &ctx, SourceLoc baseNameLoc,
               SourceLoc lParenLoc,
               ArrayRef<SourceLoc> argumentLabelLocs,
-              SourceLoc rParenLoc);
+              SourceLoc rParenLoc)
+    : DeclNameLoc(ctx, SourceLoc(), baseNameLoc,
+                  lParenLoc, argumentLabelLocs, rParenLoc) { }
 
   DeclNameLoc(ASTContext &ctx, SourceLoc moduleSelectorLoc,
               SourceLoc baseNameLoc,
               SourceLoc lParenLoc,
               ArrayRef<SourceLoc> argumentLabelLocs,
-              SourceLoc rParenLoc)
-    : DeclNameLoc(ctx, baseNameLoc, lParenLoc, argumentLabelLocs, rParenLoc) { }
+              SourceLoc rParenLoc);
 
   /// Whether the location information is valid.
   bool isValid() const { return getBaseNameLoc().isValid(); }
@@ -125,11 +133,12 @@ class DeclNameLoc {
   }
 
   SourceLoc getModuleSelectorLoc() const {
-    return SourceLoc();
+    if (!HasModuleSelectorLoc) return SourceLoc();
+    return getSourceLocs()[ModuleSelectorIndex];
   }
 
   SourceLoc getStartLoc() const {
-    return getBaseNameLoc();
+    return HasModuleSelectorLoc ? getModuleSelectorLoc() : getBaseNameLoc();
   }
 
   SourceLoc getEndLoc() const {
@@ -138,9 +147,7 @@ class DeclNameLoc {
 
   /// Retrieve the complete source range for this declaration name.
   SourceRange getSourceRange() const {
-    if (NumArgumentLabels == 0) return getBaseNameLoc();
-
-    return SourceRange(getBaseNameLoc(), getRParenLoc());
+    return SourceRange(getStartLoc(), getEndLoc());
   }
 };
 

include/swift/AST/DiagnosticsSema.def

@@ -1146,6 +1146,10 @@ ERROR(no_module_type,none,
       "no type named %0 in module %1", (DeclNameRef, Identifier))
 ERROR(ambiguous_module_type,none,
       "ambiguous type name %0 in module %1", (DeclNameRef, Identifier))
+ERROR(module_selector_dependent_member_type_not_allowed,none,
+      "module selector is not allowed on generic member type; associated types "
+      "with the same name are merged instead of shadowing one another",
+      ())
 ERROR(use_nonmatching_operator,none,
       "%0 is not a %select{binary|prefix unary|postfix unary}1 operator",
       (DeclNameRef, unsigned))
@@ -1191,6 +1195,16 @@ ERROR(cannot_find_type_in_cast_expression,none,
       "type-casting operator expects a type on its right-hand side (got: %kind0)", (const ValueDecl *))
 ERROR(cannot_find_type_in_scope_did_you_mean,none,
       "cannot find type %0 in scope; did you mean to use '%1'?", (DeclNameRef, StringRef))
+ERROR(wrong_module_selector,none,
+      "%0 is not imported through module %1", (DeclName, Identifier))
+NOTE(note_change_module_selector,none,
+     "did you mean module %0?", (Identifier))
+NOTE(note_remove_module_selector_local_decl,none,
+     "did you mean the local declaration?", ())
+NOTE(note_remove_module_selector_outer_type,none,
+     "did you mean an outer type member?", ())
+NOTE(note_add_explicit_self_with_module_selector,none,
+     "did you mean the member of 'self'?", ())
 NOTE(note_typo_candidate_implicit_member,none,
      "did you mean the implicitly-synthesized %kindbase0?", (const ValueDecl *))
 NOTE(note_remapped_type,none,
@@ -8010,7 +8024,7 @@ ERROR(expected_macro_expansion_expr,PointsToFirstBadToken,
 ERROR(expected_macro_expansion_decls,PointsToFirstBadToken,
       "expected macro expansion to produce a declaration", ())
 ERROR(macro_undefined,PointsToFirstBadToken,
-      "no macro named %0", (DeclName))
+      "no macro named %0", (DeclNameRef))
 ERROR(external_macro_not_found,none,
       "external macro implementation type '%0.%1' could not be found for "
       "macro %2; %3", (StringRef, StringRef, DeclName, StringRef))

include/swift/AST/Identifier.h

@@ -738,39 +738,76 @@ void simple_display(llvm::raw_ostream &out, DeclName name);
 /// An in-source reference to another declaration, including qualification
 /// information.
 class DeclNameRef {
-  DeclName FullName;
+  friend class ASTContext;
+  friend struct llvm::PointerLikeTypeTraits<DeclNameRef>;
+
+  /// Contains the name and module for a DeclNameRef with a module selector.
+  struct alignas(Identifier) SelectiveDeclNameRef : llvm::FoldingSetNode {
+    Identifier moduleSelector;   // Note: currently can never be empty().
+    DeclName fullName;
+
+    SelectiveDeclNameRef(Identifier moduleSelector, DeclName fullName)
+      : moduleSelector(moduleSelector), fullName(fullName) { }
+
+    /// Uniquing for the ASTContext.
+    static void Profile(llvm::FoldingSetNodeID &id, Identifier moduleSelector,
+                        DeclName fullName);
+
+    void Profile(llvm::FoldingSetNodeID &id) {
+      Profile(id, moduleSelector, fullName);
+    }
+  };
+
+  using Storage = llvm::PointerUnion<DeclName, SelectiveDeclNameRef *>;
+  Storage storage;
+
+  explicit DeclNameRef(void *_Nullable Opaque)
+    : storage(decltype(storage)::getFromOpaqueValue(Opaque)) { }
+
+  void initialize(ASTContext &C, Identifier moduleScope, DeclName fullName);
 
 public:
   static DeclNameRef createSubscript();
   static DeclNameRef createConstructor();
+  static DeclNameRef createSelf(const ASTContext &ctx);
 
-  DeclNameRef() : FullName() { }
+  DeclNameRef() : storage(DeclName()) { }
 
-  void *_Nullable getOpaqueValue() const { return FullName.getOpaqueValue(); }
+  void *_Nullable getOpaqueValue() const {
+    return storage.getOpaqueValue();
+  }
   static DeclNameRef getFromOpaqueValue(void *_Nullable p);
 
   explicit DeclNameRef(ASTContext &C, Identifier moduleSelector,
-                       DeclName fullName)
-    : FullName(fullName) { }
+                       DeclName fullName) {
+    initialize(C, moduleSelector, fullName);
+  }
 
   explicit DeclNameRef(ASTContext &C, Identifier moduleSelector,
-                       DeclBaseName baseName, ArrayRef<Identifier> argLabels)
-    : FullName(C, baseName, argLabels) { }
+                       DeclBaseName baseName, ArrayRef<Identifier> argLabels) {
+    initialize(C, moduleSelector, DeclName(C, baseName, argLabels));
+  }
 
   explicit DeclNameRef(DeclName FullName)
-    : FullName(FullName) { }
+    : storage(FullName) { }
 
   bool hasModuleSelector() const {
-    return false;
+    return isa<SelectiveDeclNameRef *>(storage);
   }
 
   Identifier getModuleSelector() const {
-    return Identifier();
+    if (!hasModuleSelector())
+      return Identifier();
+
+    return cast<SelectiveDeclNameRef *>(storage)->moduleSelector;
   }
 
   /// The name of the declaration being referenced.
   DeclName getFullName() const {
-    return FullName;
+    if (!hasModuleSelector())
+      return cast<DeclName>(storage);
+
+    return cast<SelectiveDeclNameRef *>(storage)->fullName;
   }
 
   /// The base name of the declaration being referenced.
@@ -885,7 +922,7 @@ class DeclNameRef {
 };
 
 inline DeclNameRef DeclNameRef::getFromOpaqueValue(void *_Nullable p) {
-  return DeclNameRef(DeclName::getFromOpaqueValue(p));
+  return DeclNameRef(p);
 }
 
 inline DeclNameRef DeclNameRef::withoutArgumentLabels(ASTContext &C) const {
@@ -1059,7 +1096,6 @@ namespace llvm {
   };
 
   // A DeclNameRef is "pointer like" just like DeclNames.
-  template<typename T> struct PointerLikeTypeTraits;
   template<>
   struct PointerLikeTypeTraits<swift::DeclNameRef> {
   public:
@@ -1069,7 +1105,7 @@ namespace llvm {
     static inline swift::DeclNameRef getFromVoidPointer(void *_Nullable ptr) {
       return swift::DeclNameRef::getFromOpaqueValue(ptr);
     }
-    enum { NumLowBitsAvailable = PointerLikeTypeTraits<swift::DeclName>::NumLowBitsAvailable };
+    enum { NumLowBitsAvailable = PointerLikeTypeTraits<swift::DeclNameRef::Storage>::NumLowBitsAvailable };
   };
 
   // DeclNameRefs hash just like DeclNames.

include/swift/AST/LookupKinds.h

@@ -104,6 +104,9 @@ enum class ModuleLookupFlags : unsigned {
   /// If @abi attributes are present, return the decls representing the ABI,
   /// not the API.
   ABIProviding = 1 << 1,
+  /// The lookup is qualified by a module selector which has specified this
+  /// module explicitly.
+  HasModuleSelector = 1 << 2,
 };
 
 } // end namespace swift

include/swift/AST/Module.h

@@ -481,6 +481,11 @@ class ModuleDecl
   void getDeclaredCrossImportBystanders(
       SmallVectorImpl<Identifier> &bystanderNames);
 
+  /// Returns the name that should be used for this module in a module
+  /// selector. For separately-imported overlays, this will be the declaring
+  /// module's name.
+  Identifier getNameForModuleSelector();
+
   /// Retrieve the ABI name of the module, which is used for metadata and
   /// mangling.
   Identifier getABIName() const;

include/swift/AST/ModuleNameLookup.h

@@ -44,26 +44,35 @@ enum class ResolutionKind {
 
 void simple_display(llvm::raw_ostream &out, ResolutionKind kind);
 
-/// Performs a lookup into the given module and it's imports.
+/// Performs a lookup into the given module and its imports.
 ///
-/// If 'moduleOrFile' is a ModuleDecl, we search the module and it's
+/// If 'moduleOrFile' is a ModuleDecl, we search the module and its
 /// public imports. If 'moduleOrFile' is a SourceFile, we search the
 /// file's parent module, the module's public imports, and the source
 /// file's private imports.
 ///
-/// \param moduleOrFile The module or file unit whose imports to search.
+/// \param moduleOrFile The module or file unit to search, including imports.
 /// \param name The name to look up.
+/// \param hasModuleSelector Whether \p name was originally qualified by a
+///        module selector. This information is threaded through to underlying
+///        lookup calls; the callee is responsible for actually applying the
+///        module selector.
 /// \param[out] decls Any found decls will be added to this vector.
 /// \param lookupKind Whether this lookup is qualified or unqualified.
 /// \param resolutionKind What sort of decl is expected.
 /// \param moduleScopeContext The top-level context from which the lookup is
 ///        being performed, for checking access. This must be either a
 ///        FileUnit or a Module.
+/// \param loc Source location of the lookup. Used to add contextual options,
+///        such as disabling macro expansions inside macro arguments.
 /// \param options name lookup options. Currently only used to communicate the
-/// NL_IncludeUsableFromInline option.
+///        NL_IncludeUsableFromInline option.
 void lookupInModule(const DeclContext *moduleOrFile,
-                    DeclName name, SmallVectorImpl<ValueDecl *> &decls,
-                    NLKind lookupKind, ResolutionKind resolutionKind,
+                    DeclName name,
+                    bool hasModuleSelector,
+                    SmallVectorImpl<ValueDecl *> &decls,
+                    NLKind lookupKind,
+                    ResolutionKind resolutionKind,
                     const DeclContext *moduleScopeContext,
                     SourceLoc loc, NLOptions options);