[NFC] Rework types and terms for imports' access paths

docs/Lexicon.md

@@ -45,6 +45,28 @@ introduces [reabstraction](#reabstraction) conversions when a value is used with
 different abstraction pattern. (This is where the infamous "reabstraction
 thunk helpers" sometimes seen in Swift backtraces come from.)
 
+## access path
+
+Broadly, an "access path" is a list of "accesses" which must be chained together
+to compute some output from an input. For instance, the generics system has a
+type called a `ConformanceAccessPath` which explains how to, for example,
+walk from `T: Collection` to `T: Sequence` to `T.Iterator: IteratorProtocol`.
+There are several different kinds of "access path" in different parts of the compiler,
+but they all follow this basic theme.
+
+In the specific context of imports, an "access path" is the `Bar` portion of a scoped
+import like `import class Foo.Bar`. Theoretically, it could have several identifiers
+to designate a nested type, although the compiler doesn't currently support this. It can
+also be empty, matching all top-level declarations in the module.
+
+Note, however, that there has historically been some confusion about the meaning of
+"access path" with regards to imports. You might see some code use "access path"
+to include the `Foo` part or even to describe a chain of submodule names where a
+declaration is not valid at all. (Strictly, the chain of module names is a "module path"
+and the combination of module path + access path is an "import path".)
+
+See `ImportPath` and the types nested inside it for more on this.
+
 ## archetype
 
 A placeholder for a generic parameter or an associated type within a

include/swift/AST/ASTContext.h

@@ -20,6 +20,7 @@
 #include "swift/AST/Evaluator.h"
 #include "swift/AST/GenericSignature.h"
 #include "swift/AST/Identifier.h"
+#include "swift/AST/Import.h"
 #include "swift/AST/SearchPathOptions.h"
 #include "swift/AST/Type.h"
 #include "swift/AST/Types.h"
@@ -859,12 +860,12 @@ class ASTContext final {
   ///
   /// Note that even if this check succeeds, errors may still occur if the
   /// module is loaded in full.
-  bool canImportModule(Located<Identifier> ModulePath);
+  bool canImportModule(ImportPath::Element ModulePath);
 
   /// \returns a module with a given name that was already loaded.  If the
   /// module was not loaded, returns nullptr.
   ModuleDecl *getLoadedModule(
-      ArrayRef<Located<Identifier>> ModulePath) const;
+      ImportPath::Module ModulePath) const;
 
   ModuleDecl *getLoadedModule(Identifier ModuleName) const;
 
@@ -874,10 +875,12 @@ class ASTContext final {
   /// be returned.
   ///
   /// \returns The requested module, or NULL if the module cannot be found.
-  ModuleDecl *getModule(ArrayRef<Located<Identifier>> ModulePath);
+  ModuleDecl *getModule(ImportPath::Module ModulePath);
 
   ModuleDecl *getModuleByName(StringRef ModuleName);
 
+  ModuleDecl *getModuleByIdentifier(Identifier ModuleID);
+
   /// Returns the standard library module, or null if the library isn't present.
   ///
   /// If \p loadIfAbsent is true, the ASTContext will attempt to load the module

include/swift/AST/Decl.h

@@ -1457,46 +1457,28 @@ class GenericContext : private _GenericContext, public DeclContext {
 static_assert(sizeof(_GenericContext) + sizeof(DeclContext) ==
               sizeof(GenericContext), "Please add fields to _GenericContext");
 
-/// Describes what kind of name is being imported.
-///
-/// If the enumerators here are changed, make sure to update all diagnostics
-/// using ImportKind as a select index.
-enum class ImportKind : uint8_t {
-  Module = 0,
-  Type,
-  Struct,
-  Class,
-  Enum,
-  Protocol,
-  Var,
-  Func
-};
-
 /// ImportDecl - This represents a single import declaration, e.g.:
 ///   import Swift
 ///   import typealias Swift.Int
 class ImportDecl final : public Decl,
-    private llvm::TrailingObjects<ImportDecl, Located<Identifier>> {
+    private llvm::TrailingObjects<ImportDecl, ImportPath::Element> {
   friend TrailingObjects;
   friend class Decl;
-public:
-  typedef Located<Identifier> AccessPathElement;
 
-private:
   SourceLoc ImportLoc;
   SourceLoc KindLoc;
 
   /// The resolved module.
   ModuleDecl *Mod = nullptr;
 
   ImportDecl(DeclContext *DC, SourceLoc ImportLoc, ImportKind K,
-             SourceLoc KindLoc, ArrayRef<AccessPathElement> Path);
+             SourceLoc KindLoc, ImportPath Path);
 
 public:
   static ImportDecl *create(ASTContext &C, DeclContext *DC,
                             SourceLoc ImportLoc, ImportKind Kind,
                             SourceLoc KindLoc,
-                            ArrayRef<AccessPathElement> Path,
+                            ImportPath Path,
                             ClangNode ClangN = ClangNode());
 
   /// Returns the import kind that is most appropriate for \p VD.
@@ -1511,26 +1493,21 @@ class ImportDecl final : public Decl,
   /// cannot be overloaded, returns None.
   static Optional<ImportKind> findBestImportKind(ArrayRef<ValueDecl *> Decls);
 
-  ArrayRef<AccessPathElement> getFullAccessPath() const {
-    return {getTrailingObjects<AccessPathElement>(),
-            static_cast<size_t>(Bits.ImportDecl.NumPathElements)};
+  ImportKind getImportKind() const {
+    return static_cast<ImportKind>(Bits.ImportDecl.ImportKind);
   }
 
-  ArrayRef<AccessPathElement> getModulePath() const {
-    auto result = getFullAccessPath();
-    if (getImportKind() != ImportKind::Module)
-      result = result.slice(0, result.size()-1);
-    return result;
+  ImportPath getImportPath() const {
+    return ImportPath({ getTrailingObjects<ImportPath::Element>(),
+                        static_cast<size_t>(Bits.ImportDecl.NumPathElements) });
   }
 
-  ArrayRef<AccessPathElement> getDeclPath() const {
-    if (getImportKind() == ImportKind::Module)
-      return {};
-    return getFullAccessPath().back();
+  ImportPath::Module getModulePath() const {
+    return getImportPath().getModulePath(getImportKind());
   }
 
-  ImportKind getImportKind() const {
-    return static_cast<ImportKind>(Bits.ImportDecl.ImportKind);
+  ImportPath::Access getAccessPath() const {
+    return getImportPath().getAccessPath(getImportKind());
   }
 
   bool isExported() const {
@@ -1549,9 +1526,11 @@ class ImportDecl final : public Decl,
   }
 
   SourceLoc getStartLoc() const { return ImportLoc; }
-  SourceLoc getLocFromSource() const { return getFullAccessPath().front().Loc; }
+  SourceLoc getLocFromSource() const {
+    return getImportPath().getSourceRange().Start;
+  }
   SourceRange getSourceRange() const {
-    return SourceRange(ImportLoc, getFullAccessPath().back().Loc);
+    return SourceRange(ImportLoc, getImportPath().getSourceRange().End);
   }
   SourceLoc getKindLoc() const { return KindLoc; }
 

include/swift/AST/FileUnit.h

@@ -82,20 +82,20 @@ class FileUnit : public DeclContext {
   /// Find ValueDecls in the module and pass them to the given consumer object.
   ///
   /// This does a simple local lookup, not recursively looking through imports.
-  virtual void lookupVisibleDecls(ModuleDecl::AccessPathTy accessPath,
+  virtual void lookupVisibleDecls(ImportPath::Access accessPath,
                                   VisibleDeclConsumer &consumer,
                                   NLKind lookupKind) const {}
 
   /// Finds all class members defined in this file.
   ///
   /// This does a simple local lookup, not recursively looking through imports.
-  virtual void lookupClassMembers(ModuleDecl::AccessPathTy accessPath,
+  virtual void lookupClassMembers(ImportPath::Access accessPath,
                                   VisibleDeclConsumer &consumer) const {}
 
   /// Finds class members defined in this file with the given name.
   ///
   /// This does a simple local lookup, not recursively looking through imports.
-  virtual void lookupClassMember(ModuleDecl::AccessPathTy accessPath,
+  virtual void lookupClassMember(ImportPath::Access accessPath,
                                  DeclName name,
                                  SmallVectorImpl<ValueDecl*> &results) const {}