ASTScope: Add a new lookupSingleLocalDecl() entry point

This is used in a few places that used to expect parsed but
not yet type-checked code to contain DeclRefExprs that
reference local bindings.

Instead, we can call lookupSingleLocalDecl() with an
UnresolvedDeclRefExpr instead.

Author: slavapestov

include/swift/AST/NameLookup.h

@@ -684,6 +684,14 @@ class ASTScope {
   static void unqualifiedLookup(SourceFile *, SourceLoc,
                                 namelookup::AbstractASTScopeDeclConsumer &);
 
+  /// Lookup that only finds local declarations and does not trigger
+  /// interface type computation.
+  static void lookupLocalDecls(SourceFile *, DeclName, SourceLoc,
+                               SmallVectorImpl<ValueDecl *> &);
+
+  /// Returns the result if there is exactly one, nullptr otherwise.
+  static ValueDecl *lookupSingleLocalDecl(SourceFile *, DeclName, SourceLoc);
+
   /// Entry point to record the visible statement labels from the given
   /// point.
   ///

lib/AST/UnqualifiedLookup.cpp

@@ -778,4 +778,59 @@ unsigned UnqualifiedLookupFactory::lookupCounter = 0;
 // set to ~0 when not debugging
 const unsigned UnqualifiedLookupFactory::targetLookup = ~0;
 
-#endif // NDEBUG
+namespace {
+
+class ASTScopeDeclConsumerForLocalLookup
+    : public AbstractASTScopeDeclConsumer {
+  SmallVectorImpl<ValueDecl *> &results;
+  DeclName name;
+
+public:
+  ASTScopeDeclConsumerForLocalLookup(
+      SmallVectorImpl<ValueDecl *> &results, DeclName name)
+    : results(results), name(name) {}
+
+  bool consume(ArrayRef<ValueDecl *> values, DeclVisibilityKind vis,
+               NullablePtr<DeclContext> baseDC) override {
+    for (auto *value: values) {
+      if (!value->getName().matchesRef(name))
+        continue;
+
+      results.push_back(value);
+    }
+
+    return !results.empty();
+  }
+
+  bool lookInMembers(DeclContext *const,
+                     NominalTypeDecl *const) override {
+    return true;
+  }
+
+#ifndef NDEBUG
+  void startingNextLookupStep() override {}
+  void finishingLookup(std::string) const override {}
+  bool isTargetLookup() const override { return false; }
+#endif
+};
+
+}
+
+/// Lookup that only finds local declarations and does not trigger
+/// interface type computation.
+void ASTScope::lookupLocalDecls(SourceFile *sf, DeclName name, SourceLoc loc,
+                                SmallVectorImpl<ValueDecl *> &results) {
+  ASTScopeDeclConsumerForLocalLookup consumer(results, name);
+  ASTScope::unqualifiedLookup(sf, loc, consumer);
+}
+
+ValueDecl *ASTScope::lookupSingleLocalDecl(SourceFile *sf, DeclName name,
+                                           SourceLoc loc) {
+  SmallVector<ValueDecl *, 1> result;
+  ASTScope::lookupLocalDecls(sf, name, loc, result);
+  if (result.size() != 1)
+    return nullptr;
+  return result[0];
+}
+
+#endif // NDEBUG