08-avoid-opaque-identifier-pointers.patch

When using our extractor as a plugin, it turns out there special opaque pointers
are different in the frontend and our extractor contexts, leading to special
members (subscripts, inits, deinits) to lose their name.

This avoids using this opaque data pointers and relies instead on actual data
contained therein. This special data is distinguished from normal identifiers by
using the unprintable `\1` as first character, and `s`, `c` or `d` as second
character for subscript, constructors and destructors respectively.

diff --git a/include/swift/AST/Identifier.h b/include/swift/AST/Identifier.h
index 6f65385e097..6ec0da0dd09 100644
--- a/include/swift/AST/Identifier.h
+++ b/include/swift/AST/Identifier.h
@@ -72,8 +72,12 @@ private:
            && "Identifier pointer does not use any spare bits");
   }
 
-  /// A type with the alignment expected of a valid \c Identifier::Pointer .
-  struct alignas(uint64_t) Aligner {};
+  /** A type with the alignment expected of a valid \c Identifier::Pointer
+   *  The actual value is used to distinguish special identifiers
+   */
+  struct alignas(uint64_t) Aligner {
+    char value[3];
+  };
 
   static_assert(alignof(Aligner) >= RequiredAlignment,
                 "Identifier table will provide enough spare bits");
@@ -271,7 +275,7 @@ public:
   };
   
 private:
-  /// In a special DeclName representing a subscript, this opaque pointer
+  /// In a special DeclName representing a subscript, this opaque structure
   /// is used as the data of the base name identifier.
   /// This is an implementation detail that should never leak outside of
   /// DeclName.
@@ -289,29 +293,19 @@ public:
   DeclBaseName(Identifier I) : Ident(I) {}
 
   static DeclBaseName createSubscript() {
-    return DeclBaseName(Identifier((const char *)&SubscriptIdentifierData));
+    return DeclBaseName(Identifier(SubscriptIdentifierData.value));
   }
 
   static DeclBaseName createConstructor() {
-    return DeclBaseName(Identifier((const char *)&ConstructorIdentifierData));
+    return DeclBaseName(Identifier(ConstructorIdentifierData.value));
   }
 
   static DeclBaseName createDestructor() {
-    return DeclBaseName(Identifier((const char *)&DestructorIdentifierData));
-  }
-
-  Kind getKind() const {
-    if (Ident.get() == (const char *)&SubscriptIdentifierData) {
-      return Kind::Subscript;
-    } else if (Ident.get() == (const char *)&ConstructorIdentifierData) {
-      return Kind::Constructor;
-    } else if (Ident.get() == (const char *)&DestructorIdentifierData) {
-        return Kind::Destructor;
-    } else {
-      return Kind::Normal;
-    }
+    return DeclBaseName(Identifier(DestructorIdentifierData.value));
   }
 
+  Kind getKind() const;
+
   bool isSpecial() const { return getKind() != Kind::Normal; }
 
   bool isSubscript() const { return getKind() == Kind::Subscript; }
diff --git a/lib/AST/Identifier.cpp b/lib/AST/Identifier.cpp
index da9ffbc3ee9..d870d0d85e6 100644
--- a/lib/AST/Identifier.cpp
+++ b/lib/AST/Identifier.cpp
@@ -23,9 +23,21 @@
 #include "clang/Basic/CharInfo.h"
 using namespace swift;
 
-constexpr const Identifier::Aligner DeclBaseName::SubscriptIdentifierData{};
-constexpr const Identifier::Aligner DeclBaseName::ConstructorIdentifierData{};
-constexpr const Identifier::Aligner DeclBaseName::DestructorIdentifierData{};
+constexpr const Identifier::Aligner DeclBaseName::SubscriptIdentifierData{"\1s"};
+constexpr const Identifier::Aligner DeclBaseName::ConstructorIdentifierData{"\1c"};
+constexpr const Identifier::Aligner DeclBaseName::DestructorIdentifierData{"\1d"};
+
+DeclBaseName::Kind DeclBaseName::getKind() const {
+  if (!Ident.get() || Ident.get()[0] != '\1') {
+    return Kind::Normal;
+  }
+  switch(Ident.get()[1]) {
+    case 's': return Kind::Subscript;
+    case 'c': return Kind::Constructor;
+    case 'd': return Kind::Destructor;
+    default: return Kind::Normal;
+  }
+}
 
 raw_ostream &llvm::operator<<(raw_ostream &OS, Identifier I) {
   if (I.get() == nullptr)
@@ -305,5 +317,3 @@ StringRef ObjCSelector::getString(llvm::SmallVectorImpl<char> &scratch) const {
 void ObjCSelector::dump() const {
   llvm::errs() << *this << "\n";
 }
-
-