Allow for passing a custom Archetype naming schema to the demangler.

LLDB would like to substitute the original Archetype names from the
source code when demangling symbols instead of the confusing generic
'A', 'B', ...

<rdar://problem/48259889>

Author: adrian-prantl

include/swift/Demangling/Demangle.h

@@ -2,7 +2,7 @@
 //
 // This source file is part of the Swift.org open source project
 //
-// Copyright (c) 2014 - 2017 Apple Inc. and the Swift project authors
+// Copyright (c) 2014 - 2019 Apple Inc. and the Swift project authors
 // Licensed under Apache License v2.0 with Runtime Library Exception
 //
 // See https://swift.org/LICENSE.txt for license information
@@ -35,6 +35,11 @@ namespace Demangle {
 
 enum class SymbolicReferenceKind : uint8_t;
 
+/// A simple default implementation that assigns letters to archetypes in
+/// alphabetic order.
+std::string archetypeName(uint64_t index, uint64_t depth);
+
+/// Display style options for the demangler.
 struct DemangleOptions {
   bool SynthesizeSugarOnTypes = false;
   bool DisplayDebuggerGeneratedModule = true;
@@ -52,6 +57,7 @@ struct DemangleOptions {
   bool ShortenArchetype = false;
   bool ShowPrivateDiscriminators = true;
   bool ShowFunctionArgumentTypes = true;
+  std::function<std::string(uint64_t, uint64_t)> ArchetypeName = archetypeName;
 
   DemangleOptions() {}
 
@@ -346,17 +352,19 @@ class Context {
   /// prefix: _T, _T0, $S, _$S.
   ///
   /// \returns The demangled string.
-  std::string demangleSymbolAsString(llvm::StringRef MangledName,
-                            const DemangleOptions &Options = DemangleOptions());
+  std::string demangleSymbolAsString(
+      llvm::StringRef MangledName,
+      const DemangleOptions &Options = DemangleOptions());
 
   /// Demangle the given type and return the readable name.
   ///
   /// \param MangledName The mangled type string, which does _not_ start with
   /// a mangling prefix.
   ///
   /// \returns The demangled string.
-  std::string demangleTypeAsString(llvm::StringRef MangledName,
-                            const DemangleOptions &Options = DemangleOptions());
+  std::string
+  demangleTypeAsString(llvm::StringRef MangledName,
+                       const DemangleOptions &Options = DemangleOptions());
 
   /// Returns true if the mangledName refers to a thunk function.
   ///
@@ -571,7 +579,6 @@ bool nodeConsumesGenericArgs(Node *node);
 bool isSpecialized(Node *node);
 
 NodePointer getUnspecialized(Node *node, NodeFactory &Factory);
-std::string archetypeName(Node::IndexType index, Node::IndexType depth);
 
 /// Form a StringRef around the mangled name starting at base, if the name may
 /// contain symbolic references.

lib/Demangling/NodePrinter.cpp

@@ -50,8 +50,7 @@ DemanglerPrinter &DemanglerPrinter::operator<<(long long n) & {
   return *this;
 }
 
-std::string Demangle::archetypeName(Node::IndexType index,
-                                    Node::IndexType depth) {
+std::string Demangle::archetypeName(uint64_t index, uint64_t depth) {
   DemanglerPrinter name;
   do {
     name << (char)('A' + (index % 26));
@@ -1959,7 +1958,7 @@ NodePointer NodePrinter::print(NodePointer Node, bool asPrefixContext) {
         }
         // FIXME: Depth won't match when a generic signature applies to a
         // method in generic type context.
-        Printer << archetypeName(index, depth);
+        Printer << Options.ArchetypeName(index, depth);
       }
     }
 
@@ -2036,13 +2035,8 @@ NodePointer NodePrinter::print(NodePointer Node, bool asPrefixContext) {
   }
   case Node::Kind::DependentGenericParamType: {
     unsigned index = Node->getChild(1)->getIndex();
-    do {
-      Printer << (char)('A' + (index % 26));
-      index /= 26;
-    } while (index);
     unsigned depth = Node->getChild(0)->getIndex();
-    if (depth != 0)
-      Printer << depth;
+    Printer << Options.ArchetypeName(index, depth);
     return nullptr;
   }
   case Node::Kind::DependentGenericType: {

unittests/Basic/DemangleTest.cpp

@@ -31,3 +31,15 @@ TEST(Demangle, IsObjCSymbol) {
             isObjCSymbol(llvm::StringRef("_$s3pat7inlinedSo8NSNumberCvp")));
   EXPECT_EQ(true, isObjCSymbol(llvm::StringRef("_$sSC3fooyS2d_SdtFTO")));
 }
+
+TEST(Demangle, CustomArchetypes) {
+  std::string SymbolName = "_$s1a1gyq_q__xt_tr0_lF";
+  std::string DemangledName = "a.g<Q, U>((U, Q)) -> U";
+
+  DemangleOptions Options;
+  Options.ArchetypeName = [](uint64_t index, uint64_t depth) {
+    return index ? "U" : "Q";
+  };
+  std::string Result = demangleSymbolAsString(SymbolName, Options);
+  EXPECT_STREQ(DemangledName.c_str(), Result.c_str());
+}