[Demangle][Rust] Parse bool constants

[dblaikie]

Looks good, thanks!

llvm/include/llvm/Demangle/RustDemangle.h

public:
   bool demangle(StringView MangledName);
 
 private:
   void demanglePath();
   void demangleGenericArg();
   void demangleType();
   void demangleConst();
   void demangleConstInt();
+  void demangleConstBool();
 
   Identifier parseIdentifier();
   uint64_t parseOptionalBase62Number(char Tag);
   uint64_t parseBase62Number();
   uint64_t parseDecimalNumber();
   uint64_t parseHexNumber(StringView &HexDigits);
 
   void print(char C) {

llvm/lib/Demangle/RustDemangle.cpp

if (parseBasicType(consume(), Type)) {
     case BasicType::U8:
     case BasicType::U16:
     case BasicType::U32:
     case BasicType::U64:
     case BasicType::U128:
     case BasicType::USize:
       demangleConstInt();
       break;
+    case BasicType::Bool:
+      demangleConstBool();
+      break;
     case BasicType::Placeholder:
       print('_');
       break;
     default:
-      // FIXME demangle backreferences, bool constants, and char constants.
+      // FIXME demangle backreferences and char constants.
       Error = true;
       break;
     }
   } else {
     Error = true;
   }
 }
 
 // <const-data> = ["n"] <hex-number>
 void Demangler::demangleConstInt() {
   if (consumeIf('n'))
     print('-');
 
   StringView HexDigits;
   uint64_t Value = parseHexNumber(HexDigits);
   if (HexDigits.size() <= 16) {
     printDecimalNumber(Value);
   } else {
     print("0x");
     print(HexDigits);
   }
 }
 
+// <const-data> = "0_" // false
+//              | "1_" // true
+void Demangler::demangleConstBool() {
+  StringView HexDigits;
+  parseHexNumber(HexDigits);
+  if (HexDigits == "0")
+    print("false");
+  else if (HexDigits == "1")
+    print("true");
+  else
+    Error = true;
+}
+
 // <undisambiguated-identifier> = ["u"] <decimal-number> ["_"] <bytes>
 Identifier Demangler::parseIdentifier() {
   bool Punycode = consumeIf('u');
   uint64_t Bytes = parseDecimalNumber();
 
   // Underscore resolves the ambiguity when identifier starts with a decimal
   // digit or another underscore.
   consumeIf('_');

llvm/test/Demangle/rust.test

CHECK: u16::<0>
        _RIC3u16Kt0_E
 
 CHECK: i64::<0>
        _RIC3i64Kx0_E
 
 CHECK: u64::<0>
        _RIC3u64Ky0_E
 
+; Bool constants
+
+CHECK: bool::<false>
+       _RIC4boolKb0_E
+
+CHECK: bool::<true>
+       _RIC4boolKb1_E
+
+; Invalid bool constants
+
+CHECK: _RIC4boolKb2_E
+       _RIC4boolKb2_E
+
+CHECK: _RIC4boolKbn0_E
+       _RIC4boolKbn0_E
+
 ; Invalid mangled characters
 
 CHECK: _RNvC2a.1c
        _RNvC2a.1c
 
 CHECK: _RNvC2a$1c
        _RNvC2a$1c