[Demangle][Rust] Parse const backreferences

[tmiasko]

Summary

Depends on D103847

[dblaikie]

Looks good!

llvm/lib/Demangle/RustDemangle.cpp

void Demangler::demangleOptionalBinder() {
   }
   print("> ");
 }
 
 // <const> = <basic-type> <const-data>
 //         | "p"                          // placeholder
 //         | <backref>
 void Demangler::demangleConst() {
+  if (Error || RecursionLevel >= MaxRecursionLevel) {
+    Error = true;
+    return;
+  }
+  SwapAndRestore<size_t> SaveRecursionLevel(RecursionLevel, RecursionLevel + 1);
+
+  char C = consume();
   BasicType Type;
-  if (parseBasicType(consume(), Type)) {
+  if (parseBasicType(C, Type)) {
     switch (Type) {
     case BasicType::I8:
     case BasicType::I16:
     case BasicType::I32:
     case BasicType::I64:
     case BasicType::I128:
     case BasicType::ISize:
     case BasicType::U8:
case BasicType::Bool:
       break;
     case BasicType::Char:
       demangleConstChar();
       break;
     case BasicType::Placeholder:
       print('_');
       break;
     default:
-      // FIXME demangle backreferences.
       Error = true;
       break;
     }
+  } else if (C == 'B') {
+    demangleBackref([&] { demangleConst(); });
   } else {
     Error = true;
   }
 }
 
 // <const-data> = ["n"] <hex-number>
 void Demangler::demangleConstInt() {
   if (consumeIf('n'))

llvm/test/Demangle/rust.test

 ; Backreferences
 
 CHECK: backref::<backref::ident>
        _RIC7backrefNvB0_5identE
 
 CHECK: backref::<(), ()>
        _RIC7backrefuB9_E
 
+CHECK: backref::<7, 7>
+       _RIC7backrefKi7_KBa_E
+
 ; Invalid backreferences
 
 CHECK: _RB_
        _RB_
 
 CHECK: _RB5_
        _RB5_
 
 CHECK: _RNvB_1a
        _RNvB_1a
 
 CHECK: _RIC7backrefSB9_E
        _RIC7backrefSB9_E
 
+CHECK: _RIC7backrefKBa_E
+       _RIC7backrefKBa_E
+
 ; Invalid mangled characters
 
 CHECK: _RNvC2a.1c
        _RNvC2a.1c
 
 CHECK: _RNvC2a$1c
        _RNvC2a$1c