[Demangle][Rust] Parse type backreferences

[tmiasko]

Summary

Depends on D103459

[dblaikie]

Looks good

llvm/lib/Demangle/RustDemangle.cpp

 //          | "R" [<lifetime>] <type>     // &T
 //          | "Q" [<lifetime>] <type>     // &mut T
 //          | "P" <type>                  // *const T
 //          | "O" <type>                  // *mut T
 //          | "F" <fn-sig>                // fn(...) -> ...
 //          | "D" <dyn-bounds> <lifetime> // dyn Trait<Assoc = X> + Send + 'a
 //          | <backref>                   // backref
 void Demangler::demangleType() {
-  size_t Start = Position;
+  if (Error || RecursionLevel >= MaxRecursionLevel) {
+    Error = true;
+    return;
+  }
+  SwapAndRestore<size_t> SaveRecursionLevel(RecursionLevel, RecursionLevel + 1);
 
+  size_t Start = Position;
   char C = consume();
   BasicType Type;
   if (parseBasicType(C, Type))
     return printBasicType(Type);
 
   switch (C) {
   case 'A':
     print("[");
if (consumeIf('L')) {
       if (auto Lifetime = parseBase62Number()) {
         print(" + ");
         printLifetime(Lifetime);
       }
     } else {
       Error = true;
     }
     break;
+  case 'B':
+    demangleBackref([&] { demangleType(); });
+    break;
   default:
     Position = Start;
     demanglePath(rust_demangle::InType::Yes);
     break;
   }
 }
 
 // <fn-sig> := [<binder>] ["U"] ["K" <abi>] {<type>} "E" <type>

llvm/test/Demangle/rust.test

 CHECK: _RIC4charKc1234567_E
        _RIC4charKc1234567_E
 
 ; Backreferences
 
 CHECK: backref::<backref::ident>
        _RIC7backrefNvB0_5identE
 
+CHECK: backref::<(), ()>
+       _RIC7backrefuB9_E
+
 ; Invalid backreferences
 
 CHECK: _RB_
        _RB_
 
 CHECK: _RB5_
        _RB5_
 
 CHECK: _RNvB_1a
        _RNvB_1a
 
+CHECK: _RIC7backrefSB9_E
+       _RIC7backrefSB9_E
+
 ; Invalid mangled characters
 
 CHECK: _RNvC2a.1c
        _RNvC2a.1c
 
 CHECK: _RNvC2a$1c
        _RNvC2a$1c