[Demangle][Rust] Parse path backreferences

[tmiasko]

Summary

Depends on D103364

[dblaikie]

Looks good - probably 3 separate commits, though. (handy if they're separate reviews too in the future - just a bit easier to check tests, etc)

llvm/lib/Demangle/RustDemangle.cpp

509–511

Maybe split this in two - add the two different places for backrefs separately, with separate tests? Oh, three different places (also demangleConst)?

[tmiasko]

Parse path backreferences

[tmiasko]

llvm/lib/Demangle/RustDemangle.cpp

509–511

I split patch into D103847 and D103848, while adding extra tests that exercise recursion limit in each production.

llvm/include/llvm/Demangle/RustDemangle.h

private:
   void demangleDynBounds();
   void demangleDynTrait();
   void demangleOptionalBinder();
   void demangleConst();
   void demangleConstInt();
   void demangleConstBool();
   void demangleConstChar();
 
+  template <typename Callable> void demangleBackref(Callable Demangler) {
+    uint64_t Backref = parseBase62Number();
+    if (Error || Backref >= Position) {
+      Error = true;
+      return;
+    }
+
+    if (!Print)
+      return;
+
+    SwapAndRestore<size_t> SavePosition(Position, Position);
+    Position = Backref;
+    Demangler();
+  }
+
   Identifier parseIdentifier();
   uint64_t parseOptionalBase62Number(char Tag);
   uint64_t parseBase62Number();
   uint64_t parseDecimalNumber();
   uint64_t parseHexNumber(StringView &HexDigits);
 
   void print(char C) {
     if (Error || !Print)

llvm/lib/Demangle/RustDemangle.cpp

for (size_t I = 0; !Error && !consumeIf('E'); ++I) {
       demangleGenericArg();
     }
     if (LeaveOpen == rust_demangle::LeaveOpen::Yes)
       return true;
     else
       print(">");
     break;
   }
+  case 'B': {
+    bool IsOpen = false;
+    demangleBackref([&] { IsOpen = demanglePath(InType, LeaveOpen); });
+    return IsOpen;
+  }
   default:
-    // FIXME parse remaining productions.
     Error = true;
     break;
   }
 
   return false;
 }
 
 // <impl-path> = [<disambiguator>] <path>
if (consumeIf('L')) {
       if (auto Lifetime = parseBase62Number()) {
         print(" + ");
         printLifetime(Lifetime);
       }
     } else {
       Error = true;
     }
     break;
   default:
     Position = Start;
     demanglePath(rust_demangle::InType::Yes);
     break;
   }
 }
 
 // <fn-sig> := [<binder>] ["U"] ["K" <abi>] {<type>} "E" <type>
 // <abi> = "C"
 //       | <undisambiguated-identifier>
 void Demangler::demangleFnSig() {

llvm/test/Demangle/rust.test

 CHECK: char::<'\u{10ffff}'>
        _RIC4charKc10ffff_E
 
 ; Invalid char constants
 
 CHECK: _RIC4charKc1234567_E
        _RIC4charKc1234567_E
 
+; Backreferences
+
+CHECK: backref::<backref::ident>
+       _RIC7backrefNvB0_5identE
+
+; Invalid backreferences
+
+CHECK: _RB_
+       _RB_
+
+CHECK: _RB5_
+       _RB5_
+
+CHECK: _RNvB_1a
+       _RNvB_1a
+
 ; Invalid mangled characters
 
 CHECK: _RNvC2a.1c
        _RNvC2a.1c
 
 CHECK: _RNvC2a$1c
        _RNvC2a$1c