From 82b7e822d00596ec8a02490f1d662ed0fa872b54 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Tomasz=20Mi=C4=85sko?= <tomasz.miasko@gmail.com>
Date: Mon, 7 Jun 2021 23:34:34 +0200
Subject: [PATCH] [Demangle][Rust] Parse path backreferences

Reviewed By: dblaikie

Differential Revision: https://reviews.llvm.org/D103459
---
 llvm/include/llvm/Demangle/RustDemangle.h | 15 +++++++++++++++
 llvm/lib/Demangle/RustDemangle.cpp        |  6 +++++-
 llvm/test/Demangle/rust.test              | 16 ++++++++++++++++
 3 files changed, 36 insertions(+), 1 deletion(-)

diff --git a/llvm/include/llvm/Demangle/RustDemangle.h b/llvm/include/llvm/Demangle/RustDemangle.h
index c2372cd8acb1..b377e618cda9 100644
--- a/llvm/include/llvm/Demangle/RustDemangle.h
+++ b/llvm/include/llvm/Demangle/RustDemangle.h
@@ -102,6 +102,21 @@ private:
   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();
diff --git a/llvm/lib/Demangle/RustDemangle.cpp b/llvm/lib/Demangle/RustDemangle.cpp
index 582cdbc9f749..3ce73f5d935f 100644
--- a/llvm/lib/Demangle/RustDemangle.cpp
+++ b/llvm/lib/Demangle/RustDemangle.cpp
@@ -232,8 +232,12 @@ bool Demangler::demanglePath(InType InType, LeaveOpen LeaveOpen) {
       print(">");
     break;
   }
+  case 'B': {
+    bool IsOpen = false;
+    demangleBackref([&] { IsOpen = demanglePath(InType, LeaveOpen); });
+    return IsOpen;
+  }
   default:
-    // FIXME parse remaining productions.
     Error = true;
     break;
   }
diff --git a/llvm/test/Demangle/rust.test b/llvm/test/Demangle/rust.test
index cef5d20275ac..64255336857c 100644
--- a/llvm/test/Demangle/rust.test
+++ b/llvm/test/Demangle/rust.test
@@ -420,6 +420,22 @@ CHECK: char::<'\u{10ffff}'>
 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