[Demangle][Rust] Parse inherent implementations

Part of https://reviews.llvm.org/D102549

include/llvm/Demangle/RustDemangle.h

@@ -63,6 +63,10 @@ class Demangler {
   // Position in the input string.
   size_t Position;
 
+  // When true, print methods append the output to the stream.
+  // When false, the output is suppressed.
+  bool Print;
+
   // True if an error occurred.
   bool Error;
 
@@ -76,6 +80,7 @@ public:
 
 private:
   void demanglePath();
+  void demangleImplPath();
   void demangleGenericArg();
   void demangleType();
   void demangleConst();
@@ -90,21 +95,21 @@ private:
   uint64_t parseHexNumber(StringView &HexDigits);
 
   void print(char C) {
-    if (Error)
+    if (Error || !Print)
       return;
 
     Output += C;
   }
 
   void print(StringView S) {
-    if (Error)
+    if (Error || !Print)
       return;
 
     Output += S;
   }
 
   void printDecimalNumber(uint64_t N) {
-    if (Error)
+    if (Error || !Print)
       return;
 
     Output << N;

lib/Demangle/RustDemangle.cpp

@@ -101,6 +101,7 @@ static inline bool isValid(const char C) {
 bool Demangler::demangle(StringView Mangled) {
   Position = 0;
   Error = false;
+  Print = true;
   RecursionLevel = 0;
 
   if (!Mangled.consumeFront("_R")) {
@@ -145,6 +146,13 @@ void Demangler::demanglePath() {
     print(Ident.Name);
     break;
   }
+  case 'M': {
+    demangleImplPath();
+    print("<");
+    demangleType();
+    print(">");
+    break;
+  }
   case 'N': {
     char NS = consume();
     if (!isLower(NS) && !isUpper(NS)) {
@@ -199,6 +207,14 @@ void Demangler::demanglePath() {
   }
 }
 
+// <impl-path> = [<disambiguator>] <path>
+// <disambiguator> = "s" <base-62-number>
+void Demangler::demangleImplPath() {
+  SwapAndRestore<bool> SavePrint(Print, false);
+  parseOptionalBase62Number('s');
+  demanglePath();
+}
+
 // <generic-arg> = <lifetime>
 //               | <type>
 //               | "K" <const>

test/Demangle/rust.test

@@ -33,6 +33,14 @@ CHECK: crate::{shim:reify#0}
 CHECK: crate::{Z:ident#10}
        _RNZC5crates8_5ident
 
+; Inherent impl
+
+CHECK: <_>
+       _RMC5cratep
+
+CHECK: <_>
+       _RMs_C5cratep
+
 ; Generic type arguments
 
 CHECK: generic::<_>