Fix MSVC Demangling with auto NTTP mangled names for function pointer, pointer to data and integral types (llvm#96590)

As cited here, llvm#92477, undname
needs updating to support the new auto NTTP name mangling.

In short the deduced type of the auto NTTP parameter is mangled as `$M
<type> <nttp-param>`. However the deduced type is not printed for the
undecorated name so the `$M <type>` is parsed but simply ignored when
stringifying the generated AST.

Author: MaxEW707

llvm/lib/Demangle/MicrosoftDemangle.cpp

@@ -53,6 +53,18 @@ static bool consumeFront(std::string_view &S, std::string_view C) {
   return true;
 }
 
+static bool consumeFront(std::string_view &S, std::string_view PrefixA,
+                         std::string_view PrefixB, bool A) {
+  const std::string_view &Prefix = A ? PrefixA : PrefixB;
+  return consumeFront(S, Prefix);
+}
+
+static bool startsWith(std::string_view S, std::string_view PrefixA,
+                       std::string_view PrefixB, bool A) {
+  const std::string_view &Prefix = A ? PrefixA : PrefixB;
+  return llvm::itanium_demangle::starts_with(S, Prefix);
+}
+
 static bool isMemberPointer(std::string_view MangledName, bool &Error) {
   Error = false;
   const char F = MangledName.front();
@@ -2256,6 +2268,18 @@ Demangler::demangleTemplateParameterList(std::string_view &MangledName) {
 
     NodeList &TP = **Current;
 
+    // <auto-nttp> ::= $ M <type> <nttp>
+    const bool IsAutoNTTP = consumeFront(MangledName, "$M");
+    if (IsAutoNTTP) {
+      // The deduced type of the auto NTTP parameter isn't printed so
+      // we want to ignore the AST created from demangling the type.
+      //
+      // TODO: Avoid the extra allocations to the bump allocator in this case.
+      (void)demangleType(MangledName, QualifierMangleMode::Drop);
+      if (Error)
+        return nullptr;
+    }
+
     TemplateParameterReferenceNode *TPRN = nullptr;
     if (consumeFront(MangledName, "$$Y")) {
       // Template alias
@@ -2266,15 +2290,17 @@ Demangler::demangleTemplateParameterList(std::string_view &MangledName) {
     } else if (consumeFront(MangledName, "$$C")) {
       // Type has qualifiers.
       TP.N = demangleType(MangledName, QualifierMangleMode::Mangle);
-    } else if (llvm::itanium_demangle::starts_with(MangledName, "$1") ||
-               llvm::itanium_demangle::starts_with(MangledName, "$H") ||
-               llvm::itanium_demangle::starts_with(MangledName, "$I") ||
-               llvm::itanium_demangle::starts_with(MangledName, "$J")) {
+    } else if (startsWith(MangledName, "$1", "1", !IsAutoNTTP) ||
+               startsWith(MangledName, "$H", "H", !IsAutoNTTP) ||
+               startsWith(MangledName, "$I", "I", !IsAutoNTTP) ||
+               startsWith(MangledName, "$J", "J", !IsAutoNTTP)) {
       // Pointer to member
       TP.N = TPRN = Arena.alloc<TemplateParameterReferenceNode>();
       TPRN->IsMemberPointer = true;
 
-      MangledName.remove_prefix(1);
+      if (!IsAutoNTTP)
+        MangledName.remove_prefix(1); // Remove leading '$'
+
       // 1 - single inheritance       <name>
       // H - multiple inheritance     <name> <number>
       // I - virtual inheritance      <name> <number> <number>
@@ -2342,7 +2368,7 @@ Demangler::demangleTemplateParameterList(std::string_view &MangledName) {
       }
       TPRN->IsMemberPointer = true;
 
-    } else if (consumeFront(MangledName, "$0")) {
+    } else if (consumeFront(MangledName, "$0", "0", !IsAutoNTTP)) {
       // Integral non-type template parameter
       bool IsNegative = false;
       uint64_t Value = 0;

llvm/test/Demangle/ms-auto-templates.test

@@ -0,0 +1,57 @@
+; RUN: llvm-undname < %s | FileCheck %s
+
+; CHECK-NOT: Invalid mangled name
+
+??0?$AutoNTTPClass@$MPEAH1?i@@3HA@@QEAA@XZ
+; CHECK: public: __cdecl AutoNTTPClass<&int i>::AutoNTTPClass<&int i>(void)
+
+??0?$AutoNTTPClass@$1?i@@3HA@@QEAA@XZ
+; CHECK: public: __cdecl AutoNTTPClass<&int i>::AutoNTTPClass<&int i>(void)
+
+??0?$AutoNTTPClass@$MPEAH1?i@@3HA$MPEAH1?j@@3HA@@QEAA@XZ
+; CHECK: public: __cdecl AutoNTTPClass<&int i, &int j>::AutoNTTPClass<&int i, &int j>(void)
+
+??0?$AutoNTTPClass@$1?i@@3HA$1?j@@3HA@@QEAA@XZ
+; CHECK: public: __cdecl AutoNTTPClass<&int i, &int j>::AutoNTTPClass<&int i, &int j>(void)
+
+??0?$AutoNTTPClass@$MP6AHXZ1?Func@@YAHXZ@@QEAA@XZ
+; CHECK: public: __cdecl AutoNTTPClass<&int __cdecl Func(void)>::AutoNTTPClass<&int __cdecl Func(void)>(void)
+
+??0?$AutoNTTPClass@$1?Func@@YAHXZ@@QEAA@XZ
+; CHECK: public: __cdecl AutoNTTPClass<&int __cdecl Func(void)>::AutoNTTPClass<&int __cdecl Func(void)>(void)
+
+??0?$AutoNTTPClass@$MP6AHXZ1?Func@@YAHXZ$MP6AHXZ1?Func2@@YAHXZ@@QEAA@XZ
+; CHECK: public: __cdecl AutoNTTPClass<&int __cdecl Func(void), &int __cdecl Func2(void)>::AutoNTTPClass<&int __cdecl Func(void), &int __cdecl Func2(void)>(void)
+
+??0?$AutoNTTPClass@$1?Func@@YAHXZ$1?Func2@@YAHXZ@@QEAA@XZ
+; CHECK: public: __cdecl AutoNTTPClass<&int __cdecl Func(void), &int __cdecl Func2(void)>::AutoNTTPClass<&int __cdecl Func(void), &int __cdecl Func2(void)>(void)
+
+??$AutoFunc@$MPEAH1?i@@3HA@@YA?A?<auto>@@XZ
+; CHECK: <auto> __cdecl AutoFunc<&int i>(void)
+
+??$AutoFunc@$1?i@@3HA@@YA?A?<auto>@@XZ
+; CHECK: <auto> __cdecl AutoFunc<&int i>(void)
+
+??$AutoFunc@$MP6AHXZ1?Func@@YAHXZ@@YA?A?<auto>@@XZ
+; CHECK: <auto> __cdecl AutoFunc<&int __cdecl Func(void)>(void)
+
+??$AutoFunc@$1?Func@@YAHXZ@@YA?A?<auto>@@XZ
+; CHECK: <auto> __cdecl AutoFunc<&int __cdecl Func(void)>(void)
+
+??$AutoFunc@$MH00@@YA?A?<auto>@@XZ
+; CHECK: <auto> __cdecl AutoFunc<1>(void)
+
+??$AutoFunc@$00@@YA?A?<auto>@@XZ
+; CHECK: <auto> __cdecl AutoFunc<1>(void)
+
+??0?$AutoNTTPClass@$0A@@@QEAA@XZ
+; CHECK: public: __cdecl AutoNTTPClass<0>::AutoNTTPClass<0>(void)
+
+??0?$AutoNTTPClass@$MH0A@@@QEAA@XZ
+; CHECK: public: __cdecl AutoNTTPClass<0>::AutoNTTPClass<0>(void)
+
+??0?$AutoNTTPClass@$0A@$0A@$0GB@@@QEAA@XZ
+; CHECK: public: __cdecl AutoNTTPClass<0, 0, 97>::AutoNTTPClass<0, 0, 97>(void)
+
+??0?$AutoNTTPClass@$MH0A@$M_N0A@$MD0GB@@@QEAA@XZ
+; CHECK: public: __cdecl AutoNTTPClass<0, 0, 97>::AutoNTTPClass<0, 0, 97>(void)