GNU3 demangler: ABI tags, operator<=>, multi-digit T-params, cv cast fix

- ABI tags (B<source-name>): consolidate handling after switch in
  DemangleUnqualifiedName, covering source names and operator names
  (e.g. operator<=>[abi:ne180100])
- operator<=> (ss): add to GetOperator and DemangleUnqualifiedName
- Template param indices: fix DemangleTemplateSubstitution to parse
  multi-digit decimal indices (T10_, T11_, ...) instead of only
  single-digit (fixes symbols with 10+ template parameters)
- cv cast expression: consume '_' delimiter before calling
  DemangleExpressionList for the multi-arg form (cv <type> _ <expr>* E),
  fixing decltype(cm(..., (void)())) return types

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: plafosse

demangler/gnu3/demangle_gnu3.cpp

@@ -150,6 +150,7 @@ static string GetOperator(char elm1, char elm2)
 	case hash('a','N'): return "&=";  // &=
 	case hash('o','R'): return "|=";  // |=
 	case hash('e','O'): return "^=";  // ^=
+	case hash('s','s'): return "<=>"; // <=>
 	case hash('d','l'): return "delete";   // delete
 	case hash('d','a'): return "delete[]"; // delete[]
 	case hash('n','w'): return "new";      // new
@@ -528,8 +529,10 @@ DemangledTypeNode DemangleGNU3::DemangleTemplateSubstitution()
 	}
 	else if (isdigit(elm))
 	{
-		m_reader.Consume();
-		number = elm - '0' + 1;
+		size_t n = 0;
+		while (isdigit(m_reader.Peek()))
+			n = n * 10 + (m_reader.Read() - '0');
+		number = n + 1;
 	}
 	else if (isupper(elm))
 	{
@@ -1244,6 +1247,7 @@ DemangledTypeNode DemangleGNU3::DemangleUnqualifiedName()
 	case hash('a','N'): // &=
 	case hash('o','R'): // |=
 	case hash('e','O'): // ^=
+	case hash('s','s'): // <=>
 		outType = CreateUnknownType("operator" + GetOperator(elm1, elm2));
 		outType.SetNameType(GetNameType(elm1, elm2));
 		break;
@@ -1395,13 +1399,26 @@ DemangledTypeNode DemangleGNU3::DemangleUnqualifiedName()
 			string name = DemangleSourceName();
 			if (name.size() > 11 && name.substr(0, 11) == "_GLOBAL__N_")
 				name = "(anonymous namespace)";
+			m_lastName = name;
 			outType = CreateUnknownType(name);
 		}
 		else
 		{
 			throw DemangleException();
 		}
 	}
+	// Consume ABI tags: B <source-name>  =>  [abi:tagname]
+	// Applies to source names, operator names, and unnamed types.
+	while (m_reader.Peek() == 'B')
+	{
+		m_reader.Consume();
+		string tag = "[abi:" + DemangleSourceName() + "]";
+		auto qn = outType.GetTypeName();
+		if (!qn.empty())
+			qn.back() += tag;
+		outType.SetTypeName(std::move(qn));
+		m_lastName = qn.empty() ? tag : qn.back();
+	}
 	dedent();
 	return outType;
 }
@@ -1706,7 +1723,10 @@ string DemangleGNU3::DemangleExpression()
 		DemangledTypeNode type = DemangleType();
 		out = type.GetString();
 		if (m_reader.Peek() == '_')
+		{
+			m_reader.Consume(); // consume '_' delimiter before expression list
 			out += " (" + DemangleExpressionList() + ")";
+		}
 		else
 			out += " (" + DemangleExpression() + ")";
 		return out;