[ItaniumDemangle] Set InConstraintExpr to true when demangling a constraint expression (#107385)

This prevents demangler failures until the TODO in the
[demangler](https://github.com/llvm/llvm-project/blob/3e070906eff720dc44aee86e533e12aafc8bb14b/llvm/include/llvm/Demangle/ItaniumDemangle.h#L5678)
is implemented.

This is a temporary fix for
[#89914](#89914).

Author: VitaNuo

libcxxabi/src/demangle/ItaniumDemangle.h

@@ -2677,7 +2677,7 @@ template <typename Derived, typename Alloc> struct AbstractManglingParser {
 
   bool TryToParseTemplateArgs = true;
   bool PermitForwardTemplateReferences = false;
-  bool InConstraintExpr = false;
+  bool HasIncompleteTemplateParameterTracking = false;
   size_t ParsingLambdaParamsAtLevel = (size_t)-1;
 
   unsigned NumSyntheticTemplateParameters[3] = {};
@@ -4818,7 +4818,8 @@ template <typename Derived, typename Alloc>
 Node *AbstractManglingParser<Derived, Alloc>::parseConstraintExpr() {
   // Within this expression, all enclosing template parameter lists are in
   // scope.
-  ScopedOverride<bool> SaveInConstraintExpr(InConstraintExpr, true);
+  ScopedOverride<bool> SaveIncompleteTemplateParameterTracking(
+      HasIncompleteTemplateParameterTracking, true);
   return getDerived().parseExpr();
 }
 
@@ -5676,7 +5677,7 @@ Node *AbstractManglingParser<Derived, Alloc>::parseTemplateParam() {
   // substitute them all within a <constraint-expression>, so print the
   // parameter numbering instead for now.
   // TODO: Track all enclosing template parameters and substitute them here.
-  if (InConstraintExpr) {
+  if (HasIncompleteTemplateParameterTracking) {
     return make<NameType>(std::string_view(Begin, First - 1 - Begin));
   }
 
@@ -5737,6 +5738,12 @@ Node *AbstractManglingParser<Derived, Alloc>::parseTemplateParamDecl(
   }
 
   if (consumeIf("Tk")) {
+    // We don't track enclosing template parameter levels well enough to
+    // reliably demangle template parameter substitutions, so print an arbitrary
+    // string in place of a parameter for now.
+    // TODO: Track all enclosing template parameters and demangle substitutions.
+    ScopedOverride<bool> SaveIncompleteTemplateParameterTrackingExpr(
+        HasIncompleteTemplateParameterTracking, true);
     Node *Constraint = getDerived().parseName();
     if (!Constraint)
       return nullptr;

libcxxabi/test/test_demangle.pass.cpp

@@ -30137,6 +30137,7 @@ const char* cases[][2] =
     {"_ZZN5test71fIiEEvvENKUlTyQaa1CIT_E1CITL0__ET0_E0_clIiiEEDaS3_Qaa1CIDtfp_EELb1E", "auto void test7::f<int>()::'lambda0'<typename $T> requires C<T> && C<TL0_> (auto)::operator()<int, int>(auto) const requires C<decltype(fp)> && true"},
     {"_ZZN5test71fIiEEvvENKUlTyQaa1CIT_E1CITL0__ET0_E1_clIiiEEDaS3_Q1CIDtfp_EE", "auto void test7::f<int>()::'lambda1'<typename $T> requires C<T> && C<TL0_> (auto)::operator()<int, int>(auto) const requires C<decltype(fp)>"},
     {"_ZZN5test71fIiEEvvENKUlTyT0_E_clIiiEEDaS1_", "auto void test7::f<int>()::'lambda'<typename $T>(auto)::operator()<int, int>(auto) const"},
+    {"_ZN3FooIiE6methodITk4TrueIT_EiEEvS3_", "void Foo<int>::method<int>(T)"},
 
     // C++20 requires expressions, see https://github.com/itanium-cxx-abi/cxx-abi/issues/24.
     {"_Z1fIiEviQrqXcvT__EXfp_Xeqfp_cvS0__EXplcvS0__ELi1ER5SmallXmicvS0__ELi1ENXmlcvS0__ELi2ENR11SmallerThanILi1234EETS0_T1XIS0_ETNS3_4typeETS2_IiEQ11SmallerThanIS0_Li256EEE", "void f<int>(int) requires requires { (T)(); fp; fp == (T)(); {(T)() + 1} -> Small; {(T)() - 1} noexcept; {(T)() * 2} noexcept -> SmallerThan<1234>; typename T; typename X<T>; typename X<T>::type; typename X<int>; requires SmallerThan<T, 256>; }"},

llvm/include/llvm/Demangle/ItaniumDemangle.h

@@ -2677,7 +2677,7 @@ template <typename Derived, typename Alloc> struct AbstractManglingParser {
 
   bool TryToParseTemplateArgs = true;
   bool PermitForwardTemplateReferences = false;
-  bool InConstraintExpr = false;
+  bool HasIncompleteTemplateParameterTracking = false;
   size_t ParsingLambdaParamsAtLevel = (size_t)-1;
 
   unsigned NumSyntheticTemplateParameters[3] = {};
@@ -4818,7 +4818,8 @@ template <typename Derived, typename Alloc>
 Node *AbstractManglingParser<Derived, Alloc>::parseConstraintExpr() {
   // Within this expression, all enclosing template parameter lists are in
   // scope.
-  ScopedOverride<bool> SaveInConstraintExpr(InConstraintExpr, true);
+  ScopedOverride<bool> SaveIncompleteTemplateParameterTracking(
+      HasIncompleteTemplateParameterTracking, true);
   return getDerived().parseExpr();
 }
 
@@ -5676,7 +5677,7 @@ Node *AbstractManglingParser<Derived, Alloc>::parseTemplateParam() {
   // substitute them all within a <constraint-expression>, so print the
   // parameter numbering instead for now.
   // TODO: Track all enclosing template parameters and substitute them here.
-  if (InConstraintExpr) {
+  if (HasIncompleteTemplateParameterTracking) {
     return make<NameType>(std::string_view(Begin, First - 1 - Begin));
   }
 
@@ -5737,6 +5738,12 @@ Node *AbstractManglingParser<Derived, Alloc>::parseTemplateParamDecl(
   }
 
   if (consumeIf("Tk")) {
+    // We don't track enclosing template parameter levels well enough to
+    // reliably demangle template parameter substitutions, so print an arbitrary
+    // string in place of a parameter for now.
+    // TODO: Track all enclosing template parameters and demangle substitutions.
+    ScopedOverride<bool> SaveIncompleteTemplateParameterTrackingExpr(
+        HasIncompleteTemplateParameterTracking, true);
     Node *Constraint = getDerived().parseName();
     if (!Constraint)
       return nullptr;