Demangle constrained auto types (Dk <type-constraint>).

PiperOrigin-RevId: 638831461
Change-Id: Ie30ff381e7d74a40a689b52e66b2e8bb81e0fda6

absl/debugging/internal/demangle.cc

@@ -621,6 +621,7 @@ static bool ParseExprPrimary(State *state);
 static bool ParseExprCastValueAndTrailingE(State *state);
 static bool ParseQRequiresClauseExpr(State *state);
 static bool ParseRequirement(State *state);
+static bool ParseTypeConstraint(State *state);
 static bool ParseLocalName(State *state);
 static bool ParseLocalNameSuffix(State *state);
 static bool ParseDiscriminator(State *state);
@@ -1274,6 +1275,7 @@ static bool ParseDecltype(State *state) {
 //        ::= <substitution>
 //        ::= Dp <type>          # pack expansion of (C++0x)
 //        ::= Dv <num-elems> _   # GNU vector extension
+//        ::= Dk <type-constraint>  # constrained auto
 //
 static bool ParseType(State *state) {
   ComplexityGuard guard(state);
@@ -1346,6 +1348,11 @@ static bool ParseType(State *state) {
   }
   state->parse_state = copy;
 
+  if (ParseTwoCharToken(state, "Dk") && ParseTypeConstraint(state)) {
+    return true;
+  }
+  state->parse_state = copy;
+
   // For this notation see CXXNameMangler::mangleType in Clang's source code.
   // The relevant logic and its comment "not clear how to mangle this!" date
   // from 2011, so it may be with us awhile.
@@ -2292,8 +2299,6 @@ static bool ParseQRequiresClauseExpr(State *state) {
 // <requirement> ::= T <type>
 // <requirement> ::= Q <constraint-expression>
 //
-// <type-constraint> ::= <name>
-//
 // <constraint-expression> ::= <expression>
 //
 // https://github.com/itanium-cxx-abi/cxx-abi/issues/24
@@ -2307,7 +2312,7 @@ static bool ParseRequirement(State *state) {
       Optional(ParseOneCharToken(state, 'N')) &&
       // This logic backtracks cleanly if we eat an R but a valid type doesn't
       // follow it.
-      (!ParseOneCharToken(state, 'R') || ParseName(state))) {
+      (!ParseOneCharToken(state, 'R') || ParseTypeConstraint(state))) {
     return true;
   }
   state->parse_state = copy;
@@ -2321,6 +2326,11 @@ static bool ParseRequirement(State *state) {
   return false;
 }
 
+// <type-constraint> ::= <name>
+static bool ParseTypeConstraint(State *state) {
+  return ParseName(state);
+}
+
 // <local-name> ::= Z <(function) encoding> E <(entity) name> [<discriminator>]
 //              ::= Z <(function) encoding> E s [<discriminator>]
 //              ::= Z <(function) encoding> E d [<(parameter) number>] _ <name>

absl/debugging/internal/demangle_test.cc

@@ -150,6 +150,16 @@ TEST(Demangle, FunctionTemplateTemplateParamWithConstrainedArg) {
   EXPECT_STREQ(tmp, "foo<>()");
 }
 
+TEST(Demangle, ConstrainedAutoInFunctionTemplate) {
+  char tmp[100];
+
+  // template <typename T> concept C = true;
+  // template <C auto N> void f() {}
+  // template void f<0>();
+  ASSERT_TRUE(Demangle("_Z1fITnDk1CLi0EEvv", tmp, sizeof(tmp)));
+  EXPECT_STREQ(tmp, "f<>()");
+}
+
 TEST(Demangle, NonTemplateBuiltinType) {
   char tmp[100];