Demangle sizeof...(pack captured from an alias template), sP ... E.

PiperOrigin-RevId: 640314320
Change-Id: I1020879b354c75558d3dba064bb3ea13bd667227

absl/debugging/internal/demangle.cc

@@ -1978,6 +1978,7 @@ static bool ParseBracedExpression(State *state) {
 //              ::= <function-param>
 //              ::= sZ <template-param>
 //              ::= sZ <function-param>
+//              ::= sP <template-arg>* E
 //              ::= <expr-primary>
 //              ::= dt <expression> <unresolved-name> # expr.name
 //              ::= pt <expression> <unresolved-name> # expr->name
@@ -2109,6 +2110,15 @@ static bool ParseExpression(State *state) {
   }
   state->parse_state = copy;
 
+  // sizeof...(pack) captured from an alias template
+  //
+  // <expression> ::= sP <template-arg>* E
+  if (ParseTwoCharToken(state, "sP") && ZeroOrMore(ParseTemplateArg, state) &&
+      ParseOneCharToken(state, 'E')) {
+    return true;
+  }
+  state->parse_state = copy;
+
   // Unary folds (... op pack) and (pack op ...).
   //
   // <expression> ::= fl <binary operator-name> <expression>

absl/debugging/internal/demangle_test.cc

@@ -812,6 +812,22 @@ TEST(Demangle, SizeofPacks) {
   EXPECT_STREQ("g<>()", tmp);
 }
 
+TEST(Demangle, SizeofPackInvolvingAnAliasTemplate) {
+  char tmp[80];
+
+  // Source:
+  //
+  // template <class... T> using A = char[sizeof...(T)];
+  // template <class... U> void f(const A<U..., int>&) {}
+  // template void f<int>(const A<int, int>&);
+  //
+  // Full LLVM demangling of the instantiation of f:
+  //
+  // void f<int>(char const (&) [sizeof... (int, int)])
+  EXPECT_TRUE(Demangle("_Z1fIJiEEvRAsPDpT_iE_Kc", tmp, sizeof(tmp)));
+  EXPECT_STREQ("f<>()", tmp);
+}
+
 TEST(Demangle, Spaceship) {
   char tmp[80];