2 files changed, 64 insertions, 17 deletions

diff --git a/absl/debugging/internal/demangle.cc b/absl/debugging/internal/demangle.cc
index d53a04e0..1b9ca57b 100644
--- a/absl/debugging/internal/demangle.cc
+++ b/absl/debugging/internal/demangle.cc
@@ -100,6 +100,7 @@ static const AbbrevPair kOperatorList[] = {
     {"qu", "?", 3},
     {"st", "sizeof", 0},  // Special syntax
     {"sz", "sizeof", 1},  // Not a real operator name, but used in expressions.
+    {"sZ", "sizeof...", 0},  // Special syntax
     {nullptr, nullptr, 0},
 };
 
@@ -579,6 +580,7 @@ static bool ParseTemplateArg(State *state);
 static bool ParseBaseUnresolvedName(State *state);
 static bool ParseUnresolvedName(State *state);
 static bool ParseUnionSelector(State* state);
+static bool ParseFunctionParam(State* state);
 static bool ParseExpression(State *state);
 static bool ParseExprPrimary(State *state);
 static bool ParseExprCastValue(State *state);
@@ -1751,6 +1753,34 @@ static bool ParseUnionSelector(State *state) {
   return ParseOneCharToken(state, '_') && Optional(ParseNumber(state, nullptr));
 }
 
+// <function-param> ::= fp <(top-level) CV-qualifiers> _
+//                  ::= fp <(top-level) CV-qualifiers> <number> _
+//                  ::= fL <number> p <(top-level) CV-qualifiers> _
+//                  ::= fL <number> p <(top-level) CV-qualifiers> <number> _
+static bool ParseFunctionParam(State *state) {
+  ComplexityGuard guard(state);
+  if (guard.IsTooComplex()) return false;
+
+  ParseState copy = state->parse_state;
+
+  // Function-param expression (level 0).
+  if (ParseTwoCharToken(state, "fp") && Optional(ParseCVQualifiers(state)) &&
+      Optional(ParseNumber(state, nullptr)) && ParseOneCharToken(state, '_')) {
+    return true;
+  }
+  state->parse_state = copy;
+
+  // Function-param expression (level 1+).
+  if (ParseTwoCharToken(state, "fL") && Optional(ParseNumber(state, nullptr)) &&
+      ParseOneCharToken(state, 'p') && Optional(ParseCVQualifiers(state)) &&
+      Optional(ParseNumber(state, nullptr)) && ParseOneCharToken(state, '_')) {
+    return true;
+  }
+  state->parse_state = copy;
+
+  return false;
+}
+
 // <expression> ::= <1-ary operator-name> <expression>
 //              ::= <2-ary operator-name> <expression> <expression>
 //              ::= <3-ary operator-name> <expression> <expression> <expression>
@@ -1762,16 +1792,14 @@ static bool ParseUnionSelector(State *state) {
 //              ::= st <type>
 //              ::= <template-param>
 //              ::= <function-param>
+//              ::= sZ <template-param>
+//              ::= sZ <function-param>
 //              ::= <expr-primary>
 //              ::= dt <expression> <unresolved-name> # expr.name
 //              ::= pt <expression> <unresolved-name> # expr->name
 //              ::= sp <expression>         # argument pack expansion
 //              ::= sr <type> <unqualified-name> <template-args>
 //              ::= sr <type> <unqualified-name>
-// <function-param> ::= fp <(top-level) CV-qualifiers> _
-//                  ::= fp <(top-level) CV-qualifiers> <number> _
-//                  ::= fL <number> p <(top-level) CV-qualifiers> _
-//                  ::= fL <number> p <(top-level) CV-qualifiers> <number> _
 static bool ParseExpression(State *state) {
   ComplexityGuard guard(state);
   if (guard.IsTooComplex()) return false;
@@ -1808,19 +1836,8 @@ static bool ParseExpression(State *state) {
   }
   state->parse_state = copy;
 
-  // Function-param expression (level 0).
-  if (ParseTwoCharToken(state, "fp") && Optional(ParseCVQualifiers(state)) &&
-      Optional(ParseNumber(state, nullptr)) && ParseOneCharToken(state, '_')) {
-    return true;
-  }
-  state->parse_state = copy;
-
-  // Function-param expression (level 1+).
-  if (ParseTwoCharToken(state, "fL") && Optional(ParseNumber(state, nullptr)) &&
-      ParseOneCharToken(state, 'p') && Optional(ParseCVQualifiers(state)) &&
-      Optional(ParseNumber(state, nullptr)) && ParseOneCharToken(state, '_')) {
-    return true;
-  }
+  // <expression> ::= <function-param>
+  if (ParseFunctionParam(state)) return true;
   state->parse_state = copy;
 
   // Parse the conversion expressions jointly to avoid re-parsing the <type> in
@@ -1866,6 +1883,16 @@ static bool ParseExpression(State *state) {
   }
   state->parse_state = copy;
 
+  // sizeof...(pack)
+  //
+  // <expression> ::= sZ <template-param>
+  //              ::= sZ <function-param>
+  if (ParseTwoCharToken(state, "sZ") &&
+      (ParseFunctionParam(state) || ParseTemplateParam(state))) {
+    return true;
+  }
+  state->parse_state = copy;
+
   // Object and pointer member access expressions.
   if ((ParseTwoCharToken(state, "dt") || ParseTwoCharToken(state, "pt")) &&
       ParseExpression(state) && ParseType(state)) {
diff --git a/absl/debugging/internal/demangle_test.cc b/absl/debugging/internal/demangle_test.cc
index 9db79e64..0044d420 100644
--- a/absl/debugging/internal/demangle_test.cc
+++ b/absl/debugging/internal/demangle_test.cc
@@ -329,6 +329,26 @@ TEST(Demangle, SubobjectAddresses) {
   EXPECT_STREQ("f<>()", tmp);
 }
 
+TEST(Demangle, SizeofPacks) {
+  char tmp[80];
+
+  // template <std::size_t i> struct S {};
+  //
+  // template <class... T> auto f(T... p) -> S<sizeof...(T)> { return {}; }
+  // template auto f<int, long>(int, long) -> S<2>;
+  //
+  // template <class... T> auto g(T... p) -> S<sizeof...(p)> { return {}; }
+  // template auto g<int, long>(int, long) -> S<2>;
+
+  // S<sizeof...(int, long)> f<int, long>(int, long)
+  EXPECT_TRUE(Demangle("_Z1fIJilEE1SIXsZT_EEDpT_", tmp, sizeof(tmp)));
+  EXPECT_STREQ("f<>()", tmp);
+
+  // S<sizeof... (fp)> g<int, long>(int, long)
+  EXPECT_TRUE(Demangle("_Z1gIJilEE1SIXsZfp_EEDpT_", tmp, sizeof(tmp)));
+  EXPECT_STREQ("g<>()", tmp);
+}
+
 // Test one Rust symbol to exercise Demangle's delegation path.  Rust demangling
 // itself is more thoroughly tested in demangle_rust_test.cc.
 TEST(Demangle, DelegatesToDemangleRustSymbolEncoding) {