Forbid externs as tuple arguments

Signed-off-by: Mihai Budiu <mbudiu@vmware.com>

frontends/p4/typeChecking/typeChecker.cpp

@@ -1389,7 +1389,9 @@ const IR::Node* TypeInference::postorder(IR::Type_List* type) {
 const IR::Node* TypeInference::postorder(IR::Type_Tuple* type) {
     for (auto field : type->components) {
         auto fieldType = getTypeType(field);
-        if (fieldType->is<IR::IContainer>() || fieldType->is<IR::Type_ArchBlock>()) {
+        if (auto spec = fieldType->to<IR::Type_SpecializedCanonical>()) fieldType = spec->baseType;
+        if (fieldType->is<IR::IContainer>() || fieldType->is<IR::Type_ArchBlock>() ||
+            fieldType->is<IR::Type_Extern>()) {
             typeError("%1%: not supported as a tuple field", field);
             return type;
         }

testdata/p4_16_errors/issue3750-1.p4

@@ -0,0 +1,17 @@
+extern ct {
+    void apply();
+}
+
+extern E<T> {
+    void apply();
+}
+
+void f(tuple<ct> t)
+{
+    t[0].apply();
+}
+
+void g(tuple<E<bit<32>>> t)
+{
+    t[0].apply();
+}

testdata/p4_16_errors_outputs/issue3750-1.p4

@@ -0,0 +1,14 @@
+extern ct {
+    void apply();
+}
+
+extern E<T> {
+    void apply();
+}
+
+void f(tuple<ct> t) {
+    t[0].apply();
+}
+void g(tuple<E<bit<32>>> t) {
+    t[0].apply();
+}

testdata/p4_16_errors_outputs/issue3750-1.p4-stderr

@@ -0,0 +1,6 @@
+issue3750-1.p4(9): [--Werror=type-error] error: ct: not supported as a tuple field
+void f(tuple<ct> t)
+             ^^
+issue3750-1.p4(14): [--Werror=type-error] error: E<bit<32>>: not supported as a tuple field
+void g(tuple<E<bit<32>>> t)
+             ^^^^^^^^^^