Attr: Deprecate using &default and &optional together on record fields

If &default implies re-initialization of the field, using them together
doesn't make much sense.

NEWS

@@ -365,6 +365,10 @@ Deprecated Functionality
 
   The replacement script doesn't populate the ``email_body_sections`` anymore either.
 
+- Using ``&default`` and ``&optional`` together on a record field has been deprecated
+  as it would only result in ``&default`` behavior. This will become an error starting
+  with Zeek 8.1.
+
 - The ``zeek::Event()`` constructor was deprecated. Use ``event_mgr::Enqueue()``
   or ``event_mgr::Dispatch()`` instead.
 

scripts/base/frameworks/notice/weird.zeek

@@ -52,7 +52,7 @@ export {
 		## The peer that originated this weird.  This is helpful in
 		## cluster deployments if a particular cluster node is having
 		## trouble to help identify which node is having trouble.
-		peer:   string  &log &optional &default=peer_description;
+		peer:   string  &log &default=peer_description;
 
 		## The source of the weird. When reported by an analyzer, this
 		## should be the name of the analyzer.

src/Attr.cc

@@ -5,6 +5,7 @@
 #include "zeek/Desc.h"
 #include "zeek/Expr.h"
 #include "zeek/IntrusivePtr.h"
+#include "zeek/Reporter.h"
 #include "zeek/Val.h"
 #include "zeek/input/Manager.h"
 #include "zeek/threading/SerialTypes.h"
@@ -298,6 +299,12 @@ bool Attributes::CheckAttr(Attr* a) {
         case ATTR_OPTIONAL:
             if ( global_var )
                 return AttrError("&optional is not valid for global variables");
+
+            // Remove in v8.1: Call AttrError()
+            if ( in_record && Find(ATTR_DEFAULT) )
+                zeek::reporter->Deprecation(
+                    "Remove in v8.1: Using &default and &optional together results in &default behavior");
+
             break;
 
         case ATTR_ADD_FUNC:
@@ -335,6 +342,11 @@ bool Attributes::CheckAttr(Attr* a) {
             if ( Find(ATTR_DEFAULT_INSERT) )
                 return AttrError("&default and &default_insert cannot be used together");
 
+            // Remove in v8.1: Call AttrError()
+            if ( in_record && Find(ATTR_OPTIONAL) )
+                zeek::reporter->Deprecation(
+                    "Remove in v8.1: Using &default and &optional together results in &default behavior");
+
             std::string err_msg;
             if ( ! check_default_attr(a, type, global_var, in_record, err_msg) && ! err_msg.empty() )
                 return AttrError(err_msg.c_str());

testing/btest/Baseline/language.optional-and-default-field/.stderr

@@ -0,0 +1,6 @@
+### BTest baseline data generated by btest-diff. Do not edit. Use "btest -U/-u" to update. Requires BTest >= 0.63.
+warning in <...>/optional-and-default-field.zeek, line 10: Remove in v8.1: Using &default and &optional together results in &default behavior
+warning in <...>/optional-and-default-field.zeek, line 11: Remove in v8.1: Using &default and &optional together results in &default behavior
+warning in <...>/optional-and-default-field.zeek, line 12: Remove in v8.1: Using &default and &optional together results in &default behavior
+warning in <...>/optional-and-default-field.zeek, line 13: Remove in v8.1: Using &default and &optional together results in &default behavior
+warning in <...>/optional-and-default-field.zeek, line 14: Remove in v8.1: Using &default and &optional together results in &default behavior

testing/btest/Baseline/language.optional-and-default-field/.stdout

@@ -0,0 +1,2 @@
+### BTest baseline data generated by btest-diff. Do not edit. Use "btest -U/-u" to update. Requires BTest >= 0.63.
+[c=5, i=-5, v=[], r0=[], r1=[]]

testing/btest/language/optional-and-default-field.zeek

@@ -0,0 +1,18 @@
+# @TEST-DOC: Warn on record fields that have both, &optional and &default
+#
+# @TEST-EXEC: zeek -b %INPUT
+# @TEST-EXEC: btest-diff .stdout
+# @TEST-EXEC: TEST_DIFF_CANONIFIER=$SCRIPTS/diff-remove-abspath btest-diff .stderr
+
+type R: record { };
+
+type X: record {
+        c: count &optional &default=5;
+        i: int &default=-5 &optional;
+        v: vector of string &optional &default=vector();
+        r0: R &optional &default=R();
+        r1: R &default=R() &optional;
+};
+
+global x = X();
+print x;