bolt-gen: make optional 'assignable' fields work

make assignable 'optional' fields work, add test for them

tools/gen/impl_template

@@ -303,7 +303,7 @@ bool fromwire_${msg.name}(${'const tal_t *ctx, ' if msg.needs_context() else ''}
 		% if not varsized:
 		*${f.name} = tal(ctx, ${typename});
 		% endif
-		${fromwire_phrase(f, type_, varsized)}\
+		${'*' if f.type_obj.is_assignable() else ''}${fromwire_phrase(f, type_, varsized)}\
 	}
 	    % endif ## End optional
 	% endif

tools/generate-bolts.py

@@ -75,9 +75,6 @@ class Field(object):
     def is_varlen(self):
         return not self.count
 
-    def is_optional(self):
-        return self.is_optional
-
     def is_extension(self):
         return bool(self.extension_names)
 
@@ -97,7 +94,10 @@ class Field(object):
         if self.is_array():
             return ', const {} {}[{}]'.format(type_name, self.name, self.count)
         if self.type_obj.is_assignable() and not self.is_varlen():
-            return ', {} {}'.format(type_name, self.name)
+            name = self.name
+            if self.is_optional:
+                name = '*' + name
+            return ', {} {}'.format(type_name, name)
         if self.is_varlen() and self.type_obj.is_varsize():
             return ', const {} **{}'.format(type_name, self.name)
         return ', const {} *{}'.format(type_name, self.name)
@@ -145,7 +145,7 @@ class FieldSet(object):
         return bool(self.len_fields)
 
     def needs_context(self):
-        return any([field.needs_context() for field in self.fields.values()])
+        return any([field.needs_context() or field.is_optional for field in self.fields.values()])
 
 
 class Type(FieldSet):

tools/test/test_cases

@@ -31,6 +31,8 @@ msgdata,test_msg,test_enum,e:test_enum,
 msgdata,test_msg,test_struct,test_short_id,
 # test var-size struct
 msgdata,test_msg,test_varsize_struct,test_features,
+# test optional assignable
+msgdata,test_msg,test_optional_assignable,?u32,
 # test optional struct
 msgdata,test_msg,test_optional_struct,?test_short_id,
 # test optional var-size struct