Restore behavior for non-proc/non-method callables in defaults_setter

Add documentation for using procs that accept arguments.

Update CHANGELOG.

CHANGELOG

@@ -1,5 +1,7 @@
 === master
 
+* Have defaults_setter plugin pass model instance to default_values callable if it has arity 1 (pedrocarmona) (#2195)
+
 * Support string_agg extension on SQLite 3.44+ (segiddins) (#2191)
 
 * Support schema-qualified table names when using create_table :temp with a Sequel::SQL::QualifiedIdentifier (jeremyevans) (#2185)

lib/sequel/plugins/defaults_setter.rb

@@ -26,6 +26,12 @@ module Plugins
     #   Album.default_values[:a] = lambda{Date.today}
     #   Album.new.a # => Date.today
     #
+    # If the proc accepts a single argument, it is passed the instance, allowing
+    # default values to depend on instance-specific state:
+    #
+    #   Album.default_values[:a] = lambda{|album| album.b + 1}
+    #   Album.new(b: 10).a # => 11
+    #
     # By default, default values returned are not cached:
     #
     #   Album.new.a.equal?(Album.new.a) # => false
@@ -134,10 +140,10 @@ def [](k)
           if new? && !values.has_key?(k)
             v = model.default_values.fetch(k){return}
             if v.respond_to?(:call)
-              if v.arity == 1
-                v = v.call(self)
+              v = if v.respond_to?(:arity) && v.arity == 1
+                v.call(self)
               else
-                v = v.call
+                v.call
               end
             end
             values[k] = v if model.cache_default_values?

spec/extensions/defaults_setter_spec.rb

@@ -181,6 +181,14 @@ def db.schema(*) [] end
     c.new.a.must_equal 2
   end
 
+  it "should support non-proc/non-method callables" do
+    @pr.call(2)
+    o = Object.new
+    def o.call; 3; end
+    @c.default_values[:a] = o
+    @c.new.a.must_equal 3
+  end
+
   it "should allow proc default values that depend on other values" do
     @pr.call(2)
     @c.default_values[:a] = proc{ |instance| instance.b * 2 }