Make mutation visitor visit all nodes

The test case demonstrates 3 important node types that would ignore
their children:
- Assign
- Assoc
- IfOp

The fact that MutationVisitor wouldn't traverse anything that's assigned
to a variable, a hash key, or inside a ternary operator was very
limiting.

lib/syntax_tree/mutation_visitor.rb

@@ -67,12 +67,12 @@ def visit_alias(node)
 
       # Visit a ARef node.
       def visit_aref(node)
-        node.copy(index: visit(node.index))
+        node.copy(collection: visit(node.collection), index: visit(node.index))
       end
 
       # Visit a ARefField node.
       def visit_aref_field(node)
-        node.copy(index: visit(node.index))
+        node.copy(collection: visit(node.collection), index: visit(node.index))
       end
 
       # Visit a ArgParen node.
@@ -120,17 +120,17 @@ def visit_aryptn(node)
 
       # Visit a Assign node.
       def visit_assign(node)
-        node.copy(target: visit(node.target))
+        node.copy(target: visit(node.target), value: visit(node.value))
       end
 
       # Visit a Assoc node.
       def visit_assoc(node)
-        node.copy
+        node.copy(key: visit(node.key), value: visit(node.value))
       end
 
       # Visit a AssocSplat node.
       def visit_assoc_splat(node)
-        node.copy
+        node.copy(value: visit(node.value))
       end
 
       # Visit a Backref node.
@@ -155,12 +155,12 @@ def visit_begin(node)
 
       # Visit a PinnedBegin node.
       def visit_pinned_begin(node)
-        node.copy
+        node.copy(statement: visit(node.statement))
       end
 
       # Visit a Binary node.
       def visit_binary(node)
-        node.copy
+        node.copy(left: visit(node.left), right: visit(node.right))
       end
 
       # Visit a BlockVar node.
@@ -178,6 +178,7 @@ def visit_bodystmt(node)
         node.copy(
           statements: visit(node.statements),
           rescue_clause: visit(node.rescue_clause),
+          else_keyword: visit(node.else_keyword),
           else_clause: visit(node.else_clause),
           ensure_clause: visit(node.ensure_clause)
         )
@@ -209,7 +210,11 @@ def visit_case(node)
 
       # Visit a RAssign node.
       def visit_rassign(node)
-        node.copy(operator: visit(node.operator))
+        node.copy(
+          value: visit(node.value),
+          operator: visit(node.operator),
+          pattern: visit(node.pattern)
+        )
       end
 
       # Visit a ClassDeclaration node.
@@ -238,6 +243,7 @@ def visit_command(node)
       # Visit a CommandCall node.
       def visit_command_call(node)
         node.copy(
+          receiver: visit(node.receiver),
           operator: node.operator == :"::" ? :"::" : visit(node.operator),
           message: visit(node.message),
           arguments: visit(node.arguments),
@@ -257,12 +263,12 @@ def visit_const(node)
 
       # Visit a ConstPathField node.
       def visit_const_path_field(node)
-        node.copy(constant: visit(node.constant))
+        node.copy(parent: visit(node.parent), constant: visit(node.constant))
       end
 
       # Visit a ConstPathRef node.
       def visit_const_path_ref(node)
-        node.copy(constant: visit(node.constant))
+        node.copy(parent: visit(node.parent), constant: visit(node.constant))
       end
 
       # Visit a ConstRef node.
@@ -288,7 +294,7 @@ def visit_def(node)
 
       # Visit a Defined node.
       def visit_defined(node)
-        node.copy
+        node.copy(value: visit(node.value))
       end
 
       # Visit a Block node.
@@ -325,6 +331,7 @@ def visit_else(node)
       # Visit a Elsif node.
       def visit_elsif(node)
         node.copy(
+          predicate: visit(node.predicate),
           statements: visit(node.statements),
           consequent: visit(node.consequent)
         )
@@ -366,6 +373,7 @@ def visit_excessed_comma(node)
       # Visit a Field node.
       def visit_field(node)
         node.copy(
+          parent: visit(node.parent),
           operator: node.operator == :"::" ? :"::" : visit(node.operator),
           name: visit(node.name)
         )
@@ -388,7 +396,11 @@ def visit_fndptn(node)
 
       # Visit a For node.
       def visit_for(node)
-        node.copy(index: visit(node.index), statements: visit(node.statements))
+        node.copy(
+          index: visit(node.index),
+          collection: visit(node.collection),
+          statements: visit(node.statements)
+        )
       end
 
       # Visit a GVar node.
@@ -446,7 +458,11 @@ def visit_if(node)
 
       # Visit a IfOp node.
       def visit_if_op(node)
-        node.copy
+        node.copy(
+          predicate: visit(node.predicate),
+          truthy: visit(node.truthy),
+          falsy: visit(node.falsy)
+        )
       end
 
       # Visit a Imaginary node.
@@ -457,6 +473,7 @@ def visit_imaginary(node)
       # Visit a In node.
       def visit_in(node)
         node.copy(
+          pattern: visit(node.pattern),
           statements: visit(node.statements),
           consequent: visit(node.consequent)
         )
@@ -522,7 +539,7 @@ def visit_lparen(node)
 
       # Visit a MAssign node.
       def visit_massign(node)
-        node.copy(target: visit(node.target))
+        node.copy(target: visit(node.target), value: visit(node.value))
       end
 
       # Visit a MethodAddBlock node.
@@ -565,7 +582,11 @@ def visit_op(node)
 
       # Visit a OpAssign node.
       def visit_opassign(node)
-        node.copy(target: visit(node.target), operator: visit(node.operator))
+        node.copy(
+          target: visit(node.target),
+          operator: visit(node.operator),
+          value: visit(node.value)
+        )
       end
 
       # Visit a Params node.
@@ -667,7 +688,10 @@ def visit_regexp_literal(node)
 
       # Visit a RescueEx node.
       def visit_rescue_ex(node)
-        node.copy(variable: visit(node.variable))
+        node.copy(
+          exceptions: visit(node.exceptions),
+          variable: visit(node.variable)
+        )
       end
 
       # Visit a Rescue node.
@@ -682,7 +706,7 @@ def visit_rescue(node)
 
       # Visit a RescueMod node.
       def visit_rescue_mod(node)
-        node.copy
+        node.copy(statement: visit(node.statement), value: visit(node.value))
       end
 
       # Visit a RestParam node.
@@ -707,7 +731,7 @@ def visit_rparen(node)
 
       # Visit a SClass node.
       def visit_sclass(node)
-        node.copy(bodystmt: visit(node.bodystmt))
+        node.copy(target: visit(node.target), bodystmt: visit(node.bodystmt))
       end
 
       # Visit a Statements node.
@@ -815,7 +839,7 @@ def visit_not(node)
 
       # Visit a Unary node.
       def visit_unary(node)
-        node.copy
+        node.copy(statement: visit(node.statement))
       end
 
       # Visit a Undef node.
@@ -842,7 +866,7 @@ def visit_until(node)
 
       # Visit a VarField node.
       def visit_var_field(node)
-        node.copy(value: visit(node.value))
+        node.copy(value: node.value == :nil ? :nil : visit(node.value))
       end
 
       # Visit a VarRef node.

test/mutation_test.rb

@@ -21,6 +21,26 @@ def test_mutates_based_on_patterns
       assert_equal(expected, SyntaxTree::Formatter.format(source, program))
     end
 
+    def test_deep_mutation
+      source = <<~RUBY
+        hash = { "key" => a ? foo : nil }
+      RUBY
+
+      expected = <<~RUBY
+        hash = { "key" => a ? bar : nil }
+      RUBY
+
+      rename_foo_into_bar =
+        SyntaxTree.mutation do |mutation|
+          mutation.mutate("Ident[value: 'foo']") do |node|
+            node.copy(value: "bar")
+          end
+        end
+
+      program = SyntaxTree.parse(source).accept(rename_foo_into_bar)
+      assert_equal(expected, SyntaxTree::Formatter.format(source, program))
+    end
+
     private
 
     def build_mutation