Parse tests with prism

This changes TestParser to parse with prism instead of ripper if it
is available for the current version of Ruby. It's within the margin
for the speed, and its significantly less code that is easier to
read and should be easier to maintain.

Author: kddnewton

railties/lib/rails/test_unit/test_parser.rb

@@ -12,38 +12,29 @@ module Rails
     module TestUnit
       # Parse a test file to extract the line ranges of all tests in both
       # method-style (def test_foo) and declarative-style (test "foo" do)
-      class TestParser < Prism::Visitor
+      module TestParser
         # Helper to translate a method object into the path and line range where
         # the method was defined.
         def self.definition_for(method)
           filepath, start_line = method.source_location
-          Prism.parse_file(filepath).value.accept(new(ranges = {}))
-          (end_line = ranges[start_line]) && [filepath, (start_line..end_line)]
-        end
-
-        def self.definitions_for(source, filepath)
-          Prism.parse(source, filepath: filepath).value.accept(new(ranges = {}))
-          ranges
-        end
-
-        attr_reader :ranges
-
-        def initialize(ranges)
-          @ranges = ranges
-        end
-
-        def visit_def_node(node)
-          if node.name.start_with?("test")
-            ranges[node.location.start_line] = node.location.end_line
+          queue = [Prism.parse_file(filepath).value]
+
+          while (node = queue.shift)
+            case node.type
+            when :def_node
+              if node.name.start_with?("test") && node.location.start_line == start_line
+                return [filepath, start_line..node.location.end_line]
+              end
+            when :call_node
+              if node.name == :test && node.location.start_line == start_line
+                return [filepath, start_line..node.location.end_line]
+              end
+            end
+
+            queue.concat(node.compact_child_nodes)
           end
-          super
-        end
 
-        def visit_call_node(node)
-          if node.name == :test
-            ranges[node.location.start_line] = node.location.end_line
-          end
-          super
+          nil
         end
       end
     end

railties/test/test_unit/test_parser_test.rb

@@ -5,55 +5,61 @@
 require "active_support/testing/autorun"
 require "rails/test_unit/test_parser"
 
-class TestParserTest < ActiveSupport::TestCase
-  def test_parser
-    example_test = <<~RUBY
-      require "test_helper"
+class TestParserTestFixture < ActiveSupport::TestCase
+  def test_method
+    assert true
 
-      class ExampleTest < ActiveSupport::TestCase
-        def test_method
-          assert true
+    assert true
+  end
 
+  def test_oneline; assert true; end
 
-        end
+  test "declarative" do
+    assert true
+
+    assert true
+  end
 
-        def test_oneline; assert true; end
+  test("declarative w/parens") do
+    assert true
+  end
 
-        test "declarative" do
-          assert true
-        end
+  self.test "declarative explicit receiver" do
+    assert true
 
-        test("declarative w/parens") do
-          assert true
+    assert true
+  end
 
-        end
+  test("declarative oneline") { assert true }
 
-        self.test "declarative explicit receiver" do
-          assert true
-        end
+  test("declarative oneline do") do assert true end
 
-        test("declarative oneline") { assert true }
+  test("declarative multiline w/ braces") {
+    assert true
+    assert_not false
+  }
+end
 
-        test("declarative oneline do") do assert true end
+class TestParserTest < ActiveSupport::TestCase
+  def test_parser
+    actual =
+      TestParserTestFixture
+        .instance_methods(false)
+        .map { |method| TestParserTestFixture.instance_method(method) }
+        .sort_by { |method| method.source_location[1] }
+        .map { |method| [method.name, *Rails::TestUnit::TestParser.definition_for(method)] }
 
-        test("declarative multiline w/ braces") {
-          assert true
-          refute false
-        }
-      end
-    RUBY
+    expected = [
+      [:test_method, __FILE__, 9..13],
+      [:test_oneline, __FILE__, 15..15],
+      [:test_declarative, __FILE__, 17..21],
+      [:"test_declarative_w/parens", __FILE__, 23..25],
+      [:test_declarative_explicit_receiver, __FILE__, 27..31],
+      [:test_declarative_oneline, __FILE__, 33..33],
+      [:test_declarative_oneline_do, __FILE__, 35..35],
+      [:"test_declarative_multiline_w/_braces", __FILE__, 37..40]
+    ]
 
-    actual_map = Rails::TestUnit::TestParser.definitions_for(example_test, "example_test.rb")
-    expected_map = {
-      4 => 8,   # test_method
-      10 => 10, # test_oneline
-      12 => 14, # declarative
-      16 => 19, # declarative w/parens
-      21 => 23, # declarative explicit receiver
-      25 => 25, # declarative oneline
-      27 => 27, # declarative oneilne do
-      29 => 32  # declarative multiline w/braces
-    }
-    assert_equal expected_map, actual_map
+    assert_equal expected, actual
   end
 end