+ Minitest.filter_backtrace returns original backtrace if filter come…

…s back empty.

+ Minitest::BacktraceFilter now returns entire backtrace if $MT_DEBUG set in env.

This should fix #837 and
bypasses the need for a release of
rails/rails#39304.

[git-p4: depot-paths = "//src/minitest/dev/": change = 12653]

lib/minitest.rb

@@ -238,7 +238,9 @@ def self.process_args args = [] # :nodoc:
   end
 
   def self.filter_backtrace bt # :nodoc:
-    backtrace_filter.filter bt
+    result = backtrace_filter.filter bt
+    result = bt.dup if result.empty?
+    result
   end
 
   ##
@@ -1005,12 +1007,13 @@ class BacktraceFilter
     MT_RE = %r%lib/minitest% #:nodoc:
 
     ##
-    # Filter +bt+ to something useful. Returns the whole thing if $DEBUG.
+    # Filter +bt+ to something useful. Returns the whole thing if
+    # $DEBUG (ruby) or $MT_DEBUG (env).
 
     def filter bt
       return ["No backtrace"] unless bt
 
-      return bt.dup if $DEBUG
+      return bt.dup if $DEBUG || ENV["MT_DEBUG"]
 
       new_bt = bt.take_while { |line| line !~ MT_RE }
       new_bt = bt.select     { |line| line !~ MT_RE } if new_bt.empty?

test/minitest/metametameta.rb

@@ -6,8 +6,27 @@ class Minitest::Test
   def clean s
     s.gsub(/^ {6}/, "")
   end
+
+  def with_empty_backtrace_filter
+    original = Minitest.backtrace_filter
+
+    obj = Minitest::BacktraceFilter.new
+    def obj.filter _bt
+      []
+    end
+
+    Minitest::Test.io_lock.synchronize do # try not to trounce in parallel
+      begin
+        Minitest.backtrace_filter = obj
+        yield
+      ensure
+        Minitest.backtrace_filter = original
+      end
+    end
+  end
 end
 
+
 class FakeNamedTest < Minitest::Test
   @@count = 0
 

test/minitest/test_minitest_spec.rb

@@ -571,6 +571,22 @@ def assert_success spec
         (1 + 1).must_equal 2
       end
     end
+
+    # https://github.com/seattlerb/minitest/issues/837
+    # https://github.com/rails/rails/pull/39304
+    it "deprecates expectation used without _ with empty backtrace_filter" do
+      skip "N/A" if ENV["MT_NO_EXPECTATIONS"]
+
+      @assertion_count += 3
+
+      exp = /DEPRECATED: global use of must_equal from/
+
+      with_empty_backtrace_filter do
+        assert_output "", exp do
+          (1 + 1).must_equal 2
+        end
+      end
+    end
   end
 
   it "needs to verify throw" do

test/minitest/test_minitest_test.rb

@@ -75,9 +75,13 @@ def test_filter_backtrace_unit_starts
     assert_equal ex, fu
   end
 
-  # def test_default_runner_is_minitest_unit
-  #   assert_instance_of Minitest::Unit, Minitest::Unit.runner
-  # end
+  def test_filter_backtrace__empty
+    with_empty_backtrace_filter do
+      bt = %w[first second third]
+      fu = Minitest.filter_backtrace bt.dup
+      assert_equal bt, fu
+    end
+  end
 
   def test_infectious_binary_encoding
     @tu = Class.new FakeNamedTest do