fix instrumentation to support puma >= 6.2 (#600) (#601)

Tests are failing on Puma 6.2 (and newer) when instrumentation is
enabled. This seems to be caused by PR #3072 in Puma which changes how
it handles responses. If the body (3rd argument) is a file-like object
(which Asset is) then it appears to be getting the file path and reading
the original contents which then doesn't match the modified
Content-Length header for the instrumented version.

This commit fixes the issue by returning the instrumented source as a
string rather then the Asset object.

lib/teaspoon/instrumentation.rb

@@ -35,10 +35,8 @@ def instrumented_response
 
  result = add_instrumentation(asset)
 
- asset.instance_variable_set(:@source, result)
- asset.instance_variable_set(:@length, headers["Content-Length"] = result.bytesize.to_s)
-
- [status, headers, asset]
+ headers["Content-Length"] = result.bytesize.to_s
+ [status, headers, [result]]
  end
 
  protected

spec/teaspoon/instrumentation_spec.rb

@@ -8,6 +8,7 @@
 
  let(:asset) { double(source: source, filename: "path/to/instrument.js") }
  let(:source) { "function add(a, b) { return a + b } // ☃ " }
+ let(:instrumented_source) { source + " // instrumented" }
  let(:response) { [200, { "Content-Type" => "application/javascript" }, asset] }
  let(:env) { { "QUERY_STRING" => "instrument=true" } }
 
@@ -21,7 +22,7 @@
  expect(asset).to receive(:clone).and_return(asset)
 
  allow(File).to receive(:open)
- allow_any_instance_of(subject).to receive(:instrument).and_return(source + " // instrumented")
+ allow_any_instance_of(subject).to receive(:instrument).and_return(instrumented_source)
 
  path = nil
  Dir.mktmpdir { |p| path = p }
@@ -43,7 +44,7 @@
 
  it "replaces the response array with the appropriate information" do
  response = [666, { "Content-Type" => "application/javascript" }, asset]
- expected = [666, { "Content-Type" => "application/javascript", "Content-Length" => "59" }, asset]
+ expected = [666, { "Content-Type" => "application/javascript", "Content-Length" => "59" }, [instrumented_source]]
 
  expect(subject.add_to(response, env)).to eq(expected)
  end
@@ -124,10 +125,10 @@ def ignore(paths)
 
  it "instruments a file" do
  pending("needs istanbul to be installed") unless Teaspoon::Instrumentation.executable
- status, headers, asset = subject.add_to(response, "QUERY_STRING" => "instrument=true")
+ status, headers, body = subject.add_to(response, "QUERY_STRING" => "instrument=true")
  expect(status).to eq(200)
  expect(headers).to include("Content-Type" => "application/javascript")
- expect(asset.source).to match(/var __cov_.+ = \(Function\('return this'\)\)\(\);/)
+ expect(body.first).to match(/var __cov_.+ = \(Function\('return this'\)\)\(\);/)
  end
 
  it "hooks into sprockets" do