Make backtrace_location keyword work

We had to keep backtrace_location before opts is overwritten.

lib/error_highlight/base.rb

@@ -26,9 +26,9 @@ def self.spot(obj, **opts)
     case obj
     when Exception
       exc = obj
+      loc = opts[:backtrace_location]
       opts = { point_type: opts.fetch(:point_type, :name) }
 
-      loc = opts[:backtrace_location]
       unless loc
         case exc
         when TypeError, ArgumentError
@@ -44,6 +44,8 @@ def self.spot(obj, **opts)
         opts[:name] = exc.name if NameError === obj
       end
 
+      return nil unless Thread::Backtrace::Location === loc
+
       node = RubyVM::AbstractSyntaxTree.of(loc, keep_script_lines: true)
 
       Spotter.new(node, **opts).spot

test/test_error_highlight.rb

@@ -1231,4 +1231,30 @@ def test_spoofed_filename
       end
     end
   end
+
+  def raise_name_error
+    1.time
+  end
+
+  def test_spot_with_backtrace_location
+    lineno = __LINE__
+    begin
+      raise_name_error
+    rescue NameError => exc
+    end
+
+    spot = ErrorHighlight.spot(exc).except(:script_lines)
+    assert_equal(lineno - 4, spot[:first_lineno])
+    assert_equal(lineno - 4, spot[:last_lineno])
+    assert_equal(5, spot[:first_column])
+    assert_equal(10, spot[:last_column])
+    assert_equal("    1.time\n", spot[:snippet])
+
+    spot = ErrorHighlight.spot(exc, backtrace_location: exc.backtrace_locations[1]).except(:script_lines)
+    assert_equal(lineno + 2, spot[:first_lineno])
+    assert_equal(lineno + 2, spot[:last_lineno])
+    assert_equal(6, spot[:first_column])
+    assert_equal(22, spot[:last_column])
+    assert_equal("      raise_name_error\n", spot[:snippet])
+  end
 end