Apply suggestions from code review

Co-authored-by: Eric Snow <ericsnowcurrently@gmail.com>

Author: mdboom

pyperformance/_benchmark.py

@@ -165,8 +165,11 @@ def extra_opts(self):
         return self._get_metadata_value('extra_opts', ())
 
     @property
-    def install_setup(self):
-        return self._get_metadata_value('install_setup', False)
+    def setup_py(self):
+        if not self._get_metadata_value('install_setup', False):
+            return None
+        filename = os.path.join(os.path.dirname(self.metafile), 'setup.py'))
+        return filename if os.path.exists(filename) else None
 
     # Other metadata keys:
     # * base

pyperformance/venv.py

@@ -24,8 +24,10 @@ def from_benchmarks(cls, benchmarks):
         for bench in benchmarks or ():
             filename = bench.requirements_lockfile
             self._add_from_file(filename)
-            if bench.install_setup:
-                self._add(os.path.dirname(bench.metafile))
+            if bench.setup_py:
+                # pip doesn't support installing a setup.py,
+                # but it does support installing from the directory it is in.
+                self._add(os.path.dirname(bench.setup_py))
         return self
 
     def __init__(self):