Explicitly pass out_file to benchcomp visualizers (rust-lang#2408)

This commit adds an `out_file` to the benchcomp visualizes that emit
output (currently just one visualization, dump_yaml). This is to allow
different visualizations to be written to different output files,
including stdout.

The intention (for a future commit) is that CI will save certain
visualizations as artifacts, which users can then download.

Author: karkhaz

tools/benchcomp/benchcomp/visualizers/__init__.py

@@ -6,6 +6,7 @@
 
 import yaml
 
+import benchcomp
 import benchcomp.visualizers.utils as viz_utils
 
 
@@ -54,15 +55,24 @@ def __call__(self, results):
 
 
 
-@dataclasses.dataclass
 class dump_yaml:
-    """Print the YAML-formatted results to stdout
+    """Print the YAML-formatted results to a file.
+
+    The 'out_file' key is mandatory; specify '-' to print to stdout.
 
     Sample configuration:
 
     visualize:
     - type: dump_yaml
+      out_file: '-'
     """
 
+
+    def __init__(self, out_file):
+        self.get_out_file = benchcomp.Outfile(out_file)
+
+
     def __call__(self, results):
-        print(yaml.dump(results, default_flow_style=False))
+        with self.get_out_file() as handle:
+            print(
+                yaml.dump(results, default_flow_style=False), file=handle)

tools/benchcomp/configs/perf-regression.yaml

@@ -29,6 +29,7 @@ run:
 
 visualize:
   - type: dump_yaml
+    out_file: '/tmp/result.yaml'
 
   - type: error_on_regression
     variant_pairs: [[kani_old, kani_new]]

tools/benchcomp/test/test_regression.py

@@ -95,7 +95,10 @@ def _run_kani_perf_test(self, command, expected_pass):
                     }
                 }
             },
-            "visualize": [{"type": "dump_yaml"}],
+            "visualize": [{
+                "type": "dump_yaml",
+                "out_file": "-"
+            }],
         })
         run_bc()
         self.assertEqual(run_bc.proc.returncode, 0, msg=run_bc.stderr)
@@ -423,6 +426,7 @@ def test_only_dump_yaml(self):
                 },
                 "visualize": [{
                     "type": "dump_yaml",
+                    "out_file": "-",
                 }, {
                     "type": "error_on_regression",
                     "variant_pairs": [["passed", "failed"]],
@@ -471,6 +475,7 @@ def test_ignore_dump_yaml(self):
                 },
                 "visualize": [{
                     "type": "dump_yaml",
+                    "out_file": "-",
                 }],
             })
             run_bc(flags=["--except", "dump_yaml"])