feat(cli): add --failures-only flag to smoke

bowtie/_cli.py

@@ -156,7 +156,15 @@ def __getattr__(self, attr: str) -> int:
             ],
         ),
         ("info", [("Basic Options", ["implementation", "format"])]),
-        ("smoke", [("Basic Options", ["implementation", "quiet", "format"])]),
+        (
+            "smoke",
+            [
+                (
+                    "Basic Options",
+                    ["implementation", "quiet", "failures-only", "format"],
+                )
+            ],
+        ),
         (
             "filter-dialects",
             [
@@ -2392,29 +2400,41 @@ async def download_versions_and_parse_reports_for(
     is_flag=True,
     help="Don't print any output, just exit with nonzero status on failure.",
 )
+@click.option(
+    "--failures-only",
+    is_flag=True,
+    help="Only show output for implementations that fail.",
+)
 @format_option()
-async def smoke(start: Starter, format: _F, echo: Callable[..., None]) -> int:
+async def smoke(
+    start: Starter, format: _F, echo: Callable[..., None], failures_only: bool
+) -> int:
     """
     Smoke test implementations for basic correctness against Bowtie's protocol.
     """
     results = [
         (implementation.id, implementation.info, await implementation.smoke())
         async for _, implementation in start()
     ]
+    display_results = results
+    if (
+        failures_only and format != "json"
+    ):  # keep json unfiltered for machine use
+        display_results = [
+            (id, info, r) for id, info, r in results if not r.success
+        ]
 
     match results, format:
         case [(_, _, result)], "json":
             echo(json.dumps(result.serializable(), indent=2))
         case _, "json":
             output = {id: result.serializable() for id, _, result in results}
             echo(json.dumps(output, indent=2))
-        case [(_, _, result)], "pretty":
-            STDOUT.print(result)
         case _, "pretty":
-            for _, _, each in results:
+            for _, _, each in display_results:
                 STDOUT.print(each)
         case _, "markdown":
-            for _, info, result in results:
+            for _, info, result in display_results:
                 echo(f"# {info.name} ({info.language})\n")
 
                 if result.success:

bowtie/tests/test_integration.py

@@ -1737,6 +1737,18 @@ async def test_pretty_multiple(self):
         # FIXME: We don't assert against the exact output yet, as it's a WIP
         assert dedent(stdout), stdout
 
+    @pytest.mark.asyncio
+    async def test_failures_only_hides_passing(self):
+        stdout, stderr = await bowtie(
+            "smoke",
+            "--failures-only",
+            "--format",
+            "pretty",
+            "-i",
+            miniatures.passes_smoke,
+        )
+        assert stdout == "", stderr
+
     @pytest.mark.asyncio
     async def test_json_multiple(self):
         jsonout, stderr = await bowtie(