Fix browser open after empty export

Make sampling exporters report whether output was generated, and only
open HTML reports in the browser after a successful export.

Author: lkollar

Lib/profiling/sampling/binary_collector.py

@@ -94,6 +94,7 @@ def export(self, filename=None):
             filename: Ignored (binary files are written incrementally)
         """
         self._writer.finalize()
+        return True
 
     @property
     def total_samples(self):

Lib/profiling/sampling/cli.py

@@ -789,11 +789,12 @@ def progress_callback(current, total):
             args.outfile
             or _generate_output_filename(args.format, os.getpid())
         )
-        collector.export(filename)
+        export_ok = collector.export(filename)
 
         # Auto-open browser for HTML output if --browser flag is set
         if (
-            args.format in (
+            export_ok
+            and args.format in (
                 'flamegraph', 'diff_flamegraph', 'heatmap'
             )
             and getattr(args, 'browser', False)
@@ -840,10 +841,14 @@ def _handle_output(collector, args, pid, mode):
             filename = os.path.join(args.outfile, _generate_output_filename(args.format, pid))
         else:
             filename = args.outfile or _generate_output_filename(args.format, pid)
-        collector.export(filename)
+        export_ok = collector.export(filename)
 
         # Auto-open browser for HTML output if --browser flag is set
-        if args.format in ('flamegraph', 'diff_flamegraph', 'heatmap') and getattr(args, 'browser', False):
+        if (
+            export_ok
+            and args.format in ('flamegraph', 'diff_flamegraph', 'heatmap')
+            and getattr(args, 'browser', False)
+        ):
             _open_in_browser(filename)
 
 

Lib/profiling/sampling/collector.py

@@ -163,7 +163,11 @@ def collect_failed_sample(self):
 
     @abstractmethod
     def export(self, filename):
-        """Export collected data to a file."""
+        """Export collected data.
+
+        Returns:
+            bool: True if output was generated, False if there was no data to export.
+        """
 
     @staticmethod
     def _filter_internal_frames(frames):

Lib/profiling/sampling/gecko_collector.py

@@ -699,6 +699,7 @@ def spin():
         print(
             f"Open in Firefox Profiler: https://profiler.firefox.com/"
         )
+        return True
 
     def _build_marker_schema(self):
         """Build marker schema definitions for Firefox Profiler."""

Lib/profiling/sampling/heatmap_collector.py

@@ -598,7 +598,7 @@ def export(self, output_path):
         """
         if not self.file_samples:
             print("Warning: No heatmap data to export")
-            return
+            return False
 
         try:
             output_dir = self._prepare_output_directory(output_path)
@@ -612,6 +612,7 @@ def export(self, output_path):
             self._generate_index_html(output_dir / 'index.html', file_stats)
 
             self._print_export_summary(output_dir, file_stats)
+            return True
 
         except Exception as e:
             print(f"Error: Failed to export heatmap: {e}")

Lib/profiling/sampling/jsonl_collector.py

@@ -165,6 +165,7 @@ def export(self, filename):
             )
             self._write_message(output, self._build_end_record())
         print(f"JSONL profile written to {filename}")
+        return True
 
     def _build_meta_record(self):
         record = {

Lib/profiling/sampling/pstats_collector.py

@@ -63,6 +63,7 @@ def collect(self, stack_frames, timestamps_us=None):
     def export(self, filename):
         self.create_stats()
         self._dump_stats(filename)
+        return True
 
     def _dump_stats(self, file):
         stats_with_marker = dict(self.stats)

Lib/profiling/sampling/stack_collector.py

@@ -64,6 +64,7 @@ def export(self, filename):
             for stack, count in lines:
                 f.write(f"{stack} {count}\n")
         print(f"Collapsed stack output written to {filename}")
+        return True
 
 
 class FlamegraphCollector(StackTraceCollector):
@@ -161,14 +162,15 @@ def export(self, filename):
             print(
                 "Warning: No functions found in profiling data. Check if sampling captured any data."
             )
-            return
+            return False
 
         html_content = self._create_flamegraph_html(flamegraph_data)
 
         with open(filename, "w", encoding="utf-8") as f:
             f.write(html_content)
 
         print(f"Flamegraph saved to: {filename}")
+        return True
 
     @staticmethod
     @functools.lru_cache(maxsize=None)

Lib/test/test_profiling/test_sampling_profiler/test_cli.py

@@ -7,6 +7,7 @@
 import sys
 import tempfile
 import unittest
+from types import SimpleNamespace
 from unittest import mock
 
 try:
@@ -26,6 +27,7 @@
     FORMAT_EXTENSIONS,
     _create_collector,
     _generate_output_filename,
+    _handle_output,
     main,
 )
 from profiling.sampling.constants import (
@@ -727,6 +729,26 @@ def test_async_aware_flag_defaults_to_running(self):
             call_kwargs = mock_sample.call_args[1]
             self.assertEqual(call_kwargs.get("async_aware"), "running")
 
+    def test_handle_output_browser_not_opened_when_export_fails(self):
+        for format_type in ("flamegraph", "diff_flamegraph", "heatmap"):
+            with self.subTest(format=format_type):
+                collector = mock.MagicMock()
+                collector.export.return_value = False
+                args = SimpleNamespace(
+                    format=format_type,
+                    outfile="profile.html",
+                    browser=True,
+                )
+
+                with (
+                    mock.patch("profiling.sampling.cli.os.path.isdir", return_value=False),
+                    mock.patch("profiling.sampling.cli._open_in_browser") as mock_open,
+                ):
+                    _handle_output(collector, args, pid=12345, mode=0)
+
+                collector.export.assert_called_once_with("profile.html")
+                mock_open.assert_not_called()
+
     def test_async_aware_with_async_mode_all(self):
         """Test --async-aware with --async-mode all."""
         test_args = ["profiling.sampling.cli", "attach", "12345", "--async-aware", "--async-mode", "all"]

Lib/test/test_profiling/test_sampling_profiler/test_collectors.py

@@ -502,9 +502,10 @@ def test_flamegraph_collector_export(self):
 
         # Export flamegraph
         with captured_stdout(), captured_stderr():
-            collector.export(flamegraph_out.name)
+            export_ok = collector.export(flamegraph_out.name)
 
         # Verify file was created and contains valid data
+        self.assertTrue(export_ok)
         self.assertTrue(os.path.exists(flamegraph_out.name))
         self.assertGreater(os.path.getsize(flamegraph_out.name), 0)
 
@@ -523,6 +524,21 @@ def test_flamegraph_collector_export(self):
         self.assertIn('"value":', content)
         self.assertIn('"children":', content)
 
+    def test_flamegraph_collector_empty_export_fails(self):
+        """Test empty flamegraph export reports no output."""
+        flamegraph_out = tempfile.NamedTemporaryFile(
+            suffix=".html", delete=False
+        )
+        self.addCleanup(close_and_unlink, flamegraph_out)
+
+        collector = FlamegraphCollector(1000)
+
+        with captured_stdout(), captured_stderr():
+            export_ok = collector.export(flamegraph_out.name)
+
+        self.assertFalse(export_ok)
+        self.assertEqual(os.path.getsize(flamegraph_out.name), 0)
+
     def test_gecko_collector_basic(self):
         """Test basic GeckoCollector functionality."""
         collector = GeckoCollector(1000)
@@ -1552,8 +1568,9 @@ def test_diff_flamegraph_export(self):
         self.addCleanup(close_and_unlink, flamegraph_out)
 
         with captured_stdout(), captured_stderr():
-            diff.export(flamegraph_out.name)
+            export_ok = diff.export(flamegraph_out.name)
 
+        self.assertTrue(export_ok)
         self.assertTrue(os.path.exists(flamegraph_out.name))
         self.assertGreater(os.path.getsize(flamegraph_out.name), 0)