gh-152409: Save the trace --file counts when --no-report is used (GH-152410)

https://github.com/python/cpython/commit/7f6389f48ee46df91e562d33564d02747b3f7ca3
commit: 7f6389f48ee46df91e562d33564d02747b3f7ca3
branch: main
author: tonghuaroot (童话) <[email protected]>
committer: serhiy-storchaka <[email protected]>
date: 2026-08-20T11:40:26+03:00
summary:

gh-152409: Save the trace --file counts when --no-report is used (GH-152410)

The counts were only persisted at the end of CoverageResults.write_results(),
which main() skips when --no-report is given, so --no-report --file silently
discarded them.

files:
A Misc/NEWS.d/next/Library/2026-06-27-10-30-00.gh-issue-152409.Tr8cE2.rst
M Lib/test/test_trace.py
M Lib/trace.py

diff --git a/Lib/test/test_trace.py b/Lib/test/test_trace.py
index 19eee19bdea6d5..241e841d732f5e 100644
--- a/Lib/test/test_trace.py
+++ b/Lib/test/test_trace.py
@@ -1,5 +1,5 @@
 import os
-from pickle import dump
+from pickle import dump, load
 import sys
 from test.support import captured_stdout, requires_resource
 from test.support.os_helper import (TESTFN, rmtree, unlink)
@@ -561,6 +561,28 @@ def f():
         self.assertIn('lines   cov%   module   (path)', stdout)
         self.assertIn(f'6   100.0%   {modulename}   ({filename})', stdout)
 
+    def test_count_no_report_accumulates_counts(self):
+        # --no-report must still save the --file counts so they accumulate.
+        filename = f'{TESTFN}.py'
+        countsfile = f'{TESTFN}.counts'
+        with open(filename, 'w', encoding='utf-8') as fd:
+            self.addCleanup(unlink, filename)
+            self.addCleanup(unlink, countsfile)
+            fd.write('for i in range(3):\n    pass\n')
+        argv = ('-m', 'trace', '--count', '--no-report',
+                '--file', countsfile, filename)
+        assert_python_ok(*argv, PYTHONIOENCODING='utf-8')
+        self.assertTrue(os.path.exists(countsfile))
+        with open(countsfile, 'rb') as fd:
+            counts = load(fd)[0]
+        self.assertTrue(counts)
+        # A second run accumulates into the same file.
+        assert_python_ok(*argv, PYTHONIOENCODING='utf-8')
+        with open(countsfile, 'rb') as fd:
+            accumulated = load(fd)[0]
+        self.assertEqual(accumulated,
+                         {key: 2 * value for key, value in counts.items()})
+
     def test_run_as_module(self):
         assert_python_ok('-m', 'trace', '-l', '--module', 'timeit', '-n', '1')
         assert_python_failure('-m', 'trace', '-l', '--module', 'not_a_module_zzz')
diff --git a/Lib/trace.py b/Lib/trace.py
index 43ec201c4696d1..66471f45e1c004 100644
--- a/Lib/trace.py
+++ b/Lib/trace.py
@@ -287,8 +287,11 @@ def write_results(self, show_missing=True, summary=False, coverdir=None, *,
                 n_lines, n_hits, modulename, filename = sums[m]
                 print(f"{n_lines:5d}   {n_hits/n_lines:.1%}   {modulename}   ({filename})")
 
+        self._save_counts()
+
+    def _save_counts(self):
+        """Save the accumulated counts to ``self.outfile`` if one was given."""
         if self.outfile:
-            # try and store counts and module info into self.outfile
             try:
                 with open(self.outfile, 'wb') as f:
                     pickle.dump((self.counts, self.calledfuncs, self.callers),
@@ -744,6 +747,8 @@ def parse_ignore_dir(s):
 
     if not opts.no_report:
         results.write_results(opts.missing, opts.summary, opts.coverdir)
+    else:
+        results._save_counts()
 
 if __name__=='__main__':
     main()
diff --git a/Misc/NEWS.d/next/Library/2026-06-27-10-30-00.gh-issue-152409.Tr8cE2.rst b/Misc/NEWS.d/next/Library/2026-06-27-10-30-00.gh-issue-152409.Tr8cE2.rst
new file mode 100644
index 00000000000000..2e6a759a102e66
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2026-06-27-10-30-00.gh-issue-152409.Tr8cE2.rst
@@ -0,0 +1,3 @@
+Fix the :mod:`trace` command-line tool not saving the ``--file`` counts
+when ``--no-report`` is used, which prevented accumulating counts over
+several runs.  Patch by tonghuaroot.

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