From e6df5b39be55c44205ea67811bb812e085599d5e Mon Sep 17 00:00:00 2001
From: Ned Batchelder <ned@nedbatchelder.com>
Date: Sun, 22 May 2022 18:53:51 -0400
Subject: [PATCH] fix: don't create a data file when just trying to read one.
 #1328

---
 CHANGES.rst           | 5 +++++
 coverage/sqldata.py   | 5 +++--
 tests/test_data.py    | 7 +++++++
 tests/test_summary.py | 1 +
 tests/test_xml.py     | 1 +
 5 files changed, 17 insertions(+), 2 deletions(-)

diff --git a/CHANGES.rst b/CHANGES.rst
index 7a200ee1a..86d5b11eb 100644
--- a/CHANGES.rst
+++ b/CHANGES.rst
@@ -41,6 +41,10 @@ Version 6.4 — 2022-05-22
 - A new debug option ``debug=sqldata`` adds more detail to ``debug=sql``,
   logging all the data being written to the database.
 
+- Previously, running ``coverage report`` (or any of the reporting commands) in
+  an empty directory would create a .coverage data file.  Now they do not,
+  fixing `issue 1328`_.
+
 - On Python 3.11, the ``[toml]`` extra no longer installs tomli, instead using
   tomllib from the standard library.  Thanks `Shantanu <pull 1359_>`_.
 
@@ -48,6 +52,7 @@ Version 6.4 — 2022-05-22
 
 .. _issue 1310: https://github.com/nedbat/coveragepy/issues/1310
 .. _issue 1323: https://github.com/nedbat/coveragepy/issues/1323
+.. _issue 1328: https://github.com/nedbat/coveragepy/issues/1328
 .. _issue 1351: https://github.com/nedbat/coveragepy/issues/1351
 .. _pull 1354: https://github.com/nedbat/coveragepy/pull/1354
 .. _pull 1359: https://github.com/nedbat/coveragepy/pull/1359
diff --git a/coverage/sqldata.py b/coverage/sqldata.py
index 1d6f626ea..c0fa6916a 100644
--- a/coverage/sqldata.py
+++ b/coverage/sqldata.py
@@ -783,8 +783,9 @@ def erase(self, parallel=False):
 
     def read(self):
         """Start using an existing data file."""
-        with self._connect():       # TODO: doesn't look right
-            self._have_used = True
+        if os.path.exists(self._filename):
+            with self._connect():
+                self._have_used = True
 
     def write(self):
         """Ensure the data is written to the data file."""
diff --git a/tests/test_data.py b/tests/test_data.py
index 9f9a92bd5..3cb519ca4 100644
--- a/tests/test_data.py
+++ b/tests/test_data.py
@@ -118,6 +118,13 @@ class CoverageDataTest(CoverageTest):
     def test_empty_data_is_false(self):
         covdata = DebugCoverageData()
         assert not covdata
+        self.assert_doesnt_exist(".coverage")
+
+    def test_empty_data_is_false_when_read(self):
+        covdata = DebugCoverageData()
+        covdata.read()
+        assert not covdata
+        self.assert_doesnt_exist(".coverage")
 
     def test_line_data_is_true(self):
         covdata = DebugCoverageData()
diff --git a/tests/test_summary.py b/tests/test_summary.py
index 4bce80f6d..d603062be 100644
--- a/tests/test_summary.py
+++ b/tests/test_summary.py
@@ -450,6 +450,7 @@ def test_report_skip_covered_no_data(self):
         cov.load()
         with pytest.raises(NoDataError, match="No data to report."):
             self.get_report(cov, skip_covered=True)
+        self.assert_doesnt_exist(".coverage")
 
     def test_report_skip_empty(self):
         self.make_file("main.py", """
diff --git a/tests/test_xml.py b/tests/test_xml.py
index 1e94dfa2e..fda11087b 100644
--- a/tests/test_xml.py
+++ b/tests/test_xml.py
@@ -139,6 +139,7 @@ def test_no_data(self):
         with pytest.raises(NoDataError, match="No data to report."):
             self.run_xml_report()
         self.assert_doesnt_exist("coverage.xml")
+        self.assert_doesnt_exist(".coverage")
 
     def test_no_source(self):
         # Written while investigating a bug, might as well keep it.