From 1899bdc7abb9c6bdd252b42b080841c63fb1994b Mon Sep 17 00:00:00 2001
From: Ned Batchelder <ned@nedbatchelder.com>
Date: Sun, 16 Jan 2022 17:47:28 -0500
Subject: fix: create the db as needed when accessed

---
 coverage/sqldata.py | 49 ++++++++++++++++++++-----------------------------
 tests/test_data.py  | 17 ++---------------
 2 files changed, 22 insertions(+), 44 deletions(-)

diff --git a/coverage/sqldata.py b/coverage/sqldata.py
index e3c59fcb..1742976f 100644
--- a/coverage/sqldata.py
+++ b/coverage/sqldata.py
@@ -256,26 +256,6 @@ class CoverageData(SimpleReprMixin):
         self._have_used = False
         self._current_context_id = None
 
-    def _create_db(self):
-        """Create a db file that doesn't exist yet.
-
-        Initializes the schema and certain metadata.
-        """
-        if self._debug.should("dataio"):
-            self._debug.write(f"Creating data file {self._filename!r}")
-        self._dbs[threading.get_ident()] = db = SqliteDb(self._filename, self._debug)
-        with db:
-            db.executescript(SCHEMA)
-            db.execute("insert into coverage_schema (version) values (?)", (SCHEMA_VERSION,))
-            db.executemany(
-                "insert into meta (key, value) values (?, ?)",
-                [
-                    ("sys_argv", str(getattr(sys, "argv", None))),
-                    ("version", __version__),
-                    ("when", datetime.datetime.now().strftime("%Y-%m-%d %H:%M:%S")),
-                ]
-            )
-
     def _open_db(self):
         """Open an existing db file, and read its metadata."""
         if self._debug.should("dataio"):
@@ -289,11 +269,25 @@ class CoverageData(SimpleReprMixin):
             try:
                 schema_version, = db.execute_one("select version from coverage_schema")
             except Exception as exc:
-                raise DataError(
-                    "Data file {!r} doesn't seem to be a coverage data file: {}".format(
-                        self._filename, exc
+                if "no such table: coverage_schema" in str(exc):
+                    if self._debug.should("dataio"):
+                        self._debug.write(f"Initing data file {self._filename!r}")
+                    db.executescript(SCHEMA)
+                    db.execute("insert into coverage_schema (version) values (?)", (SCHEMA_VERSION,))
+                    db.executemany(
+                        "insert or ignore into meta (key, value) values (?, ?)",
+                        [
+                            ("sys_argv", str(getattr(sys, "argv", None))),
+                            ("version", __version__),
+                            ("when", datetime.datetime.now().strftime("%Y-%m-%d %H:%M:%S")),
+                        ]
                     )
-                ) from exc
+                else:
+                    raise DataError(
+                        "Data file {!r} doesn't seem to be a coverage data file: {}".format(
+                            self._filename, exc
+                        )
+                    ) from exc
             else:
                 if schema_version != SCHEMA_VERSION:
                     raise DataError(
@@ -312,10 +306,7 @@ class CoverageData(SimpleReprMixin):
     def _connect(self):
         """Get the SqliteDb object to use."""
         if threading.get_ident() not in self._dbs:
-            if os.path.exists(self._filename):
-                self._open_db()
-            else:
-                self._create_db()
+            self._open_db()
         return self._dbs[threading.get_ident()]
 
     def __bool__(self):
@@ -521,7 +512,7 @@ class CoverageData(SimpleReprMixin):
             self._has_arcs = arcs
             with self._connect() as con:
                 con.execute(
-                    "insert into meta (key, value) values (?, ?)",
+                    "insert or ignore into meta (key, value) values (?, ?)",
                     ("has_arcs", str(int(arcs)))
                 )
 
diff --git a/tests/test_data.py b/tests/test_data.py
index bc06eb23..9a694c6c 100644
--- a/tests/test_data.py
+++ b/tests/test_data.py
@@ -592,12 +592,6 @@ class CoverageDataInTempDirTest(CoverageTest):
             covdata.read()
         assert not covdata
 
-        self.make_file("empty.dat", "")
-        with pytest.raises(DataError, match=msg.format("empty.dat")):
-            covdata = DebugCoverageData("empty.dat")
-            covdata.read()
-        assert not covdata
-
     def test_hard_read_error(self):
         self.make_file("noperms.dat", "go away")
         os.chmod("noperms.dat", 0)
@@ -626,14 +620,6 @@ class CoverageDataInTempDirTest(CoverageTest):
             covdata.read()
         assert not covdata
 
-        with sqlite3.connect("no_schema.db") as con:
-            con.execute("create table foobar (baz text)")
-        msg = r"Couldn't .* '.*[/\\]no_schema.db': \S+"
-        with pytest.raises(DataError, match=msg):
-            covdata = DebugCoverageData("no_schema.db")
-            covdata.read()
-        assert not covdata
-
 
 class CoverageDataFilesTest(CoverageTest):
     """Tests of CoverageData file handling."""
@@ -667,7 +653,8 @@ class CoverageDataFilesTest(CoverageTest):
 
         assert re.search(
             r"^Erasing data file '.*\.coverage'\n" +
-            r"Creating data file '.*\.coverage'\n" +
+            r"Opening data file '.*\.coverage'\n" +
+            r"Initing data file '.*\.coverage'\n" +
             r"Opening data file '.*\.coverage'\n$",
             debug.get_output()
         )
-- 
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