fix: avoid a SQLite error when async mode isn't available. #1646

CHANGES.rst

@@ -22,6 +22,11 @@ Unreleased
 
 - Dropped support for Python 3.7.
 
+- Fix: in unusual circumstances, SQLite cannot be set to asynchronous mode.
+  Coverage.py would fail with the error ``Safety level may not be changed
+  inside a transaction.`` This is now avoided, closing `issue 1646`_.  Thanks
+  to Michael Bell for the detailed bug report.
+
 - Docs: examples of configuration files now include separate examples for the
   different syntaxes: .coveragerc, pyproject.toml, setup.cfg, and tox.ini.
 
@@ -32,6 +37,7 @@ Unreleased
 - Added a CITATION.cff file, thanks to `Ken Schackart <pull 1641_>`_.
 
 .. _pull 1641: https://github.com/nedbat/coveragepy/pull/1641
+.. _issue 1646: https://github.com/nedbat/coveragepy/issues/1646
 
 
 .. scriv-start-here

CONTRIBUTORS.txt

@@ -147,6 +147,7 @@ Matthew Desmarais
 Matus Valo
 Max Linke
 Mayank Singhal
+Michael Bell
 Michael Krebs
 Michał Bultrowicz
 Michał Górny

coverage/debug.py

@@ -15,6 +15,7 @@
 import re
 import reprlib
 import sys
+import traceback
 import types
 import _thread
 
@@ -172,6 +173,12 @@ def write_formatted_info(
         write(f" {line}")
 
 
+def exc_one_line(exc: Exception) -> str:
+    """Get a one-line summary of an exception, including class name and message."""
+    lines = traceback.format_exception_only(type(exc), exc)
+    return "|".join(l.rstrip() for l in lines)
+
+
 def short_stack(limit: Optional[int] = None, skip: int = 0) -> str:
     """Return a string summarizing the call stack.
 

coverage/sqldata.py

@@ -26,7 +26,7 @@
     Optional, Sequence, Set, Tuple, TypeVar, Union,
 )
 
-from coverage.debug import NoDebugging, AutoReprMixin, clipped_repr
+from coverage.debug import NoDebugging, AutoReprMixin, clipped_repr, exc_one_line
 from coverage.exceptions import CoverageException, DataError
 from coverage.files import PathAliases
 from coverage.misc import file_be_gone, isolate_module
@@ -1130,11 +1130,11 @@ def _connect(self) -> None:
         self.con.create_function("REGEXP", 2, lambda txt, pat: re.search(txt, pat) is not None)
 
         # This pragma makes writing faster. It disables rollbacks, but we never need them.
-        # PyPy needs the .close() calls here, or sqlite gets twisted up:
-        # https://bitbucket.org/pypy/pypy/issues/2872/default-isolation-mode-is-different-on
         self.execute_void("pragma journal_mode=off")
-        # This pragma makes writing faster.
-        self.execute_void("pragma synchronous=off")
+        # This pragma makes writing faster. It can fail in unusual situations
+        # (https://github.com/nedbat/coveragepy/issues/1646), so use fail_ok=True
+        # to keep things going.
+        self.execute_void("pragma synchronous=off", fail_ok=True)
 
     def close(self) -> None:
         """If needed, close the connection."""
@@ -1159,7 +1159,7 @@ def __exit__(self, exc_type, exc_value, traceback) -> None:     # type: ignore[n
                 self.close()
             except Exception as exc:
                 if self.debug.should("sql"):
-                    self.debug.write(f"EXCEPTION from __exit__: {exc}")
+                    self.debug.write(f"EXCEPTION from __exit__: {exc_one_line(exc)}")
                 raise DataError(f"Couldn't end data file {self.filename!r}: {exc}") from exc
 
     def _execute(self, sql: str, parameters: Iterable[Any]) -> sqlite3.Cursor:
@@ -1191,7 +1191,7 @@ def _execute(self, sql: str, parameters: Iterable[Any]) -> sqlite3.Cursor:
             except Exception:   # pragma: cant happen
                 pass
             if self.debug.should("sql"):
-                self.debug.write(f"EXCEPTION from execute: {msg}")
+                self.debug.write(f"EXCEPTION from execute: {exc_one_line(exc)}")
             raise DataError(f"Couldn't use data file {self.filename!r}: {msg}") from exc
 
     @contextlib.contextmanager
@@ -1210,9 +1210,18 @@ def execute(
         finally:
             cur.close()
 
-    def execute_void(self, sql: str, parameters: Iterable[Any] = ()) -> None:
-        """Same as :meth:`python:sqlite3.Connection.execute` when you don't need the cursor."""
-        self._execute(sql, parameters).close()
+    def execute_void(self, sql: str, parameters: Iterable[Any] = (), fail_ok: bool = False) -> None:
+        """Same as :meth:`python:sqlite3.Connection.execute` when you don't need the cursor.
+
+        If `fail_ok` is True, then SQLite errors are ignored.
+        """
+        try:
+            # PyPy needs the .close() calls here, or sqlite gets twisted up:
+            # https://bitbucket.org/pypy/pypy/issues/2872/default-isolation-mode-is-different-on
+            self._execute(sql, parameters).close()
+        except DataError:
+            if not fail_ok:
+                raise
 
     def execute_for_rowid(self, sql: str, parameters: Iterable[Any] = ()) -> int:
         """Like execute, but returns the lastrowid."""

tests/test_debug.py

@@ -19,9 +19,10 @@
 from coverage import env
 from coverage.debug import (
     DebugOutputFile,
-    clipped_repr, filter_text, info_formatter, info_header, relevant_environment_display,
-    short_id, short_stack,
+    clipped_repr, exc_one_line, filter_text, info_formatter, info_header,
+    relevant_environment_display, short_id, short_stack,
 )
+from coverage.exceptions import DataError
 
 from tests.coveragetest import CoverageTest
 from tests.helpers import re_line, re_lines, re_lines_text
@@ -317,3 +318,10 @@ def test_relevant_environment_display() -> None:
         ("SOME_PYOTHER", "xyz123"),
         ("TMP", "temporary"),
     ]
+
+
+def test_exc_one_line() -> None:
+    try:
+        raise DataError("wtf?")
+    except Exception as exc:
+        assert exc_one_line(exc) == "coverage.exceptions.DataError: wtf?"