fix: only write "Wrote report" message if report succeeded.

For example, see [issue
1554](#1554) for the previous
misleading behavior when the exception being raised wasn't a
CoverageException.

Author: nedbat

CHANGES.rst

@@ -23,6 +23,10 @@ Unreleased
 - Added a :meth:`.CoverageData.purge_files` method to remove recorded data for
   a particular file.  Contributed by `Stephan Deibel <pull 1547_>`_.
 
+- Fix: when reporting commands fail, they will no longer congratulate
+  themselves with messages like "Wrote XML report to file.xml" before spewing a
+  traceback about their failure.
+
 - Fix: In some embedded environments, an IndexError could occur on stop() when
   the originating thread exits before completion.  This is now fixed, thanks to
   `Russell Keith-Magee <pull 1543_>`_, closing `issue 1542`_.

coverage/report.py

@@ -9,7 +9,7 @@
 
 from typing import Callable, Iterable, Iterator, IO, Optional, Tuple, TYPE_CHECKING
 
-from coverage.exceptions import CoverageException, NoDataError, NotPython
+from coverage.exceptions import NoDataError, NotPython
 from coverage.files import prep_patterns, GlobMatcher
 from coverage.misc import ensure_dir_for_file, file_be_gone
 from coverage.plugin import FileReporter
@@ -47,26 +47,25 @@ def render_report(
     if output_path == "-":
         outfile = sys.stdout
     else:
-        # Ensure that the output directory is created; done here
-        # because this report pre-opens the output file.
-        # HTMLReport does this using the Report plumbing because
-        # its task is more complex, being multiple files.
+        # Ensure that the output directory is created; done here because this
+        # report pre-opens the output file.  HtmlReporter does this on its own
+        # because its task is more complex, being multiple files.
         ensure_dir_for_file(output_path)
         outfile = open(output_path, "w", encoding="utf-8")
         file_to_close = outfile
+        delete_file = True
 
     try:
-        return reporter.report(morfs, outfile=outfile)
-    except CoverageException:
-        delete_file = True
-        raise
+        ret = reporter.report(morfs, outfile=outfile)
+        if file_to_close is not None:
+            msgfn(f"Wrote {reporter.report_type} to {output_path}")
+        delete_file = False
+        return ret
     finally:
-        if file_to_close:
+        if file_to_close is not None:
             file_to_close.close()
             if delete_file:
                 file_be_gone(output_path)           # pragma: part covered (doesn't return)
-            else:
-                msgfn(f"Wrote {reporter.report_type} to {output_path}")
 
 
 def get_analysis_to_report(

tests/test_report.py

@@ -5,7 +5,7 @@
 
 from __future__ import annotations
 
-from typing import IO, Iterable, List, Optional
+from typing import IO, Iterable, List, Optional, Type
 
 import pytest
 
@@ -21,7 +21,7 @@ class FakeReporter:
 
     report_type = "fake report file"
 
-    def __init__(self, output: str = "", error: bool = False) -> None:
+    def __init__(self, output: str = "", error: Optional[Type[Exception]] = None) -> None:
         self.output = output
         self.error = error
         self.morfs: Optional[Iterable[TMorf]] = None
@@ -31,7 +31,7 @@ def report(self, morfs: Optional[Iterable[TMorf]], outfile: IO[str]) -> float:
         self.morfs = morfs
         outfile.write(self.output)
         if self.error:
-            raise CoverageException("You asked for it!")
+            raise self.error("You asked for it!")
         return 17.25
 
 
@@ -57,10 +57,11 @@ def test_file(self) -> None:
             assert f.read().rstrip() == b"Gr\xc3\xa9\xc3\xa8tings!"
         assert msgs == ["Wrote fake report file to output.txt"]
 
-    def test_exception(self) -> None:
-        fake = FakeReporter(error=True)
+    @pytest.mark.parametrize("error", [CoverageException, ZeroDivisionError])
+    def test_exception(self, error: Type[Exception]) -> None:
+        fake = FakeReporter(error=error)
         msgs: List[str] = []
-        with pytest.raises(CoverageException, match="You asked for it!"):
+        with pytest.raises(error, match="You asked for it!"):
             render_report("output.txt", fake, [], msgs.append)
         assert self.stdout() == ""
         self.assert_doesnt_exist("output.txt")