fix: raise chained errors with "from" #998

This makes exceptions report their causes correctly, as "The above exception was
the direct cause of the following exception" instead of "During handling of the
above exception, another exception occurred."

1 files changed, 8 insertions, 8 deletions

diff --git a/coverage/execfile.py b/coverage/execfile.py
index 2a3776bf..66020019 100644
--- a/coverage/execfile.py
+++ b/coverage/execfile.py
@@ -42,7 +42,7 @@ def find_module(modulename):
     try:
         spec = importlib.util.find_spec(modulename)
     except ImportError as err:
-        raise NoSource(str(err))
+        raise NoSource(str(err)) from err
     if not spec:
         raise NoSource(f"No module named {modulename!r}")
     pathname = spec.origin
@@ -193,7 +193,7 @@ class PyRunner:
             raise
         except Exception as exc:
             msg = "Couldn't run '{filename}' as Python code: {exc.__class__.__name__}: {exc}"
-            raise CoverageException(msg.format(filename=self.arg0, exc=exc))
+            raise CoverageException(msg.format(filename=self.arg0, exc=exc)) from exc
 
         # Execute the code object.
         # Return to the original directory in case the test code exits in
@@ -226,7 +226,7 @@ class PyRunner:
                 sys.excepthook(typ, err, tb.tb_next)
             except SystemExit:                      # pylint: disable=try-except-raise
                 raise
-            except Exception:
+            except Exception as exc:
                 # Getting the output right in the case of excepthook
                 # shenanigans is kind of involved.
                 sys.stderr.write("Error in sys.excepthook:\n")
@@ -236,7 +236,7 @@ class PyRunner:
                     err2.__traceback__ = err2.__traceback__.tb_next
                 sys.__excepthook__(typ2, err2, tb2.tb_next)
                 sys.stderr.write("\nOriginal exception was:\n")
-                raise ExceptionDuringRun(typ, err, tb.tb_next)
+                raise ExceptionDuringRun(typ, err, tb.tb_next) from exc
             else:
                 sys.exit(1)
         finally:
@@ -277,8 +277,8 @@ def make_code_from_py(filename):
     # Open the source file.
     try:
         source = get_python_source(filename)
-    except (OSError, NoSource):
-        raise NoSource("No file to run: '%s'" % filename)
+    except (OSError, NoSource) as exc:
+        raise NoSource("No file to run: '%s'" % filename) from exc
 
     code = compile_unicode(source, filename, "exec")
     return code
@@ -288,8 +288,8 @@ def make_code_from_pyc(filename):
     """Get a code object from a .pyc file."""
     try:
         fpyc = open(filename, "rb")
-    except OSError:
-        raise NoCode("No file to run: '%s'" % filename)
+    except OSError as exc:
+        raise NoCode("No file to run: '%s'" % filename) from exc
 
     with fpyc:
         # First four bytes are a version-specific magic number.  It has to