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, 3 insertions, 5 deletions

diff --git a/coverage/parser.py b/coverage/parser.py
index abaa2e50..ed049685 100644
--- a/coverage/parser.py
+++ b/coverage/parser.py
@@ -41,9 +41,7 @@ class PythonParser:
             try:
                 self.text = get_python_source(self.filename)
             except OSError as err:
-                raise NoSource(
-                    f"No source for code: '{self.filename}': {err}"
-                )
+                raise NoSource(f"No source for code: '{self.filename}': {err}") from err
 
         self.exclude = exclude
 
@@ -243,7 +241,7 @@ class PythonParser:
                 "Couldn't parse '%s' as Python source: '%s' at line %d" % (
                     self.filename, err.args[0], lineno
                 )
-            )
+            ) from err
 
         self.excluded = self.first_lines(self.raw_excluded)
 
@@ -363,7 +361,7 @@ class ByteParser:
                     "Couldn't parse '%s' as Python source: '%s' at line %d" % (
                         filename, synerr.msg, synerr.lineno
                     )
-                )
+                ) from synerr
 
         # Alternative Python implementations don't always provide all the
         # attributes on code objects that we need to do the analysis.