Overhaul debugging environment variables

`HY_DEBUG` and `HY_FILTER_INTERNAL_ERRORS` were redundant in intention, but `HY_DEBUG` worked more reliably because `hy_exc_handler` is called explicitly in a few places. The new environment variable `HY_SHOW_INTERNAL_ERRORS` uses a more specific name while avoiding the awkwardness of how `HY_FILTER_INTERNAL_ERRORS` had to be set to an empty string to have an effect.

The new environment variable is still untested, because it's only for internal use, and is documented merely for completeness.

NEWS.rst

@@ -11,6 +11,8 @@ Removals
   or Python's built-in `keyword` module instead.
 * `doc` has been removed. Use `(help (get-macro foo))` or `(help
   (get-macro :reader foo))` instead.
+* The environment variables `HY_DEBUG` and `HY_FILTER_INTERNAL_ERRORS`
+  have been replaced with `HY_SHOW_INTERNAL_ERRORS`.
 
 Breaking Changes
 ------------------------------

docs/env_var.rst

@@ -11,14 +11,9 @@ set to anything else.
    (Default: nothing) Path to a file containing Hy source code to execute when
    starting the REPL.
 
-.. envvar:: HY_DEBUG
+.. envvar:: HY_SHOW_INTERNAL_ERRORS
 
-   (Default: false) Does something mysterious that's probably similar to
-   ``HY_FILTER_INTERNAL_ERRORS``.
-
-.. envvar:: HY_FILTER_INTERNAL_ERRORS
-
-   (Default: true) Whether to hide some parts of tracebacks that point to
+   (Default: false) Whether to show some parts of tracebacks that point to
    internal Hy code and won't be helpful to the typical Hy user.
 
 .. envvar:: HY_HISTORY

hy/errors.py

@@ -8,7 +8,7 @@
 from hy import _initialize_env_var
 from hy._compat import PYPY
 
-_hy_filter_internal_errors = _initialize_env_var("HY_FILTER_INTERNAL_ERRORS", True)
+_hy_show_internal_errors = _initialize_env_var("HY_SHOW_INTERNAL_ERRORS", False)
 
 
 class HyError(Exception):
@@ -270,11 +270,11 @@ def hy_exc_filter(exc_type, exc_value, exc_traceback):
 
 def hy_exc_handler(exc_type, exc_value, exc_traceback):
     """A `sys.excepthook` handler that uses `hy_exc_filter` to
-    remove internal Hy frames from a traceback print-out.
+    remove internal Hy frames from a traceback print-out, so long
+    as `_hy_show_internal_errors` is false.
     """
-    if os.environ.get("HY_DEBUG", False):
+    if _hy_show_internal_errors:
         return sys.__excepthook__(exc_type, exc_value, exc_traceback)
-
     try:
         output = hy_exc_filter(exc_type, exc_value, exc_traceback)
         sys.stderr.write(output)
@@ -289,14 +289,10 @@ def filtered_hy_exceptions():
     from tracebacks.
 
     Filtering can be controlled by the variable
-    `hy.errors._hy_filter_internal_errors` and environment variable
-    `HY_FILTER_INTERNAL_ERRORS`.
+    `hy.errors._hy_show_internal_errors` and environment variable
+    `HY_SHOW_INTERNAL_ERRORS`.
     """
-    global _hy_filter_internal_errors
-    if _hy_filter_internal_errors:
-        current_hook = sys.excepthook
-        sys.excepthook = hy_exc_handler
-        yield
-        sys.excepthook = current_hook
-    else:
-        yield
+    current_hook = sys.excepthook
+    sys.excepthook = hy_exc_handler
+    yield
+    sys.excepthook = current_hook

tests/test_bin.py

@@ -410,9 +410,6 @@ def test_macro_require():
 def test_tracebacks():
     """Make sure the printed tracebacks are correct."""
 
-    # We want the filtered tracebacks.
-    os.environ["HY_DEBUG"] = ""
-
     def req_err(x):
         assert x == "hy.errors.HyRequireError: No module named 'not_a_real_module'"