Add LazyImportError

[chuanzzx]

Summary

Wrap every deferred import exception in a new exception type LazyImportError, chained to the original exception.

Test Plan

• When Lazy Imports is not enabled, every error will change nothing.
• When Lazy Imports is enabled, every error cause by a (lazy) import action will wrap into LazyImportError. Thus, the error will show LazyImportError and link back to the original exception with tracebacks.

Pre-req

Create foo.py, value_error.py, run_foo.py, and run_value_error.py under the same path of python.exe.

foo.py

import applepie
applepie

value_error.py

raise ValueError("")

run_foo.py

import foo
foo

run_value_error.py

import value_error
value_error

Test without Lazy Imports

Test ModuleNotFoundError

Run

./python.exe run_foo.py

Expected results:

Traceback (most recent call last):
  File "/Users/harperlin/Documents/GitHub/crashy_0623/run_foo.py", line 1, in <module>
    import foo
    ^^^^^^^^^^
  File "/Users/harperlin/Documents/GitHub/crashy_0623/foo.py", line 1, in <module>
    import applepie
    ^^^^^^^^^^^^^^^
ModuleNotFoundError: No module named 'applepie'

Test ValueError

Run

./python.exe run_value_error.py

Expected results:

Traceback (most recent call last):
  File "/Users/harperlin/Documents/GitHub/crashy_0623/run_value_error.py", line 1, in <module>
    import value_error
    ^^^^^^^^^^^^^^^^^^
  File "/Users/harperlin/Documents/GitHub/crashy_0623/value_error.py", line 1, in <module>
    raise ValueError("")
    ^^^^^^^^^^^^^^^^^^^^
ValueError

Test with Lazy Imports

Test ModuleNotFoundError

Run

./python.exe -L run_foo.py

Expected results:

Traceback (most recent call last):
  File "<frozen importlib._bootstrap>", line 1178, in _find_and_load
  File "<frozen importlib._bootstrap>", line 1142, in _find_and_load_unlocked
ModuleNotFoundError: No module named 'applepie'

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "/Users/harperlin/Documents/GitHub/crashy_0623/run_foo.py", line 2, in <module>
    foo
    ^^^
  File "/Users/harperlin/Documents/GitHub/crashy_0623/foo.py", line 2, in <module>
    applepie
    ^^^^^^^^
LazyImportError: Error occurred when loading a lazy import. Original import was at file /Users/harperlin/Documents/GitHub/crashy_0623/foo.py, line 1

Test ValueError

Run

./python.exe -L run_value_error.py

Expected results:

Traceback (most recent call last):
  File "/Users/harperlin/Documents/GitHub/crashy_0623/value_error.py", line 1, in <module>
    raise ValueError("")
    ^^^^^^^^^^^^^^^^^^^^
ValueError

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "/Users/harperlin/Documents/GitHub/crashy_0623/run_value_error.py", line 2, in <module>
    value_error
    ^^^^^^^^^^^
LazyImportError: Error occurred when loading a lazy import. Original import was at file /Users/harperlin/Documents/GitHub/crashy_0623/run_value_error.py, line 1