Refactor error msg stack handling, add TORCH_RETHROW (#37101)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/37101
Fixes #36954.
The basic concept is to streamline the process of rethrowing
c10::Error with extra error information. This is in a few
steps:
- I completely remodeled the Error data type and the internal
invariants. Instead of manually adding in newlines, the
message stack formatting process is responsible for inserting
newlines and spacing as necessary. Call sites are then
modified to respect the new API model.
- TORCH_RETHROW macro is added, which adds context to an error
message and then rethrows it.
New internal assert failure looks like:
```
0 INTERNAL ASSERT FAILED at ../c10/test/util/exception_test.cpp:64, please report a bug to PyTorch.
Exception raised from TestBody at ../c10/test/util/exception_test.cpp:64 (most recent call first):
frame #0: <unknown function> + 0x6aab9 (0x7ff611d3aab9 in /data/users/ezyang/pytorch-tmp/build/lib/libc10.so)
frame #1: ...
```
Error message with context looks like:
```
This is an error
This is context 1
This is context 2
```
Signed-off-by: Edward Z. Yang <ezyang@fb.com>
Test Plan: Imported from OSS
Differential Revision: D21202891
Pulled By: ezyang
fbshipit-source-id: 361cadd16bc52e5886dba08e79277771ada76169
