Fix #18423 - reveal_type not run in "unreachable" branches

[SANTHOSH-SACHIN]

Fix #18423 - reveal_type not run in "unreachable" branches

Currently, reveal_type does not output type information in unreachable code branches, such as those following assert_never. This is because mypy considers such code unreachable and skips type-checking it. However, for debugging purposes, it is useful to see the type information even in unreachable branches.

Solution

This PR modifies the reveal_type function to explicitly handle unreachable code by checking for UninhabitedType, which mypy uses to represent unreachable branches. When UninhabitedType is encountered, reveal_type outputs "Never".

Changes

1. reveal_type Function:
   • Added a check for UninhabitedType to handle unreachable code.
   • If the type is UninhabitedType, the function outputs "Never".
   • Otherwise, it behaves as before, using TypeStrVisitor to print the type.

Why This Fix Works

• UninhabitedType Represents Unreachable Code:
  • mypy uses UninhabitedType to represent unreachable code, such as after assert_never. By checking for UninhabitedType, we can detect and handle this case.
• Maintains Compatibility:
  • This fix does not introduce any new types or changes to the mypy type system. It leverages the existing UninhabitedType to represent the "never" case.

[github-actions]

According to mypy_primer, this change doesn't affect type check results on a corpus of open source code. ✅