Use doctest directly to get docstring examples

[samestep]

This PR addresses a two-year-old TODO in test/test_type_hints.py by replacing most of the body of our custom get_examples_from_docstring function with a function from Python's built-in doctest.DocTestParser class. This mostly made the parser more strict, catching a few errors in existing doctests:

• missing ... in multiline statements
• missing space after >>>
• unmatched closing parenthesis

Also, as shown by the resulting diff of the untracked test/generated_type_hints_smoketest.py file (also linked from the test plan below), this introduces a few incidental changes as well:

• standalone comments are no longer preserved
• indentation is now visually correct
• example_torch_promote_types is now present
• an example called example_torch_tensor___array_priority__ is added, although I can't tell where it comes from
• the last nine lines of code from example_torch_tensor_align_as are now present
• the previously-misformatted third line from example_torch_tensor_stride is now present

Test plan:

Checkout the base commit, typecheck the doctests, and save the generated file:

$ python test/test_type_hints.py TestTypeHints.test_doc_examples
$ cp test/generated_type_hints_smoketest.py /tmp

Then checkout this PR, do the same thing, and compare:

$ python test/test_type_hints.py TestTypeHints.test_doc_examples
$ git diff --no-index {/tmp,test}/generated_type_hints_smoketest.py

The test should succeed, and the diff should match this paste.

[facebook-github-bot]

@samestep has imported this pull request. If you are a Facebook employee, you can view this diff on Phabricator.

[facebook-github-bot]

@samestep has imported this pull request. If you are a Facebook employee, you can view this diff on Phabricator.

[walterddr]

looks good.

[facebook-github-bot]

@samestep has imported this pull request. If you are a Facebook employee, you can view this diff on Phabricator.

[facebook-github-bot]

@samestep has imported this pull request. If you are a Facebook employee, you can view this diff on Phabricator.

[codecov]

Codecov Report

Merging #50596 (1e1159f) into master (1f5c3b3) will decrease coverage by 0.00%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master   #50596      +/-   ##
==========================================
- Coverage   81.07%   81.06%   -0.01%     
==========================================
  Files        1915     1915              
  Lines      208621   208621              
==========================================
- Hits       169139   169126      -13     
- Misses      39482    39495      +13     

[facebook-github-bot]

@samestep merged this pull request in c147aa3.