Revert "Fix Python VarIntCoder OverflowError on uint64 values"

[Abacn]

Reverts #39047 due to performance regression

encoding values>INT_MAX with varint coder is undefined behavior. Guarding it at the cost of performance degradation isn't preferred

more context: #39047 (comment)

closes #39216

[Abacn]

R: @jrmccluskey

[github-actions]

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[gemini-code-assist]

Summary of Changes

Hello, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request reverts a previous change that aimed to fix Python VarIntCoder OverflowError on uint64 values. The reversion is necessary due to an identified performance regression caused by the previous implementation. The changes effectively restore the previous behavior where the coder is limited to 64-bit signed integers.

Highlights

• Reversion of uint64 handling: This PR reverts the changes that attempted to handle uint64 values in VarIntCoder, as it introduced a performance regression.
• Removal of helper functions: The _as_signed_int64 helper function and associated logic for folding uint64 values into signed int64 have been removed.
• Test cleanup: The test_varint_coder_uint64 test case has been removed as it is no longer applicable following the reversion.

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[gemini-code-assist]

Code Review

This pull request simplifies VarIntCoderImpl by removing the folding of uint64 values into signed int64 integers, restricting the coder strictly to 64-bit signed integers. Feedback suggests wrapping the type cast in encode with a try...except block to prevent Cython from raising an unhandled OverflowError before reaching the custom error handling. Additionally, it is recommended to add a test case verifying that out-of-range values correctly raise an OverflowError to maintain test coverage after the removal of test_varint_coder_uint64.

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[gemini-code-assist]

In Cython compiled mode, ivalue is declared as int64_t in .pxd. The assignment ivalue = value performs a type cast. If value is an integer that overflows the 64-bit signed integer range, this assignment will raise an OverflowError immediately.

This bypasses the fallback to StreamCoderImpl.encode(self, value) and the custom OverflowError handling in encode_to_stream (lines 1048-1053), which is designed to provide a helpful error message explaining the 64-bit signed integer limit. Instead, the user receives a generic Cython OverflowError.

Wrapping the type cast and small integer check in a try...except OverflowError block allows the overflow to be caught and safely delegated to StreamCoderImpl.encode, which will then raise the descriptive error message.

  def encode(self, value):
    try:
      ivalue = value  # type cast
      if 0 <= ivalue < len(small_ints):
        return small_ints[ivalue]
    except OverflowError:
      pass
    return StreamCoderImpl.encode(self, value)

[gemini-code-assist]

Since test_varint_coder_uint64 is being removed, we should ensure that we still have test coverage verifying that values outside the supported 64-bit signed integer range (such as 1 << 63, 1 << 64, and -(1 << 63) - 1) correctly raise OverflowError.

Suggested change

	def test_varint32_coder(self):
	def test_varint_coder_overflow(self):
	coder = coders.VarIntCoder()
	for v in [1 << 63, 1 << 64, -(1 << 63) - 1]:
	with self.assertRaises(OverflowError):
	coder.encode(v)
	def test_varint32_coder(self):