Fix subprocess.communicate("") raising IOError: closed stream

[qaisjp]

subprocess.communicate("") would raise IOError: closed stream because the code closed stdin immediately when input.empty?, but then later tried to use the closed stdin file descriptor in IO.select

This only occurs with empty strings (""), not with nil or non-empty strings.

We've fixed that by excluding @stdin from wait_w when @stdin.closed?

Backward compatibility

This fix maintains full backward compatibility:

• nil input behaviour unchanged
• Non-empty string input behaviour unchanged
• Only empty string input is fixed (was previously broken)

[Copilot]

Pull Request Overview

This PR fixes an IOError: closed stream bug that occurred when calling subprocess.communicate("") with an empty string input. The issue arose because the code closed stdin when input was empty but then tried to use the closed file descriptor in IO.select.

• Fixed stdin handling logic to exclude closed stdin from IO.select operations
• Added comprehensive test coverage for empty string, nil, and non-empty string inputs
• Ensured backward compatibility by only fixing the broken empty string case

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
lib/subprocess.rb	Updated stdin handling to check if stdin is closed before including it in wait operations
test/test_empty_stdin.rb	Added comprehensive test suite covering empty string, nil input, non-empty string, and edge cases

Comments suppressed due to low confidence (1)

test/test_empty_stdin.rb:45

• This test creates a subprocess but doesn't handle cleanup if an assertion fails before p.wait is called. Consider wrapping in an ensure block or using the block form of check_call for automatic cleanup.

      p = Subprocess.popen(['cat'], stdin: Subprocess::PIPE, stdout: Subprocess::PIPE)