Simon Jakobi pushed to branch wip/sjakobi/T12934-line-buffer-stdout at Glasgow Haskell Compiler / GHC

Commits:

• cd91c746
  by Simon Jakobi at 2026-08-28T20:26:37+02:00

  testsuite: Line-buffer the driver's stdout
  
  The driver prints a progress line every ~100 tests, but when stdout is
  a pipe — as under hadrian and in CI — Python block-buffers it at 8 KiB,
  which is more than a clean run's entire progress output. So CI logs
  would show no sign of life until the run ended.
  
  The type-ignore is for mypy, which types sys.stdout as TextIO — an
  interface without reconfigure.
  
  Fixes #12934.
  
  Assisted-by: Claude Fable 5
  

1 changed file:

• testsuite/driver/runtests.py

Changes:

 from term_color import Color, colored

 import cpu_features

+# Line-buffer stdout: when it is a pipe (hadrian, CI), the block-buffered

+# default can delay all progress output until the run ends (#12934).

+sys.stdout.reconfigure(line_buffering=True)  # type: ignore[union-attr]

+

 # Readline sometimes spews out ANSI escapes for some values of TERM,

 # which result in test failures. Thus set TERM to a nice, simple, safe

 # value.