Make colourize_console() a function

Currently, colourize_console is a constant, set at process
initialization.

To allow the actual stdout to be easily compared with the expected when
running tests, we want to allow colourization to be on for the test
driver, but not for the in-process configure done by run_configure,
which has stdout redirected from a tty to a pipe.

v2:
Cache _colorize_console per file object

v3:
Reset cache on setup_console()

1 files changed, 23 insertions, 6 deletions

diff --git a/mesonbuild/mlog.py b/mesonbuild/mlog.py
index 8cbd248..7b8aec7 100644
--- a/mesonbuild/mlog.py
+++ b/mesonbuild/mlog.py
@@ -40,15 +40,32 @@ def _windows_ansi() -> bool:
     # original behavior
     return bool(kernel.SetConsoleMode(stdout, mode.value | 0x4) or os.environ.get('ANSICON'))
 
-def setup_console() -> bool:
+def colorize_console() -> bool:
+    _colorize_console = getattr(sys.stdout, 'colorize_console', None)  # type: bool
+    if _colorize_console is not None:
+        return _colorize_console
+
     try:
         if platform.system().lower() == 'windows':
-            return os.isatty(sys.stdout.fileno()) and _windows_ansi()
-        return os.isatty(sys.stdout.fileno()) and os.environ.get('TERM') != 'dumb'
+            _colorize_console = os.isatty(sys.stdout.fileno()) and _windows_ansi()
+        else:
+            _colorize_console = os.isatty(sys.stdout.fileno()) and os.environ.get('TERM', 'dumb') != 'dumb'
     except Exception:
-        return False
+        _colorize_console = False
+
+    sys.stdout.colorize_console = _colorize_console  # type: ignore[attr-defined]
+    return _colorize_console
+
+def setup_console():
+    # on Windows, a subprocess might call SetConsoleMode() on the console
+    # connected to stdout and turn off ANSI escape processing. Call this after
+    # running a subprocess to ensure we turn it on again.
+    if platform.system().lower() == 'windows':
+        try:
+            delattr(sys.stdout, 'colorize_console')
+        except AttributeError:
+            pass
 
-colorize_console = setup_console()
 log_dir = None               # type: T.Optional[str]
 log_file = None              # type: T.Optional[T.TextIO]
 log_fname = 'meson-log.txt'  # type: str
@@ -204,7 +221,7 @@ def log(*args: T.Union[str, AnsiDecorator], is_error: bool = False,
     if log_file is not None:
         print(*arr, file=log_file, **kwargs)
         log_file.flush()
-    if colorize_console:
+    if colorize_console():
         arr = process_markup(args, True)
     if not log_errors_only or is_error:
         force_print(*arr, **kwargs)