scripts: make clang tools obey b_colorout

Right now, the clang-tidy and clang-format targets use the program default
and do not let b_colorout decide whether to colorize output.

However, the wrappers that run the tool are going to be changed to buffer
output, and that would disable colorization unconditionally.  So pass
a --color option to the tools and use it when building the command line.

clang-format's -fcolor-diagnostics option simply does not work, and the
"right" (or at least working) option is --color which is undocumented.
--color is present all the way back to clang 10, but I digged into
clang-format's source code to figure out what's happening.  The problem
is that -fcolor-diagnostics is a complete no-operation; in fact it is
a bool that is initialized to true.  gdb shows:

  (gdb) p ShowColors
  $2 = {<llvm::cl::Option> = {
    ... <llvm::cl::opt_storage<bool, false, false>> = {Value = true,  ... }, ...}

on entry to clang-format's main, meaning that specifying the option on
the command line does nothing at all.

To see how clang-format determines whether to use colors you need to look
at enters SMDiagnostic::print, which simply does

  ColorMode Mode = ShowColors ? ColorMode::Auto : ColorMode::Disable;

showing once more that in fact the option cannot force-on the colors (
-fno-color-diagnostics instead works).  Continuing in SMDiagnostic::print,
this RAII constructor would write the escape sequence to the terminal:

  WithColor S(OS, raw_ostream::SAVEDCOLOR, true, false, Mode);

It ends up in WithColor::changeColor, which does

  if (colorsEnabled())
    OS.changeColor(Color, Bold, BG);

Digging further down, colorsEnabled() is where the Mode member is consulted:

  bool WithColor::colorsEnabled() {
    switch (Mode) {
      case ColorMode::Enable:
        return true;
      case ColorMode::Disable:
        return false;
      case ColorMode::Auto:
        return AutoDetectFunction(OS);
      }
      llvm_unreachable("All cases handled above.");
    }

and the "AutoDetectFunction" is

  static bool DefaultAutoDetectFunction(const raw_ostream &OS) {
    return *UseColor == cl::BOU_UNSET ? OS.has_colors()
                                      : *UseColor == cl::BOU_TRUE;
  }

UseColor is controlled by the "--color" option, so if that option was
unset you go to OS.has_colors() even in the presence of -fcolor-diagnostics.
This has been around for over 5 years in clang-format, and it was present
even earlier, so use it in meson as well.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

0 files changed, 0 insertions, 0 deletions