How can I get Clang colors to work in boost-bjam?

Question

b2 release link=static toolset=clang works, but it does not show the nice colors that I find useful in clang's output.

Answer 1

Disclaimer: this is not an answer solving your problem, but it takes too much space to put this in a comment.

Here's a brief Holmesian elimination process. First, according to the Clang documentation, color is enabled only when a color-capable terminal is detected. And secondly, according to the Boost.Jam documentation, all environment variables are automatically imported into its built-in .ENVIRON module. Finally, you do indeed have a color-capable terminal. Yet it does not work. Even forcing the issue with an explicit Clang command line argument

./b2 install --toolset=clang --cxxflag=-fcolor-diagnostics

fails to display colored diagnostics. My only conclusion is that somehow b2 does not launch its build inside a color coded terminal. Upon further digging based on your comments, I found a related problem on another build system:

The reason for this is that ninja sets subprocess stdout/stderr to a pipe (Subprocess::Start(), subprocess.cc), and clang checks if StandardErrHasColors() (tools/clang/lib/Driver/Tools.cpp), which is false if !isatty(2) (lib/Support/Unix/Process.inc).

I looked around a bit, and the way to do this seems to be to call fork_pty() to run the child in a pseudo terminal. I don't know if this would impact subprocess creation time, and if opening ~4000 pseudo ttys (a chrome build at -j10000) is considered good form.

(It's possible to force clang to always emit color escaped codes using "-Xclang -fcolor-diagnostics", but that's pretty hacky. make doesn't seem to override stderr on unix as far as I can tell, child_execute_job() in job.c)

Conclusion: you might have to dig into the b2 internals to see if there is some output redirection taking place that prevents the color-coding. Alternatively, you could ask on the Boost.Build mailinglist. Hopefully this helps you along a bit further.

Update: there is a long standing ticket on the Boost SVN site that deals with this.

Answer 2

Seems the core issue was somehow solved, but there's a little more explaining to be done regarding it.

If you want colors, you can use this in user-config.jam:

using clang : : : <compileflags>-fcolor-diagnostics ;

However, my personal preference is to handle this in my Jamroot by using project requirements so others don't need to deal with it:

project my_project : requirements
  <toolset>clang:<cflags>-fcolor-diagnostics
  <toolset>clang:<cxxflags>-fcolor-diagnostics
;