custom targets: Add a 'console' kwarg for long-running commands

Ninja buffers all commands and prints them only after they are
complete. Because of this, long-running commands such as `cargo
build` show no output at all and it's impossible to know if the
command is merely taking too long or is stuck somewhere.

To cater to such use-cases, Ninja has a 'pool' with depth 1 called
'console', and all processes in this pool have the following
properties:

1. stdout is connected to the program, so output can be seen in
   real-time
2. The output of all other commands is buffered and displayed after
   a command in this pool finishes running
3. Commands in this pool are executed serially (normal commands
   continue to run in the background)

This feature is available since Ninja v1.5

https://ninja-build.org/manual.html#_the_literal_console_literal_pool

1 files changed, 2 insertions, 0 deletions

diff --git a/mesonbuild/backend/ninjabackend.py b/mesonbuild/backend/ninjabackend.py
index ca65893..913830f 100644
--- a/mesonbuild/backend/ninjabackend.py
+++ b/mesonbuild/backend/ninjabackend.py
@@ -560,6 +560,8 @@ int dummy;
             abs_pdir = os.path.join(self.environment.get_build_dir(), self.get_target_dir(target))
             os.makedirs(abs_pdir, exist_ok=True)
             elem.add_item('DEPFILE', rel_dfile)
+        if target.console:
+            elem.add_item('pool', 'console')
         cmd = self.replace_paths(target, cmd)
         elem.add_item('COMMAND', cmd)
         elem.add_item('description', desc.format(target.name, cmd_type))