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, 6 insertions, 0 deletions

diff --git a/mesonbuild/build.py b/mesonbuild/build.py
index 65438b0..a3cd993 100644
--- a/mesonbuild/build.py
+++ b/mesonbuild/build.py
@@ -1638,6 +1638,7 @@ class CustomTarget(Target):
         'depfile',
         'build_by_default',
         'override_options',
+        'console',
     ])
 
     def __init__(self, name, subdir, subproject, kwargs, absolute_paths=False):
@@ -1756,6 +1757,11 @@ class CustomTarget(Target):
         self.capture = kwargs.get('capture', False)
         if self.capture and len(self.outputs) != 1:
             raise InvalidArguments('Capturing can only output to a single file.')
+        self.console = kwargs.get('console', False)
+        if not isinstance(self.console, bool):
+            raise InvalidArguments('"console" kwarg only accepts booleans')
+        if self.capture and self.console:
+            raise InvalidArguments("Can't both capture output and output to console")
         if 'command' not in kwargs:
             raise InvalidArguments('Missing keyword argument "command".')
         if 'depfile' in kwargs: