scripts: add --dry-run flags to west build

Analogously to the Make options with the same names, these print the
commands which would have run without running them.

Signed-off-by: Marti Bolivar <marti.bolivar@nordicsemi.no>

scripts/west_commands/build.py

@@ -18,7 +18,7 @@ _ARG_SEPARATOR = '--'
 BUILD_USAGE = '''\
 west build [-h] [-b BOARD] [-d BUILD_DIR]
            [-t TARGET] [-p {auto, always, never}] [-c] [--cmake-only]
-           [-f] [source_dir] -- [cmake_opt [cmake_opt ...]]
+           [-n] [-f] [source_dir] -- [cmake_opt [cmake_opt ...]]
 '''
 
 BUILD_DESCRIPTION = '''\
@@ -139,6 +139,10 @@ class Build(Forceable):
                             help='Force CMake to run')
         parser.add_argument('--cmake-only', action='store_true',
                             help="Just run CMake; don't build. Implies -c.")
+        parser.add_argument('-n', '--just-print', '--dry-run', '--recon',
+                            dest='dry_run', action='store_true',
+                            help='''Just print the build commands which would
+                            have run, without actually running them.''')
         self.add_force_arg(parser)
         return parser
 
@@ -409,7 +413,7 @@ class Build(Forceable):
                                                      DEFAULT_CMAKE_GENERATOR))]
         if cmake_opts:
             final_cmake_args.extend(cmake_opts)
-        run_cmake(final_cmake_args)
+        run_cmake(final_cmake_args, dry_run=self.args.dry_run)
 
     def _run_pristine(self):
         log.inf('Making build dir {} pristine'.format(self.build_dir))
@@ -424,8 +428,9 @@ class Build(Forceable):
                     'Zephyr build system')
 
         cmake_args = ['-P', '{}/cmake/pristine.cmake'.format(zb)]
-        run_cmake(cmake_args, cwd=self.build_dir)
+        run_cmake(cmake_args, cwd=self.build_dir, dry_run=self.args.dry_run)
 
     def _run_build(self, target):
         extra_args = ['--target', target] if target else []
-        run_build(self.build_dir, extra_args=extra_args)
+        run_build(self.build_dir, extra_args=extra_args,
+                  dry_run=self.args.dry_run)

scripts/west_commands/zcmake.py

@@ -24,12 +24,22 @@ DEFAULT_CACHE = 'CMakeCache.txt'
 DEFAULT_CMAKE_GENERATOR = 'Ninja'
 '''Name of the default CMake generator.'''
 
-def run_cmake(args, cwd=None, capture_output=False):
-    '''Run cmake to (re)generate a build system.
+
+def run_cmake(args, cwd=None, capture_output=False, dry_run=False):
+    '''Run cmake to (re)generate a build system, a script, etc.
+
+    :param args: arguments to pass to CMake
+    :param cwd: directory to run CMake in, cwd is default
+    :param capture_output: if True, the output is returned instead of being
+                           displayed (None is returned by default, or if
+                           dry_run is also True)
+    :param dry_run: don't actually execute the command, just print what
+                    would have been run
+
     If capture_output is set to True, returns the output of the command instead
     of displaying it on stdout/stderr..'''
     cmake = shutil.which('cmake')
-    if cmake is None:
+    if cmake is None and not dry_run:
         log.die('CMake is not installed or cannot be found; cannot build.')
     cmd = [cmake] + args
     kwargs = dict()
@@ -39,6 +49,12 @@ def run_cmake(args, cwd=None, capture_output=False):
         kwargs['stderr'] = subprocess.STDOUT
     if cwd:
         kwargs['cwd'] = cwd
+
+    if dry_run:
+        in_cwd = ' (in {})'.format(cwd) if cwd else ''
+        log.inf('Dry run{}:'.format(in_cwd), quote_sh_list(cmd))
+        return None
+
     log.dbg('Running CMake:', quote_sh_list(cmd), level=log.VERBOSE_NORMAL)
     p = subprocess.Popen(cmd, **kwargs)
     out, err = p.communicate()
@@ -52,10 +68,18 @@ def run_cmake(args, cwd=None, capture_output=False):
         raise subprocess.CalledProcessError(p.returncode, p.args)
 
 
-def run_build(build_directory, extra_args=(), cwd=None, capture_output=False):
-    '''Run cmake in build tool mode in `build_directory`'''
-    run_cmake(['--build', build_directory] + list(extra_args),
-              capture_output=capture_output)
+def run_build(build_directory, **kwargs):
+    '''Run cmake in build tool mode.
+
+    :param build_directory: runs "cmake --build build_directory"
+    :param extra_args: optional kwarg. List of additional CMake arguments;
+                       these come after "--build <build_directory>"
+                       on the command line.
+
+    Any additional keyword arguments are passed as-is to run_cmake().
+    '''
+    extra_args = kwargs.pop('extra_args', [])
+    return run_cmake(['--build', build_directory] + extra_args, **kwargs)
 
 
 def make_c_identifier(string):