pw_presubmit: Skip filtered steps when listing

Skip filtered steps when running 'pw presubmit' with
'--only-list-steps'.

LUCI uses '--only-list-steps' to expand programs so individual steps in
a program show as separate steps in MILO. This change makes it clearer
that some steps didn't actually run because there were no files for them
to run on.

Change-Id: Ifb1b768c97312a255c0281a1b0d97d022df6a096
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/58983
Pigweed-Auto-Submit: Rob Mohr <mohrr@google.com>
Commit-Queue: Auto-Submit <auto-submit@pigweed.google.com.iam.gserviceaccount.com>
Reviewed-by: Wyatt Hepler <hepler@google.com>

2 files changed, 10 insertions, 7 deletions

diff --git a/pw_presubmit/py/pw_presubmit/cli.py b/pw_presubmit/py/pw_presubmit/cli.py
index 746984298..7f7ce053e 100644
--- a/pw_presubmit/py/pw_presubmit/cli.py
+++ b/pw_presubmit/py/pw_presubmit/cli.py
@@ -188,14 +188,10 @@ def run(
 
         return 0
 
-    if only_list_steps:
-        for step in program:
-            print(step.__name__)
-        return 0
-
     if presubmit.run(program,
                      root,
                      repositories,
+                     only_list_steps=only_list_steps,
                      output_directory=output_directory,
                      package_root=package_root,
                      **other_args):
diff --git a/pw_presubmit/py/pw_presubmit/presubmit.py b/pw_presubmit/py/pw_presubmit/presubmit.py
index dffd3d2b4..dc82110f8 100644
--- a/pw_presubmit/py/pw_presubmit/presubmit.py
+++ b/pw_presubmit/py/pw_presubmit/presubmit.py
@@ -226,7 +226,7 @@ class Presubmit:
     def run(self, program: Program, keep_going: bool = False) -> bool:
         """Executes a series of presubmit checks on the paths."""
 
-        checks = self._apply_filters(program)
+        checks = self.apply_filters(program)
 
         _LOG.debug('Running %s for %s', program.title(), self._root.name)
         _print_ui(_title(f'{self._root.name}: {program.title()}'))
@@ -250,7 +250,7 @@ class Presubmit:
 
         return not failed and not skipped
 
-    def _apply_filters(
+    def apply_filters(
             self, program: Sequence[Callable]
     ) -> List[Tuple['_Check', Sequence[Path]]]:
         """Returns list of (check, paths) for checks that should run."""
@@ -395,6 +395,7 @@ def run(program: Sequence[Callable],
         exclude: Sequence[Pattern] = (),
         output_directory: Optional[Path] = None,
         package_root: Path = None,
+        only_list_steps: bool = False,
         keep_going: bool = False) -> bool:
     """Lists files in the current Git repo and runs a Presubmit with them.
 
@@ -418,6 +419,7 @@ def run(program: Sequence[Callable],
         exclude: regular expressions for Posix-style paths to exclude
         output_directory: where to place output files
         package_root: where to place package files
+        only_list_steps: print step names instead of running them
         keep_going: whether to continue running checks if an error occurs
 
     Returns:
@@ -456,6 +458,11 @@ def run(program: Sequence[Callable],
         package_root=package_root,
     )
 
+    if only_list_steps:
+        for check, _ in presubmit.apply_filters(program):
+            print(check.name)
+        return True
+
     if not isinstance(program, Program):
         program = Program('', program)