fix(util/process): collect complete output from subprocess (#1036)

Run subprocess output one last time before exiting the combined output
processing loop.

Fix #1025

Signed-off-by: Claudio Matsuoka <claudio.matsuoka@canonical.com>

Author: cmatsuoka

craft_parts/utils/process.py

@@ -151,6 +151,7 @@ def run(
 
         with closing(BytesIO()) as combined_io:
             while True:
+                finished = proc.poll() is not None
                 try:
                     # Time out if we don't have any event to handle
                     for key, mask in selector.select(0.1):
@@ -164,7 +165,7 @@ def run(
                 except BlockingIOError:
                     pass
 
-                if proc.poll() is not None:
+                if finished:
                     combined = combined_io.getvalue()
                     break
 

docs/reference/changelog.rst

@@ -2,6 +2,13 @@
 Changelog
 *********
 
+2.4.3 (unreleased)
+------------------
+
+Bug fixes:
+
+- Address race condition when collecting subprocess output.
+
 2.4.2 (2025-03-04)
 ------------------