fix build warnings (#38025)

system/manager/build.py

@@ -11,7 +11,6 @@ from openpilot.system.hardware import HARDWARE, AGNOS
 def build() -> None:
   spinner = Spinner()
   spinner.update_progress(0, 100)
-  env = os.environ.copy()
 
   HARDWARE.set_power_save(False)
   if AGNOS:
@@ -21,35 +20,37 @@ def build() -> None:
   compile_output: list[bytes] = []
   for parallelism in ([], ["-j4"], ["-j1"]):
     compile_output.clear()
-    scons: subprocess.Popen = subprocess.Popen(["scons", *parallelism], cwd=BASEDIR, env=env, stderr=subprocess.PIPE)
-    assert scons.stderr is not None
+    with subprocess.Popen(["scons", *parallelism], cwd=BASEDIR, env={**os.environ, "PWD": BASEDIR}, stderr=subprocess.PIPE) as scons:
+      assert scons.stderr is not None
 
-    # Read progress from stderr and update spinner
-    while scons.poll() is None:
-      try:
-        line = scons.stderr.readline()
-        if line is None:
-          continue
+      # Read progress from stderr and update spinner
+      while scons.poll() is None:
+        try:
+          line = scons.stderr.readline()
+          if line is None:
+            continue
+          line = line.rstrip()
+
+          prefix = b'progress: '
+          if line.startswith(prefix):
+            progress = float(line[len(prefix):])
+            spinner.update_progress(100 * min(1., progress / 100.), 100.)
+          elif len(line):
+            compile_output.append(line)
+            print(line.decode('utf8', 'replace'))
+        except Exception:
+          pass
+
+      # Drain and close the pipe before retrying or returning.
+      for line in scons.stderr.read().split(b'\n'):
         line = line.rstrip()
-
-        prefix = b'progress: '
-        if line.startswith(prefix):
-          progress = float(line[len(prefix):])
-          spinner.update_progress(100 * min(1., progress / 100.), 100.)
-        elif len(line):
+        if len(line):
           compile_output.append(line)
-          print(line.decode('utf8', 'replace'))
-      except Exception:
-        pass
 
     if scons.returncode == 0:
       break
 
   if scons.returncode != 0:
-    # Read remaining output
-    if scons.stderr is not None:
-      compile_output += scons.stderr.read().split(b'\n')
-
     # Build failed log errors
     error_s = b"\n".join(compile_output).decode('utf8', 'replace')