fix(Base): log the output of successful commands as debug.

craft_providers/base.py

@@ -1223,4 +1223,10 @@ def _execute_run(
             if verify_network and not cls._network_connected(executor=executor):
                 raise NetworkError from exc
             raise
+
+        if proc.stdout:
+            logger.debug("Command stdout: %s", proc.stdout)
+        if proc.stderr:
+            logger.debug("Command stderr: %s", proc.stderr)
+
         return proc

tests/unit/bases/test_ubuntu_buildd.py

@@ -1674,6 +1674,53 @@ def test_execute_run_bad_check_verifynetwork_combination(fake_executor):
         )
 
 
+def test_execute_run_logs_output_at_debug(fake_executor, fake_process, logs):
+    """_execute_run() should log command stdout at debug level.
+
+    Regression test for https://github.com/canonical/craft-providers/issues/250
+    """
+    base_config = ubuntu.BuilddBase(alias=ubuntu.BuilddBaseAlias.JAMMY)
+    command = ["the", "command"]
+    fake_process.register_subprocess(
+        [*DEFAULT_FAKE_CMD, *command],
+        returncode=0,
+        stdout=b"important command output",
+    )
+
+    base_config._execute_run(command, executor=fake_executor)
+
+    assert "important command output" in logs.debug
+
+
+def test_execute_run_output_included_in_error_details(fake_executor, fake_process):
+    """When a subprocess fails, its stdout must appear in the error details.
+
+    Regression test for https://github.com/canonical/craft-providers/issues/250
+    """
+    base_config = ubuntu.BuilddBase(alias=ubuntu.BuilddBaseAlias.JAMMY)
+
+    fake_process.register_subprocess(
+        [*DEFAULT_FAKE_CMD, "cat", "/etc/os-release"],
+        stdout="UBUNTU_CODENAME=jammy",
+    )
+    fake_process.register_subprocess(
+        [*DEFAULT_FAKE_CMD, "apt-get", "update"],
+        returncode=100,
+        stdout=b"Err:1 http://archive.ubuntu.com/ubuntu jammy InRelease\n  Connection refused",
+    )
+    fake_process.register_subprocess(
+        [*DEFAULT_FAKE_CMD, "bash", "-c", "exec 3<> /dev/tcp/snapcraft.io/443"],
+    )
+
+    with pytest.raises(BaseConfigurationError) as exc_info:
+        base_config._pre_setup_packages(executor=fake_executor)
+
+    assert "Connection refused" in str(exc_info.value), (
+        "stdout from the failed subprocess must appear in the error details "
+        "so the user knows why apt-get update failed"
+    )
+
+
 @pytest.mark.usefixtures("stub_verify_network")
 def test_network_connectivity_yes(fake_executor, fake_process):
     """Connectivity is ok."""