python: add flux.conf_builtin.conf_builtin_get()

Problem: Python programs do not have access to libflux builtin
configuration values via flux_conf_builtin_get().

Add flux.conf_builtin.conf_builtin_get() which provides access to this
function from Python. Unfortunately, the bahavior of FLUX_CONF_AUTO
must be duplicated because the builtin libflux intree vs installed
tests do not work when `python` is the executable (since it isn't
part of Flux).

src/bindings/python/flux/Makefile.am

@@ -11,6 +11,7 @@ nobase_fluxpy_PYTHON = \
 	memoized_property.py \
 	debugged.py \
 	importer.py \
+	conf_builtin.py \
 	cli/__init__.py \
 	cli/base.py \
 	cli/alloc.py \

src/bindings/python/flux/conf_builtin.py

@@ -0,0 +1,64 @@
+###############################################################
+# Copyright 2024 Lawrence Livermore National Security, LLC
+# (c.f. AUTHORS, NOTICE.LLNS, COPYING)
+#
+# This file is part of the Flux resource manager framework.
+# For details, see https://github.com/flux-framework.
+#
+# SPDX-License-Identifier: LGPL-3.0
+###############################################################
+
+import threading
+from pathlib import Path
+
+from flux.core.inner import raw
+
+tls = threading.local()
+tls.FLUX_CONF_AUTO_FLAG = None
+
+
+def _conf_builtin_get_flag():
+    """Simulate the use of FLUX_CONF_AUTO for Python
+
+    FLUX_CONF_AUTO will not work from Python since the executable will
+    be python and not something part of the Flux build tree or installed
+    by Flux. This function simulates FLUX_CONF_AUTO by returning the
+    correct FLUX_CONF_FLAG based on whether this module is under the
+    in tree PYTHONPATH or not.
+    """
+    if tls.FLUX_CONF_AUTO_FLAG is None:
+        # Resolve builtin installed python path:
+        pythonpath = conf_builtin_get("python_path", which="intree").split(":")
+        for path in pythonpath:
+            if Path(path).resolve() in Path(__file__).resolve().parents:
+                # If path is one of this module's parents,
+                # then this module is in tree:
+                tls.FLUX_CONF_AUTO_FLAG = raw.FLUX_CONF_INTREE
+                return tls.FLUX_CONF_AUTO_FLAG
+        # O/w, assume we're installed
+        tls.FLUX_CONF_AUTO_FLAG = raw.FLUX_CONF_INSTALLED
+    return tls.FLUX_CONF_AUTO_FLAG
+
+
+def conf_builtin_get(name, which="auto"):
+    """Get builtin (compiled-in) configuration values from libflux
+
+    Args:
+        name (str): name of config value
+        which (str): one of "installed", "intree", or "auto" to return
+            the installed path, in tree path, or automatically determine
+            which to use. default=auto.
+    """
+    if which == "auto":
+        flag = _conf_builtin_get_flag()
+    elif which == "installed":
+        flag = raw.FLUX_CONF_INSTALLED
+    elif which == "intree":
+        flag = raw.FLUX_CONF_INTREE
+    else:
+        raise ValueError("which must be one of auto, installed, or intree")
+
+    try:
+        return raw.flux_conf_builtin_get(name, flag).decode("utf-8")
+    except OSError:
+        raise ValueError(f"No builtin config value for '{name}'")