Added debugging of local config loading

src/python/pimlico/cli/main.py

@@ -154,6 +154,10 @@ def run_command(self, pipeline, opts):
     parser = argparse.ArgumentParser(description="Main command line interface to PiMLiCo")
     parser.add_argument("pipeline_config", help="Config file to load a pipeline from")
     parser.add_argument("--debug", "-d", help="Output verbose debugging info", action="store_true")
+    parser.add_argument("--trace-config",
+                        help="Trace the process of resolving which local config file(s) to use. Useful for debugging "
+                             "the resolution on a given server or with a given set of config files",
+                        action="store_true")
     parser.add_argument("--non-interactive",
                         help="Don't output things like progress bars that rely on being in a terminal or similar. "
                              "Equivalent to setting environment variable PIM_NON_INT=1",
@@ -192,6 +196,21 @@ def run_command(self, pipeline, opts):
         )
     else:
         override_local = {}
+
+    if opts.trace_config:
+        # Trace the loading of local config files
+        if opts.override_local_config is not None:
+            print("Using some local config overrides from command line: {}".format(
+                ", ".join(opts.override_local_config)))
+        if opts.local_config:
+            print("Using local config source given on command line: {}".format(opts.local_config))
+
+        # Run the usual LC loading routine that the pipeline config loader uses
+        for l, line in enumerate(
+                PipelineConfig.trace_load_local_config(filename=opts.local_config, override=override_local)):
+            print("{}: {}".format(l, line))
+        sys.exit(0)
+
     if opts.processes is not None:
         # Override the processes local config setting
         override_local["processes"] = opts.processes

src/python/pimlico/core/config.py

@@ -1151,6 +1151,67 @@ def _load_config_file(fn):
 
         return local_config_data, used_config_sources
 
+    @staticmethod
+    def trace_load_local_config(filename=None, override={}, only_override=False):
+        """
+        Trace the process of loading local config file(s). Follows exactly the same logic
+        as load_local_config(), but documents what it finds/doesn't find.
+
+        """
+        # Keep a record of where we got config from, for debugging purposes
+        config_sources = []
+
+        if only_override:
+            config_sources.append("Using only the overriden LC settings")
+        else:
+            if filename is None:
+                home_dir = os.path.expanduser("~")
+                # Use the default locations for local config file
+                # First, look for the basic config
+                # If other config files are found below, we don't complain about this not existing,
+                # but usually it must exist: we will complain below if nothing else is found
+                basic_config_filename = os.path.join(home_dir, ".pimlico")
+                if os.path.exists(basic_config_filename):
+                    config_sources.append("Basic config in home dir: {}".format(basic_config_filename))
+
+                # Allow other files to override the settings in this basic one
+                # Look for any files matching the pattern .pimlico_*
+
+                # You may specify config files for specific hosts
+                hostname = gethostname()
+                if hostname is not None and len(hostname) > 0:
+                    alt_config_files = [f for f in os.listdir(home_dir) if f.startswith(".pimlico_")]
+                    found_already = False
+                    for alt_config_filename in alt_config_files:
+                        suffix = alt_config_filename[9:]
+                        if hostname == suffix:
+                            # Our hostname matches a hostname-specific config file .pimlico_<hostname>
+                            if found_already:
+                                config_sources.append("Host-specific config file {} matches, but won't be used, as "
+                                                      "another match has already been found".format(alt_config_filename))
+                            else:
+                                config_sources.append("Hostname ({}) matches host-specific config file: {}".format(
+                                    hostname, alt_config_filename
+                                ))
+                                # Only allow one host-specific config file
+                                found_already = True
+                        elif suffix.endswith("-") and hostname.startswith(suffix[:-1]):
+                            # Hostname match hostname-prefix-specific config file .pimlico_<hostname_prefix>-
+                            if found_already:
+                                config_sources.append("Host-specific config file {} matches, but won't be used, as "
+                                                      "another match has already been found".format(alt_config_filename))
+                            else:
+                                config_sources.append("Hostname ({}) matches host-prefix-specific config file: {}".format(
+                                    hostname, alt_config_filename
+                                ))
+                                found_already = True
+                        else:
+                            config_sources.append("Config file {} does not match the hostname ({})".format(
+                                alt_config_filename, hostname))
+            else:
+                config_sources.append("Using giving local config filename: {}".format(filename))
+        return config_sources
+
     @staticmethod
     def empty(local_config=None, override_local_config={}, override_pipeline_config={}, only_override_config=False):
         """