Add entry_points for modifying a hab config when being flattened

- `hab.cfg.reduce.env` is run after the global env is finalized but before aliases.
- `hab.cfg.reduce.aliases` is run after aliases are finalized.

This should allow you to modify global env vars that are then modified
by aliases as well as let you modify aliases after being resolved.

README.md

@@ -438,6 +438,8 @@ for details on each item.
 | [Group][tt-group] | Description | [\*\*kwargs][tt-kwargs] | [Return][tt-return] | [Multiple][tt-multi] |
 |---|---|---|---|---|
 | hab.cli | Used by the hab cli to add extra commands. This is expected to be a `click.command` or `click.group` decorated function. |  |  | [All][tt-multi-all] |
+| hab.cfg.reduce.env | Used to make any modifications to a config after the global env is resolved but before aliases are resolved. | `cfg` |  | [All][tt-multi-all] |
+| hab.cfg.reduce.finalize | Used to make any modifications to a config after aliases are resolved and just before the the config finishes reducing. | `cfg` |  | [All][tt-multi-all] |
 | hab.launch_cls | Used as the default `cls` by `hab.parsers.Config.launch()` to launch aliases from inside of python. This should be a subclass of subprocess.Popen. A [complex alias](#complex-aliases) may override this per alias. Defaults to [`hab.launcher.Launcher`](hab/launcher.py). [Example](tests/site/site_entry_point_a.json) |  |  | [First][tt-multi-first] |
 | hab.uri.validate | Used to validate and modify a URI. If the URI is invalid, this should raise an exception. If the URI should be modified, then return the modified URI as a string. | `resolver`, `uri` | Updated URI as string or None. | [All][tt-multi-all] |
 

hab/parsers/flat_config.py

@@ -35,6 +35,9 @@ def _finalize_values(self):
         # This call ensures that `self.frozen_data["environment"]` is populated.
         self.environment
 
+        # Run any configured entry_points before aliases are calculated
+        self.resolver.site.run_entry_points_for_group("hab.cfg.reduce.env", cfg=self)
+
         # Process version aliases, merging global env vars.
         platform_aliases = {}
         self.frozen_data["aliases"] = platform_aliases
@@ -44,6 +47,11 @@ def _finalize_values(self):
             ):
                 platform_aliases.setdefault(platform, {})[alias] = data
 
+        # Run any configured entry_points before finishing
+        self.resolver.site.run_entry_points_for_group(
+            "hab.cfg.reduce.finalize", cfg=self
+        )
+
     def _process_version(self, version, existing=None):
         """Generator that yields each finalized alias definition dictionary
         to be stored in the frozen_data for aliases.

hab/site.py

@@ -1,10 +1,13 @@
+import logging
 import os
 from collections import UserDict
 from pathlib import Path, PurePosixPath, PureWindowsPath
 
 from . import utils
 from .merge_dict import MergeDict
 
+logger = logging.getLogger(__name__)
+
 
 class Site(UserDict):
     """Provides site configuration to hab.
@@ -184,6 +187,28 @@ def platform_path_map(self, path, platform=None):
 
         return str(path)
 
+    def run_entry_points_for_group(
+        self, group, default=None, entry_points=None, **kwargs
+    ):
+        """Iterates over `entry_points_for_group` calling the resolved object.
+
+        Args:
+            group (str): The name of the group of entry_points to process.
+            default (dict, optional): If the entry_point is not defined, return
+                the entry points defined by this dictionary. This is the contents
+                of the entry_points group, not the entire entry_points dict. For
+                example: `{"gui": "hab_gui.cli:gui"}`
+            entry_points (dict, optional): Use this dictionary instead of the one
+                defined on this Site object.
+            **kwargs: Any other kwargs are passed to the loaded entry_point record.
+        """
+        for ep in self.entry_points_for_group(
+            group, default=default, entry_points=entry_points
+        ):
+            logger.debug(f"Running {group} entry_point: {ep}")
+            func = ep.load()
+            func(**kwargs)
+
     def standardize_platform_path_maps(self):
         """Ensure the mappings defined in platform_path_maps are converted to
         the correct PurePath classes."""

tests/hab_test_entry_points.py

@@ -9,6 +9,22 @@ def gui_alt():
     raise NotImplementedError("hab_test_entry_points.gui_alt called successfully")
 
 
+def cfg_reduce_env(cfg):
+    """Used to test that an entry point is called by raising an exception when
+    called. See `tests/site/eps/README.md` for details."""
+    raise NotImplementedError(
+        "hab_test_entry_points.cfg_reduce_env called successfully"
+    )
+
+
+def cfg_reduce_finalize(cfg):
+    """Used to test that an entry point is called by raising an exception when
+    called. See `tests/site/eps/README.md` for details."""
+    raise NotImplementedError(
+        "hab_test_entry_points.cfg_reduce_finalize called successfully"
+    )
+
+
 def uri_validate_error(resolver, uri):
     """Used to test that an entry point is called by raising an exception when
     called. See `tests/site/eps/README.md` for details."""

tests/site/eps/cfg_reduce_env.json

@@ -0,0 +1,9 @@
+{
+    "append": {
+        "entry_points": {
+            "hab.cfg.reduce.env": {
+                "a": "hab_test_entry_points:cfg_reduce_env"
+            }
+        }
+    }
+}

tests/site/eps/cfg_reduce_finalize.json

@@ -0,0 +1,9 @@
+{
+    "append": {
+        "entry_points": {
+            "hab.cfg.reduce.finalize": {
+                "a": "hab_test_entry_points:cfg_reduce_finalize"
+            }
+        }
+    }
+}

tests/test_site.py

@@ -522,6 +522,14 @@ def test_site_cli(self, config_root, site_files, import_name, fname):
     @pytest.mark.parametrize(
         "site_file,except_match",
         (
+            (
+                "cfg_reduce_env.json",
+                "hab_test_entry_points.cfg_reduce_env called successfully",
+            ),
+            (
+                "cfg_reduce_finalize.json",
+                "hab_test_entry_points.cfg_reduce_finalize called successfully",
+            ),
             (
                 "cfg_uri_validate.json",
                 "hab_test_entry_points.uri_validate_error called successfully",