Add omittable_distros support for configs

Author: MHendricks

README.md

@@ -1286,6 +1286,32 @@ the `-r`/`--requirement` option.
 Users can see the optional distros in the dump output with verbosity level of 1
 or higher. `hab dump - -v`
 
+### Omittable Distros
+
+The `omittable_distros` key in [config](#config) definitions are used to specify distros
+that are not required to use this hab configuration. This can be used to make it
+so not all hosts need to have a dcc installed. For example a producer likely will
+never need to open houdini but does need access to external tools. You would need
+to install Houdini(or create a empty .hab.json distro) so hab doesn't raise an
+`InvalidRequirementError` when it can't find Houdini.
+
+```json5
+    "distros": [
+        "houdini20.0==20.0.688",
+        "SideFXLabs20.0==20.0.506",
+        "python_tools"
+    ],
+    "omittable_distros": [
+        "houdini20.0",
+        "SideFXLabs20.0"
+    ]
+```
+This will make it so `houdini20.0` and `SideFXLabs20.0` will be loaded if found,
+but if not they will be ignored. `python_tools` will always need to be installed.
+
+Note: `omittable_distros` is a list of distro names. It does not accept specifier
+arguments like `==20.0.688`.
+
 ### Platform specific code
 
 Hab works on windows, linux and osx(needs tested). To make it easier to handle

hab/parsers/config.py

@@ -129,8 +129,19 @@ def load(self, filename):
         data = super().load(filename)
         self._alias_mods = data.get("alias_mods", NotSet)
         self.inherits = data.get("inherits", NotSet)
+        if self.omittable_distros is NotSet:
+            self.omittable_distros = data.get("omittable_distros", NotSet)
         return data
 
+    @hab_property(verbosity=3, process_order=50)
+    def omittable_distros(self):
+        """A collection of distro names that are ignored if required by distros."""
+        return self.frozen_data.get("omittable_distros", NotSet)
+
+    @omittable_distros.setter
+    def omittable_distros(self, value):
+        self.frozen_data["omittable_distros"] = value
+
     @hab_property(verbosity=1, group=0)
     def uri(self):
         # Mark uri as a HabProperty so it is included in _properties

hab/parsers/flat_config.py

@@ -223,7 +223,9 @@ def versions(self):
                 self._alias_mods = {}
             self.frozen_data["versions"] = versions
 
-            reqs = self.resolver.resolve_requirements(distros)
+            reqs = self.resolver.resolve_requirements(
+                distros, omittable=self.omittable_distros
+            )
             for req in reqs.values():
                 version = self.resolver.find_distro(req)
                 versions.append(version)

hab/resolver.py

@@ -356,18 +356,23 @@ def resolve(self, uri, forced_requirements=None):
             if forced_requirements is not None:
                 self.forced_requirements = current
 
-    def resolve_requirements(self, requirements):
+    def resolve_requirements(self, requirements, omittable=None):
         """Recursively solve the provided requirements into a final list of requirements.
 
         Args:
             requirements (list): The requirements to resolve.
+            omittable (list, optional): A list of distro names that are not required.
+                If a suitable distro can not be found, normally an `InvalidRequirementError`
+                is raised. If that distro name is in this list a warning is logged instead.
 
         Raises:
             MaxRedirectError: Redirect limit reached, unable to resolve the requested
                 requirements.
         """
 
-        solver = Solver(requirements, self, forced=self.forced_requirements)
+        solver = Solver(
+            requirements, self, forced=self.forced_requirements, omittable=omittable
+        )
         return solver.resolve()
 
     def uri_validate(self, uri):

hab/solvers.py

@@ -18,14 +18,18 @@ class Solver(object):
         forced (dict, optional): Forces this distro requirement replacing any resolved
             requirements. Using this may lead to configuring your environment
             incorrectly, use with caution.
+        omittable (list, optional): A list of distro names that are not required.
+            If a suitable distro can not be found, normally an `InvalidRequirementError`
+            is raised. If that distro name is in this list a warning is logged instead.
 
     Attributes:
         invalid (dict, optional): If a recursive requirement makes a already resolved
             version invalid, that version is added to this list as an exclusive exclude.
     """
 
-    def __init__(self, requirements, resolver, forced=None):
+    def __init__(self, requirements, resolver, forced=None, omittable=None):
         self.forced = forced if forced else {}
+        self.omittable = omittable if omittable else []
         self.invalid = {}
         self.max_redirects = 2
         self.requirements = requirements
@@ -126,6 +130,10 @@ def _resolve(
                 logger.warning(f"Forced Requirement: {req}")
                 reported.add(name)
 
+            if name in self.omittable and name not in self.resolver.distros:
+                logger.warning(f"Skipping missing omitted requirement: {req}")
+                continue
+
             # Update the requirement to match all current requirements
             req = self.append_requirement(resolved, req)
             if name in self.invalid:

tests/site_omit/README.md

@@ -0,0 +1,10 @@
+This is a isolated site configuration specifically for testing omittable_distros.
+This allows for custom configuration of the default config without affecting other tests.
+
+* The [default](configs/default.json) config defines `omittable_distros` that can be
+inherited by other distros. It lists two distros that do not exist for this site.
+* [omittable/defined](omittable/defined.json) defines `omittable_distros` replacing it with a modified
+list of distros to omit for this URI and its children.
+* [omittable/inherited](omittable/inherited.json) does not define the `omittable_distros` and inherits
+from its parents which aren't defined so it finally inherits the value defined
+in the  `default` config.

tests/site_omit/configs/default.json

@@ -0,0 +1,20 @@
+{
+    "name": "default",
+    "context": [],
+    "inherits": false,
+    "distros": {
+        "maya2020": [
+            "the_dcc_plugin_a",
+            "the_dcc_plugin_b",
+            "the_dcc_plugin_c"
+        ],
+        "houdini19.5": [
+            "the_dcc_plugin_d"
+        ]
+    },
+    "omittable_distros": [
+        "missing_dcc",
+        "non-existent-distro",
+        "the_dcc_plugin_b"
+    ]
+}

tests/site_omit/configs/omittable_defined.json

@@ -0,0 +1,25 @@
+{
+    "name": "defined",
+    "context": ["omittable"],
+    "description": "This config defines omittable_distros and will ignore the default.",
+    "inherits": true,
+    "distros": {
+        "maya2020": [
+            "the_dcc_plugin_a",
+            "the_dcc_plugin_b",
+            "the_dcc_plugin_c"
+        ],
+        "houdini19.5": [
+            "the_dcc_plugin_d"
+        ],
+        "missing_dcc": [
+            "the_dcc_plugin_d",
+            "non-existent-distro"
+        ]
+    },
+    "omittable_distros": [
+        "houdini19.5",
+        "missing_dcc",
+        "non-existent-distro"
+    ]
+}

tests/site_omit/configs/omittable_inherited.json

@@ -0,0 +1,16 @@
+{
+    "name": "inherited",
+    "context": ["omittable"],
+    "description": "This config doesn't define omittable_distros and will inherit from default.",
+    "inherits": true,
+    "distros": {
+        "maya2020": [
+            "the_dcc_plugin_a",
+            "the_dcc_plugin_b"
+        ],
+        "missing_dcc": [
+            "the_dcc_plugin_d",
+            "non-existent-distro"
+        ]
+    }
+}

tests/site_omit/configs/omittable_invalid.json

@@ -0,0 +1,24 @@
+{
+    "name": "invalid",
+    "context": ["omittable"],
+    "description": "This config doesn't mark the distro missing_dcc as omittable_distros and will cause an InvalidRequirementError.",
+    "inherits": true,
+    "distros": {
+        "maya2020": [
+            "the_dcc_plugin_a",
+            "the_dcc_plugin_b",
+            "the_dcc_plugin_c"
+        ],
+        "houdini19.5": [
+            "the_dcc_plugin_d"
+        ],
+        "missing_dcc": [
+            "the_dcc_plugin_d",
+            "non-existent-distro"
+        ]
+    },
+    "omittable_distros": [
+        "houdini19.5",
+        "non-existent-distro"
+    ]
+}