Implement "onchange" support

"onchange" specifies execution prerequisites. It is specified in the same way
as "require", it implies "require", but it specifies that object is executed
only if any of specified prerequisites has changed target's state. This means
that any of specified prerequisites has generated code to be executed, either
local or remote or both.

Object has generated code if it itself has generated code or if any of its
children object has generated code.

Resolve #843.

cdist/config.py

@@ -788,11 +788,14 @@ class Config:
 
     def object_prepare(self, cdist_object, transfer_type_explorers=True):
         """Prepare object: Run type explorer + manifest"""
+
+        if cdist_object.processing_preconditions_satisfied():
             self._handle_deprecation(cdist_object)
             self.log.verbose("Preparing object %s", cdist_object.name)
             self.log.verbose("Running manifest and explorers for %s",
                              cdist_object.name)
-        self.explorer.run_type_explorers(cdist_object, transfer_type_explorers)
+            self.explorer.run_type_explorers(cdist_object,
+                                             transfer_type_explorers)
             try:
                 self.manifest.run_type_manifest(cdist_object)
                 self.log.trace("[ORDER_DEP] Removing order dep files for %s",
@@ -801,6 +804,15 @@ class Config:
                 cdist_object.state = core.CdistObject.STATE_PREPARED
             except cdist.Error as e:
                 raise cdist.CdistObjectError(cdist_object, e)
+        else:
+            cdist_object.state = core.CdistObject.STATE_DONE
+            cdist_object.skipped = True
+            cdist_object.skipped_reason = (
+                "Processing preconditions not satisfied for object {0}: {1}, "
+                "skipping {0} object processing".format(
+                    cdist_object.name, cdist_object.processing_preconditions)
+            )
+            self.log.verbose(cdist_object.skipped_reason)
 
     def object_run(self, cdist_object):
         """Run gencode and code for an object"""
@@ -817,9 +829,12 @@ class Config:
                 cdist_object)
             if cdist_object.code_local or cdist_object.code_remote:
                 cdist_object.changed = True
+                cdist_object.code_generated = True
+            else:
+                cdist_object.changed = False
 
             # Execute
-            if cdist_object.code_local or cdist_object.code_remote:
+            if cdist_object.changed:
                 self.log.info("Processing %s", cdist_object.name)
             if not self.dry_run:
                 if cdist_object.code_local:

cdist/core/cdist_object.py

@@ -229,6 +229,8 @@ class CdistObject:
 
     requirements = fsproperty.FileListProperty(
             lambda obj: os.path.join(obj.absolute_path, 'require'))
+    processing_preconditions = fsproperty.FileListProperty(
+            lambda obj: os.path.join(obj.absolute_path, 'onchange'))
     autorequire = fsproperty.FileListProperty(
             lambda obj: os.path.join(obj.absolute_path, 'autorequire'))
     parameters = fsproperty.DirectoryDictProperty(
@@ -254,6 +256,12 @@ class CdistObject:
     # types
     children = fsproperty.FileListProperty(
             lambda obj: os.path.join(obj.absolute_path, 'children'))
+    code_generated = fsproperty.FileBooleanProperty(
+            lambda obj: os.path.join(obj.absolute_path, "code_generated"))
+    skipped = fsproperty.FileBooleanProperty(
+            lambda obj: os.path.join(obj.absolute_path, "skipped"))
+    skipped_reason = fsproperty.FileStringProperty(
+            lambda obj: os.path.join(obj.absolute_path, "skipped_reason"))
 
     def cleanup(self):
         try:
@@ -291,3 +299,24 @@ class CdistObject:
                 object_list.append(cdist_object)
 
         return object_list
+
+    def _processing_preconditions_satisfied_dfs(self, current):
+        # DFS (depth first search) for type that generated code.
+        obj = self.object_from_name(current)
+        if obj.code_generated:
+            return True
+        # As soon as one child that generated code is found, result with True.
+        for child in obj.children:
+            rv = self._processing_preconditions_satisfied_dfs(child)
+            if rv:
+                return True
+        return False
+
+    def processing_preconditions_satisfied(self):
+        """Return state whether processing preconditions are satisfied"""
+
+        for onchange in self.processing_preconditions:
+            if self._processing_preconditions_satisfied_dfs(onchange):
+                return True
+
+        return len(self.processing_preconditions) == 0

cdist/emulator.py

@@ -104,7 +104,7 @@ class Emulator:
         with flock.Flock(self.flock_path):
             self.setup_object()
             self.save_stdin()
-            self.record_requirements()
+            self.record_requirements_and_processing_preconditions()
             self.record_auto_requirements()
             self.record_parent_child_relationships()
             self.log.trace("Finished %s %s", self.cdist_object.path,
@@ -294,30 +294,43 @@ class Emulator:
             except EnvironmentError as e:
                 raise cdist.Error('Failed to read from stdin: {}'.format(e))
 
-    def record_requirement(self, requirement):
-        """record requirement and return recorded requirement"""
+    def _record_dep(self, object_name, attr_name, msg):
+        """
+        Record dependency for attr_name and return recorded value.
+        """
 
         # Raises an error, if object cannot be created
         try:
-            cdist_object = self.cdist_object.object_from_name(requirement)
+            cdist_object = self.cdist_object.object_from_name(object_name)
         except core.cdist_type.InvalidTypeError as e:
-            self.log.error("%s requires object %s, but type %s does not"
-                           " exist. Defined at %s", self.cdist_object.name,
-                           requirement, e.name, self.object_source)
+            self.log.error("%s %s object %s, but type %s does not exist."
+                           " Defined at %s", msg, self.cdist_object.name,
+                           object_name, e.name, self.object_source)
             raise
         except core.cdist_object.MissingObjectIdError:
-            self.log.error("%s requires object %s without object id."
-                           " Defined at %s", self.cdist_object.name,
-                           requirement, self.object_source)
+            self.log.error("%s %s object %s without object id. Defined at %s",
+                           self.cdist_object.name, msg, object_name,
+                           self.object_source)
             raise
 
-        self.log.debug("Recording requirement %s for %s",
-                       requirement, self.cdist_object.name)
+        self.log.debug("Recording %s in %s for %s",
+                       object_name, attr_name, self.cdist_object.name)
 
         # Save the sanitised version, not the user supplied one
         # (__file//bar => __file/bar)
         # This ensures pattern matching is done against sanitised list
-        self.cdist_object.requirements.append(cdist_object.name)
+        attr_list = getattr(self.cdist_object, attr_name)
+        if cdist_object.name not in attr_list:
+            attr_list.append(cdist_object.name)
+
+    def _record_requirement(self, requirement):
+        """record requirement and return recorded requirement"""
+        self._record_dep(requirement, 'requirements', 'requires')
+
+    def _record_processing_precondition(self, onchange):
+        """record processing precondition and return t"""
+        self._record_dep(onchange, 'processing_preconditions',
+                         'has processing precondition')
 
     def _order_dep_on(self):
         return os.path.exists(self.order_dep_state_path)
@@ -351,8 +364,25 @@ class Emulator:
         except FileNotFoundError:
             return []
 
-    def record_requirements(self):
-        """Record requirements."""
+    def _inject_dependency(self, lastcreatedtype, dep_var):
+        if dep_var in self.env:
+            if lastcreatedtype not in self.env[dep_var]:
+                self.env[dep_var] += " " + lastcreatedtype
+        else:
+            self.env[dep_var] = lastcreatedtype
+
+    def _process_dep_var(self, func, dep_var):
+        if dep_var in self.env:
+            objects = self.env[dep_var]
+            self.log.debug("reqs for %s = %s", dep_var, objects)
+            for requirement in self._parse_require(objects):
+                # Ignore empty fields - probably the only field anyway
+                if len(requirement) == 0:
+                    continue
+                func(requirement)
+
+    def record_requirements_and_processing_preconditions(self):
+        """Record requirements and processing precondition."""
 
         order_dep_on = self._order_dep_on()
 
@@ -373,27 +403,23 @@ class Emulator:
                     typeorder = self._read_typeorder_dep()
                 # get the type created before this one
                 lastcreatedtype = typeorder[-2].strip()
-                if 'require' in self.env:
-                    if lastcreatedtype not in self.env['require']:
-                        self.env['require'] += " " + lastcreatedtype
-                else:
-                    self.env['require'] = lastcreatedtype
-                self.log.debug("Injecting require for"
-                               " CDIST_ORDER_DEPENDENCY: %s for %s",
-                               lastcreatedtype, self.cdist_object.name)
+                self.log.debug(("Injecting require for "
+                                "CDIST_ORDER_DEPENDENCY: %s for %s"),
+                               lastcreatedtype,
+                               self.cdist_object.name)
+                self._inject_dependency(lastcreatedtype, 'require')
             except IndexError:
                 # if no second last line, we are on the first type,
                 # so do not set a requirement
                 pass
 
-        if "require" in self.env:
-            requirements = self.env['require']
-            self.log.debug("reqs = %s", requirements)
-            for requirement in self._parse_require(requirements):
-                # Ignore empty fields - probably the only field anyway
-                if len(requirement) == 0:
-                    continue
-                self.record_requirement(requirement)
+        self._process_dep_var(func=self._record_requirement,
+                              dep_var='require')
+        # onchange implies require
+        self._process_dep_var(func=self._record_requirement,
+                              dep_var='onchange')
+        self._process_dep_var(func=self._record_processing_precondition,
+                              dep_var='onchange')
 
     def _parse_require(self, require):
         return re.split(r'[ \t\n]+', require)

cdist/test/emulator/__init__.py

@@ -207,6 +207,40 @@ class EmulatorTestCase(test.CdistTestCase):
                     self.assertTrue(len(reqs) == 0)
         # if we get here all is fine
 
+    def test_onchange(self):
+        argv = ['__planet', 'erde']
+        emu = emulator.Emulator(argv, env=self.env)
+        emu.run()
+        argv = ['__planet', 'mars']
+        emu = emulator.Emulator(argv, env=self.env)
+        emu.run()
+        self.env['onchange'] = '__planet/erde __planet/mars'
+        argv = ['__file', '/tmp/cdisttest']
+        emu = emulator.Emulator(argv, env=self.env)
+        emu.run()
+        # now load the objects and verify the require parameter of the objects
+        cdist_type = core.CdistType(self.local.type_path, '__planet')
+        erde_object = core.CdistObject(cdist_type, self.local.object_path,
+                                       self.local.object_marker_name, 'erde')
+        mars_object = core.CdistObject(cdist_type, self.local.object_path,
+                                       self.local.object_marker_name, 'mars')
+        cdist_type = core.CdistType(self.local.type_path, '__file')
+        file_object = core.CdistObject(cdist_type, self.local.object_path,
+                                       self.local.object_marker_name,
+                                       '/tmp/cdisttest')
+        # now test the recorded exec prerequisites and requirements
+        self.assertTrue(len(erde_object.requirements) == 0)
+        self.assertTrue(len(mars_object.requirements) == 0)
+        self.assertTrue(len(file_object.requirements) > 0)
+        self.assertTrue(len(erde_object.processing_preconditions) == 0)
+        self.assertTrue(len(mars_object.processing_preconditions) == 0)
+        self.assertTrue(len(file_object.processing_preconditions) > 0)
+        self.assertEqual(list(file_object.requirements),
+                         ['__planet/erde', '__planet/mars'])
+        self.assertEqual(list(file_object.processing_preconditions),
+                         ['__planet/erde', '__planet/mars'])
+        # if we get here all is fine
+
 
 class EmulatorConflictingRequirementsTestCase(test.CdistTestCase):
 

docs/src/cdist-manifest.rst

@@ -154,6 +154,16 @@ You can find a more in depth description of the flow execution of manifests
 in `cdist execution stages <cdist-stages.html>`_ and of how types work in `cdist type <cdist-type.html>`_.
 
 
+Processing preconditions
+------------------------
+If you want to describe that something should be processed only if specified
+objects changed target's state, i.e. specified objects generated either
+"code-local" or "code-remote", or both, just setup the variable "onchange" to
+contain processing preconditions. "onchange" is specified in the same way as
+"require", and it implies "require". If processing preconditions are not
+satisfied then it means that object's explorers are not run, manifest is not
+run, and gencode scripts are not run. Object processing is skipped.
+
 Create dependencies from execution order
 -----------------------------------------
 You can tell cdist to execute all types in the order in which they are created 
@@ -375,3 +385,13 @@ Dependencies defined by execution order work as following:
     require="__some_type_somewhere/id __sample_type/1" __sample_type 2
     require="__sample_type/2" __example_type 23
     __not_in_order_type 42
+
+This example makes use of processing preconditions:
+
+.. code-block:: sh
+
+    __foo bar
+    __spam eggs
+    # execute __baz type only if any of __foo/bar, __spam/eggs has changed
+    # target's state, i.e. code-local or code-remote is generated (or both)
+    onchange='__foo/bar __spam/eggs' __baz

docs/src/cdist-reference.rst.sh

@@ -314,6 +314,9 @@ The following environment variables influence the behaviour of cdist:
 require
     Setup dependencies between objects (see \`cdist manifest <cdist-manifest.html>\`_).
 
+onchange
+    Setup processing preconditions (implies dependencies) between objects (see `cdist manifest <cdist-manifest.html>`_).
+
 __cdist_log_level
     cdist log level value. One of: