Track component initialisations for error messages

CHANGES.md

@@ -5,6 +5,7 @@
 -----------------------
 
 - batou migrate now writes .batou.json with a newline at the end as `pre-commit` hooks expect (usually).
+- Unused Components, that is, Components that are initialized, but not used in the deployment, are now reported as warnings.
 
 
 ## 2.5.0b2 (2024-05-15)

src/batou/__init__.py

@@ -473,6 +473,37 @@ def report(self):
             )
 
 
+class UnusedComponentsInitialized(ConfigurationError):
+    """Some components were initialized but never used."""
+
+    sort_key = (5, "unused")
+
+    @classmethod
+    def from_context(cls, components, root):
+        self = cls()
+        self.unused_components = []
+        self.breadcrumbs = []
+        for component in components:
+            self.unused_components.append(repr(component.__class__.__name__))
+            self.breadcrumbs.append(component._init_breadcrumbs)
+        self.root_name = root.name
+        return self
+
+    def __str__(self):
+        out_str = "Unused components: "
+        for i, component in enumerate(self.unused_components):
+            out_str += f"\n    {component}: {' -> '.join(self.breadcrumbs[i])}"
+        return out_str
+
+    def report(self):
+        output.error(f"Unused components:")
+        for i, component in enumerate(self.unused_components):
+            output.line(
+                f"    {component}: {' -> '.join(self.breadcrumbs[i])}", red=True
+            )
+        output.tabular("Root", self.root_name, red=True)
+
+
 class UnsatisfiedResources(ConfigurationError):
     """Some required resources were never provided."""
 

src/batou/component.py

@@ -7,6 +7,7 @@
 import sys
 import types
 import weakref
+from typing import List
 
 import batou
 import batou.c
@@ -146,6 +147,13 @@ class Component(object):
     #: working directory to this.
     workdir: str = None
 
+    #: A list of all component instances that have been created. When
+    #: a component is created (__init__) it is added to this list.
+    #: After the configuration phase, this list is checked for
+    #: components that have component._prepared == False and
+    #: warns about them.
+    instances: List["Component"] = []
+
     @property
     def defdir(self):
         """(*readonly*) The definition directory
@@ -188,6 +196,30 @@ def root(self):
     _prepared = False
 
     def __init__(self, namevar=None, **kw):
+        init_stack = inspect.stack()
+        init_stack.reverse()
+        init_breadcrumbs = []
+        for frame in init_stack:
+            if (
+                "self" in frame.frame.f_locals
+                and isinstance(frame.frame.f_locals["self"], Component)
+                and frame.frame.f_code.co_name == "configure"
+            ):
+                component = frame.frame.f_locals["self"]
+                try:
+                    init_breadcrumbs.append(component._breadcrumb)
+                except AttributeError:
+                    # some ._breadcrumb are broken
+                    breadcrumb = component.__class__.__name__
+                    if component.namevar:
+                        breadcrumb += (
+                            f"({getattr(component, component.namevar, None)})"
+                        )
+                    init_breadcrumbs.append(breadcrumb)
+
+        self._init_breadcrumbs = init_breadcrumbs
+
+        Component.instances.append(self)
         self.timer = batou.utils.Timer(self.__class__.__name__)
         # Are any keyword arguments undefined attributes?
         # This is a somewhat rough implementation as it allows overriding

src/batou/environment.py

@@ -28,10 +28,11 @@
     SuperfluousSection,
     UnknownComponentConfigurationError,
     UnsatisfiedResources,
+    UnusedComponentsInitialized,
     UnusedResources,
 )
 from batou._output import output
-from batou.component import ComponentDefinition, RootComponent
+from batou.component import Component, ComponentDefinition, RootComponent
 from batou.provision import Provisioner
 from batou.repository import Repository
 from batou.utils import CycleError, cmd
@@ -497,6 +498,7 @@ def configure(self):
 
             for root in working_set:
                 try:
+                    Component.instances.clear()
                     self.resources.reset_component_resources(root)
                     root.overrides = self.overrides.get(root.name, {})
                     root.prepare()
@@ -516,6 +518,19 @@ def configure(self):
                         )
                     )
                 else:
+                    unprepared_components = []
+                    for component in Component.instances:
+                        if not component._prepared:
+                            unprepared_components.append(component)
+                    if unprepared_components:
+                        # TODO: activate in future
+                        unused_exception = (
+                            UnusedComponentsInitialized.from_context(
+                                unprepared_components, root
+                            )
+                        )
+                        # exceptions.append(unused_exception)
+                        output.warn(str(unused_exception))
                     # configured this component successfully
                     # we won't have to retry it later
                     continue

src/batou/remote_core.py

@@ -107,6 +107,12 @@ def error(self, message, exc_info=None, debug=False):
             out = "      " + out.replace("\n", "\n      ") + "\n"
             self.backend.write(out, red=True)
 
+    def warn(self, message, debug=False):
+        if debug and not self.enable_debug:
+            return
+        self.flush_buffer()
+        self.step("WARN", message, yellow=True)
+
 
 class ChannelBackend(object):
     def __init__(self, channel):

src/batou/tests/fixture/sample_service/components/hello/component.py

@@ -62,3 +62,12 @@ def configure(self):
 class Sub(Component):
     def configure(self):
         self.log("Sub!")
+
+
+class Unused(Component):
+    pass
+
+
+class BadUnused(Component):
+    def configure(self):
+        Unused()

src/batou/tests/fixture/sample_service/environments/test-unused/environment.cfg

@@ -0,0 +1,5 @@
+[environment]
+connect_method = local
+
+[hosts]
+localhost = badunused

src/batou/tests/test_environment.py

@@ -4,6 +4,7 @@
 
 import batou
 import batou.utils
+from batou.component import Component, RootComponent
 from batou.environment import Config, Environment
 from batou.host import Host
 
@@ -331,3 +332,13 @@ def test_resolver_overrides_invalid_address(sample_service):
     errors = e.configure()
     assert len(errors) == 1
     assert "thisisinvalid" == errors[0].address
+
+
+def test_unused_components_get_reported(sample_service, output):
+    e = Environment("test-unused")
+    e.load()
+
+    output.backend.output = ""
+    e.configure()
+
+    assert "'Unused': BadUnused" in output.backend.output