Feature: distinct Composition and Aggregation arrows (#7836)

* Update Linker to add aggregations_type and associations_type to nodes

Update logic of nodes to check what kind of relationship does nodes have (association, aggregation)

Signed-off-by: Alvaro Frias Garay <alvaro.frias@eclypsium.com>

* Update ClassDiagram's extrac_relationship method to add aggregations links

Signed-off-by: Alvaro Frias Garay <alvaro.frias@eclypsium.com>

* Update DiagramWriter to generate AGGREGATION edges

Signed-off-by: Alvaro Frias Garay <alvaro.frias@eclypsium.com>

* Update printers to show aggregations

Signed-off-by: Alvaro Frias Garay <alvaro.frias@eclypsium.com>

* Update tests with changes on aggregations

Signed-off-by: Alvaro Frias Garay <alvaro.frias@eclypsium.com>

* Update Linker to add aggregations_type and associations_type to nodes

Update logic of nodes to check what kind of relationship does nodes have (association, aggregation)

Signed-off-by: Alvaro Frias Garay <alvaro.frias@eclypsium.com>

* Update ClassDiagram's extrac_relationship method to add aggregations links

Signed-off-by: Alvaro Frias Garay <alvaro.frias@eclypsium.com>

* Update DiagramWriter to generate AGGREGATION edges

Signed-off-by: Alvaro Frias Garay <alvaro.frias@eclypsium.com>

* Update tests with changes on aggregations

Signed-off-by: Alvaro Frias Garay <alvaro.frias@eclypsium.com>

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* Apply pylint pre-commit correction

Signed-off-by: Alvaro Frias Garay <alvaro.frias@eclypsium.com>

* Apply mypy corrections

Signed-off-by: Alvaro Frias Garay <alvaro.frias@eclypsium.com>

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* Add towrncrier fragment

Signed-off-by: Alvaro Frias Garay <alvaro.frias@eclypsium.com>

* Update towncrier fragment

Signed-off-by: Alvaro Frias Garay <alvaro.frias@eclypsium.com>

* Update towncrier fragment

Signed-off-by: Alvaro Frias Garay <alvaro.frias@eclypsium.com>

* Update doc/whatsnew/fragments/6543.feature

Co-authored-by: Andreas Finkler <3929834+DudeNr33@users.noreply.github.com>

* Add documentation

Signed-off-by: Alvaro Frias Garay <alvaro.frias@eclypsium.com>

* fix typo

Signed-off-by: Alvaro Frias Garay <alvaro.frias@eclypsium.com>

* Add type hints

Signed-off-by: Alvaro Frias Garay <alvaro.frias@eclypsium.com>

* Update pylint/pyreverse/diagrams.py

Co-authored-by: Daniël van Noord <13665637+DanielNoord@users.noreply.github.com>

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* Update type hints

Signed-off-by: Alvaro Frias Garay <alvaro.frias@eclypsium.com>

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* Update fragment

* Update fragment

Signed-off-by: Alvaro Frias Garay <alvaro.frias@eclypsium.com>
Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: Andreas Finkler <3929834+DudeNr33@users.noreply.github.com>
Co-authored-by: Daniël van Noord <13665637+DanielNoord@users.noreply.github.com>

8 files changed, 115 insertions, 11 deletions

diff --git a/pylint/pyreverse/diagrams.py b/pylint/pyreverse/diagrams.py
index a9dcd1c5e..382d76bf7 100644
--- a/pylint/pyreverse/diagrams.py
+++ b/pylint/pyreverse/diagrams.py
@@ -214,20 +214,35 @@ class ClassDiagram(Figure, FilterMixIn):
                     self.add_relationship(obj, impl_obj, "implements")
                 except KeyError:
                     continue
-            # associations link
-            for name, values in list(node.instance_attrs_type.items()) + list(
+
+            # associations & aggregations links
+            for name, values in list(node.aggregations_type.items()):
+                for value in values:
+                    self.assign_association_relationship(
+                        value, obj, name, "aggregation"
+                    )
+
+            for name, values in list(node.associations_type.items()) + list(
                 node.locals_type.items()
             ):
+
                 for value in values:
-                    if value is astroid.Uninferable:
-                        continue
-                    if isinstance(value, astroid.Instance):
-                        value = value._proxied
-                    try:
-                        associated_obj = self.object_from_node(value)
-                        self.add_relationship(associated_obj, obj, "association", name)
-                    except KeyError:
-                        continue
+                    self.assign_association_relationship(
+                        value, obj, name, "association"
+                    )
+
+    def assign_association_relationship(
+        self, value: astroid.NodeNG, obj: ClassEntity, name: str, type_relationship: str
+    ) -> None:
+        if value is astroid.Uninferable:
+            return
+        if isinstance(value, astroid.Instance):
+            value = value._proxied
+        try:
+            associated_obj = self.object_from_node(value)
+            self.add_relationship(associated_obj, obj, type_relationship, name)
+        except KeyError:
+            return
 
 
 class PackageDiagram(ClassDiagram):
diff --git a/pylint/pyreverse/dot_printer.py b/pylint/pyreverse/dot_printer.py
index 7579d2877..1d5f2c32b 100644
--- a/pylint/pyreverse/dot_printer.py
+++ b/pylint/pyreverse/dot_printer.py
@@ -39,6 +39,12 @@ ARROWS: dict[EdgeType, dict[str, str]] = {
         "arrowhead": "diamond",
         "style": "solid",
     },
+    EdgeType.AGGREGATION: {
+        "fontcolor": "green",
+        "arrowtail": "none",
+        "arrowhead": "odiamond",
+        "style": "solid",
+    },
     EdgeType.USES: {"arrowtail": "none", "arrowhead": "open"},
 }
 
diff --git a/pylint/pyreverse/inspector.py b/pylint/pyreverse/inspector.py
index 042d3845e..8c403ffc6 100644
--- a/pylint/pyreverse/inspector.py
+++ b/pylint/pyreverse/inspector.py
@@ -13,6 +13,7 @@ import collections
 import os
 import traceback
 import warnings
+from abc import ABC, abstractmethod
 from collections.abc import Generator
 from typing import Any, Callable, Optional
 
@@ -123,6 +124,12 @@ class Linker(IdGeneratorMixIn, utils.LocalsVisitor):
     * instance_attrs_type
       as locals_type but for klass member attributes (only on astroid.Class)
 
+    * associations_type
+      as instance_attrs_type but for association relationships
+
+    * aggregations_type
+      as instance_attrs_type but for aggregations relationships
+
     * implements,
       list of implemented interface _objects_ (only on astroid.Class nodes)
     """
@@ -134,6 +141,8 @@ class Linker(IdGeneratorMixIn, utils.LocalsVisitor):
         self.tag = tag
         # visited project
         self.project = project
+        self.associations_handler = AggregationsHandler()
+        self.associations_handler.set_next(OtherAssociationsHandler())
 
     def visit_project(self, node: Project) -> None:
         """Visit a pyreverse.utils.Project node.
@@ -178,9 +187,12 @@ class Linker(IdGeneratorMixIn, utils.LocalsVisitor):
             baseobj.specializations = specializations
         # resolve instance attributes
         node.instance_attrs_type = collections.defaultdict(list)
+        node.aggregations_type = collections.defaultdict(list)
+        node.associations_type = collections.defaultdict(list)
         for assignattrs in tuple(node.instance_attrs.values()):
             for assignattr in assignattrs:
                 if not isinstance(assignattr, nodes.Unknown):
+                    self.associations_handler.handle(assignattr, node)
                     self.handle_assignattr_type(assignattr, node)
         # resolve implemented interface
         try:
@@ -313,6 +325,61 @@ class Linker(IdGeneratorMixIn, utils.LocalsVisitor):
                 mod_paths.append(mod_path)
 
 
+class AssociationHandlerInterface(ABC):
+    @abstractmethod
+    def set_next(
+        self, handler: AssociationHandlerInterface
+    ) -> AssociationHandlerInterface:
+        pass
+
+    @abstractmethod
+    def handle(self, node: nodes.AssignAttr, parent: nodes.ClassDef) -> None:
+        pass
+
+
+class AbstractAssociationHandler(AssociationHandlerInterface):
+    """
+    Chain of Responsibility for handling types of association, useful
+    to expand in the future if we want to add more distinct associations.
+
+    Every link of the chain checks if it's a certain type of association.
+    If no association is found it's set as a generic association in `associations_type`.
+
+    The default chaining behavior is implemented inside the base handler
+    class.
+    """
+
+    _next_handler: AssociationHandlerInterface
+
+    def set_next(
+        self, handler: AssociationHandlerInterface
+    ) -> AssociationHandlerInterface:
+        self._next_handler = handler
+        return handler
+
+    @abstractmethod
+    def handle(self, node: nodes.AssignAttr, parent: nodes.ClassDef) -> None:
+        if self._next_handler:
+            self._next_handler.handle(node, parent)
+
+
+class AggregationsHandler(AbstractAssociationHandler):
+    def handle(self, node: nodes.AssignAttr, parent: nodes.ClassDef) -> None:
+        if isinstance(node.parent.value, astroid.node_classes.Name):
+            current = set(parent.aggregations_type[node.attrname])
+            parent.aggregations_type[node.attrname] = list(
+                current | utils.infer_node(node)
+            )
+        else:
+            super().handle(node, parent)
+
+
+class OtherAssociationsHandler(AbstractAssociationHandler):
+    def handle(self, node: nodes.AssignAttr, parent: nodes.ClassDef) -> None:
+        current = set(parent.associations_type[node.attrname])
+        parent.associations_type[node.attrname] = list(current | utils.infer_node(node))
+
+
 def project_from_files(
     files: list[str],
     func_wrapper: _WrapperFuncT = _astroid_wrapper,
diff --git a/pylint/pyreverse/mermaidjs_printer.py b/pylint/pyreverse/mermaidjs_printer.py
index 07cad97be..a8f3c576b 100644
--- a/pylint/pyreverse/mermaidjs_printer.py
+++ b/pylint/pyreverse/mermaidjs_printer.py
@@ -24,6 +24,7 @@ class MermaidJSPrinter(Printer):
         EdgeType.INHERITS: "--|>",
         EdgeType.IMPLEMENTS: "..|>",
         EdgeType.ASSOCIATION: "--*",
+        EdgeType.AGGREGATION: "--o",
         EdgeType.USES: "-->",
     }
 
diff --git a/pylint/pyreverse/plantuml_printer.py b/pylint/pyreverse/plantuml_printer.py
index f3f639f5c..56463165d 100644
--- a/pylint/pyreverse/plantuml_printer.py
+++ b/pylint/pyreverse/plantuml_printer.py
@@ -24,6 +24,7 @@ class PlantUmlPrinter(Printer):
         EdgeType.INHERITS: "--|>",
         EdgeType.IMPLEMENTS: "..|>",
         EdgeType.ASSOCIATION: "--*",
+        EdgeType.AGGREGATION: "--o",
         EdgeType.USES: "-->",
     }
 
diff --git a/pylint/pyreverse/printer.py b/pylint/pyreverse/printer.py
index 55ce2c8b1..cdbf7e3c8 100644
--- a/pylint/pyreverse/printer.py
+++ b/pylint/pyreverse/printer.py
@@ -25,6 +25,7 @@ class EdgeType(Enum):
     INHERITS = "inherits"
     IMPLEMENTS = "implements"
     ASSOCIATION = "association"
+    AGGREGATION = "aggregation"
     USES = "uses"
 
 
diff --git a/pylint/pyreverse/vcg_printer.py b/pylint/pyreverse/vcg_printer.py
index 6f28a24e8..b9e2e94f3 100644
--- a/pylint/pyreverse/vcg_printer.py
+++ b/pylint/pyreverse/vcg_printer.py
@@ -177,6 +177,11 @@ ARROWS: dict[EdgeType, dict[str, str | int]] = {
         "backarrowstyle": "none",
         "textcolor": "green",
     },
+    EdgeType.AGGREGATION: {
+        "arrowstyle": "solid",
+        "backarrowstyle": "none",
+        "textcolor": "green",
+    },
 }
 ORIENTATION: dict[Layout, str] = {
     Layout.LEFT_TO_RIGHT: "left_to_right",
diff --git a/pylint/pyreverse/writer.py b/pylint/pyreverse/writer.py
index b19286a87..68a49eea1 100644
--- a/pylint/pyreverse/writer.py
+++ b/pylint/pyreverse/writer.py
@@ -120,6 +120,14 @@ class DiagramWriter:
                 label=rel.name,
                 type_=EdgeType.ASSOCIATION,
             )
+        # generate aggregations
+        for rel in diagram.get_relationships("aggregation"):
+            self.printer.emit_edge(
+                rel.from_object.fig_id,
+                rel.to_object.fig_id,
+                label=rel.name,
+                type_=EdgeType.AGGREGATION,
+            )
 
     def set_printer(self, file_name: str, basename: str) -> None:
         """Set printer."""