Pyreverse: Don't show multiple class association arrows (#9055)

Co-authored-by: Pierre Sassoulas <pierre.sassoulas@gmail.com>

doc/whatsnew/fragments/9045.bugfix

@@ -0,0 +1,3 @@
+Pyreverse doesn't show multiple class association arrows anymore, but only the strongest one.
+
+Refs #9045

pylint/pyreverse/writer.py

@@ -9,6 +9,7 @@
 import argparse
 import itertools
 import os
+from collections import defaultdict
 from collections.abc import Iterable
 
 from astroid import modutils, nodes
@@ -133,8 +134,10 @@ def write_classes(self, diagram: ClassDiagram) -> None:
                 rel.to_object.fig_id,
                 type_=EdgeType.INHERITS,
             )
+        associations: dict[str, set[str]] = defaultdict(set)
         # generate associations
         for rel in diagram.get_relationships("association"):
+            associations[rel.from_object.fig_id].add(rel.to_object.fig_id)
             self.printer.emit_edge(
                 rel.from_object.fig_id,
                 rel.to_object.fig_id,
@@ -143,6 +146,8 @@ def write_classes(self, diagram: ClassDiagram) -> None:
             )
         # generate aggregations
         for rel in diagram.get_relationships("aggregation"):
+            if rel.to_object.fig_id in associations[rel.from_object.fig_id]:
+                continue
             self.printer.emit_edge(
                 rel.from_object.fig_id,
                 rel.to_object.fig_id,

tests/pyreverse/functional/class_diagrams/aggregation/fields.mmd

@@ -21,4 +21,3 @@ classDiagram
   P --* D : x
   P --* E : x
   P --o B : x
-  P --o C : x