fix(eda): inherit KiCad reference prefix from ancestor categories

src/Services/EDA/KiCadHelper.php

@@ -211,7 +211,7 @@ public function getKiCADPart(Part $part): array
         ];
 
         $result["fields"]["footprint"] = $this->createField($part->getEdaInfo()->getKicadFootprint() ?? $part->getFootprint()?->getEdaInfo()->getKicadFootprint() ?? "");
-        $result["fields"]["reference"] = $this->createField($part->getEdaInfo()->getReferencePrefix() ?? $part->getCategory()?->getEdaInfo()->getReferencePrefix() ?? 'U', true);
+        $result["fields"]["reference"] = $this->createField($this->getReferencePrefix($part), true);
         $result["fields"]["value"] = $this->createField($part->getEdaInfo()->getValue() ?? $part->getName(), true);
         $result["fields"]["keywords"] = $this->createField($part->getTags());
 
@@ -355,6 +355,36 @@ public function getKiCADPart(Part $part): array
         return $result;
     }
 
+    /**
+     * Resolve the reference prefix for the given part.
+     *
+     * A part without its own reference prefix inherits the prefix of the closest category
+     * ancestor that defines one (a category tree can be several levels deep, see issue #1535).
+     * If neither the part nor any category ancestor defines a prefix, 'U' is used as fallback.
+     */
+    private function getReferencePrefix(Part $part): string
+    {
+        $prefix = $part->getEdaInfo()->getReferencePrefix();
+        if ($prefix !== null && $prefix !== '') {
+            return $prefix;
+        }
+
+        //Walk the category tree upwards: the closest ancestor with a prefix wins.
+        $category = $part->getCategory();
+        $depth = 0;
+        while ($category !== null && $depth < 20) {
+            $prefix = $category->getEdaInfo()->getReferencePrefix();
+            if ($prefix !== null && $prefix !== '') {
+                return $prefix;
+            }
+
+            $category = $category->getParent();
+            ++$depth;
+        }
+
+        return 'U';
+    }
+
     /**
      * Determine if the given part should be visible for the EDA.
      * @param  Category  $category

tests/Services/EDA/KiCadHelperTest.php

@@ -633,6 +633,78 @@ public function testParameterWithEmptyNameIsSkipped(): void
         self::assertArrayNotHasKey('', $result['fields']);
     }
 
+    public function testReferencePrefixIsInheritedFromAncestorCategory(): void
+    {
+        $part = $this->em->find(Part::class, 1);
+        $part->getEdaInfo()->setReferencePrefix(null);
+
+        $parent = (new Category())->setName('Connectors');
+        $parent->getEdaInfo()->setReferencePrefix('J');
+
+        $child = (new Category())->setName('D-sub');
+        $child->setParent($parent);
+
+        $part->setCategory($child);
+
+        $result = $this->helper->getKiCADPart($part);
+
+        self::assertSame('J', $result['fields']['reference']['value']);
+    }
+
+    public function testNearestCategoryWithPrefixWins(): void
+    {
+        $part = $this->em->find(Part::class, 1);
+        $part->getEdaInfo()->setReferencePrefix(null);
+
+        $parent = (new Category())->setName('Connectors');
+        $parent->getEdaInfo()->setReferencePrefix('J');
+
+        $child = (new Category())->setName('D-sub');
+        $child->getEdaInfo()->setReferencePrefix('X');
+        $child->setParent($parent);
+
+        $part->setCategory($child);
+
+        $result = $this->helper->getKiCADPart($part);
+
+        self::assertSame('X', $result['fields']['reference']['value']);
+    }
+
+    public function testPartReferencePrefixOverridesCategory(): void
+    {
+        $part = $this->em->find(Part::class, 1);
+        $part->getEdaInfo()->setReferencePrefix('C');
+
+        $parent = (new Category())->setName('Connectors');
+        $parent->getEdaInfo()->setReferencePrefix('J');
+
+        $child = (new Category())->setName('D-sub');
+        $child->setParent($parent);
+
+        $part->setCategory($child);
+
+        $result = $this->helper->getKiCADPart($part);
+
+        self::assertSame('C', $result['fields']['reference']['value']);
+    }
+
+    public function testReferencePrefixFallsBackToUWhenNothingIsSet(): void
+    {
+        $part = $this->em->find(Part::class, 1);
+        $part->getEdaInfo()->setReferencePrefix(null);
+
+        $parent = (new Category())->setName('Connectors');
+
+        $child = (new Category())->setName('D-sub');
+        $child->setParent($parent);
+
+        $part->setCategory($child);
+
+        $result = $this->helper->getKiCADPart($part);
+
+        self::assertSame('U', $result['fields']['reference']['value']);
+    }
+
     /**
      * Category 1 (from fixtures) has a KiCad symbol set, so its parts are visible to the EDA.
      * The listing must carry the fields, so KiCad does not have to request each part separately.