Generics to narrow types to item only when appropriate (deephaven#1909)

packages/components/src/spectrum/utils/itemUtils.ts

@@ -67,6 +67,9 @@ export type NormalizedSection = KeyedItem<
   Key | undefined
 >;
 
+export type NormalizedItemOrSection<TItemOrSection extends ItemOrSection> =
+  TItemOrSection extends SectionElement ? NormalizedSection : NormalizedItem;
+
 export type NormalizedSpectrumPickerProps = SpectrumPickerProps<NormalizedItem>;
 
 export type TooltipOptions = { placement: PopperOptions['placement'] };
@@ -114,14 +117,19 @@ export function isItemElement<T>(
 }
 
 /**
- * Determine if a node is an array containing normalized items with keys.
- * Note that this only checks the first node in the array.
+ * Determine if a node is an array containing normalized items or sections with
+ * keys. Note that this only checks the first node in the array.
  * @param node The node to check
- * @returns True if the node is a normalized item with keys array
+ * @returns True if the node is a normalized item or section with keys array
  */
-export function isNormalizedItemsWithKeysList(
-  node: ItemOrSection | ItemOrSection[] | (NormalizedItem | NormalizedSection)[]
-): node is (NormalizedItem | NormalizedSection)[] {
+export function isNormalizedItemsWithKeysList<
+  TItemOrSection extends ItemOrSection,
+>(
+  node:
+    | TItemOrSection
+    | TItemOrSection[]
+    | NormalizedItemOrSection<TItemOrSection>[]
+): node is NormalizedItemOrSection<TItemOrSection>[] {
   if (!Array.isArray(node)) {
     return false;
   }
@@ -225,9 +233,9 @@ function normalizeTextValue(item: ItemElementOrPrimitive): string | undefined {
  * @param itemOrSection item to normalize
  * @returns NormalizedItem or NormalizedSection object
  */
-function normalizeItem(
-  itemOrSection: ItemOrSection
-): NormalizedItem | NormalizedSection {
+function normalizeItem<TItemOrSection extends ItemOrSection>(
+  itemOrSection: TItemOrSection
+): NormalizedItemOrSection<TItemOrSection> {
   if (!isItemOrSection(itemOrSection)) {
     log.debug(INVALID_ITEM_ERROR_MESSAGE, itemOrSection);
     throw new Error(INVALID_ITEM_ERROR_MESSAGE);
@@ -244,7 +252,7 @@ function normalizeItem(
 
     return {
       item: { key, title, items },
-    };
+    } as NormalizedItemOrSection<TItemOrSection>;
   }
 
   const key = normalizeItemKey(itemOrSection);
@@ -255,23 +263,23 @@ function normalizeItem(
 
   return {
     item: { key, content, textValue },
-  };
+  } as NormalizedItemOrSection<TItemOrSection>;
 }
 
 /**
- * Get normalized items from an item or array of items.
- * @param itemsOrSections An item or array of items
- * @returns An array of normalized items
+ * Normalize an item or section or a list of items or sections.
+ * @param itemsOrSections An item or section or array of items or sections
+ * @returns An array of normalized items or sections
  */
-export function normalizeItemList(
-  itemsOrSections: ItemOrSection | ItemOrSection[] | NormalizedItem[]
-): (NormalizedItem | NormalizedSection)[] {
+export function normalizeItemList<TItemOrSection extends ItemOrSection>(
+  itemsOrSections: TItemOrSection | TItemOrSection[] | NormalizedItem[]
+): NormalizedItemOrSection<TItemOrSection>[] {
   // If already normalized, just return as-is
   if (isNormalizedItemsWithKeysList(itemsOrSections)) {
-    return itemsOrSections;
+    return itemsOrSections as NormalizedItemOrSection<TItemOrSection>[];
   }
 
-  const itemsArray = Array.isArray(itemsOrSections)
+  const itemsArray: TItemOrSection[] = Array.isArray(itemsOrSections)
     ? itemsOrSections
     : [itemsOrSections];