perf: eliminate repeated favorites sort map and grid recompute

1 files changed, 47 insertions, 0 deletions

diff --git a/SoraTests/ViewDerivedDataTests.swift b/SoraTests/ViewDerivedDataTests.swift
index b8a4bba..da5ad0d 100644
--- a/SoraTests/ViewDerivedDataTests.swift
+++ b/SoraTests/ViewDerivedDataTests.swift
@@ -55,6 +55,53 @@ final class ViewDerivedDataTests: XCTestCase {
     )
   }
 
+  func testFavoritesViewDerivedCollectionsAreReferencedOncePerRenderPass() throws {
+    let source = try loadSource(at: "Sora/Views/FavoritesView.swift")
+    let normalizedSource = strippingCommentsAndStrings(from: source)
+
+    let filteredFavoritesUsages = referenceCount(
+      for: "filteredFavorites",
+      in: normalizedSource
+    )
+    let sortedFilteredFavoritesUsages = referenceCount(
+      for: "sortedFilteredFavorites",
+      in: normalizedSource
+    )
+    let inlinePostMappingCount = tokenCount(
+      matching: #"\bsortedFilteredFavorites\s*\.\s*map\s*\{"#,
+      in: normalizedSource
+    )
+    let columnsSplitterUsages = invocationCount(
+      forFunction: "getColumnsData",
+      in: normalizedSource
+    )
+
+    // swiftlint:disable:next prefer_nimble
+    XCTAssertLessThanOrEqual(
+      filteredFavoritesUsages,
+      1,
+      "filteredFavorites should be consumed once per dependency change."
+    )
+    // swiftlint:disable:next prefer_nimble
+    XCTAssertLessThanOrEqual(
+      sortedFilteredFavoritesUsages,
+      1,
+      "sortedFilteredFavorites should be consumed once per dependency change."
+    )
+    // swiftlint:disable:next prefer_nimble
+    XCTAssertEqual(
+      inlinePostMappingCount,
+      0,
+      "Favorites grid should not remap sorted favorites to posts inline on each cell render."
+    )
+    // swiftlint:disable:next prefer_nimble
+    XCTAssertLessThanOrEqual(
+      columnsSplitterUsages,
+      1,
+      "Favorites grid column distribution should be derived once per dependency change."
+    )
+  }
+
   private func referenceCount(for symbol: String, in source: String) -> Int {
     let totalMatches = tokenCount(
       matching: #"\b\#(symbol)\b"#,