RSS/Podcast feeds: Invalidate cache when item count changed (#18)

When new items were added, even if those items don’t have a later
modification date than the previous generated site, always re-generate
all RSS and podcast feeds.

Author: JohnSundell

Sources/Publish/Internal/PodcastFeedGenerator.swift

@@ -21,7 +21,7 @@ internal struct PodcastFeedGenerator<Site: Website> where Site.ItemMetadata: Pod
         let items = section.items.sorted(by: { $0.date > $1.date })
 
         if let date = context.lastGenerationDate, let cache = oldCache {
-            if cache.config == config {
+            if cache.config == config, cache.itemCount == items.count {
                 let newlyModifiedItem = items.first { $0.lastModified > date }
 
                 guard newlyModifiedItem != nil else {
@@ -33,7 +33,7 @@ internal struct PodcastFeedGenerator<Site: Website> where Site.ItemMetadata: Pod
         let feed = try makeFeed(containing: items, section: section)
             .render(indentedBy: config.indentation)
 
-        let newCache = Cache(config: config, feed: feed)
+        let newCache = Cache(config: config, feed: feed, itemCount: items.count)
         try cacheFile.write(newCache.encoded())
         try outputFile.write(feed)
     }
@@ -43,6 +43,7 @@ private extension PodcastFeedGenerator {
     struct Cache: Codable {
         let config: PodcastFeedConfiguration<Site>
         let feed: String
+        let itemCount: Int
     }
 
     func makeFeed(containing items: [Item<Site>],

Sources/Publish/Internal/RSSFeedGenerator.swift

@@ -27,7 +27,7 @@ internal struct RSSFeedGenerator<Site: Website> {
         items.sort { $0.date > $1.date }
 
         if let date = context.lastGenerationDate, let cache = oldCache {
-            if cache.config == config {
+            if cache.config == config, cache.itemCount == items.count {
                 let newlyModifiedItem = items.first { $0.lastModified > date }
 
                 guard newlyModifiedItem != nil else {
@@ -38,7 +38,7 @@ internal struct RSSFeedGenerator<Site: Website> {
 
         let feed = makeFeed(containing: items).render(indentedBy: config.indentation)
 
-        let newCache = Cache(config: config, feed: feed)
+        let newCache = Cache(config: config, feed: feed, itemCount: items.count)
         try cacheFile.write(newCache.encoded())
         try outputFile.write(feed)
     }
@@ -48,6 +48,7 @@ private extension RSSFeedGenerator {
     struct Cache: Codable {
         let config: RSSFeedConfiguration
         let feed: String
+        let itemCount: Int
     }
 
     func makeFeed(containing items: [Item<Site>]) -> RSS {

Tests/PublishTests/Tests/PodcastFeedGenerationTests.swift

@@ -82,6 +82,47 @@ final class PodcastFeedGenerationTests: PublishTestCase {
 
         XCTAssertNotEqual(feedA, feedB)
     }
+
+    func testNotReusingPreviousFeedIfItemWasAdded() throws {
+        let folder = try Folder.createTemporary()
+
+        let audio = try Audio(
+            url: require(URL(string: "https://audio.mp3")),
+            duration: Audio.Duration(),
+            byteSize: 55
+        )
+
+        let itemA = Item<Site>(
+            path: "a",
+            sectionID: .one,
+            metadata: .init(podcast: .init()),
+            content: Content(audio: audio)
+        )
+
+        let itemB = Item<Site>(
+            path: "b",
+            sectionID: .one,
+            metadata: .init(podcast: .init()),
+            content: Content(
+                lastModified: itemA.lastModified,
+                audio: audio
+            )
+        )
+
+        try generateFeed(in: folder, generationSteps: [
+            .addItem(itemA)
+        ])
+
+        let feedA = try folder.file(at: "Output/feed.rss").readAsString()
+
+        try generateFeed(in: folder, generationSteps: [
+            .addItem(itemA),
+            .addItem(itemB)
+        ])
+
+        let feedB = try folder.file(at: "Output/feed.rss").readAsString()
+        XCTAssertNotEqual(feedA, feedB)
+    }
 }
 
 extension PodcastFeedGenerationTests {
@@ -90,13 +131,15 @@ extension PodcastFeedGenerationTests {
             ("testOnlyIncludingSpecifiedSection", testOnlyIncludingSpecifiedSection),
             ("testConvertingRelativeLinksToAbsolute", testConvertingRelativeLinksToAbsolute),
             ("testReusingPreviousFeedIfNoItemsWereModified", testReusingPreviousFeedIfNoItemsWereModified),
-            ("testNotReusingPreviousFeedIfConfigChanged", testNotReusingPreviousFeedIfConfigChanged)
+            ("testNotReusingPreviousFeedIfConfigChanged", testNotReusingPreviousFeedIfConfigChanged),
+            ("testNotReusingPreviousFeedIfItemWasAdded", testNotReusingPreviousFeedIfItemWasAdded)
         ]
     }
 }
 
 private extension PodcastFeedGenerationTests {
-    typealias Configuration = PodcastFeedConfiguration<WebsiteStub.WithPodcastMetadata>
+    typealias Site = WebsiteStub.WithPodcastMetadata
+    typealias Configuration = PodcastFeedConfiguration<Site>
 
     func makeConfigStub() throws -> Configuration {
         try Configuration(
@@ -123,12 +166,17 @@ private extension PodcastFeedGenerationTests {
         """
     }
 
-    func generateFeed(in folder: Folder,
-                      config: Configuration? = nil,
-                      date: Date = Date(),
-                      content: [Path : String] = [:]) throws {
+    func generateFeed(
+        in folder: Folder,
+        config: Configuration? = nil,
+        generationSteps: [PublishingStep<Site>] = [
+            .addMarkdownFiles()
+        ],
+        date: Date = Date(),
+        content: [Path : String] = [:]
+    ) throws {
         try publishWebsiteWithPodcast(in: folder, using: [
-            .addMarkdownFiles(),
+            .group(generationSteps),
             .generatePodcastFeed(
                 for: .one,
                 config: config ?? makeConfigStub(),

Tests/PublishTests/Tests/RSSFeedGenerationTests.swift

@@ -76,6 +76,26 @@ final class RSSFeedGenerationTests: PublishTestCase {
 
         XCTAssertNotEqual(feedA, feedB)
     }
+
+    func testNotReusingPreviousFeedIfItemWasAdded() throws {
+        let folder = try Folder.createTemporary()
+        let itemA = Item.stub()
+        let itemB = Item.stub().setting(\.lastModified, to: itemA.lastModified)
+
+        try generateFeed(in: folder, generationSteps: [
+            .addItem(itemA)
+        ])
+
+        let feedA = try folder.file(at: "Output/feed.rss").readAsString()
+
+        try generateFeed(in: folder, generationSteps: [
+            .addItem(itemA),
+            .addItem(itemB)
+        ])
+
+        let feedB = try folder.file(at: "Output/feed.rss").readAsString()
+        XCTAssertNotEqual(feedA, feedB)
+    }
 }
 
 extension RSSFeedGenerationTests {
@@ -84,18 +104,26 @@ extension RSSFeedGenerationTests {
             ("testOnlyIncludingSpecifiedSections", testOnlyIncludingSpecifiedSections),
             ("testConvertingRelativeLinksToAbsolute", testConvertingRelativeLinksToAbsolute),
             ("testReusingPreviousFeedIfNoItemsWereModified", testReusingPreviousFeedIfNoItemsWereModified),
-            ("testNotReusingPreviousFeedIfConfigChanged", testNotReusingPreviousFeedIfConfigChanged)
+            ("testNotReusingPreviousFeedIfConfigChanged", testNotReusingPreviousFeedIfConfigChanged),
+            ("testNotReusingPreviousFeedIfItemWasAdded", testNotReusingPreviousFeedIfItemWasAdded)
         ]
     }
 }
 
 private extension RSSFeedGenerationTests {
-    func generateFeed(in folder: Folder,
-                      config: RSSFeedConfiguration = .default,
-                      date: Date = Date(),
-                      content: [Path : String] = [:]) throws {
+    typealias Site = WebsiteStub.WithoutItemMetadata
+
+    func generateFeed(
+        in folder: Folder,
+        config: RSSFeedConfiguration = .default,
+        generationSteps: [PublishingStep<Site>] = [
+            .addMarkdownFiles()
+        ],
+        date: Date = Date(),
+        content: [Path : String] = [:]
+    ) throws {
         try publishWebsite(in: folder, using: [
-            .addMarkdownFiles(),
+            .group(generationSteps),
             .generateRSSFeed(
                 including: [.one],
                 config: config,