fix(settings): stop the Themes list jumping when accessibility reads it

TablePro/Views/Settings/Appearance/ThemeLibrarySection.swift

@@ -30,6 +30,9 @@ internal struct ThemeLibrarySection: View {
     }
 
     private static let minimumListHeight: CGFloat = 160
+    // A two-line theme row. The table sizes a row it has not measured at this estimate, and an
+    // accessibility read makes it drop and remeasure off-screen rows, so any other value moves the rows.
+    private static let rowHeight: CGFloat = 42
     /// A grouped Form centers its sections at most this wide (measured on macOS 27), so the list keeps
     /// the edges of the sections above it.
     private static let formContentWidth: CGFloat = 704
@@ -121,6 +124,7 @@ internal struct ThemeLibrarySection: View {
                 }
             }
             .listStyle(.bordered(alternatesRowBackgrounds: false))
+            .environment(\.defaultMinListRowHeight, Self.rowHeight)
             .frame(minHeight: Self.minimumListHeight, maxHeight: .infinity)
             .accessibilityIdentifier("appearance-themes-list")
             .contextMenu(forSelectionType: ThemeLibraryItem.self) { items in

TableProTests/Views/Settings/AppearancePaneListTests.swift

@@ -1,4 +1,5 @@
 import AppKit
+import ApplicationServices
 @testable import TablePro
 import SwiftUI
 import Testing
@@ -7,6 +8,14 @@ import Testing
 /// themes below the first few rows could never be reached.
 @MainActor
 struct AppearancePaneListTests {
+    private struct HostedPane {
+        let window: NSWindow
+        let table: NSTableView
+        let scrollView: NSScrollView
+    }
+
+    private static let windowTitle = "AppearancePaneListTests"
+
     private static func find<T: NSView>(_ type: T.Type, in view: NSView) -> [T] {
         var found: [T] = []
         var pending = [view]
@@ -33,8 +42,7 @@ struct AppearancePaneListTests {
         return try #require(NSEvent(cgEvent: event))
     }
 
-    @Test("The Themes list scrolls on its own when it holds more themes than it shows")
-    func themesListScrolls() throws {
+    private static func hostPane() throws -> HostedPane {
         let paneSize = SettingsPaneTabViewController.paneSize
         let window = NSWindow(
             contentRect: NSRect(origin: .zero, size: paneSize),
@@ -43,28 +51,88 @@ struct AppearancePaneListTests {
             defer: false
         )
         window.isReleasedWhenClosed = false
+        window.title = windowTitle
         // As the Settings window hosts a pane: the window keeps its size whatever the content asks.
         let hosting = NSHostingController(rootView: AppearanceSettingsView(settings: .constant(.default)))
         hosting.sizingOptions = []
         window.contentViewController = hosting
         window.setContentSize(paneSize)
         window.layoutIfNeeded()
         RunLoop.main.run(until: Date(timeIntervalSinceNow: 0.3))
-        defer { window.orderOut(nil) }
 
         let content = try #require(window.contentView)
         let table = try #require(
-            Self.find(NSTableView.self, in: content).first { $0.numberOfRows > 10 },
+            find(NSTableView.self, in: content).first { $0.numberOfRows > 10 },
             "The pane should show the Themes list"
         )
         let scrollView = try #require(table.enclosingScrollView)
-        #expect(table.frame.height > scrollView.contentView.bounds.height, "The fixture needs more themes than fit")
+        return HostedPane(window: window, table: table, scrollView: scrollView)
+    }
+
+    private static func elements(_ attribute: String, of element: AXUIElement) -> [AXUIElement] {
+        var value: CFTypeRef?
+        guard AXUIElementCopyAttributeValue(element, attribute as CFString, &value) == .success else { return [] }
+        return value as? [AXUIElement] ?? []
+    }
+
+    private static func title(of element: AXUIElement) -> String? {
+        var value: CFTypeRef?
+        guard AXUIElementCopyAttributeValue(element, kAXTitleAttribute as CFString, &value) == .success else { return nil }
+        return value as? String
+    }
+
+    // The AX API reaches rows outside the visible rect, as an XCUITest snapshot or VoiceOver does;
+    // accessibilityChildren() called in process stops at the visible ones.
+    private static func readTree(of element: AXUIElement) -> Int {
+        for attribute in [kAXPositionAttribute, kAXSizeAttribute, kAXValueAttribute] {
+            var value: CFTypeRef?
+            _ = AXUIElementCopyAttributeValue(element, attribute as CFString, &value)
+        }
+        return elements(kAXChildrenAttribute, of: element).reduce(1) { $0 + readTree(of: $1) }
+    }
+
+    @Test("The Themes list scrolls on its own when it holds more themes than it shows")
+    func themesListScrolls() throws {
+        let pane = try Self.hostPane()
+        defer { pane.window.orderOut(nil) }
+        let scrollView = pane.scrollView
+        #expect(pane.table.frame.height > scrollView.contentView.bounds.height, "The fixture needs more themes than fit")
 
         let before = scrollView.contentView.bounds.origin.y
-        scrollView.scrollWheel(with: try Self.scrollEvent(over: scrollView, in: window))
+        scrollView.scrollWheel(with: try Self.scrollEvent(over: scrollView, in: pane.window))
         RunLoop.main.run(until: Date(timeIntervalSinceNow: 0.2))
 
         #expect(scrollView.contentView.bounds.origin.y > before, "A scroll over the list should move its rows")
         #expect(scrollView.verticalScrollElasticity != .none)
     }
+
+    @Test("Reading the Themes list for accessibility leaves its rows where they are")
+    func themesListHoldsStillWhileAccessibilityReadsIt() throws {
+        let pane = try Self.hostPane()
+        pane.window.orderFront(nil)
+        defer { pane.window.orderOut(nil) }
+        let table = pane.table
+        let clipView = pane.scrollView.contentView
+
+        let window = try #require(
+            Self.elements(kAXWindowsAttribute, of: AXUIElementCreateApplication(getpid()))
+                .first { Self.title(of: $0) == Self.windowTitle },
+            "The pane's window should be in the accessibility tree"
+        )
+        #expect(Self.readTree(of: window) > table.numberOfRows, "The read should reach every row")
+
+        for _ in 0..<12 {
+            pane.scrollView.scrollWheel(with: try Self.scrollEvent(over: pane.scrollView, in: pane.window))
+            RunLoop.main.run(until: Date(timeIntervalSinceNow: 0.3))
+            let shown = table.rows(in: clipView.documentVisibleRect)
+            _ = Self.readTree(of: window)
+            RunLoop.main.run(until: Date(timeIntervalSinceNow: 0.1))
+            let after = table.rows(in: clipView.documentVisibleRect)
+            #expect(after.location == shown.location, "Rows \(shown) moved to \(after) while nothing scrolled")
+        }
+        #expect(
+            table.rows(in: clipView.documentVisibleRect).contains(table.numberOfRows - 1),
+            "Scrolling to the end should show the last theme"
+        )
+    }
 }