sidebar: keep the selected row clear of the footer

Sources/Sidebar/AppKitList/SidebarWorkspaceTableController.swift

@@ -2822,14 +2822,52 @@ final class SidebarWorkspaceTableController: NSObject, NSTableViewDataSource, NS
     }
 
     private func scrollSelectedRowToVisibleIfNeeded() {
-        guard let table = containerView?.tableView,
+        guard let container = containerView,
               let selectedScrollTargetWorkspaceId,
               let row = rows.firstIndex(where: { $0.workspaceId == selectedScrollTargetWorkspaceId }) else {
             return
         }
-        let visibleRect = table.visibleRect
-        guard !visibleRect.contains(table.rect(ofRow: row)) else { return }
-        table.scrollRowToVisible(row)
+        let table = container.tableView
+        let scrollView = container.scrollView
+        let clipView = scrollView.contentView
+        // `visibleRect` and `scrollRowToVisible` count the strips under the
+        // content insets (the titlebar scrim and the footer) as visible, so a
+        // selected row pushed down by a reorder could stay behind the footer.
+        guard let origin = Self.selectedRowScrollOrigin(
+            rowRect: table.convert(table.rect(ofRow: row), to: clipView),
+            clipBounds: clipView.bounds,
+            insets: scrollView.contentInsets,
+            documentHeight: table.frame.height
+        ) else { return }
+        clipView.scroll(to: NSPoint(x: clipView.bounds.origin.x, y: origin))
+        scrollView.reflectScrolledClipView(clipView)
+    }
+
+    /// The clip view origin that brings `rowRect` fully between the top and
+    /// bottom insets, moving as little as possible, or nil when it already is.
+    /// All rects are in the (flipped) clip view's coordinates.
+    nonisolated static func selectedRowScrollOrigin(
+        rowRect: NSRect,
+        clipBounds: NSRect,
+        insets: NSEdgeInsets,
+        documentHeight: CGFloat
+    ) -> CGFloat? {
+        let unobscuredMinY = clipBounds.minY + insets.top
+        let unobscuredMaxY = clipBounds.maxY - insets.bottom
+        let target: CGFloat
+        // A row taller than the clear area aligns its top, like a short row
+        // scrolled down to.
+        if rowRect.minY < unobscuredMinY || rowRect.height > unobscuredMaxY - unobscuredMinY {
+            target = rowRect.minY - insets.top
+        } else if rowRect.maxY > unobscuredMaxY {
+            target = rowRect.maxY + insets.bottom - clipBounds.height
+        } else {
+            return nil
+        }
+        let lowest = -insets.top
+        let highest = max(lowest, documentHeight + insets.bottom - clipBounds.height)
+        let clamped = min(max(target, lowest), highest)
+        return clamped == clipBounds.origin.y ? nil : clamped
     }
 
     private func configureDropViews(

cmux.xcodeproj/project.pbxproj

@@ -2975,6 +2975,7 @@
 		951635C63E1D44A9BF7E61D4 /* SidebarSearchFieldCoordinator.swift in Sources */ = {isa = PBXBuildFile; fileRef = A01600A90E464973B8D8122C /* SidebarSearchFieldCoordinator.swift */; };
 		F6528A82B7124269968F9A99 /* SidebarSearchFieldTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = 7C270D11DD3C408DBB9A0B09 /* SidebarSearchFieldTests.swift */; };
 		5A1180B9BE6B4395A220318A /* SidebarSearchFieldView.swift in Sources */ = {isa = PBXBuildFile; fileRef = C31DD7A6E10E483D915E7F2B /* SidebarSearchFieldView.swift */; };
+		4A435919EC29E25A2E139D7A /* SidebarSelectedRowScrollTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = 8E924EBE2A4B7D8798B993C1 /* SidebarSelectedRowScrollTests.swift */; };
 		B804A0280000000000000028 /* SidebarSelectionCoalescer.swift in Sources */ = {isa = PBXBuildFile; fileRef = B804B0280000000000000028 /* SidebarSelectionCoalescer.swift */; };
 		B804C0020000000000000002 /* SidebarSelectionCoalescerTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = B804D0020000000000000002 /* SidebarSelectionCoalescerTests.swift */; };
 		E62155868BB29FEB5DAAAF25 /* SidebarSelectionState.swift in Sources */ = {isa = PBXBuildFile; fileRef = 9AD52285508B1D6A9875E7B3 /* SidebarSelectionState.swift */; };
@@ -6961,6 +6962,7 @@
 		A01600A90E464973B8D8122C /* SidebarSearchFieldCoordinator.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = SidebarSearchFieldCoordinator.swift; sourceTree = "<group>"; };
 		7C270D11DD3C408DBB9A0B09 /* SidebarSearchFieldTests.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = SidebarSearchFieldTests.swift; sourceTree = "<group>"; };
 		C31DD7A6E10E483D915E7F2B /* SidebarSearchFieldView.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = SidebarSearchFieldView.swift; sourceTree = "<group>"; };
+		8E924EBE2A4B7D8798B993C1 /* SidebarSelectedRowScrollTests.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = "SidebarSelectedRowScrollTests.swift"; sourceTree = "<group>"; };
 		B804B0280000000000000028 /* SidebarSelectionCoalescer.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = Sidebar/AppKitList/SidebarSelectionCoalescer.swift; sourceTree = "<group>"; };
 		B804D0020000000000000002 /* SidebarSelectionCoalescerTests.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = SidebarSelectionCoalescerTests.swift; sourceTree = "<group>"; };
 		9AD52285508B1D6A9875E7B3 /* SidebarSelectionState.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = SidebarSelectionState.swift; sourceTree = "<group>"; };
@@ -12190,6 +12192,7 @@
 				A634CA3FCA39C6F02FA78DC7 /* UpdateRelaunchAgentResumeTests.swift */,
 				D87FDCA31298C3B71D50F9E7 /* PasteLastScreenshotShortcutTests.swift */,
 				AFD49B60E1A7F637C0ADFEF4 /* TerminalPasteFailureNoticeTests.swift */,
+				8E924EBE2A4B7D8798B993C1 /* SidebarSelectedRowScrollTests.swift */,
 			);
 			path = cmuxTests;
 			sourceTree = "<group>";
@@ -16574,6 +16577,7 @@
 				C12791000000000000000005 /* SidebarRowSnapshotCacheTests.swift in Sources */,
 				C9A57513C9A57513C9A57513 /* SidebarScrollViewConfiguratorTests.swift in Sources */,
 				F6528A82B7124269968F9A99 /* SidebarSearchFieldTests.swift in Sources */,
+				4A435919EC29E25A2E139D7A /* SidebarSelectedRowScrollTests.swift in Sources */,
 				B804C0020000000000000002 /* SidebarSelectionCoalescerTests.swift in Sources */,
 				C12791000000000000000007 /* SidebarSnapshotOwnerTests.swift in Sources */,
 				D73440010000000000000001 /* SidebarTabDragPayloadProviderTests.swift in Sources */,

cmuxTests/SidebarSelectedRowScrollTests.swift

@@ -0,0 +1,52 @@
+import AppKit
+import Testing
+@testable import cmux_DEV
+
+/// The AppKit workspace list scrolls the selected row fully between its
+/// content insets: the top titlebar scrim and the bottom footer overlay.
+/// A row behind the footer used to count as visible.
+@Suite
+struct SidebarSelectedRowScrollTests {
+    private let insets = NSEdgeInsets(top: 30, left: 0, bottom: 58, right: 0)
+    private let documentHeight: CGFloat = 1000
+
+    private func origin(row minY: CGFloat, height: CGFloat = 50, clipOriginY: CGFloat) -> CGFloat? {
+        SidebarWorkspaceTableController.selectedRowScrollOrigin(
+            rowRect: NSRect(x: 0, y: minY, width: 240, height: height),
+            clipBounds: NSRect(x: 0, y: clipOriginY, width: 240, height: 600),
+            insets: insets,
+            documentHeight: documentHeight
+        )
+    }
+
+    @Test
+    func aRowBetweenTheInsetsDoesNotScroll() {
+        #expect(origin(row: 100, clipOriginY: 0) == nil)
+    }
+
+    @Test
+    func aRowBehindTheFooterScrollsUpUntilItClearsIt() {
+        // Visible by the clip bounds (ends at 570 < 600), hidden by the
+        // footer (unobscured area ends at 600 - 58 = 542).
+        #expect(origin(row: 520, clipOriginY: 0) == 28)
+    }
+
+    @Test
+    func aRowUnderTheTitlebarScrimScrollsDown() {
+        #expect(origin(row: 210, clipOriginY: 200) == 180)
+    }
+
+    @Test
+    func aRowTallerThanTheClearAreaAlignsItsTop() {
+        // Clear area is 512 tall; this row starts in view and runs past the footer.
+        #expect(origin(row: 100, height: 600, clipOriginY: 0) == 70)
+    }
+
+    @Test
+    func scrollingStopsAtTheEndsOfTheList() {
+        // The last row can go no further than the bottom inset allows.
+        #expect(origin(row: 960, height: 40, clipOriginY: 0) == documentHeight + insets.bottom - 600)
+        // The first row can go no higher than the top inset allows.
+        #expect(origin(row: 0, clipOriginY: 100) == -insets.top)
+    }
+}