fix(panel): position cursor on active file when toggling panel open

lua/diffview/scene/views/diff/file_panel.lua

@@ -73,6 +73,7 @@ function FilePanel:open()
   if not (conf.type == "split" and conf.width == "auto") then
     vim.cmd("wincmd =")
   end
+  self:highlight_cur_file()
 end
 
 function FilePanel:setup_buffer()

lua/diffview/scene/views/file_history/file_history_panel.lua

@@ -117,6 +117,9 @@ function FileHistoryPanel:open()
   if not (conf.type == "split" and conf.width == "auto") then
     vim.cmd("wincmd =")
   end
+  if self.cur_item[2] then
+    self:highlight_item(self.cur_item[2])
+  end
 end
 
 ---@override
@@ -645,15 +648,17 @@ function FileHistoryPanel:set_entry_fold(entry, open)
     self:render()
     self:redraw()
 
-    if entry.folded then
-      -- Set the cursor at the top of the log entry
-      self.components.log.entries.comp:some(function(comp, _, _)
-        if comp.context == entry then
-          utils.set_cursor(self.winid, comp.lstart + 1)
-          return true
-        end
-      end)
+    if not (self:is_open() and entry.folded) then
+      return
     end
+
+    -- Set the cursor at the top of the log entry.
+    self.components.log.entries.comp:some(function(comp, _, _)
+      if comp.context == entry then
+        utils.set_cursor(self.winid, comp.lstart + 1)
+        return true
+      end
+    end)
   end
 end
 

lua/diffview/tests/functional/cdiff_view_spec.lua

@@ -328,6 +328,74 @@ describe("diffview.api.CDiffView", function()
         end
       end)
     )
+
+    it(
+      "places the cursor on the active file when the panel is toggled open (#161)",
+      test_utils.async_test(function()
+        local repo = make_repo()
+        local view
+
+        local ok, err = pcall(function()
+          config.get_config().file_panel.show = false
+
+          view = CDiffView({
+            git_root = repo,
+            left = Rev(RevType.STAGE),
+            right = Rev(RevType.LOCAL),
+            files = make_files({
+              make_file_data("a.txt"),
+              make_file_data("b.txt"),
+              make_file_data("c.txt"),
+            }),
+            update_files = function()
+              return make_files({
+                make_file_data("a.txt"),
+                make_file_data("b.txt"),
+                make_file_data("c.txt"),
+              })
+            end,
+            get_file_data = function()
+              return {}
+            end,
+          })
+
+          view:open()
+          local loaded = vim.wait(1000, function()
+            return not view.is_loading
+          end, 10)
+          assert.is_true(loaded, "view did not finish loading within 1s")
+
+          -- Pick a non-first file as the active entry; the bug is that the
+          -- cursor lands on line 1 instead of on this file's row.
+          local target_file
+          for _, f in view.files:iter() do
+            if f.path == "b.txt" then
+              target_file = f
+              break
+            end
+          end
+          assert.is_not_nil(target_file)
+          view.panel:set_cur_file(target_file)
+
+          assert.falsy(view.panel:is_open())
+
+          -- Toggle the panel open (simulates :DiffviewToggleFiles).
+          view.panel:toggle(true)
+          assert.is_true(view.panel:is_open())
+
+          -- The cursor should land on the active file rather than the top of
+          -- the buffer.
+          local item = view.panel:get_item_at_cursor()
+          assert.equals(target_file, item)
+        end)
+
+        close_view(view)
+        cleanup_repo(repo)
+        if not ok then
+          error(err)
+        end
+      end)
+    )
   end)
 
   -- -----------------------------------------------------------------------

lua/diffview/tests/functional/panel_spec.lua

@@ -1054,6 +1054,134 @@ describe("diffview.ui.panel", function()
     end)
   end)
 
+  describe("FileHistoryPanel show=false lifecycle", function()
+    local FileHistoryPanel =
+      require("diffview.scene.views.file_history.file_history_panel").FileHistoryPanel
+
+    -- Build a stub FileHistoryPanel that bypasses real window creation:
+    -- `is_open`/`buf_loaded` short-circuit `Panel:open`, and `get_config`
+    -- returns split+auto so the post-open `wincmd =` branch is skipped.
+    local function make_panel(cur_item, on_highlight)
+      return setmetatable({
+        cur_item = cur_item or {},
+        is_open = function()
+          return true
+        end,
+        buf_loaded = function()
+          return true
+        end,
+        get_config = function()
+          return { type = "split", width = "auto" }
+        end,
+        highlight_item = function(_, item)
+          if on_highlight then
+            on_highlight(item)
+          end
+        end,
+      }, { __index = FileHistoryPanel })
+    end
+
+    it("places the cursor on cur_item[2] when toggled open (#161)", function()
+      local file = { path = "a.txt" }
+      local entry = { files = { file } }
+      local highlighted
+
+      local panel = make_panel({ entry, file }, function(item)
+        highlighted = item
+      end)
+
+      panel:open()
+      eq(file, highlighted)
+    end)
+
+    it("does not call highlight_item when cur_item is empty", function()
+      local panel = make_panel({}, function()
+        error("highlight_item should not be called")
+      end)
+
+      assert.has_no.errors(function()
+        panel:open()
+      end)
+    end)
+
+    -- Regression: pressing `<tab>`/`<s-tab>` while the panel is toggled off
+    -- routes through `set_file_by_offset` -> `set_entry_fold`, which used to
+    -- call `utils.set_cursor` against `self.winid` unconditionally. Once the
+    -- panel was closed the stored winid was stale, so `nvim_win_get_buf`
+    -- raised "Invalid window id".
+    it("set_entry_fold does not touch the cursor when the panel is closed", function()
+      local cursor_calls = 0
+      local entry = {
+        folded = false,
+        files = {},
+      }
+
+      local panel = setmetatable({
+        single_file = false,
+        winid = 999999,
+        is_open = function()
+          return false
+        end,
+        render = function() end,
+        redraw = function() end,
+        components = {
+          log = {
+            entries = {
+              comp = {
+                some = function(_, _)
+                  cursor_calls = cursor_calls + 1
+                end,
+              },
+            },
+          },
+        },
+      }, { __index = FileHistoryPanel })
+
+      assert.has_no.errors(function()
+        panel:set_entry_fold(entry, false)
+      end)
+      eq(true, entry.folded)
+      eq(0, cursor_calls)
+    end)
+
+    -- Companion to the regression above: when the panel *is* open the
+    -- iteration must still run so the cursor lands on the collapsed entry.
+    it("set_entry_fold iterates components when the panel is open", function()
+      local iter_calls = 0
+      local entry = {
+        folded = false,
+        files = {},
+      }
+
+      local panel = setmetatable({
+        single_file = false,
+        winid = 1,
+        is_open = function()
+          return true
+        end,
+        render = function() end,
+        redraw = function() end,
+        components = {
+          log = {
+            entries = {
+              comp = {
+                some = function(_, _)
+                  iter_calls = iter_calls + 1
+                end,
+              },
+            },
+          },
+        },
+      }, { __index = FileHistoryPanel })
+
+      assert.has_no.errors(function()
+        panel:set_entry_fold(entry, false)
+      end)
+      eq(true, entry.folded)
+      eq(1, iter_calls)
+    end)
+  end)
+
   describe("Panel on_autocmd dispatch", function()
     local Panel = require("diffview.ui.panel").Panel