fix(window): display loaded buffer even if file got deactivated mid-yield

lua/diffview/scene/window.lua

@@ -142,16 +142,24 @@ Window.open_file = async.void(function(self)
   ---@diagnostic disable: invisible
   assert(self.file)
 
-  if not (self:is_valid() and self.file.active) then
+  if not self:is_valid() then
     return
   end
 
   if not self.file:is_valid() then
+    -- Skip the load entirely if the file was already deactivated by the
+    -- time we got here -- the user has navigated past this target, so a
+    -- fresh `git show` would be wasted work. Once the load is in flight,
+    -- `create_buffer` raises `CANCELLED` on its own active checks, which
+    -- surfaces as `ok = false` below.
+    if not self.file.active then
+      return
+    end
     local ok = await(self:load_file())
     await(async.scheduler())
 
     -- Ensure validity after await
-    if not (self:is_valid() and self.file.active) then
+    if not self:is_valid() then
       return
     end
 
@@ -161,6 +169,19 @@ Window.open_file = async.void(function(self)
     end
   end
 
+  -- The file is loaded; display it regardless of `self.file.active`.
+  -- `Layout.open_files` yields on `async.scheduler()` between its load
+  -- loop and its open loop, and a rapid navigation in that gap can
+  -- deactivate the file. Bailing here on `active=false` used to leave
+  -- the window holding the prior `open_null` placeholder while
+  -- `file.loaded=true` claimed the buffer was ready -- a stale state
+  -- that trips `jump_to_first_change` (silent `]c` on an empty buffer
+  -- in the default branch; `Cursor position outside buffer` in
+  -- `diff1_inline`, which looks up hunks on `file.bufnr` and writes the
+  -- cursor in `main.id`'s current buffer). The buffer is already
+  -- populated, so setting it in the window is cheap; the next worker
+  -- iteration replaces it with the user's actual target.
+
   self.emitter:emit("pre_open")
 
   -- Disable context plugins BEFORE the buffer enters the window.

lua/diffview/tests/functional/window_spec.lua

@@ -303,6 +303,38 @@ describe("diffview.scene.window", function()
         vim.api.nvim_buf_delete(bufnr, { force = true })
       end)
     )
+
+    -- Regression: `Layout.open_files` yields between its load loop and its
+    -- open loop. A rapid navigation in that gap deactivates the in-flight
+    -- file; bailing on `active=false` here used to leave the window holding
+    -- the `open_null` placeholder while `file.loaded=true` claimed the
+    -- buffer was ready, tripping `jump_to_first_change` (silent `]c` on an
+    -- empty buffer; "Cursor position outside buffer" in `diff1_inline`).
+    -- Once the buffer is populated, displaying it is cheap, so `open_file`
+    -- proceeds regardless of `active`.
+    it(
+      "displays an already-loaded buffer even when the file got deactivated",
+      helpers.async_test(function()
+        local adapter = mock_adapter()
+        local bufnr = vim.api.nvim_create_buf(false, true)
+        local win, file = make_window(adapter)
+        file.bufnr = bufnr
+        file.loaded = true
+        file.active = false -- deactivated post-load.
+        win.parent = stub_parent()
+
+        async.await(win:open_file())
+
+        assert.equals(bufnr, vim.api.nvim_win_get_buf(win.id))
+
+        if vim.api.nvim_win_is_valid(test_winid) then
+          vim.api.nvim_win_close(test_winid, true)
+        end
+        test_winid = nil
+        Window.winopt_store[bufnr] = nil
+        vim.api.nvim_buf_delete(bufnr, { force = true })
+      end)
+    )
   end)
 
   it(