refactor(diffsplit): clarify diff side API

lua/git/diffsplit.lua

@@ -6,13 +6,15 @@ local util = require("git.core.util")
 local M = {}
 
 ---@class ow.Git.Diffsplit.OpenOpts
----@field target string?
+---@field other string?
+---@field layout ("vertical"|"horizontal")?
 ---@field mods vim.api.keyset.cmd.mods?
+---@field focus ("current"|"other")?
 
 ---@param cur_buf integer
----@return string? target
+---@return string? other
 ---@return string? err
-local function infer_target(cur_buf)
+local function infer_other(cur_buf)
     local cur_name = vim.api.nvim_buf_get_name(cur_buf)
     local cur_rev = object.parse_uri(cur_name)
     if cur_rev then
@@ -48,16 +50,16 @@ local function infer_target(cur_buf)
     return object.format_uri(Revision.new({ stage = 0, path = rel })), nil
 end
 
----@param target string
+---@param other string
 ---@param cur_buf integer
 ---@return string? resolved
 ---@return string? err
-local function resolve_target(target, cur_buf)
-    if vim.startswith(target, object.URI_PREFIX) then
-        return target, nil
+local function resolve_other(other, cur_buf)
+    if vim.startswith(other, object.URI_PREFIX) then
+        return other, nil
     end
-    if vim.fn.filereadable(target) == 1 then
-        return target, nil
+    if vim.fn.filereadable(other) == 1 then
+        return other, nil
     end
     local cur_name = vim.api.nvim_buf_get_name(cur_buf)
     local cur_rev = object.parse_uri(cur_name)
@@ -78,57 +80,141 @@ local function resolve_target(target, cur_buf)
     if not rel then
         return nil, "current buffer has no path"
     end
-    if not r:rev_parse(target, true) then
-        return nil, "invalid rev: " .. target
+    if not r:rev_parse(other, true) then
+        return nil, "invalid rev: " .. other
     end
-    return object.format_uri(Revision.new({ base = target, path = rel })), nil
+    return object.format_uri(Revision.new({ base = other, path = rel })), nil
 end
 
 ---@param cur_buf integer
----@param target string
+---@param other string
 ---@return 'aboveleft'|'belowright'|nil
-local function default_split(cur_buf, target)
+local function default_split(cur_buf, other)
     local cur_rev = object.parse_uri(vim.api.nvim_buf_get_name(cur_buf))
-    local target_rev = object.parse_uri(target)
-    if not cur_rev and target_rev then
+    local other_rev = object.parse_uri(other)
+    if not cur_rev and other_rev then
         return "aboveleft"
     end
-    if cur_rev and not target_rev then
+    if cur_rev and not other_rev then
         return "belowright"
     end
-    if cur_rev and target_rev then
-        if cur_rev.stage == 0 and target_rev.base then
+    if cur_rev and other_rev then
+        if cur_rev.stage == 0 and other_rev.base then
             return "aboveleft"
         end
-        if cur_rev.base and target_rev.stage == 0 then
+        if cur_rev.base and other_rev.stage == 0 then
             return "belowright"
         end
     end
     return nil
 end
 
+---@alias ow.Git.Diffsplit.Side string|integer
+
+---@class ow.Git.Diffsplit.OpenPairOpts
+---@field layout ("vertical"|"horizontal")?
+---@field mods vim.api.keyset.cmd.mods?
+---@field focus ("old"|"new")?
+
+---@param mods vim.api.keyset.cmd.mods?
+---@param layout ("vertical"|"horizontal")?
+---@return vim.api.keyset.cmd.mods
+local function layout_mods(mods, layout)
+    mods = vim.tbl_extend("force", {}, mods or {})
+    if mods.vertical == nil then
+        mods.vertical = layout ~= "horizontal"
+    end
+    return mods
+end
+
+---@param side ow.Git.Diffsplit.Side
+---@param cur_buf integer
+---@return string? name
+---@return integer? buf
+---@return string? err
+local function resolve_side(side, cur_buf)
+    if type(side) == "number" then
+        local name = vim.api.nvim_buf_get_name(side)
+        if name == "" then
+            return nil, nil, "diff side buffer has no name"
+        end
+        return name, side, nil
+    end
+    local name, err = resolve_other(side, cur_buf)
+    return name, nil, err
+end
+
+---@param side ow.Git.Diffsplit.Side
+---@param cur_buf integer
+---@return integer? buf
+---@return string? err
+local function buf_for_side(side, cur_buf)
+    local name, buf, err = resolve_side(side, cur_buf)
+    if not name then
+        return nil, err
+    end
+    if buf then
+        return buf, nil
+    end
+    buf = vim.fn.bufadd(name)
+    vim.fn.bufload(buf)
+    return buf, nil
+end
+
 ---@param opts? ow.Git.Diffsplit.OpenOpts
 function M.open(opts)
     opts = opts or {}
     local cur_buf = vim.api.nvim_get_current_buf()
-    local target, err
-    if opts.target then
-        target, err = resolve_target(opts.target, cur_buf)
+    local other, err
+    if opts.other then
+        other, err = resolve_other(opts.other, cur_buf)
     else
-        target, err = infer_target(cur_buf)
+        other, err = infer_other(cur_buf)
     end
-    if not target then
-        util.error("%s", err or "no diff target")
+    if not other then
+        util.error("%s", err or "no diff side")
         return
     end
-    local mods = opts.mods
-    if not mods or mods.split == nil then
-        local placement = default_split(cur_buf, target)
+    local mods = layout_mods(opts.mods, opts.layout)
+    if mods.split == nil then
+        local placement = default_split(cur_buf, other)
         if placement then
             mods = vim.tbl_extend("force", mods or {}, { split = placement })
         end
     end
-    vim.cmd.diffsplit({ args = { target }, mods = mods })
+    local cur_win = vim.api.nvim_get_current_win()
+    vim.cmd.diffsplit({ args = { other }, mods = mods })
+    if opts.focus == "current" and vim.api.nvim_win_is_valid(cur_win) then
+        vim.api.nvim_set_current_win(cur_win)
+    end
+end
+
+---@param old ow.Git.Diffsplit.Side
+---@param new ow.Git.Diffsplit.Side
+---@param opts? ow.Git.Diffsplit.OpenPairOpts
+function M.open_pair(old, new, opts)
+    opts = opts or {}
+    local cur_buf = vim.api.nvim_get_current_buf()
+    local new_buf, err = buf_for_side(new, cur_buf)
+    if not new_buf then
+        util.error("%s", err or "no new diff side")
+        return
+    end
+    local old_name, _, old_err = resolve_side(old, cur_buf)
+    if not old_name then
+        util.error("%s", old_err or "no old diff side")
+        return
+    end
+
+    vim.cmd.normal({ "m'", bang = true })
+    vim.api.nvim_set_current_buf(new_buf)
+
+    local mods = layout_mods(opts.mods, opts.layout)
+    mods.split = mods.split or "aboveleft"
+    vim.cmd.diffsplit({ args = { old_name }, mods = mods })
+    if opts.focus ~= "old" then
+        vim.cmd.wincmd("p")
+    end
 end
 
 return M

lua/git/object.lua

@@ -395,11 +395,9 @@ local function open_section(r, commit, section)
     local left = side(r, commit, true, section.blob_a, section.path_a)
     local right = side(r, commit, false, section.blob_b, section.path_b)
     if left and right then
-        vim.cmd.normal({ "m'", bang = true })
-        vim.api.nvim_set_current_buf(right)
-        require("git.diffsplit").open({
-            target = vim.api.nvim_buf_get_name(left),
-            mods = { vertical = true },
+        require("git.diffsplit").open_pair(left, right, {
+            layout = "vertical",
+            focus = "new",
         })
         return
     end

lua/git/status_view.lua

@@ -391,17 +391,11 @@ local function view_row(s, row, focus_left)
     ---@cast left ow.Git.StatusView.Pane
     ---@cast right ow.Git.StatusView.Pane
 
-    vim.api.nvim_win_set_buf(target, right.buf)
-    if right.name then
-        util.set_buf_name(right.buf, right.name)
-    end
-
-    local older = left.name or vim.api.nvim_buf_get_name(left.buf)
     local left_win
     vim.api.nvim_win_call(target, function()
-        diffsplit.open({
-            target = older,
-            mods = { vertical = true },
+        diffsplit.open_pair(left.buf, right.buf, {
+            layout = "vertical",
+            focus = "old",
         })
         left_win = vim.api.nvim_get_current_win()
         vim.api.nvim_win_set_cursor(left_win, { 1, 0 })

plugin/git.lua

@@ -183,16 +183,16 @@ local DIFF_DIRECTIONS = { "vertical", "horizontal" }
 
 vim.api.nvim_create_user_command("Gdiffsplit", function(opts)
     local fargs = opts.fargs
-    local mods = nil
+    local layout = nil
     local rev_idx = 1
     if fargs[1] == "vertical" then
-        mods = { vertical = true }
+        layout = "vertical"
         rev_idx = 2
     elseif fargs[1] == "horizontal" then
-        mods = { vertical = false }
+        layout = "horizontal"
         rev_idx = 2
     end
-    require("git.diffsplit").open({ target = fargs[rev_idx], mods = mods })
+    require("git.diffsplit").open({ other = fargs[rev_idx], layout = layout })
 end, {
     nargs = "*",
     complete = function(arg_lead, cmd_line, _)
@@ -253,21 +253,21 @@ vim.keymap.set("n", "<Plug>(git-edit)", function()
 end, { silent = true, desc = "Edit a git object" })
 
 vim.keymap.set("n", "<Plug>(git-diffsplit-vertical)", function()
-    require("git.diffsplit").open({ mods = { vertical = true } })
+    require("git.diffsplit").open({ layout = "vertical" })
 end, { silent = true, desc = "Open a diff split against index (vertical)" })
 vim.keymap.set("n", "<Plug>(git-diffsplit-horizontal)", function()
-    require("git.diffsplit").open({ mods = { vertical = false } })
+    require("git.diffsplit").open({ layout = "horizontal" })
 end, { silent = true, desc = "Open a diff split against index (horizontal)" })
 vim.keymap.set("n", "<Plug>(git-diffsplit-vertical-head)", function()
     require("git.diffsplit").open({
-        target = "HEAD",
-        mods = { vertical = true },
+        other = "HEAD",
+        layout = "vertical",
     })
 end, { silent = true, desc = "Open a diff split against HEAD (vertical)" })
 vim.keymap.set("n", "<Plug>(git-diffsplit-horizontal-head)", function()
     require("git.diffsplit").open({
-        target = "HEAD",
-        mods = { vertical = false },
+        other = "HEAD",
+        layout = "horizontal",
     })
 end, { silent = true, desc = "Open a diff split against HEAD (horizontal)" })
 

test/git/diffsplit_test.lua

@@ -0,0 +1,129 @@
+local Revision = require("git.core.revision")
+local h = require("test.git.helpers")
+local t = require("test")
+
+---@return integer[]
+local function diff_wins()
+    local wins = {}
+    for _, win in ipairs(vim.api.nvim_tabpage_list_wins(0)) do
+        if vim.wo[win].diff then
+            table.insert(wins, win)
+        end
+    end
+    return wins
+end
+
+---@param role "left"|"right"
+---@return integer
+local function vertical_diff_win(role)
+    local wins = diff_wins()
+    table.sort(wins, function(a, b)
+        return vim.api.nvim_win_get_position(a)[2]
+            < vim.api.nvim_win_get_position(b)[2]
+    end)
+    local win = role == "left" and wins[1] or wins[#wins]
+    if not win then
+        error("diff window not found")
+    end
+    return win
+end
+
+---@param dir string
+local function cleanup_dir_buffers(dir)
+    for _, buf in ipairs(vim.api.nvim_list_bufs()) do
+        local name = vim.api.nvim_buf_get_name(buf)
+        if name:find(dir, 1, true) then
+            pcall(vim.api.nvim_buf_delete, buf, { force = true })
+        end
+    end
+end
+
+t.test("open from worktree focuses the index pane", function()
+    local dir = h.make_repo({ ["a.txt"] = "old\n" })
+    t.write(dir, "a.txt", "new\n")
+    vim.cmd.edit(vim.fs.joinpath(dir, "a.txt"))
+
+    local current_buf = vim.api.nvim_get_current_buf()
+    require("git.diffsplit").open()
+
+    t.wait_for(function()
+        return #diff_wins() == 2
+    end, "diff windows to open")
+
+    t.eq(vim.api.nvim_get_current_win(), vertical_diff_win("left"))
+    t.truthy(
+        vim.api.nvim_get_current_buf() ~= current_buf,
+        "worktree buffer should lose focus"
+    )
+end)
+
+t.test("open from index focuses the worktree pane", function()
+    local dir = h.make_repo({ ["a.txt"] = "old\n" })
+    t.write(dir, "a.txt", "new\n")
+    local r = assert(require("git.core.repo").resolve(dir))
+    local index_buf = require("git.object").buf_for(
+        r,
+        Revision.new({ stage = 0, path = "a.txt" })
+    )
+    vim.api.nvim_set_current_buf(index_buf)
+
+    require("git.diffsplit").open({ layout = "vertical" })
+
+    t.wait_for(function()
+        return #diff_wins() == 2
+    end, "diff windows to open")
+
+    local right = vertical_diff_win("right")
+    t.eq(
+        vim.api.nvim_get_current_win(),
+        right,
+        "worktree buffer should be focused"
+    )
+    t.truthy(
+        vim.api.nvim_get_current_buf() ~= index_buf,
+        "index buffer should lose focus"
+    )
+end)
+
+t.test("open_pair keeps old on the left when splitright is set", function()
+    local dir = vim.fn.tempname()
+    vim.fn.mkdir(dir, "p")
+    t.defer(function()
+        cleanup_dir_buffers(dir)
+        vim.fn.delete(dir, "rf")
+    end)
+
+    local old = vim.fs.joinpath(dir, "old.txt")
+    local new = vim.fs.joinpath(dir, "new.txt")
+    vim.fn.writefile({ "old" }, old)
+    vim.fn.writefile({ "new" }, new)
+
+    local prev_splitright = vim.o.splitright
+    vim.o.splitright = true
+    t.defer(function()
+        vim.o.splitright = prev_splitright
+    end)
+
+    local old_buf = vim.fn.bufadd(old)
+    local new_buf = vim.fn.bufadd(new)
+    vim.fn.bufload(old_buf)
+    vim.fn.bufload(new_buf)
+
+    require("git.diffsplit").open_pair(old_buf, new_buf, {
+        layout = "vertical",
+    })
+
+    t.wait_for(function()
+        return #diff_wins() == 2
+    end, "diff windows to open")
+
+    local left = vertical_diff_win("left")
+    local right = vertical_diff_win("right")
+    t.eq(vim.api.nvim_win_get_buf(left), old_buf, "old pane should be left")
+    t.eq(vim.api.nvim_win_get_buf(right), new_buf, "new pane should be right")
+    t.eq(
+        vim.api.nvim_get_current_win(),
+        right,
+        "new pane should be focused by default"
+    )
+end)

test/git/status_view_test.lua

@@ -341,7 +341,7 @@ t.test(
             error("a non-sidebar window should remain after close")
         end
         vim.api.nvim_set_current_win(remaining)
-        require("git.diffsplit").open({ mods = { vertical = true } })
+        require("git.diffsplit").open({ layout = "vertical" })
         t.wait_for(function()
             local count = 0
             for _, w in ipairs(vim.api.nvim_tabpage_list_wins(0)) do