Add diff split (#13)

lua/jj/cmd.lua

@@ -2,6 +2,7 @@
 local M = {}
 
 local utils = require("jj.utils")
+local diff = require("jj.diff")
 
 -- Config for cmd module
 M.config = {
@@ -551,7 +552,7 @@ local function execute_describe(description)
 		return
 	end
 
-	-- Use --stdin to properly handle multi-line  and special characters
+	-- Use --stdin to properly handle multi-line and special characters
 	local _, success = utils.execute_command("jj describe --stdin", "Failed to describe", description)
 	if success then
 		utils.notify("Description set.", vim.log.levels.INFO)
@@ -896,7 +897,7 @@ function M.j(args)
 	end
 
 	if #args == 0 then
-		-- Use the user's default command and do not try to parse anythng else
+		-- Use the user's default command and do not try to parse anything else
 		run("jj")
 		return
 	end
@@ -940,7 +941,7 @@ local function handle_j_command(opts)
 	M.j(args)
 end
 
---- Register the J command
+--- Register the J and Jdiff commands
 function M.register_command()
 	vim.api.nvim_create_user_command("J", handle_j_command, {
 		nargs = "*",
@@ -973,6 +974,19 @@ function M.register_command()
 		end,
 		desc = "Execute jj commands with subcommand support",
 	})
+
+	vim.api.nvim_create_user_command("Jdiff", diff.open_vdiff, {
+		nargs = "?",
+		desc = "Diff against jj revision",
+	})
+	vim.api.nvim_create_user_command("Jhdiff", diff.open_hdiff, {
+		nargs = "?",
+		desc = "Horizontal diff against jj revision",
+	})
+	vim.api.nvim_create_user_command("Jvdiff", diff.open_vdiff, {
+		nargs = "?",
+		desc = "Vertical diff against jj revision",
+	})
 end
 
 return M

lua/jj/diff.lua

@@ -0,0 +1,68 @@
+---@class jj.diff
+local M = {}
+
+local utils = require("jj.utils")
+
+--- Get the content of a file at a specific revision
+--- @param rev string The revision
+--- @param path string The file path
+--- @return table lines The file content
+local function get_file_content(rev, path)
+	local cmd = string.format("jj file show -r %s %s", rev, vim.fn.shellescape(path))
+	local content = vim.fn.system(cmd)
+	local success = vim.v.shell_error == 0
+	if success then
+		return vim.split(content, "\n", { trimempty = true })
+	else
+		-- File does not exist at revision
+		return {}
+	end
+end
+
+--- Open a read-only buffer for a specific revision of a file
+--- @param rev string The revision
+--- @param path string The file path
+function M.open_revision(rev, path)
+	local lines = get_file_content(rev, path)
+
+	local buf = vim.api.nvim_create_buf(false, true)
+
+	local buf_name = string.format("jj://%s/%s", rev, path)
+	vim.api.nvim_buf_set_name(buf, buf_name)
+	vim.api.nvim_buf_set_lines(buf, 0, -1, false, lines)
+
+	vim.bo[buf].buftype = "nofile"
+	vim.bo[buf].bufhidden = "wipe"
+	vim.bo[buf].readonly = true
+	vim.bo[buf].swapfile = false
+	vim.bo[buf].modifiable = true
+
+	vim.api.nvim_win_set_buf(0, buf)
+end
+
+--- Open a diff split for a specific revision of the current file
+--- @param split_fun function Split function for the diff
+--- @param args table Any passed arguments
+function M.open_diff(split_fun, args)
+	if not utils.ensure_jj() then
+		return
+	end
+
+	local rev = args[1] or "@-"
+	local path = vim.api.nvim_buf_get_name(0)
+
+	vim.cmd.diffthis()
+	split_fun({ mods = { split = "aboveleft" } })
+	M.open_revision(rev, path)
+	vim.cmd.diffthis()
+end
+
+function M.open_vdiff(opts)
+	M.open_diff(vim.cmd.vsplit, opts.fargs)
+end
+
+function M.open_hdiff(opts)
+	M.open_diff(vim.cmd.split, opts.fargs)
+end
+
+return M