Feat: Rewrite diff module to allow for external dependencies as jj.nvim's diff tool (#74)

- Refactor diff into modular architecture (native, diffview, codediff)
- Add the possibility for users to define their own diff backend
- Support external diff tools like diffview.nvim codediff.nvim
- Enable visual mode selection to diff two changes in log buffer
- Add summary tooltip integration with terminal
- Update documentation with new diff workflows

lua/jj/cmd/log.lua

@@ -6,6 +6,7 @@ local runner = require("jj.core.runner")
 local parser = require("jj.core.parser")
 local terminal = require("jj.ui.terminal")
 local buffer = require("jj.core.buffer")
+local diff = require("jj.diff")
 
 local log_selected_hl_group = "JJLogSelectedHlGroup"
 local log_selected_ns_id = vim.api.nvim_create_namespace(log_selected_hl_group)
@@ -332,13 +333,23 @@ end
 
 --- Handle diffing a log line
 function M.handle_log_diff()
-	local revset = get_revset()
-
-	if revset then
-		local cmd = string.format("jj show --no-pager %s", revset)
-		terminal.run_floating(cmd, require("jj.cmd").floating_keymaps())
-	else
+	local revsets = extract_revsets_from_terminal_buffer()
+	if not revsets then
 		utils.notify("No valid revision found in the log line", vim.log.levels.ERROR)
+		return
+	end
+
+	-- Delete the pipes from the revsets string since jj new expects space separated revsets
+	revsets = revsets:gsub("| ", "")
+
+	local is_multiple = revsets:find(" ") ~= nil
+
+	if not is_multiple then
+		diff.show_revision({ rev = revsets })
+	else
+		-- Get the first and the last revset to diff
+		local list = vim.split(revsets, "%s+", { trimempty = true })
+		diff.diff_revisions({ left = list[1], right = list[#list] })
 	end
 end
 
@@ -731,40 +742,11 @@ function M.handle_summary_diff(revset)
 		terminal.keep_tooltip_open(true)
 	end
 
-	-- Add custom close behavior that returns to tooltip
-	local function close_and_return()
-		-- Close the floating diff
-		terminal.close_floating_buffer()
-		-- Return focus to tooltip if still valid
-		if terminal.state.tooltip_win and vim.api.nvim_win_is_valid(terminal.state.tooltip_win) then
-			vim.api.nvim_set_current_win(terminal.state.tooltip_win)
-		end
-		-- Clear suppress flag
-		if terminal.state.tooltip_buf and vim.api.nvim_buf_is_valid(terminal.state.tooltip_buf) then
-			terminal.keep_tooltip_open(false)
-		end
-	end
-
-	local cmd = require("jj.cmd")
-	local cfg = cmd.config.keymaps.floating or {}
-	-- In this specific case we override the behaviour of the default terminal close and return to the old buffer
-	local specs = {
-		close = {
-			modes = { "n", "v" },
-			handler = close_and_return,
-			desc = "Close diff and return to tooltip",
-		},
-		hide = {
-			modes = { "n", "v" },
-			handler = close_and_return,
-			desc = "Close diff and return to tooltip",
-		},
-	}
-
-	terminal.run_floating(
-		string.format("jj diff -r %s %s", revset, filepath.new_path),
-		cmd.resolve_keymaps_from_specs(cfg, specs)
-	)
+	-- Use the diff module to show what changed in this revision for this file
+	diff.show_revision({
+		rev = revset,
+		path = filepath.new_path,
+	})
 end
 
 --- Handle edit action in summary tooltip (opens file after jj edit)
@@ -936,7 +918,7 @@ function M.log_keymaps()
 		diff = {
 			desc = "Diff revision under cursor",
 			handler = M.handle_log_diff,
-			modes = { "n" },
+			modes = { "n", "v" },
 		},
 		new = {
 			desc = "Create new change branching off revision under cursor",