fix(file): show files added since the diffed revision as empty instead of erroring (#130)

Co-authored-by: Roman Konoval <roman@jiko.io>

lua/jj/core/runner.lua

@@ -42,14 +42,15 @@ end
 --- @param silent boolean|nil Optional to silent the notification
 --- @return string|nil output Raw stdout bytes, or nil if failed
 --- @return boolean success Whether the command succeeded
+--- @return string stderr The command's stderr (empty on success)
 function M.execute_command_raw(cmd, error_prefix, silent)
 	local result = vim.system({ "sh", "-c", cmd }):wait()
 	if result.code ~= 0 then
 		local msg = result.stderr ~= "" and result.stderr or result.stdout or ""
 		error_notify(msg, error_prefix, silent)
-		return nil, false
+		return nil, false, msg
 	end
-	return result.stdout or "", true
+	return result.stdout or "", true, ""
 end
 
 --- Execute a system command synchronously and call success callback.

lua/jj/diff/codediff.lua

@@ -172,8 +172,10 @@ diff.register_backend("codediff", {
 			-- side is decoded in the same way as the current file.
 			-- Assumes the encoding didn't change between revisions.
 			local enc = file.get_buf_encoding(0)
-			local base_lines, base_had_eol, ok_read = file.get_file_content(revset, path, enc)
-			if not ok_read then
+			-- A file added since `revset` has no content there; show it as empty
+			-- so it diffs as fully added rather than aborting the diff.
+			local base_lines, base_had_eol, ok_read, _, absent = file.get_file_content(revset, path, enc)
+			if not ok_read and not absent then
 				utils.notify(string.format("Could not read `%s` from `%s` for CodeDiff", path, revset), vim.log.levels.ERROR)
 				return
 			end

lua/jj/diff/native.lua

@@ -28,8 +28,10 @@ local function open_revision(rev, path, enc)
 		return
 	end
 
-	local lines, had_eol, ok_read, used_enc = file.get_file_content(change_id, rel_path, enc)
-	if not ok_read then
+	-- A file added since `rev` has no content there; show it as empty so it
+	-- diffs as fully added rather than aborting the diff.
+	local lines, had_eol, ok_read, used_enc, absent = file.get_file_content(change_id, rel_path, enc)
+	if not ok_read and not absent then
 		utils.notify(string.format("Could not read `%s` from `%s`", rel_path, change_id), vim.log.levels.ERROR)
 		return
 	end

lua/jj/file.lua

@@ -219,23 +219,26 @@ M._encode = encode
 ---				(default: auto-detected from content)
 --- @return string[] lines
 --- @return boolean had_eol Whether the content had a trailing newline
---- @return boolean ok Whether the command succeeded
+--- @return boolean ok Whether the read succeeded
 --- @return jj.file.enc used_enc The encoding used to decode the content
+--- @return boolean absent True when the path does not exist in `rev` (e.g. a
+---				file added since `rev`).
 local function get_file_content(rev, path, enc)
-	local raw, ok = runner.execute_command_raw(
+	local raw, ok, stderr = runner.execute_command_raw(
 		string.format("jj file show -r %s %s", vim.fn.shellescape(rev), vim.fn.shellescape(path)),
 		nil,
 		true
 	)
 	if not ok or not raw then
-		return {}, false, false, enc or { fenc = "", bomb = false, ff = "unix" }
+		local absent = stderr ~= nil and stderr:find("No such path", 1, true) ~= nil
+		return {}, false, false, enc or { fenc = "", bomb = false, ff = "unix" }, absent
 	end
 	local lines, had_eol, used_enc = decode(raw, enc)
 	if not lines then
 		utils.notify(had_eol --[[@as string]], vim.log.levels.ERROR)
-		return {}, false, false, used_enc
+		return {}, false, false, used_enc, false
 	end
-	return lines, had_eol --[[@as boolean]], true, used_enc
+	return lines, had_eol --[[@as boolean]], true, used_enc, false
 end
 M.get_file_content = get_file_content
 
@@ -436,8 +439,9 @@ function M.register_command()
 			local name = vim.api.nvim_buf_get_name(0)
 			local change_id, path = utils.parse_jj_uri(name)
 			if not change_id or not path then return end
-			local lines, had_eol, ok_read, used_enc = get_file_content(change_id, path)
-			if not ok_read then
+			-- Keep reloads of an added-file diff buffer empty rather than erroring.
+			local lines, had_eol, ok_read, used_enc, absent = get_file_content(change_id, path)
+			if not ok_read and not absent then
 				utils.notify(string.format("Could not read `%s` from `%s`", path, change_id), vim.log.levels.ERROR)
 				return
 			end

tests/run_tests.lua

@@ -793,6 +793,63 @@ run_test("decode: roundtrip reproduces the bytes exactly", function()
 	end
 end)
 
+print("\n=== Running get_file_content tests ===\n")
+
+run_test("get_file_content: reads existing file content", function()
+	local runner = require("jj.core.runner")
+	local original = runner.execute_command_raw
+	runner.execute_command_raw = function()
+		return "a\nb\n", true, ""
+	end
+	local ok_test, err = pcall(function()
+		local lines, had_eol, ok, _, absent = jj_file.get_file_content("abc123", "src/file.py")
+		assert_table_equals({ "a", "b" }, lines)
+		assert_equals(true, had_eol)
+		assert_equals(true, ok)
+		assert_equals(false, absent)
+	end)
+	runner.execute_command_raw = original
+	if not ok_test then
+		error(err)
+	end
+end)
+
+run_test("get_file_content: absent path in revision reports absent (not a read error)", function()
+	local runner = require("jj.core.runner")
+	local original = runner.execute_command_raw
+	runner.execute_command_raw = function()
+		return nil, false, "Error: No such path: src/new_file.py\n"
+	end
+	local ok_test, err = pcall(function()
+		local lines, had_eol, ok, _, absent = jj_file.get_file_content("abc123", "src/new_file.py")
+		assert_table_equals({}, lines)
+		assert_equals(false, had_eol)
+		assert_equals(false, ok)
+		assert_equals(true, absent)
+	end)
+	runner.execute_command_raw = original
+	if not ok_test then
+		error(err)
+	end
+end)
+
+run_test("get_file_content: genuine read error returns failure without absent", function()
+	local runner = require("jj.core.runner")
+	local original = runner.execute_command_raw
+	runner.execute_command_raw = function()
+		return nil, false, "Error: Revision `nope` doesn't exist\n"
+	end
+	local ok_test, err = pcall(function()
+		local _, _, ok, _, absent = jj_file.get_file_content("nope", "src/file.py")
+		assert_equals(false, ok)
+		assert_equals(false, absent)
+	end)
+	runner.execute_command_raw = original
+	if not ok_test then
+		error(err)
+	end
+end)
+
 -- Print summary
 print(string.format("\n=== Test Summary ==="))
 print(string.format("Passed: %d", tests_passed))