console: configure continuation

Continuation marker can be set up with `\set continuation` command.
Works on both server and client side in any language.

Closes tarantool#4317
Requires tarantool#7357

@TarantoolBot document
Title: introduce line carrying slash

Now we can use multiline commands with lines ending by configuring
continuation symbol. Works only when there is no set delimiter.
There is also an alias `\set c on|off`, that does the same.
Consider the example where the marker is set, used and removed:
```
tarantool> \set continuation on
---
- true
...

tarantool> a = 10\
         > + 12
---
...

tarantool> \set continuation off
---
- true
...

tarantool> a = 10\
---
- error: '[string "a = 10\"]:1: unexpected symbol near ''\'''
...

tarantool>

```

changelogs/unreleased/gh-4317-console-add-line-carrying-backslash.md

@@ -0,0 +1,4 @@
+## feature/console
+
+* Now multiline commands can be used by setting up continuation marker
+  with `\set continuation` command.

src/box/lua/console.lua

@@ -51,6 +51,9 @@ local output_eos = { ["yaml"] = '\n...\n', ["lua"] = ';' }
 
 local default_local_eos = ''
 
+-- Each but the last string of multiline command should end with this string.
+local continuation_symbol = '\\'
+
 output_handlers["yaml"] = function(status, _opts, ...)
     local err, ok, res
      -- Using pcall, because serializer can raise an exception
@@ -294,6 +297,14 @@ local function set_output(storage, value)
     return true
 end
 
+local function set_continuation(storage, value)
+    if value ~= 'on' and value ~= 'off' then
+        return error('usage: \\set continuation on|off')
+    end
+    storage.continuation_on = value == 'on'
+    return true
+end
+
 local param_handlers = {
     language = set_language,
     lang = set_language,
@@ -302,7 +313,8 @@ local param_handlers = {
     o = set_output,
     delimiter = set_delimiter,
     delim = set_delimiter,
-    d = set_delimiter
+    d = set_delimiter,
+    continuation = set_continuation,
 }
 
 local function set_param(storage, _func, param, value)
@@ -497,6 +509,14 @@ local text_connection_mt = {
                     end
                 end
             end
+            if operators[items[1]] == set_param and
+                param_handlers[items[2]] == set_continuation then
+
+                local continuation = items[3]
+                if (continuation == 'on' or continuation == 'off') then
+                   self.continuation_on = continuation == 'on'
+               end
+            end
             return text
         end,
         --
@@ -573,7 +593,8 @@ local function wrap_text_socket(connection, url, print_f)
         print_f = print_f,
         eos = current_eos(),
         fmt = current_output()["fmt"],
-        local_eos = default_local_eos
+        local_eos = default_local_eos,
+        continuation_on = false,
     }, text_connection_mt)
     --
     -- Prepare the connection: setup EOS symbol
@@ -649,19 +670,29 @@ local function local_read(self)
             break
         end
         if delim == "" then
-            local lang = self.language
-            if not lang or lang == 'lua' then
-                -- stop once a complete Lua statement is entered
-                if local_check_lua(buf) then
-                    break
-                end
+            local continuation_on
+            if self.remote ~= nil then
+                continuation_on = self.remote.continuation_on
             else
-                break
+                continuation_on = self.continuation_on
+            end
+            local lang = self.language or 'lua'
+            -- Interpret continuation_symbol as a line continuation marker.
+            if continuation_on and line:endswith(continuation_symbol) then
+                buf = buf:sub(1, -1 - #continuation_symbol)
+                goto continue
+            end
+            -- Continue reading if Lua input seems incomplete according to
+            -- internal heuristic.
+            if lang == 'lua' and not local_check_lua(buf) then
+                goto continue
             end
+            break
         elseif #buf >= #delim and buf:sub(#buf - #delim + 1) == delim then
             buf = buf:sub(0, #buf - #delim)
             break
         end
+        ::continue::
         buf = buf.."\n"
         prompt = string.rep(' ', #self.prompt)
     end
@@ -689,9 +720,12 @@ local function local_print(self, output)
 end
 
 --
--- Read command from connected client console.listen()
+-- Read a line or a chunk from connected client console.listen().
 --
-local function client_read(self)
+-- The value is returned without delimiter (if any) and trailing
+-- newline character.
+--
+local function client_read_line(self)
     --
     -- Byte sequences that come over the network and come from
     -- the local client console may have a different terminal
@@ -712,6 +746,31 @@ local function client_read(self)
     return buf:sub(1, -#self.delimiter-2)
 end
 
+--
+-- Read a command from connected client console.listen().
+--
+local function client_read(self)
+    local buf = ''
+    local continuation_on = self.continuation_on
+    while true do
+        local line = client_read_line(self)
+        if line == nil then
+            -- EOF or error.
+            --
+            -- Note: Even if `buf` is not empty, skip unfinished
+            -- command.
+            return nil
+        end
+        buf = buf .. line
+        if continuation_on and line:endswith(continuation_symbol) then
+            buf = buf:sub(1, -1 - #continuation_symbol)
+        else
+            break
+        end
+    end
+    return buf
+end
+
 --
 -- Print result to connected client from console.listen()
 --
@@ -733,6 +792,7 @@ local repl_mt = {
         completion = internal.completion_handler;
         ac = true;
         local_eos = default_local_eos;
+        continuation_on = false;
     };
 }
 

test/app-luatest/gh_4317_console_backslash_test.lua

@@ -0,0 +1,63 @@
+local t = require('luatest')
+local g = t.group()
+
+local result_str =  [[tarantool> \set continuation on
+---
+- true
+...
+
+tarantool> local a = 0\
+         > for i = 1, 10 do
+         > a = a + i
+         > end\
+         > print(a)
+55
+---
+...
+
+tarantool> ]]
+
+local TARANTOOL_PATH = arg[-1]
+
+g.test_using_backslash_on_local_console = function()
+    local tarantool_command = [[\\set continuation on\nlocal a = 0\\\n]] ..
+                              [[for i = 1, 10 do\na = a + i\nend\\\n]] ..
+                              [[print(a)\n]]
+
+    local cmd = "printf '%s' | %s -i 2>/dev/null"
+    cmd = (cmd):format(tarantool_command, TARANTOOL_PATH)
+    local fh = io.popen(cmd, 'r')
+
+    -- XXX: Readline on CentOS 7 produces \e[?1034h escape sequence before
+    -- tarantool> prompt, remove it.
+    local result = fh:read('*a'):gsub('\x1b%[%?1034h', '')
+
+    fh:close()
+    t.assert_equals(result, result_str)
+end
+
+g.test_using_backslash_on_remote_console = function()
+    local console = require('console')
+    local socket = require('socket')
+    local log = require('log')
+
+    -- Suppress console log messages.
+    log.level(4)
+    local CONSOLE_SOCKET = '/tmp/tarantool-test-gh-4317.sock'
+    local EOL = '\n...\n'
+    console.listen(CONSOLE_SOCKET)
+    socket.tcp_connect('unix/', CONSOLE_SOCKET)
+    local tarantool_command = '\\set continuation on\nlocal a = 0 \\\n' ..
+                              'for i = 1, 10 do\\\n a = a + i \\\n end \\\n' ..
+                              'return a'
+
+    local client = socket.tcp_connect('unix/', CONSOLE_SOCKET)
+    client:write(('%s\n'):format(tarantool_command))
+    -- Read 'true' after '\set continuation on' and then read result.
+    client:read(EOL)
+    local result = client:read(EOL)
+    t.assert_str_contains(result, '- 55')
+    t.assert_not_str_contains(result, 'error')
+    client:close()
+    os.remove(CONSOLE_SOCKET)
+end