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.
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