config: add --help-env-list CLI option

It lists the environment variables that are taken into account by the
config module.

TBD: Part of #xxxx

NO_DOC=reflected in tarantool/doc#3544

Author: Totktonada

changelogs/unreleased/config-help-env-list.md

@@ -0,0 +1,3 @@
+## feature/config
+
+* Added `--help-env-list` CLI option (gh-8862).

src/box/lua/config/init.lua

@@ -336,6 +336,11 @@ function methods._startup(self, instance_name, config_file)
     broadcast(self)
 end
 
+function methods._print_env_list(self)
+    local env_source = require('internal.config.source.env').new()
+    io.stdout:write(env_source:_env_list())
+end
+
 function methods.get(self, path)
     selfcheck(self, 'get')
     if self._status == 'uninitialized' then

src/box/lua/config/source/env.lua

@@ -1,4 +1,5 @@
 local schema = require('internal.config.utils.schema')
+local tabulate = require('internal.config.utils.tabulate')
 local instance_config = require('internal.config.instance_config')
 
 local methods = {}
@@ -14,6 +15,62 @@ function methods._env_var_name(self, path_in_schema)
     return env_var_name
 end
 
+function methods._env_list(self)
+    local rows = {}
+
+    local ce = 'Community Edition'
+    local ee = 'Enterprise Edition'
+
+    -- A header of the table.
+    table.insert(rows, {
+        'ENVIRONMENT VARIABLE',
+        'TYPE',
+        'DEFAULT',
+        'AVAILABILITY',
+    })
+    table.insert(rows, tabulate.SPACER)
+
+    -- Environment variables that duplicate CLI options.
+    table.insert(rows, {
+        'TT_INSTANCE_NAME',
+        'string',
+        'N/A',
+        ce,
+    })
+    table.insert(rows, {
+        'TT_CONFIG',
+        'string',
+        'nil',
+        ce,
+    })
+    table.insert(rows, tabulate.SPACER)
+
+    -- Collect the options from the schema and sort them
+    -- lexicographically.
+    local options = instance_config:pairs():totable()
+    table.sort(options, function(a, b)
+        return table.concat(a.path, '_') < table.concat(b.path, '_')
+    end)
+
+    -- Transform the schema nodes (options) into the environment
+    -- variables description.
+    for _, w in ipairs(options) do
+        local default = w.schema.default
+        if default == nil and type(default) == 'cdata' then
+            default = 'box.NULL'
+        end
+
+        table.insert(rows, {
+            self._env_var_name(self, w.path),
+            w.schema.type,
+            tostring(default),
+            w.annotations.enterprise_edition and ee or ce,
+        })
+    end
+
+    return tabulate.encode(rows)
+end
+
 -- Gather most actual config values.
 function methods.sync(self, _config_module, _iconfig)
     local values = {}

src/lua/init.c

@@ -1042,6 +1042,7 @@ run_script_f(va_list ap)
 	bool interactive = opt_mask & O_INTERACTIVE;
 	bool bytecode = opt_mask & O_BYTECODE;
 	bool debugging = opt_mask & O_DEBUGGING;
+	bool help_env_list = opt_mask & O_HELP_ENV_LIST;
 	/*
 	 * An error is returned via an external diag. A caller
 	 * can't use fiber_join(), because the script can call
@@ -1108,6 +1109,23 @@ run_script_f(va_list ap)
 		}
 	}
 
+	/*
+	 * Show a list of environment variables that are
+	 * considered by tarantool and exit.
+	 */
+	if (help_env_list) {
+		/* require('config'):_print_env_list() */
+		if (lua_require_lib(L, "config") != 0)
+			goto error;
+		lua_pushstring(L, "_print_env_list");
+		lua_gettable(L, -2);
+		lua_pushvalue(L, -2);
+		if (luaT_call(L, 1, 0) != 0)
+			goto error;
+		lua_settop(L, 0);
+		goto end;
+	}
+
 	/*
 	 * Start an instance using an externally provided
 	 * configuration if the --name option is passed.

src/lua/init.h

@@ -55,6 +55,7 @@ struct instance_state {
 #define O_BYTECODE    0x2
 #define O_DEBUGGING   0x4
 #define O_EXECUTE     0x8
+#define O_HELP_ENV_LIST 0x10
 
 /**
  * Create tarantool_L and initialize built-in Lua modules.

src/main.cc

@@ -632,6 +632,7 @@ print_help(FILE *stream, const char *program)
 		"  %s [OPTIONS] [SCRIPT [ARGS]]\n\n"
 		"Options:\n\n"
 		" -h, --help             display this help and exit\n"
+		" --help-env-list        display env variables taken into account\n"
 		" -v, --version          print program version and exit\n"
 		" -c, --config PATH      set a path to yaml config file as 'PATH'\n"
 		" -n, --name INSTANCE    set an instance name as 'INSTANCE'\n"
@@ -677,6 +678,7 @@ main(int argc, char **argv)
 		{"version", no_argument, 0, 'v'},
 		{"config", required_argument, 0, 'c'},
 		{"name", required_argument, 0, 'n'},
+		{"help-env-list", no_argument, 0, 'E'},
 		{NULL, 0, 0, 0},
 	};
 	static const char *opts = "+hVvb::ij:e:l:dc:n:";
@@ -706,6 +708,9 @@ main(int argc, char **argv)
 		case 'h':
 			print_help(stdout, basename(argv[0]));
 			return 0;
+		case 'E':
+			opt_mask |= O_HELP_ENV_LIST;
+			break;
 		case 'i':
 			/* Force interactive mode */
 			opt_mask |= O_INTERACTIVE;
@@ -805,8 +810,8 @@ main(int argc, char **argv)
 	if (strlen(tarantool_path) < strlen(tarantool_bin))
 		panic("executable path is trimmed");
 
-	if (script == NULL && (opt_mask & (O_INTERACTIVE | O_EXECUTE)) == 0 &&
-	    instance.name == NULL) {
+	if (script == NULL && (opt_mask & (O_INTERACTIVE | O_EXECUTE |
+	    O_HELP_ENV_LIST)) == 0 && instance.name == NULL) {
 		static const char misuse_msg[] = "Invalid usage: "
 			"please either provide a Lua script name\n"
 			"or specify an instance name to be started\n"

test/box-py/args.result

@@ -24,6 +24,7 @@ Usage:
 Options:
 
  -h, --help             display this help and exit
+ --help-env-list        display env variables taken into account
  -v, --version          print program version and exit
  -c, --config PATH      set a path to yaml config file as 'PATH'
  -n, --name INSTANCE    set an instance name as 'INSTANCE'
@@ -65,6 +66,7 @@ Usage:
 Options:
 
  -h, --help             display this help and exit
+ --help-env-list        display env variables taken into account
  -v, --version          print program version and exit
  -c, --config PATH      set a path to yaml config file as 'PATH'
  -n, --name INSTANCE    set an instance name as 'INSTANCE'

test/config-luatest/cli_test.lua

@@ -0,0 +1,72 @@
+local t = require('luatest')
+local justrun = require('test.justrun')
+
+local g = t.group()
+
+g.test_help_env_list = function()
+    local res = justrun.tarantool('.', {}, {'--help-env-list'}, {nojson = true})
+    t.assert_equals(res.exit_code, 0)
+
+    -- Pick up several well-known env variables to verify the idea
+    -- of the listing, but at the same time, don't list all the
+    -- options in the test case.
+    local cases = {
+        -- Verify that the env variables that duplicates CLI
+        -- options are present.
+        {
+            name = 'TT_INSTANCE_NAME',
+            type = 'string',
+            default = 'N/A',
+            availability = 'Community Edition',
+        },
+        {
+            name = 'TT_CONFIG',
+            type = 'string',
+            default = 'nil',
+            availability = 'Community Edition',
+        },
+        -- An env variable that accepts a numeric value and has
+        -- explicit default value.
+        {
+            name = 'TT_MEMTX_MEMORY',
+            type = 'integer',
+            default = '268435456',
+            availability = 'Community Edition',
+        },
+        -- An env variable that has box.NULL default.
+        {
+            name = 'TT_DATABASE_MODE',
+            type = 'string',
+            default = 'box.NULL',
+            availability = 'Community Edition',
+        },
+        -- An option with a template default.
+        {
+            name = 'TT_CONSOLE_SOCKET',
+            type = 'string',
+            default = '{{ instance_name }}.control',
+            availability = 'Community Edition',
+        },
+        -- An Enterprise Edition option and, at the same time,
+        -- an option with non-string type.
+        {
+            name = 'TT_CONFIG_ETCD_ENDPOINTS',
+            type = 'array',
+            default = 'nil',
+            availability = 'Enterprise Edition',
+        },
+        -- Yet another Enterprise Edition option.
+        {
+            name = 'TT_WAL_EXT_NEW',
+            type = 'boolean',
+            default = 'nil',
+            availability = 'Enterprise Edition',
+        },
+    }
+
+    for _, case in ipairs(cases) do
+        local needle = ('%s.*%s.*%s.*%s'):format(case.name, case.type,
+            case.default, case.availability)
+        t.assert(res.stdout:find(needle), case.name)
+    end
+end