Command table: Sorted subcommands (#9951)

Sort the sub-commands so that every time we execute the script it generates the exact same results.
This will case less merge conflicts if two PRs edit different json files.

also:
* make the script agnostic to where it is executed (more flexible).
* add documentation about commands.c and the json files in the readme.

Co-authored-by: Oran Agra <oran@redislabs.com>

utils/generate-command-code.py

@@ -4,8 +4,6 @@ import os
 import glob
 import json
 
-# Note: This script should be run from the src/ dir: ../utils/generate-command-code.py
-
 ARG_TYPES = {
     "string": "ARG_TYPE_STRING",
     "integer": "ARG_TYPE_INTEGER",
@@ -305,12 +303,13 @@ class Command(object):
 
     def write_internal_structs(self, f):
         if self.subcommands:
-            for subcommand in sorted(self.subcommands, key=lambda cmd: cmd.name):
+            subcommand_list = sorted(self.subcommands, key=lambda cmd: cmd.name)
+            for subcommand in subcommand_list:
                 subcommand.write_internal_structs(f)
 
             f.write("/* %s command table */\n" % self.fullname())
             f.write("struct redisCommand %s[] = {\n" % self.subcommand_table_name())
-            for subcommand in self.subcommands:
+            for subcommand in subcommand_list:
                 f.write("{%s},\n" % subcommand.struct_code())
             f.write("{0}\n")
             f.write("};\n\n")
@@ -367,9 +366,12 @@ def create_command(name, desc):
 
 # MAIN
 
+# Figure out where the sources are
+srcdir = os.path.abspath(os.path.dirname(os.path.abspath(__file__)) + "/../src")
+
 # Create all command objects
 print("Processing json files...")
-for filename in glob.glob('commands/*.json'):
+for filename in glob.glob('%s/commands/*.json' % srcdir):
     with open(filename,"r") as f:
         d = json.load(f)
         for name, desc in d.items():
@@ -387,7 +389,7 @@ for command in commands.values():
         command.subcommands.append(subcommand)
 
 print("Generating commands.c...")
-with open("commands.c","w") as f:
+with open("%s/commands.c" % srcdir,"w") as f:
     f.write("/* Automatically generated by %s, do not edit. */\n\n" % os.path.basename(__file__))
     f.write("#include \"server.h\"\n")
     f.write(