Add 'Available since' to module API function docs (#10229)

The script which generates the markdown docs from module.c is updated to include
the version in which each module API function was introduced.

The script uses git tags to find this information. If git is not available or if we're not in
a git repo, the 'since' is silently skipped.

The line `**Available since:** (version)` is added after the function prototype

Rename to utils/generate-module-api-doc.rb

utils/generate-module-api-doc.rb

@@ -78,6 +78,7 @@ def docufy(src,i)
     puts "<span id=\"#{name}\"></span>\n\n"
     puts "### `#{name}`\n\n"
     puts "    #{proto}\n"
+    puts "**Available since:** #{$since[name]}\n\n" if $since[name]
     comment = ""
     while true
         i = i-1
@@ -135,8 +136,9 @@ def is_func_line(src, i)
 end
 
 puts "# Modules API reference\n\n"
-puts "<!-- This file is generated from module.c using gendoc.rb -->\n\n"
+puts "<!-- This file is generated from module.c using\n"
-src = File.open(File.dirname(__FILE__) ++ "/../module.c").to_a
+puts "     utils/generate-module-api-doc.rb -->\n\n"
+src = File.open(File.dirname(__FILE__) ++ "/../src/module.c").to_a
 
 # Build function index
 $index = {}
@@ -148,6 +150,24 @@ src.each_with_index do |line,i|
     end
 end
 
+# Populate the 'since' map (name => version) if we're in a git repo.
+$since = {}
+git_dir = File.dirname(__FILE__) ++ "/../.git"
+if File.directory?(git_dir) && `which git` != ""
+    `git --git-dir="#{git_dir}" tag --sort=v:refname`.each_line do |version|
+        next if version !~ /^(\d+)\.\d+\.\d+?$/ || $1.to_i < 4
+        version.chomp!
+        `git --git-dir="#{git_dir}" cat-file blob "#{version}:src/module.c"`.each_line do |line|
+            if line =~ /^\w.*[ \*]RM_([A-z0-9]+)/
+                name = "RedisModule_#{$1}"
+                if ! $since[name]
+                    $since[name] = version
+                end
+            end
+        end
+    end
+end
+
 # Print TOC
 puts "## Sections\n\n"
 src.each_with_index do |_line,i|