Adds --dev flag for development-branch sub-repositories. (#736)

This adds support for easily requesting `dev` modules from
LuaRocks.org, as in:

```
luarocks install --dev luafilesystem
```

The list of URLs configured in `rocks_servers` is prepended
with a list containing "/dev" in their paths.

4 files changed, 19 insertions, 2 deletions

diff --git a/src/luarocks/cmd/help.lua b/src/luarocks/cmd/help.lua
index b986534c..d58fdcc0 100644
--- a/src/luarocks/cmd/help.lua
+++ b/src/luarocks/cmd/help.lua
@@ -52,6 +52,8 @@ function help.command(flags, command)
       util.printout([[
         These apply to all commands, as appropriate:
 
+        --dev                  Enable the sub-repositories in rocks servers
+                               for rockspecs of in-development versions
         --server=<server>      Fetch rocks/rockspecs from this server
                                (takes priority over config file)
         --only-server=<server> Fetch rocks/rockspecs from this server only
diff --git a/src/luarocks/command_line.lua b/src/luarocks/command_line.lua
index 6a1cc519..9d33fe15 100644
--- a/src/luarocks/command_line.lua
+++ b/src/luarocks/command_line.lua
@@ -10,6 +10,7 @@ local path = require("luarocks.path")
 local dir = require("luarocks.dir")
 local deps = require("luarocks.deps")
 local fs = require("luarocks.fs")
+local fun = require("luarocks.fun")
 
 local program = util.this_program("luarocks")
 
@@ -172,11 +173,23 @@ function command_line.run_command(...)
    cfg.variables.SCRIPTS_DIR = cfg.deploy_bin_dir
 
    if flags["server"] then
-      local protocol, path = dir.split_url(flags["server"])
-      table.insert(cfg.rocks_servers, 1, protocol.."://"..path)
+      local protocol, pathname = dir.split_url(flags["server"])
+      table.insert(cfg.rocks_servers, 1, protocol.."://"..pathname)
+   end
+
+   if flags["dev"] then
+      local append_dev = function(s) return dir.path(s, "dev") end
+      local dev_servers = fun.traverse(cfg.rocks_servers, append_dev)
+      cfg.rocks_servers = fun.concat(dev_servers, cfg.rocks_servers)
    end
    
    if flags["only-server"] then
+      if flags["dev"] then
+         die("--only-server cannot be used with --dev")
+      end
+      if flags["server"] then
+         die("--only-server cannot be used with --server")
+      end
       cfg.rocks_servers = { flags["only-server"] }
    end
 
diff --git a/src/luarocks/core/vers.lua b/src/luarocks/core/vers.lua
index 1c016bbb..864cc5b5 100644
--- a/src/luarocks/core/vers.lua
+++ b/src/luarocks/core/vers.lua
@@ -6,6 +6,7 @@ local require = nil
 --------------------------------------------------------------------------------
 
 local deltas = {
+   dev =    120000000,
    scm =    110000000,
    cvs =    100000000,
    rc =    -1000,
diff --git a/src/luarocks/util.lua b/src/luarocks/util.lua
index 0af23df6..1bc24be7 100644
--- a/src/luarocks/util.lua
+++ b/src/luarocks/util.lua
@@ -89,6 +89,7 @@ local supported_flags = {
    ["deps"] = true,
    ["deps-mode"] = "<mode>",
    ["detailed"] = "\"<text>\"",
+   ["dev"] = true,
    ["force"] = true,
    ["force-fast"] = true,
    ["from"] = "<server>",