Add `luarocks which` command. (#733)

3 files changed, 35 insertions, 3 deletions

diff --git a/src/bin/luarocks b/src/bin/luarocks
index 88a1d1ca..491809dd 100755
--- a/src/bin/luarocks
+++ b/src/bin/luarocks
@@ -28,6 +28,7 @@ commands = {
    doc = "luarocks.cmd.doc",
    upload = "luarocks.cmd.upload",
    config = "luarocks.cmd.config",
+   which = "luarocks.cmd.which",
 }
 
 command_line.run_command(...)
diff --git a/src/luarocks/cmd/which.lua b/src/luarocks/cmd/which.lua
new file mode 100644
index 00000000..0116fdb8
--- /dev/null
+++ b/src/luarocks/cmd/which.lua
@@ -0,0 +1,30 @@
+
+--- @module luarocks.which_cmd
+-- Driver for the `luarocks which` command.
+local which_cmd = {}
+
+local loader = require("luarocks.loader")
+local cfg = require("luarocks.core.cfg")
+local util = require("luarocks.util")
+
+which_cmd.help_summary = "Tell which file corresponds to a given module name."
+which_cmd.help_arguments = "<modname>"
+which_cmd.help = [[
+Given a module name like "foo.bar", output which file would be loaded to resolve
+that module by luarocks.loader, like "/usr/local/lua/]]..cfg.lua_version..[[/foo/bar.lua".
+]]
+
+--- Driver function for "lua" command.
+-- @return boolean This function terminates the interpreter.
+function which_cmd.command(_, modname)
+   local pathname, rock_name, rock_version = loader.which(modname)
+   if not pathname then
+      return nil, "Module '" .. modname .. "' not found by luarocks.loader."
+   end
+   util.printout(pathname)
+   util.printout("(provided by " .. tostring(rock_name) .. " " .. tostring(rock_version) .. ")")
+   return true
+end
+
+return which_cmd
+
diff --git a/src/luarocks/loader.lua b/src/luarocks/loader.lua
index c8259689..84cdd696 100644
--- a/src/luarocks/loader.lua
+++ b/src/luarocks/loader.lua
@@ -222,10 +222,11 @@ end
 
 --- Return the pathname of the file that would be loaded for a module.
 -- @param module string: module name (eg. "socket.core")
--- @return string: filename of the module (eg. "/usr/local/lib/lua/5.1/socket/core.so")
+-- @return filename of the module (eg. "/usr/local/lib/lua/5.1/socket/core.so"),
+-- the rock name and the rock version.
 function loader.which(module)
-   local _, _, file_name = select_module(module, path.which_i)
-   return file_name
+   local rock_name, rock_version, file_name = select_module(module, path.which_i)
+   return file_name, rock_name, rock_version
 end
 
 --- Package loader for LuaRocks support.