6 files changed, 36 insertions, 10 deletions

diff --git a/src/luarocks/build/cmake.lua b/src/luarocks/build/cmake.lua
index e5b29147..c8f5a669 100644
--- a/src/luarocks/build/cmake.lua
+++ b/src/luarocks/build/cmake.lua
@@ -23,8 +23,9 @@ function cmake.run(rockspec)
 
    util.variable_substitutions(variables, rockspec.variables)
 
-   if not fs.execute_quiet(rockspec.variables.CMAKE, "--help") then
-      return nil, "'"..rockspec.variables.CMAKE.."' program not found. Is cmake installed? You may want to edit variables.CMAKE"
+   local ok, err_msg = fs.is_tool_available(rockspec.variables.CMAKE, "CMake")
+   if not ok then
+      return nil, err_msg
    end
 
    -- If inline cmake is present create CMakeLists.txt from it.
diff --git a/src/luarocks/fetch/cvs.lua b/src/luarocks/fetch/cvs.lua
index fad1ca0d..ccf928c4 100644
--- a/src/luarocks/fetch/cvs.lua
+++ b/src/luarocks/fetch/cvs.lua
@@ -21,8 +21,9 @@ function cvs.get_sources(rockspec, extract, dest_dir)
    assert(type(dest_dir) == "string" or not dest_dir)
 
    local cvs_cmd = rockspec.variables.CVS
-   if not fs.execute_quiet(cvs_cmd, "--version") then
-      return nil, "'"..cvs_cmd.."' program not found. Is CVS installed? You may want to edit variables.CVS"
+   local ok, err_msg = fs.is_tool_available(cvs_cmd, "CVS")
+   if not ok then
+      return nil, err_msg
    end
 
    local name_version = rockspec.name .. "-" .. rockspec.version
diff --git a/src/luarocks/fetch/git.lua b/src/luarocks/fetch/git.lua
index bea53fc8..e540d696 100644
--- a/src/luarocks/fetch/git.lua
+++ b/src/luarocks/fetch/git.lua
@@ -40,8 +40,9 @@ function git.get_sources(rockspec, extract, dest_dir, depth)
    -- Strip off .git from base name if present
    module = module:gsub("%.git$", "")
 
-   if not fs.execute_quiet(git_cmd, "--version") then
-      return nil, "'"..git_cmd.."' program not found. Is git installed? You may want to edit variables.GIT"
+   local ok, err_msg = fs.is_tool_available(git_cmd, "Git")
+   if not ok then
+      return nil, err_msg
    end
 
    local store_dir
diff --git a/src/luarocks/fetch/hg.lua b/src/luarocks/fetch/hg.lua
index 055e3bbe..518130b4 100644
--- a/src/luarocks/fetch/hg.lua
+++ b/src/luarocks/fetch/hg.lua
@@ -21,8 +21,9 @@ function hg.get_sources(rockspec, extract, dest_dir)
    assert(type(dest_dir) == "string" or not dest_dir)
 
    local hg_cmd = rockspec.variables.HG
-   if not fs.execute_quiet(hg_cmd, "--version") then
-      return nil, "'"..hg_cmd.."' program not found. Is Mercurial installed? You may want to edit variables.HG"
+   local ok, err_msg = fs.is_tool_available(hg_cmd, "Mercurial")
+   if not ok then
+      return nil, err_msg
    end
 
    local name_version = rockspec.name .. "-" .. rockspec.version
diff --git a/src/luarocks/fetch/svn.lua b/src/luarocks/fetch/svn.lua
index 8fe582f6..755e5e32 100644
--- a/src/luarocks/fetch/svn.lua
+++ b/src/luarocks/fetch/svn.lua
@@ -21,8 +21,9 @@ function svn.get_sources(rockspec, extract, dest_dir)
    assert(type(dest_dir) == "string" or not dest_dir)
 
    local svn_cmd = rockspec.variables.SVN
-   if not fs.execute_quiet(svn_cmd, "--version") then
-      return nil, "'"..svn_cmd.."' program not found. Is Subversion installed? You may want to edit variables.SVN"
+   local ok, err_msg = fs.is_tool_available(svn_cmd, "--version", "Subversion")
+   if not ok then
+      return nil, err_msg
    end
 
    local name_version = rockspec.name .. "-" .. rockspec.version
diff --git a/src/luarocks/fs/lua.lua b/src/luarocks/fs/lua.lua
index c0f6c1c6..73ae2698 100644
--- a/src/luarocks/fs/lua.lua
+++ b/src/luarocks/fs/lua.lua
@@ -122,6 +122,27 @@ function fs_lua.execute_quiet(command, ...)
    end
 end
 
+--- Checks if the given tool is available.
+-- The tool is executed using a flag, usually just to ask its version.
+-- @param tool_cmd string: The command to be used to check the tool's presence (e.g. hg in case of Mercurial)
+-- @param tool_name string: The actual name of the tool (e.g. Mercurial)
+-- @param arg string: The flag to pass to the tool. '--version' by default.
+function fs_lua.is_tool_available(tool_cmd, tool_name, arg)
+   assert(type(tool_cmd) == "string")
+   assert(type(tool_name) == "string")
+
+   arg = arg or "--version"
+   assert(type(arg) == "string")
+
+   if not fs.execute_quiet(tool_cmd, arg) then
+      local msg = "'%s' program not found. Make sure %s is installed and is available in your PATH " ..
+                  "(or you may want to edit the 'variables.%s' value in file 'config.lua')"
+      return nil, msg:format(tool_cmd, tool_name, tool_cmd:upper())
+   else
+      return true
+   end
+end
+
 --- Check the MD5 checksum for a file.
 -- @param file string: The file to be checked.
 -- @param md5sum string: The string with the expected MD5 checksum.