Improve Arch Linux compatibility and etc/errors.lua

 - The makefile now uses either the "lua5.1" (Debian/Ubuntu) or the
   "lua" (Arch Linux) pkg-config name
 - The makefile now expands the pkg-config invocations using $(shell ..)
   instead of passing them on literally to every build command line
 - etc/errors.lua now also checks /usr/include/apr-1/apr_errno.h,
   this means it should work on Arch Linux and Mac OS X
 - The repository now includes a generated src/errno.c just in case
   the error handling code generator doesn't work for everyone
 - I added a file header to etc/docs.lua while I was at it

Makefile

@@ -1,7 +1,7 @@
 # This is the UNIX makefile for the Lua/APR binding.
 #
 # Author: Peter Odding <peter@peterodding.com>
-# Last Change: February 19, 2011
+# Last Change: February 20, 2011
 # Homepage: http://peterodding.com/code/lua/apr/
 # License: MIT
 #
@@ -55,9 +55,14 @@ SOURCES = src/base64.c \
 OBJECTS = $(patsubst %.c,%.o,$(SOURCES))
 
 # If you're building Lua/APR with LuaRocks it should locate the external
-# dependencies automatically, otherwise we fall back to `pkg-config'.
-CFLAGS = `pkg-config --cflags lua5.1` `pkg-config --cflags apr-1` `pkg-config --cflags apr-util-1`
-LFLAGS = `pkg-config --libs apr-1` `pkg-config --libs apr-util-1`
+# dependencies automatically, otherwise we fall back to `pkg-config'. On
+# Debian/Ubuntu the Lua pkg-config file is called "lua5.1", on Arch Linux its
+# just "lua".
+CFLAGS = $(shell pkg-config --cflags lua5.1 --silence-errors || pkg-config --cflags lua) \
+		 $(shell pkg-config --cflags apr-1) \
+		 $(shell pkg-config --cflags apr-util-1)
+LFLAGS = $(shell pkg-config --libs apr-1) \
+		 $(shell pkg-config --libs apr-util-1)
 
 # Create debug builds by default but enable release
 # builds using the command line "make RELEASE=1".

etc/errors.lua

@@ -1,3 +1,20 @@
+--[[
+
+ Error handling code generator for the Lua/APR binding.
+
+ Author: Peter Odding <peter@peterodding.com>
+ Last Change: February 20, 2011
+ Homepage: http://peterodding.com/code/lua/apr/
+ License: MIT
+
+ The Apache Portable Runtime defines a long list of error codes whose integer
+ value differs between platforms and to make it even more complex several
+ integer values can map to the same error code. This script goes through the
+ APR header file, extracts the defined error codes (by name) and generates some
+ C source code that will convert APR error codes to symbolic strings.
+
+--]]
+
 local verbose = false
 local constants = {}
 local tests = {}
@@ -27,14 +44,35 @@ local ignored = {
   APR_UTIL_START_STATUS = true,
 }
 
+local function check(path)
+  io.stderr:write("Looking for headers at ", path, " .. ")
+  local status, msg = io.input(path)
+  if status then
+    io.stderr:write "Found them!\n"
+    return true
+  end
+  io.stderr:write("\nFailed to open headers: ", msg, "\n")
+end
+
+if not (check '/usr/include/apr-1.0/apr_errno.h' -- Debian / Ubuntu
+     or check '/usr/include/apr-1/apr_errno.h') then -- Arch Linux / Mac OS X
+  io.stderr:write [[
+Failed to determine where apr_errno.h is defined! This means the error
+handling module can't be regenerated, but don't worry: The Lua/APR
+repository includes a generated "errno.c" for just these situations.
+]]
+  os.exit(1)
+end
+
+-- Parse the header file. {{{1
+
 local function add(table, token)
   if not table[token] then
     table[#table + 1] = token
     table[token] = true
   end
 end
 
-assert(io.input '/usr/include/apr-1.0/apr_errno.h')
 local source = io.read '*a'
 source = source:gsub('/%*.-%*/', '')
 local longest_constant, longest_test = 0, 0
@@ -53,6 +91,8 @@ end
 table.sort(constants)
 table.sort(tests)
 
+-- Report intermediate results? {{{1
+
 if verbose then
 
   io.write('Found ', #constants, ' error constants:\n')
@@ -77,6 +117,10 @@ if verbose then
 
 end
 
+-- Generate the error handling module's source code. {{{1
+
+-- Documentation. {{{2
+
 io.write([[
 /* Error handling module for the Lua/APR binding.
  *
@@ -159,6 +203,8 @@ void status_to_name(lua_State *L, apr_status_t status)
   switch (status) {
 ]])
 
+-- }}}2
+
 local template = '    case %s: %slua_pushliteral(L, %q); %sreturn;\n'
 for i, constant in ipairs(constants) do
   local name = constant:gsub('^APR_', '')