Improving Lua support in etags

It seems it's Lua time again!

So for my new project I'm starting in openresty+lua, I needed some kind of support for tags. Lua is a very simple language syntaxwise (it's whole grammar fits in a screen of code).

Etags support is quite poor, in fact, if you read the emacs-devel message when it got added, you'll see how basic is it.

+ * Lua tag functions
+ *  look for function, local function.
+ */
+
+static void
+Lua_functions (inf)
+     FILE *inf;
+{
+  register char *bp;
+
+  LOOP_ON_INPUT_LINES (inf, lb, bp)
+    {
+      if (bp[0] != 'f' && bp[0] != 'l')
+       continue;
+
+      LOOKING_AT (bp, "local");
+
+      if (LOOKING_AT (bp, "function"))
+       get_tag (bp, NULL);
     }
 }

The regex version of this would be:   /^(local)?\s+function\s+(\w)/ .

So I wanted to add support for lines not in the beginning, and also to add support for things like

local foo = function (p1, p2) .... end

So it turned out to not be very difficult to augment etags to do that.

tags:
 etags --language=lua --regex='/.*\([^. \t]\)*[ \t]*=[ \t]*function/\1/' \
 --regex='/.*\(local\|\)[ \t][ \t]*function[ \t]\([^ \t(]*\)[ \t]*(/\2/'  **/*lua

Just adding this to the Makefile allows me to catch the other forms of lua functions. Again, regex to the rescue! :)