filetype: support filetype detection via hashbang

add 2 tables, hashbang and utility for vis.ftdetect.filetypes.<lang>

fetch utility from /usr/bin/env args (mostly)
Support -S for /usr/bin/env args, discard variables=value args

lua/plugins/filetype.lua

@@ -37,9 +37,12 @@ vis.ftdetect.filetypes = {
 		ext = { "%.au3$", "%.a3x$" },
 	},
 	awk = {
+		hashbang = { "^/usr/bin/[mng]awk%s+%-f" },
+		utility = { "^[mgn]?awk$", "^goawk$" },
 		ext = { "%.awk$" },
 	},
 	bash = {
+		utility = { "^[db]ash$", "^sh$","^t?csh$","^zsh$" },
 		ext = { "%.bash$", "%.csh$", "%.sh$", "%.zsh$" ,"^APKBUILD$", "%.ebuild$"},
 		mime = { "text/x-shellscript", "application/x-shellscript" },
 	},
@@ -133,6 +136,7 @@ vis.ftdetect.filetypes = {
 		ext = { "%.fnl$" },
 	},
 	fish = {
+		utility = { "^fish$" },
 		ext = { "%.fish$" },
 	},
 	forth = {
@@ -241,15 +245,15 @@ vis.ftdetect.filetypes = {
 		ext = { "%.lgt$" },
 	},
 	lua = {
+		utility = {"^lua%-?5?%d?$", "^lua%-?5%.%d$" },
 		ext = { "%.lua$" },
 		mime = { "text/x-lua" },
 	},
 	makefile = {
+		hashbang = {"^#!/usr/bin/make"},
+		utility = {"^make$"},
 		ext = { "%.iface$", "%.mak$", "%.mk$", "GNUmakefile", "makefile", "Makefile" },
 		mime = { "text/x-makefile" },
-		detect = function(_, data)
-			return data:match("^#!/usr/bin/make")
-		end
 	},
 	man = {
 		ext = {
@@ -329,13 +333,15 @@ vis.ftdetect.filetypes = {
 		ext = { "%.pure$" },
 	},
 	python = {
+		utility = { "^python%d?" },
 		ext = { "%.sc$", "%.py$", "%.pyw$" },
 		mime = { "text/x-python", "text/x-script.python" },
 	},
 	reason = {
 		ext = { "%.re$" },
 	},
 	rc = {
+		utility = {"^rc$"},
 		ext = { "%.rc$", "%.es$" },
 	},
 	rebol = {
@@ -409,6 +415,7 @@ vis.ftdetect.filetypes = {
 		ext = { "%.taskpaper$" },
 	},
 	tcl = {
+		utility = {"^tclsh$", "^jimsh$" },
 		ext = { "%.tcl$", "%.tk$" },
 	},
 	texinfo = {
@@ -536,6 +543,56 @@ vis.events.subscribe(vis.events.WIN_OPEN, function(win)
 				return
 			end
 		end
+
+--[[ hashbang check
+	hashbangs only have command <SPACE> argument
+		if /env, find utility in args
+			discard first arg if /-[^S]*S/; and all subsequent /=/
+			NOTE: this means you can't have a command with /^-|=/
+	return first field, which should be the utility.
+	NOTE: long-options unsupported
+--]]
+		local fullhb, utility = data:match"^#![ \t]*(/+[^/\n]+[^\n]*)"
+		if fullhb then
+			local i, field = 1, {}
+			for m in fullhb:gmatch"%g+" do field[i],i = m,i+1 end
+			-- NOTE: executables should not have a space (or =, see below)
+			if field[1]:match"/env$" then
+				table.remove(field,1)
+				-- it is assumed that the first argument are short options, with -S inside
+				if string.match(field[1] or "", "^%-[^S-]*S") then -- -S found
+					table.remove(field,1)
+					-- skip all name=value
+					while string.match(field[1] or "","=") do
+						table.remove(field,1)
+					end
+					-- (hopefully) whatever is left in field[1] should be the utility or nil
+				end
+			end
+			utility = string.match(field[1] or "", "[^/]+$") -- remove filepath
+		end
+
+		local function searcher(tbl, subject)
+			for i, pattern in ipairs(tbl or {}) do
+				if string.match(subject, pattern) then
+					return true
+				end
+			end
+			return false
+		end
+
+		if utility or fullhb then
+			for lang, ft in pairs(vis.ftdetect.filetypes) do
+				if
+					utility and searcher(ft.utility, utility)
+					or
+					fullhb and searcher(ft.hashbang, fullhb)
+				then
+					set_filetype(lang, ft)
+					return
+				end
+			end
+		end
 	end
 
 	-- try text lexer as a last resort