Lua do-attibute

This is a patched version of Lua 5.4.2. The original lua README was moved in doc/README: please refer to it for build instructions.

The patch lets you to mark a do/end block in this way: do <attrib> --[[block-content]] end

The accepted attibutes are:

• <defer> - the block is executed at end of the current scope instead of immediately
• <withupvalue> - a free name inside this block raises an error instead of being translated to __ENV.name
• <localonly> - an error is raised when accessing an upvalue too (so local variables only are allowed)
• <autoglobal> - it overwrites <withupvalue> or <localonly> to make the block work again like the common do/end block

The command

./script/doattr_test.sh

will download the official lua test suite, it will add some do attribute tests, and it will run them all.

NOTE: The body of a <defer> block works like the body of a function set as __close metatamethod of a <close> variable (i.e. the return statements are executed outside the current thread).

NOTE: <defer> uses a new global function "defer" to work. It is equivalent to local _--[[var-name]] <close> = defer(function() --[[block-content]] end). The user can change its behaviour by re-defining defer.

NOTE: <autoglobal>, <wihtupvalue> and <localonly> logic:

• A non-marked do/end block inherits the behaviour from the parent block.
• The main chunk starts in the <autoglobal> mode (as usual).

NOTE: <autoglobal>, <wihtupvalue> and <localonly> rises error at compile time, so the performance should not be affected.

NOTE: <autoglobal>, <wihtupvalue> and <localonly> are somehow "Compatible" with the regular lua: if you write a script that works as expected with the patch, you can remove any mark from the do/end blocks, and the result is valid for the regular lua too.