- new error message for "attempt to assign to const variable"
- note in the manual about compatibility options
- comments
- small changes in 'read_line' and 'pushstr'
The flag for to-be-closed variables was changed from '*toclose'
to '<toclose>'. Several people found confusing the old syntax and
the new one has a clear terminator, making it more flexible for
future changes.
Back to how it was, a coroutine does not unwind its stack in case of
errors (and therefore do not close its to-be-closed variables). This
allows the stack to be examined after the error. The program can
use 'coroutine.kill' to close the variables.
The function created by 'coroutine.wrap', however, closes the
coroutine's variables in case of errors, as it is impossible to examine
the stack any way.
To-be-closed variables must contain objects with '__toclose'
metamethods (or nil). Functions were removed for several reasons:
* Functions interact badly with sandboxes. If a sandbox raises
an error to interrupt a script, a to-be-closed function still
can hijack control and continue running arbitrary sandboxed code.
* Functions interact badly with coroutines. If a coroutine yields
and is never resumed again, its to-be-closed functions will never
run. To-be-closed objects, on the other hand, will still be closed,
provided they have appropriate finalizers.
* If you really need a function, it is easy to create a dummy
object to run that function in its '__toclose' metamethod.
This comit also adds closing of variables in case of panic.
A to-be-closed variable must be closed when a block ends, so even
a 'return foo()' cannot directly returns the results of 'foo'; the
function must close the scope before returning.
It is an error for a to-be-closed variable to have a non-closable
non-nil value when it is being closed. This situation does not seem to
be useful and often hints to an error. (Particularly in the C API, it is
easy to change a to-be-closed index by mistake.)
To remove a to-be-closed variable from the stack in the C API a
function must use 'lua_settop' or 'lua_pop'. Previous implementation of
'luaL_pushresult' was not closing the box. (This commit also added
tests to check that box is being closed "as soon as possible".)
The variable to be closed in a generic 'for' loop now is the
4th value produced in the loop initialization, instead of being
the loop state (the 2nd value produced). That allows a loop to
use a state with a '__toclose' metamethod but do not close it.
(As an example, 'f:lines()' might use the file 'f' as a state
for the loop, but it should not close the file when the loop ends.)
The new syntax is <local *toclose x = f()>. The mark '*' allows other
attributes to be added later without the need of new keywords; it
also allows better error messages. The API function was also renamed
('lua_tobeclosed' -> 'lua_toclose').
The implicit variable 'state' in a generic 'for' is marked as a
to-be-closed variable, so that the state will be closed as soon
as the loop ends, no matter how.
Taking advantage of this new facility, the call 'io.lines(filename)'
now returns the open file as a second result. Therefore,
an iteraction like 'for l in io.lines(name)...' will close the
file even when the loop ends with a break or an error.
A closing method cannot be called in its own stack slot, as there may
be returning values in the stack after that slot, and the call would
corrupt those values. Instead, the closing method must be copied to the
top of the stack to be called.
Moreover, even when a function returns no value, its return istruction
still has to have its position (which will set the stack top) after
the local variables, otherwise a closing method might corrupt another
not-yet-called closing method.
Start of the implementation of "scoped variables" or "to be closed"
variables, local variables whose '__close' (or themselves) are called
when they go out of scope. This commit implements the syntax, the
opcode, and the creation of the corresponding upvalue, but it still
does not call the finalizations when the variable goes out of scope
(the most important part).
Currently, the syntax is 'local scoped name = exp', but that will
probably change.
From the point of view of 'git', all names are relative to the root
directory of the project. So, file names in '$Id:' also should be
relative to that directory: the proper name for test file 'all.lua'
is 'testes/all.lua'.
Roberto Ierusalimschy