ISO C is silent about the return of 'system'. Windows sets 'errno' in
case of errors. Linux has several different error cases, with different
return values. ISO C allows 'system' to set 'errno' even if there are no
errors. Here we assume that a status==0 is success (which is the case
on several platforms), otherwise it is an error. If there is an error
number, gives the error based on it. (The worst a spurious 'errno'
can do is to generate a bad error message.) Otherwise uses the normal
results.
The macro 'luaL_pushfail' documents all places in the standard libraries
that return nil to signal some kind of failure. It is defined as
'lua_pushnil'. The manual also got a notation (@fail) to document those
returns. The tests were changed to be agnostic regarding whether 'fail'
is 'nil' or 'false'.
The loop does not end on end of file, but when the iterator function
fails to read a value. (In particular, the format "a" never fails,
so a loop with 'io.lines(fname, "a")' never ends.)
In the 'io' library, changed the use of the metatable also as its
own "method table", so that metamethods cannot be accessed as if they
were methods. (For instance, 'io.stdin.__gc' does not result in
the finalizer metamethod anymore.)
- 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 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 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.
These operations also can give errors for lack of resources, so they
also will try "emergency collections" in case of resource errors.
Because there are now two libraries with that kind of handling,
'resourcetryagain' was moved to the auxiliary library to be shared
by the libraries.
If a file operation fails do to lack of resources (too many open
files or not enough memory), it does a full garbage collection and
tries the operation again. Lack of resources are "too many open
files" (process wise and system wise) and "not enough memory".
The code is full of '#if's because error codes are not part
of the standard ISO C.
