ash: eval: Variable assignments on functions are no longer persistent

ash: eval: Variable assignments on functions are no longer persistent

Upstream commit:

    Date: Wed, 4 Apr 2018 17:54:01 +0800
    eval: Variable assignments on functions are no longer persistent

    Dirk Fieldhouse <fieldhouse@gmx.net> wrote:
    > In POSIX.1-2017 ("simultaneously IEEE Std 1003.1™-2017 and The Open
    > Group Technical Standard Base Specifications, Issue 7")
    > <http://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_09>,
    > we read under '2.9.1 Simple Commands'
    >
    > "Variable assignments shall be performed as follows:
    > ...
    > -    If the command name is a standard utility implemented as a function
    > (see XBD Utility), the effect of variable assignments shall be as if the
    > utility was not implemented as a function.
    > ...
    > -    If the command name is a function that is not a standard utility
    > implemented as a function, variable assignments shall affect the current
    > execution environment during the execution of the function. It is
    > unspecified:
    >
    >     *   Whether or not the variable assignments persist after the
    > completion of the function
    >
    >     *   Whether or not the variables gain the export attribute during
    > the execution of the function
    >
    >     *   Whether or not export attributes gained as a result of the
    > variable assignments persist after the completion of the function (if
    > variable assignments persist after the completion of the function)"

    POSIX used to require the current dash behaviour.  However, you're
    right that this is no longer the case.

    This patch will remove the persistence of the variable assignment.

    I have considered the exporting the variables during the function
    execution but have decided against it because:

    1) It makes the code bigger.
    2) dash has never done this in the past.
    3) You cannot use this portably anyway.

    Reported-by: Dirk Fieldhouse <fieldhouse@gmx.net>
    Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
function                                             old     new   delta
evalcommand                                         1606    1635     +29
evalcase                                             313     317      +4
evalfun                                              280     268     -12
pushlocalvars                                         48       -     -48
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(add/remove: 0/1 grow/shrink: 2/1 up/down: 33/-60)            Total: -27 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>