Vi::QuickFix - Support for vim's QuickFix mode

      use Vi::QuickFix;
      use Vi::QuickFix <errorfile>;
      use Vi::QuickFix <options>;
      use Vi::QuickFix <options> <errorfile>;

    where "<options>" is one or more of "silent", "sig", "tie", and "fork".

    When "Vi::QuickFix" is active, Perl logs errors and warnings to an
    *error file* named, by default, "errors.err". This file is picked up
    when you type ":cf" in a running vim editor. Vim will jump to the
    location of the first error recorded in the error file. ":cn" takes you
    to the next error, switching files if necessary. There are more QuickFix
    commands in vim. Type ":help quickfix" for a description.

    To activate QuickFix support for a Perl source, add

        use Vi::QuickFix;

    or, specifying an error file

        use Vi::QuickFix '/my/errorfile';

    early in the main program, before other "use" statements.

    To leave the program file unaltered, Vi::QuickFix can be invoked from
    the command line as

        perl -MVi::QuickFix program
        perl -MVi::QuickFix=/my/errorfile program

    "Vi::QuickFix" is meant to be used as a development tool, not to remain
    in a distributed product. When the program ends, a warning is issued,
    indicating that "Vi::QuickFix" was active. This has the side effect that
    there is always an entry in the error file which points to the source
    file where "Vi::QuickFix" was invoked, normally the main program. ":cf"
    will take you there when other error entries don't point it elsewhere.
    Use the "silent" option with "Vi::QuickFix" to suppress this warning.

    When the error file cannot be opened, a warning is issued and the
    program continues running without QuickFix support. If the error file is
    empty after the run (can only happen with "silent"), it is removed.

    "Vi::QuickFix" recognizes the environment variable

    When Perl reads its source from "STDIN", error messages and warnings
    will contain the string "-" where the source file name would otherwise
    appear. The environment variable "VI_QUICKFIX_SOURCEFILE" can be set to
    a filename, which will replace "-" in those messages. If no "-" appears
    as a file name, setting the variable has no effect.

    This somewhat peculiar behavior can be useful if you call perl (with
    "Vi::QuickFix") from within a vim run, as in ":w !perl -MVi::QickFix".
    When you set the environment variable "VI_QUICKFIX_SOURCEFILE" to the
    name of the file you are editing, this fools vim into doing the right
    thing when it encounters the modified messages.

    This is an experimental feature, the behavior may change in future

    The module file .../Vi/ can also be called as an executable.
    In that mode, it behaves basically like the "cat" command, but also
    monitors the stream and logs Perl warnings and error messages to the
    error file. The error file can be set through the switches "-f" or "-q".
    No warning about QuickFix activity is issued in this mode.

    Called with -v, it prints the version and exits.

    For a debugging tool, an implementation note is in order.

    Perl offers three obvious ways to watch and capture its error output.
    One is through the (pseudo-) signal handlers $SIG{__WARN__} and
    $SIG{__DIE__}. The other is through "tie"-ing the "STDERR" file handle.
    A third method involves forking a child process for the capturing and
    redirect "STDERR" to there.

    "Vi::QuickFix" can use these three methods to create the error file. As
    it turns out, the ability to tie "STDERR" is relatively new with Perl,
    as of version 5.8.1. With Versions 5.8.0 and earlier, a number of
    internal errors and warnings don't respect tie, so this method cannot be
    used. With Perl versions ealier than 5.8.1, "Vi::QuickFix" uses %SIG
    handlers to catch messages. With newer versions, "Vi::Quickfix" ties
    "STDERR" so that it (additionally) writes to the error file. The forking
    method can be used with any version of Perl.

    A specific method can be requested through the options "sig", "tie" and
    "fork", as in

        use Vi::QuickFix qw(sig);
        use Vi::QuickFix qw(tie);
        use Vi::QuickFix qw(fork);

    The forking method appears to work well in practice, but a race
    condition exists that intermittently leads to failing tests. It is not
    tested in the standard test suite and must be considered experimental.

    Requesting "tie" with a Perl version that can't handle it is a fatal
    error, so the only option that does anything useful is "sig" with a
    new-ish Perl. It can be useful when "tie"-ing "STDERR" conflicts with
    the surrounding code.

    Similar conflicts can occur with the "sig" method as well, and it can
    happen in two ways. Either "Vi::QuickFix" already finds a resource (a
    %SIG handler or a tie on "STDERR") occupied at "use" time, or the
    surrounding code commandeers the resource after the fact.

    However, if "STDERR" is already tied when "Vi::QuickFix" is "use"d, it
    cannot employ the "tie" method, and by default reverts to "sig". If the
    "tie" method is specifically requested, a fatal error results.

    If the "sig" method finds one of the handlers ("__WARN__" and "__DIE__")
    already occupied, it chains to the previous handler after doing its
    thing, so that is not considered an obstacle. "Chaining" file ties is
    harder, and has not been attempted.

    If "Vi::QuickFix" is already active, the surrounding code may later
    occupy a resource it is using. There is little that can be done when
    that happens, except issue a warning which is also logged to the error
    file. This can help in finding the source of the conflict. In "silent"
    mode, no such warning is given.

    The warning is triggered when the corresponding resource is overwritten,
    except when the overwriting program keeps a copy of it. It is then
    assumed that the program will keep it functioning. Since we're still
    talking implementation -- it is actually triggered through a DESTROY
    method when the corresponding object goes out of scope. %SIG handlers
    are code objects just for this reason.

    This document pertains to "Vi::Quickfix" version 1.134

    "no Vi::QuickFix" has no effect

            Anno Siegel
            CPAN ID: ANNO

    This program is free software; you can redistribute it and/or modify it
    under the same terms as Perl itself.

    The full text of the license can be found in the LICENSE file included
    with this module.

    perl(1), vim(1).