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237 lines
7.4 KiB
237 lines
7.4 KiB
package Carp;
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our $VERSION = '1.0701';
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# this file is an utra-lightweight stub. The first time a function is
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# called, Carp::Heavy is loaded, and the real short/longmessmess_jmp
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# subs are installed
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our $MaxEvalLen = 0;
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our $Verbose = 0;
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our $CarpLevel = 0;
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our $MaxArgLen = 64; # How much of each argument to print. 0 = all.
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our $MaxArgNums = 8; # How many arguments to print. 0 = all.
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require Exporter;
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our @ISA = ('Exporter');
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our @EXPORT = qw(confess croak carp);
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our @EXPORT_OK = qw(cluck verbose longmess shortmess);
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our @EXPORT_FAIL = qw(verbose); # hook to enable verbose mode
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# if the caller specifies verbose usage ("perl -MCarp=verbose script.pl")
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# then the following method will be called by the Exporter which knows
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# to do this thanks to @EXPORT_FAIL, above. $_[1] will contain the word
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# 'verbose'.
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sub export_fail { shift; $Verbose = shift if $_[0] eq 'verbose'; @_ }
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# fixed hooks for stashes to point to
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sub longmess { goto &longmess_jmp }
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sub shortmess { goto &shortmess_jmp }
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# these two are replaced when Carp::Heavy is loaded
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sub longmess_jmp {
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local($@, $!);
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eval { require Carp::Heavy };
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return $@ if $@;
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goto &longmess_real;
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}
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sub shortmess_jmp {
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local($@, $!);
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eval { require Carp::Heavy };
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return $@ if $@;
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goto &shortmess_real;
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}
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sub croak { die shortmess @_ }
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sub confess { die longmess @_ }
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sub carp { warn shortmess @_ }
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sub cluck { warn longmess @_ }
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1;
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__END__
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=head1 NAME
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carp - warn of errors (from perspective of caller)
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cluck - warn of errors with stack backtrace
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(not exported by default)
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croak - die of errors (from perspective of caller)
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confess - die of errors with stack backtrace
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=head1 SYNOPSIS
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use Carp;
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croak "We're outta here!";
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use Carp qw(cluck);
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cluck "This is how we got here!";
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=head1 DESCRIPTION
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The Carp routines are useful in your own modules because
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they act like die() or warn(), but with a message which is more
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likely to be useful to a user of your module. In the case of
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cluck, confess, and longmess that context is a summary of every
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call in the call-stack. For a shorter message you can use C<carp>
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or C<croak> which report the error as being from where your module
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was called. There is no guarantee that that is where the error
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was, but it is a good educated guess.
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You can also alter the way the output and logic of C<Carp> works, by
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changing some global variables in the C<Carp> namespace. See the
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section on C<GLOBAL VARIABLES> below.
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Here is a more complete description of how c<carp> and c<croak> work.
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What they do is search the call-stack for a function call stack where
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they have not been told that there shouldn't be an error. If every
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call is marked safe, they give up and give a full stack backtrace
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instead. In other words they presume that the first likely looking
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potential suspect is guilty. Their rules for telling whether
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a call shouldn't generate errors work as follows:
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=over 4
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=item 1.
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Any call from a package to itself is safe.
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=item 2.
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Packages claim that there won't be errors on calls to or from
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packages explicitly marked as safe by inclusion in C<@CARP_NOT>, or
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(if that array is empty) C<@ISA>. The ability to override what
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@ISA says is new in 5.8.
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=item 3.
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The trust in item 2 is transitive. If A trusts B, and B
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trusts C, then A trusts C. So if you do not override C<@ISA>
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with C<@CARP_NOT>, then this trust relationship is identical to,
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"inherits from".
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=item 4.
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Any call from an internal Perl module is safe. (Nothing keeps
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user modules from marking themselves as internal to Perl, but
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this practice is discouraged.)
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=item 5.
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Any call to Perl's warning system (eg Carp itself) is safe.
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(This rule is what keeps it from reporting the error at the
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point where you call C<carp> or C<croak>.)
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=item 6.
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C<$Carp::CarpLevel> can be set to skip a fixed number of additional
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call levels. Using this is not recommended because it is very
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difficult to get it to behave correctly.
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=back
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=head2 Forcing a Stack Trace
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As a debugging aid, you can force Carp to treat a croak as a confess
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and a carp as a cluck across I<all> modules. In other words, force a
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detailed stack trace to be given. This can be very helpful when trying
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to understand why, or from where, a warning or error is being generated.
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This feature is enabled by 'importing' the non-existent symbol
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'verbose'. You would typically enable it by saying
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perl -MCarp=verbose script.pl
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or by including the string C<MCarp=verbose> in the PERL5OPT
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environment variable.
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Alternately, you can set the global variable C<$Carp::Verbose> to true.
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See the C<GLOBAL VARIABLES> section below.
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=head1 GLOBAL VARIABLES
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=head2 $Carp::MaxEvalLen
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This variable determines how many characters of a string-eval are to
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be shown in the output. Use a value of C<0> to show all text.
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Defaults to C<0>.
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=head2 $Carp::MaxArgLen
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This variable determines how many characters of each argument to a
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function to print. Use a value of C<0> to show the full length of the
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argument.
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Defaults to C<64>.
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=head2 $Carp::MaxArgNums
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This variable determines how many arguments to each function to show.
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Use a value of C<0> to show all arguments to a function call.
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Defaults to C<8>.
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=head2 $Carp::Verbose
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This variable makes C<carp> and C<cluck> generate stack backtraces
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just like C<cluck> and C<confess>. This is how C<use Carp 'verbose'>
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is implemented internally.
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Defaults to C<0>.
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=head2 %Carp::Internal
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This says what packages are internal to Perl. C<Carp> will never
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report an error as being from a line in a package that is internal to
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Perl. For example:
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$Carp::Internal{ __PACKAGE__ }++;
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# time passes...
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sub foo { ... or confess("whatever") };
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would give a full stack backtrace starting from the first caller
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outside of __PACKAGE__. (Unless that package was also internal to
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Perl.)
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=head2 %Carp::CarpInternal
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This says which packages are internal to Perl's warning system. For
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generating a full stack backtrace this is the same as being internal
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to Perl, the stack backtrace will not start inside packages that are
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listed in C<%Carp::CarpInternal>. But it is slightly different for
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the summary message generated by C<carp> or C<croak>. There errors
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will not be reported on any lines that are calling packages in
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C<%Carp::CarpInternal>.
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For example C<Carp> itself is listed in C<%Carp::CarpInternal>.
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Therefore the full stack backtrace from C<confess> will not start
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inside of C<Carp>, and the short message from calling C<croak> is
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not placed on the line where C<croak> was called.
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=head2 $Carp::CarpLevel
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This variable determines how many additional call frames are to be
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skipped that would not otherwise be when reporting where an error
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occurred on a call to one of C<Carp>'s functions. It is fairly easy
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to count these call frames on calls that generate a full stack
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backtrace. However it is much harder to do this accounting for calls
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that generate a short message. Usually people skip too many call
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frames. If they are lucky they skip enough that C<Carp> goes all of
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the way through the call stack, realizes that something is wrong, and
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then generates a full stack backtrace. If they are unlucky then the
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error is reported from somewhere misleading very high in the call
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stack.
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Therefore it is best to avoid C<$Carp::CarpLevel>. Instead use
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C<@CARP_NOT>, C<%Carp::Internal> and %Carp::CarpInternal>.
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Defaults to C<0>.
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=head1 BUGS
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The Carp routines don't handle exception objects currently.
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If called with a first argument that is a reference, they simply
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call die() or warn(), as appropriate.
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