For 5.12: saner behaviour for `length`

(Make C<length undef> return undef).
Patch mostly by Rafael, with some fine tuning by me.

p4raw-id: //depot/perl@32969

4 files changed, 44 insertions, 10 deletions

diff --git a/t/lib/warnings/9uninit b/t/lib/warnings/9uninit
index e2e6ef9fec..1e4344ae3b 100644
--- a/t/lib/warnings/9uninit
+++ b/t/lib/warnings/9uninit
@@ -826,8 +826,8 @@ $v = eval {log $m1};
 $v = sqrt $m1;
 $v = hex $m1;
 $v = oct $m1;
-$v = length $m1;
-$v = length;
+$v = oct;
+$v = length; # does not warn
 EXPECT
 Use of uninitialized value $g1 in atan2 at - line 5.
 Use of uninitialized value $m1 in atan2 at - line 5.
@@ -840,8 +840,7 @@ Use of uninitialized value $m1 in log at - line 11.
 Use of uninitialized value $m1 in sqrt at - line 12.
 Use of uninitialized value $m1 in hex at - line 13.
 Use of uninitialized value $m1 in oct at - line 14.
-Use of uninitialized value $m1 in length at - line 15.
-Use of uninitialized value $_ in length at - line 16.
+Use of uninitialized value $_ in oct at - line 15.
 ########
 use warnings 'uninitialized';
 my ($m1, $v);
diff --git a/t/lib/warnings/mg b/t/lib/warnings/mg
index 2e2d4aa0f3..8915c2866b 100644
--- a/t/lib/warnings/mg
+++ b/t/lib/warnings/mg
@@ -46,15 +46,15 @@ EXPECT
 # mg.c
 use warnings 'uninitialized';
 'foo' =~ /(foo)/;
-length $3;
+oct $3;
 EXPECT
-Use of uninitialized value $3 in length at - line 4.
+Use of uninitialized value $3 in oct at - line 4.
 ########
 # mg.c
 use warnings 'uninitialized';
-length $3;
+oct $3;
 EXPECT
-Use of uninitialized value $3 in length at - line 3.
+Use of uninitialized value $3 in oct at - line 3.
 ########
 # mg.c
 use warnings 'uninitialized';
diff --git a/t/op/length.t b/t/op/length.t
index 41d34aee8e..eb357203ec 100644
--- a/t/op/length.t
+++ b/t/op/length.t
@@ -6,7 +6,7 @@ BEGIN {
     @INC = '../lib';
 }
 
-plan (tests => 22);
+plan (tests => 28);
 
 print "not " unless length("")    == 0;
 print "ok 1\n";
@@ -161,3 +161,38 @@ tie $u, 'Tie::StdScalar', chr 256;
 is(length $u, 1, "Length of a UTF-8 scalar returned from tie");
 is(length $u, 1, "Again! Again!");
 
+$^W = 1;
+
+my $warnings = 0;
+
+$SIG{__WARN__} = sub {
+    $warnings++;
+    warn @_;
+};
+
+is(length(undef), undef, "Length of literal undef");
+
+my $u;
+
+is(length($u), undef, "Length of regular scalar");
+
+$u = "Gotcha!";
+
+tie $u, 'Tie::StdScalar';
+
+is(length($u), undef, "Length of tied scalar (MAGIC)");
+
+is($u, undef);
+
+{
+    package U;
+    use overload '""' => sub {return undef;};
+}
+
+my $uo = bless [], 'U';
+
+is(length($uo), undef, "Length of overloaded reference");
+
+# ok(!defined $uo); Turns you can't test this. FIXME for pp_defined?
+
+is($warnings, 0, "There were no warnings");
diff --git a/t/op/vec.t b/t/op/vec.t
index 4ca23f1a94..aed1d0f170 100755
--- a/t/op/vec.t
+++ b/t/op/vec.t
@@ -11,7 +11,7 @@ plan( tests => 31 );
 my $Is_EBCDIC = (ord('A') == 193) ? 1 : 0;
 
 is(vec($foo,0,1), 0);
-is(length($foo), 0);
+is(length($foo), undef);
 vec($foo,0,1) = 1;
 is(length($foo), 1);
 is(unpack('C',$foo), 1);