optional warning on join(/foo/...) (reworked suggested patch

by Mark-Jason Dominus <mjd@plover.com>)

p4raw-id: //depot/perl@4083

3 files changed, 16 insertions, 1 deletions

diff --git a/pod/perldelta.pod b/pod/perldelta.pod
index a228530b07..cf975594bb 100644
--- a/pod/perldelta.pod
+++ b/pod/perldelta.pod
@@ -725,6 +725,13 @@ of a subroutine attribute, and it wasn't a semicolon or the start of a
 block.  Perhaps you terminated the parameter list of the previous attribute
 too soon.
 
+=item /%s/ should probably be written as "%s"
+
+(W) You have used a pattern where Perl expected to find a string,
+like in the first argument to C<join>.  Perl will treat the true
+or false result of matching the pattern against $_ as the string,
+which is probably not what you had in mind.
+
 =head1 Obsolete Diagnostics
 
 Todo.
diff --git a/pod/perldiag.pod b/pod/perldiag.pod
index 10808ff516..1c07a31fa6 100644
--- a/pod/perldiag.pod
+++ b/pod/perldiag.pod
@@ -112,6 +112,13 @@ your signed integers.  See L<perlfunc/unpack>.
 by Perl.  This combination appears in an interpolated variable or a 
 C<'>-delimited regular expression.
 
+=item /%s/ should probably be written as "%s"
+
+(W) You have used a pattern where Perl expected to find a string,
+like in the first argument to C<join>.  Perl will treat the true
+or false result of matching the pattern against $_ as the string,
+which is probably not what you had in mind.
+
 =item %s (...) interpreted as function
 
 (W) You've run afoul of the rule that says that any list operator followed
diff --git a/pod/perlfunc.pod b/pod/perlfunc.pod
index d420059d4c..f830478d23 100644
--- a/pod/perlfunc.pod
+++ b/pod/perlfunc.pod
@@ -2064,7 +2064,8 @@ separated by the value of EXPR, and returns that new string.  Example:
 
     $rec = join(':', $login,$passwd,$uid,$gid,$gcos,$home,$shell);
 
-See L</split>.
+Beware that unlike C<split>, C<join> doesn't take a pattern as its
+first argument.  Compare L</split>.
 
 =item keys HASH