protect $@ whenever a block using $@ is non-trivial

As noted in the Try::Tiny man page, eval/$@ can be quite awkward in
corner cases, because $@ has the same properties and problems as C's
errno. While writing a regression test for definetemplate
in which it couldn't find an appropriate template, I received

    <span class="error">Error: failed to process template
    <span class="createlink">deftmpl</span> </span>

instead of the intended

    <span class="error">Error: failed to process template
    <span class="createlink">deftmpl</span> template deftmpl not
    found</span>

which turned out to be because the "catch"-analogous block called
gettext before it used $@, and gettext can call define_gettext,
which uses eval.

This commit alters all current "catch"-like blocks that use $@, except
those that just do trivial things with $@ (string interpolation, string
concatenation) and call a function (die, error, print, etc.)

1 files changed, 4 insertions, 2 deletions

diff --git a/IkiWiki/Plugin/attachment.pm b/IkiWiki/Plugin/attachment.pm
index 83dd120f6..d56dd18ad 100644
--- a/IkiWiki/Plugin/attachment.pm
+++ b/IkiWiki/Plugin/attachment.pm
@@ -229,8 +229,10 @@ sub attachment_store {
 		check_canattach($session, $final_filename, $tempfile);
 	};
 	if ($@) {
-		json_response($q, $form, $dest."/".$filename, $@);
-		error $@;
+		# save error in case called functions clobber $@
+		my $error = $@;
+		json_response($q, $form, $dest."/".$filename, $error);
+		error $error;
 	}
 
 	# Move the attachment into holding directory.