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, 3 insertions, 1 deletions

diff --git a/IkiWiki/Plugin/edittemplate.pm b/IkiWiki/Plugin/edittemplate.pm
index c7f1e4fa7..e3ce5e3d9 100644
--- a/IkiWiki/Plugin/edittemplate.pm
+++ b/IkiWiki/Plugin/edittemplate.pm
@@ -130,9 +130,11 @@ sub filltemplate ($$) {
 		$template=template("/".$template_page);
 	};
 	if ($@) {
+		# gettext can clobber $@
+		my $error = $@;
 		# Indicate that the earlier preprocessor directive set 
 		# up a template that doesn't work.
-		return "[[!edittemplate ".gettext("failed to process template:")." $@]]";
+		return "[[!edittemplate ".gettext("failed to process template:")." $error]]";
 	}
 
 	$template->param(name => $page);