Support `else` statements in builtin templates

test/test_unit_template_builtin.py

@@ -13,11 +13,19 @@ builtin os     = >{{{{yadm.os}}}}<
 builtin host   = >{{{{yadm.hostname}}}}<
 builtin user   = >{{{{yadm.user}}}}<
 builtin distro = >{{{{yadm.distro}}}}<
+{{% if yadm.class == "else1" %}}
+wrong else 1
+{{% else %}}
+Included section from else
+{{% endif %}}
 {{% if yadm.class == "wrongclass1" %}}
 wrong class 1
 {{% endif %}}
 {{% if yadm.class == "{LOCAL_CLASS}" %}}
 Included section for class = {{{{yadm.class}}}} ({{{{yadm.class}}}} repeated)
+Multiple lines
+{{% else %}}
+Should not be included...
 {{% endif %}}
 {{% if yadm.class == "wrongclass2" %}}
 wrong class 2
@@ -67,7 +75,9 @@ builtin os     = >{LOCAL_SYSTEM}<
 builtin host   = >{LOCAL_HOST}<
 builtin user   = >{LOCAL_USER}<
 builtin distro = >{LOCAL_DISTRO}<
+Included section from else
 Included section for class = {LOCAL_CLASS} ({LOCAL_CLASS} repeated)
+Multiple lines
 Included section for os = {LOCAL_SYSTEM} ({LOCAL_SYSTEM} repeated)
 Included section for host = {LOCAL_HOST} ({LOCAL_HOST} again)
 Included section for user = {LOCAL_USER} ({LOCAL_USER} repeated)

yadm

@@ -290,21 +290,30 @@ BEGIN {
   c["hostname"] = host
   c["user"]     = user
   c["distro"]   = distro
-  valid         = conditions()
+  vld           = conditions()
+  ifs           = "^{%" blank "*if"
+  els           = "^{%" blank "*else" blank "*%}$"
   end           = "^{%" blank "*endif" blank "*%}$"
-  skip          = "^{%" blank "*(if|endif)"
+  skp           = "^{%" blank "*(if|else|endif)"
+  prt           = 1
 }
 { replace_vars() } # variable replacements
-$0 ~ valid, $0 ~ end { if ($0 ~ skip) next } # valid conditional blocks
-$0 ~ ("^{%" blank "*if"), $0 ~ end { next } # invalid conditional blocks
-{ print }
-
+$0 ~ vld, $0 ~ end {
+  if ($0 ~ vld || $0 ~ end) prt=1;
+  if ($0 ~ els) prt=0;
+  if ($0 ~ skp) next;
+}
+($0 ~ ifs && $0 !~ vld), $0 ~ end {
+  if ($0 ~ ifs && $0 !~ vld) prt=0;
+  if ($0 ~ els || $0 ~ end) prt=1;
+  if ($0 ~ skp) next;
+}
+{ if (prt) print }
 function replace_vars() {
   for (label in c) {
     gsub(("{{" blank "*yadm\\." label blank "*}}"), c[label])
   }
 }
-
 function conditions() {
   pattern = "^{%" blank "*if" blank "*("
   for (label in c) {