idl-api - add static analysis of the interface description

idl/idl_api.ysl2

@@ -19,6 +19,29 @@ def "func:exists" {
 // ----------------------------------------------------------------------
 // idl-api (ysl2)
 // ----------------------------------------------------------------------
+template "/" {
+    choose {
+        when "func:idl_static_analysis_is_ok()"
+            apply "/pEpACIDLang", 0
+    }
+}
+
+def "func:idl_static_analysis_is_ok" {
+    const "pepacidlang_count", "count(/pEpACIDLang)";
+    const "idl_count", "count(/pEpACIDLang/idl)";
+
+    choose {
+        when "$pepacidlang_count < 1"
+            error > idl_static_analysis_is_ok - root node pEpACIDLang not found
+        when "$idl_count < 1"
+            error > idl_static_analysis_is_ok - pEpACIDLang idl data not found, include pEpACIDLang.yml2 exactly once.
+        when "$idl_count < 1"
+            error > idl_static_analysis_is_ok - ambiguous idl data, include pEpACIDLang.yml2 exactly once.
+        otherwise
+            result "true()";
+    }
+}
+
 def "func:idl_get_package_name" {
     result "/pEpACIDLang/package/@name"
 }