disallow fieldnames to start or end with '.' to avoid mapping problems

on indexing.

Author: Hendrik Muhs

x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/transform/transforms/pivot/PivotConfig.java

@@ -211,6 +211,16 @@ static List<String> aggFieldValidation(List<String> usedNames) {
                 validationFailures.add("duplicate field [" + usedNames.get(i) + "] detected");
             }
         }
+
+        for (String name : usedNames) {
+            if (name.startsWith(".")) {
+                validationFailures.add("field [" + name + "] must not start with '.'");
+            }
+            if (name.endsWith(".")) {
+                validationFailures.add("field [" + name + "] must not end with '.'");
+            }
+        }
+
         return validationFailures;
     }
 

x-pack/plugin/core/src/test/java/org/elasticsearch/xpack/core/transform/transforms/pivot/PivotConfigTests.java

@@ -205,6 +205,20 @@ public void testAggNameValidationsWithDuplicatesAndNestingIssues() {
         );
     }
 
+    public void testAggNameValidationsWithInvalidFieldnames() {
+        List<String> failures = PivotConfig.aggFieldValidation(Arrays.asList(".at_start", "at_end.", ".start_and_end."));
+
+        assertThat(
+            failures,
+            containsInAnyOrder(
+                "field [.at_start] must not start with '.'",
+                "field [at_end.] must not end with '.'",
+                "field [.start_and_end.] must not start with '.'",
+                "field [.start_and_end.] must not end with '.'"
+            )
+        );
+    }
+
     private static String dotJoin(String... fields) {
         return Strings.arrayToDelimitedString(fields, ".");
     }