Fixing lastIndexOf incosistent behaviour

PiperOrigin-RevId: 751599256

Author: CEL Dev Team

extensions/src/main/java/dev/cel/extensions/CelStringExtensions.java

@@ -360,6 +360,10 @@ private static Long lastIndexOf(String str, String substr) throws CelEvaluationE
       return (long) strCpa.length();
     }
 
+    if (strCpa.length() < substrCpa.length()) {
+      return -1L;
+    }
+
     return lastIndexOf(strCpa, substrCpa, (long) strCpa.length() - 1);
   }
 

extensions/src/test/java/dev/cel/extensions/CelStringExtensionsTest.java

@@ -887,6 +887,7 @@ public void join_separatorIsNonString_throwsException() {
   }
 
   @Test
+  @TestParameters("{string: '@', lastIndexOf: '@@', expectedResult: -1}")
   @TestParameters("{string: '', lastIndexOf: '', expectedResult: 0}")
   @TestParameters("{string: 'hello mellow', lastIndexOf: '', expectedResult: 12}")
   @TestParameters("{string: 'hello mellow', lastIndexOf: 'hello', expectedResult: 0}")
@@ -953,21 +954,20 @@ public void lastIndexOf_unicode_success(String string, String lastIndexOf, int e
   }
 
   @Test
+  @TestParameters("{lastIndexOf: '@@'}")
   @TestParameters("{lastIndexOf: '  '}")
   @TestParameters("{lastIndexOf: 'a'}")
   @TestParameters("{lastIndexOf: 'abc'}")
   @TestParameters("{lastIndexOf: '나'}")
   @TestParameters("{lastIndexOf: '😁'}")
-  public void lastIndexOf_onEmptyString_throwsException(String lastIndexOf) throws Exception {
+  public void lastIndexOf_strLengthLessThanSubstrLength_returnsMinusOne(String lastIndexOf)
+      throws Exception {
     CelAbstractSyntaxTree ast = COMPILER.compile("''.lastIndexOf(indexOfParam)").getAst();
     CelRuntime.Program program = RUNTIME.createProgram(ast);
 
-    CelEvaluationException exception =
-        assertThrows(
-            CelEvaluationException.class,
-            () -> program.eval(ImmutableMap.of("indexOfParam", lastIndexOf)));
+    Object evaluatedResult = program.eval(ImmutableMap.of("s", "", "indexOfParam", lastIndexOf));
 
-    assertThat(exception).hasMessageThat().contains("lastIndexOf failure: Offset out of range");
+    assertThat(evaluatedResult).isEqualTo(-1);
   }
 
   @Test