feat: remove minimum 1 dimension validation

since EMF supports no dimension as well

Author: Pankaj Agrawal

docs/core/metrics.md

@@ -108,7 +108,6 @@ if no metrics are provided no exception will be raised. If metrics are provided,
 not met, `ValidationException` exception will be raised.
 
 !!! tip "Metric validation"
-    * Minimum of 1 dimension
     * Maximum of 9 dimensions
 
 If you want to ensure that at least one metric is emitted, you can pass `raiseOnEmptyMetrics = true` to the **@Metrics** annotation:

powertools-metrics/src/main/java/software/amazon/lambda/powertools/metrics/internal/LambdaMetricsAspect.java

@@ -95,8 +95,8 @@ private void validateBeforeFlushingMetrics(Metrics metrics) {
             throw new ValidationException("No metrics captured, at least one metrics must be emitted");
         }
 
-        if (dimensionsCount() == 0 || dimensionsCount() > 9) {
-            throw new ValidationException(String.format("Number of Dimensions must be in range of 1-9." +
+        if (dimensionsCount() > 9) {
+            throw new ValidationException(String.format("Number of Dimensions must be in range of 0-9." +
                     " Actual size: %d.", dimensionsCount()));
         }
     }

powertools-metrics/src/test/java/software/amazon/lambda/powertools/metrics/handlers/PowertoolsMetricsNoDimensionsHandler.java

@@ -3,17 +3,19 @@
 import com.amazonaws.services.lambda.runtime.Context;
 import com.amazonaws.services.lambda.runtime.RequestHandler;
 import software.amazon.cloudwatchlogs.emf.logger.MetricsLogger;
+import software.amazon.cloudwatchlogs.emf.model.DimensionSet;
 import software.amazon.lambda.powertools.metrics.Metrics;
 
 import static software.amazon.lambda.powertools.metrics.MetricsUtils.metricsLogger;
 
 public class PowertoolsMetricsNoDimensionsHandler implements RequestHandler<Object, Object> {
 
     @Override
-    @Metrics(namespace = "ExampleApplication", service = "booking", captureColdStart = true)
+    @Metrics(namespace = "ExampleApplication", service = "booking")
     public Object handleRequest(Object input, Context context) {
         MetricsLogger metricsLogger = metricsLogger();
-        metricsLogger.setDimensions();
+        metricsLogger.putMetric("CoolMetric", 1);
+        metricsLogger.setDimensions(new DimensionSet());
 
         return null;
     }

powertools-metrics/src/test/java/software/amazon/lambda/powertools/metrics/internal/LambdaMetricsAspectTest.java

@@ -296,16 +296,22 @@ public void noExceptionWhenNoMetricsEmitted() {
     }
 
     @Test
-    public void exceptionWhenNoDimensionsSet() {
+    public void allowWhenNoDimensionsSet() {
         try (MockedStatic<SystemWrapper> mocked = mockStatic(SystemWrapper.class)) {
             mocked.when(() -> SystemWrapper.getenv("AWS_EMF_ENVIRONMENT")).thenReturn("Lambda");
-
             MetricsUtils.defaultDimensionSet(new DimensionSet());
+
             requestHandler = new PowertoolsMetricsNoDimensionsHandler();
+            requestHandler.handleRequest("input", context);
 
-            assertThatExceptionOfType(ValidationException.class)
-                    .isThrownBy(() -> requestHandler.handleRequest("input", context))
-                    .withMessage("Number of Dimensions must be in range of 1-9. Actual size: 0.");
+            assertThat(out.toString())
+                    .satisfies(s -> {
+                        Map<String, Object> logAsJson = readAsJson(s);
+                        assertThat(logAsJson)
+                                .containsEntry("CoolMetric", 1.0)
+                                .containsEntry("function_request_id", "123ABC")
+                                .containsKey("_aws");
+                    });
         }
     }
 
@@ -321,7 +327,7 @@ public void exceptionWhenTooManyDimensionsSet() {
 
             assertThatExceptionOfType(ValidationException.class)
                     .isThrownBy(() -> requestHandler.handleRequest("input", context))
-                    .withMessage("Number of Dimensions must be in range of 1-9. Actual size: 14.");
+                    .withMessage("Number of Dimensions must be in range of 0-9. Actual size: 14.");
         }
     }