fix(metrics): account for all dimensions in setDefaultDimensions() li…

packages/metrics/src/Metrics.ts

@@ -798,9 +798,13 @@ class Metrics extends Utility implements MetricsInterface {
     const newDimensions = this.#sanitizeDimensions(dimensions);
     const currentDefaultDimensions =
       this.#dimensionsStore.getDefaultDimensions();
-    const currentCount = Object.keys(currentDefaultDimensions).length;
-    const newSetCount = Object.keys(newDimensions).length;
-    if (currentCount + newSetCount >= MAX_DIMENSION_COUNT) {
+    const newKeysCount = Object.keys(newDimensions).filter(
+      (key) => !Object.hasOwn(currentDefaultDimensions, key)
+    ).length;
+    if (
+      this.#dimensionsStore.getDimensionCount() + newKeysCount >=
+      MAX_DIMENSION_COUNT
+    ) {
       throw new RangeError(
         `The number of metric dimensions must be lower than ${MAX_DIMENSION_COUNT}`
       );

packages/metrics/tests/unit/dimensions.test.ts

@@ -361,6 +361,42 @@ describe('Working with dimensions', () => {
     );
   });
 
+  it('throws when setDefaultDimensions would exceed the limit with existing regular dimensions', () => {
+    // Prepare
+    const metrics = new Metrics({
+      singleMetric: true,
+    });
+
+    // Act
+    for (let i = 1; i < MAX_DIMENSION_COUNT - 1; i++) {
+      metrics.addDimension(`regular-${i}`, 'test');
+    }
+
+    // Assess
+    expect(() =>
+      metrics.setDefaultDimensions({ 'new-default': 'test' })
+    ).toThrow(
+      `The number of metric dimensions must be lower than ${MAX_DIMENSION_COUNT}`
+    );
+  });
+
+  it('allows overriding existing default dimension keys without triggering the limit', () => {
+    // Prepare
+    const metrics = new Metrics({
+      singleMetric: true,
+    });
+
+    // Act
+    for (let i = 1; i < MAX_DIMENSION_COUNT - 1; i++) {
+      metrics.setDefaultDimensions({ [`dimension-${i}`]: 'test' });
+    }
+
+    // Assess
+    expect(() =>
+      metrics.setDefaultDimensions({ 'dimension-1': 'updated' })
+    ).not.toThrow();
+  });
+
   it('throws when adding dimension sets would exceed the limit', () => {
     // Prepare
     const metrics = new Metrics({