[pdata] Fix Map.EnsureCapacity bug when the Map is not empty (open-te…

…lemetry#8040)

EnsureCapacity was incorrectly clearing the Map when increasing the
capacity. It will now correctly preserve existing elements.

---------

Co-authored-by: Alex Boten <alex@boten.ca>

pdata/pcommon/map.go

@@ -35,11 +35,11 @@ func (m Map) Clear() {
 // EnsureCapacity increases the capacity of this Map instance, if necessary,
 // to ensure that it can hold at least the number of elements specified by the capacity argument.
 func (m Map) EnsureCapacity(capacity int) {
-	if capacity <= cap(*m.getOrig()) {
+	oldOrig := *m.getOrig()
+	if capacity <= cap(oldOrig) {
 		return
 	}
-	oldOrig := *m.getOrig()
-	*m.getOrig() = make([]otlpcommon.KeyValue, 0, capacity)
+	*m.getOrig() = make([]otlpcommon.KeyValue, len(oldOrig), capacity)
 	copy(*m.getOrig(), oldOrig)
 }
 

pdata/pcommon/map_test.go

@@ -375,6 +375,38 @@ func TestMap_EnsureCapacity(t *testing.T) {
 	assert.Equal(t, 8, cap(*am.getOrig()))
 }
 
+func TestMap_EnsureCapacity_Existing(t *testing.T) {
+	am := NewMap()
+	am.PutStr("foo", "bar")
+
+	assert.Equal(t, 1, am.Len())
+
+	// Add more capacity.
+	am.EnsureCapacity(5)
+
+	// Ensure previously existing element is still there.
+	assert.Equal(t, 1, am.Len())
+	v, ok := am.Get("foo")
+	assert.Equal(t, v.Str(), "bar")
+	assert.True(t, ok)
+
+	assert.Equal(t, 5, cap(*am.getOrig()))
+
+	// Add one more element.
+	am.PutStr("abc", "xyz")
+
+	// Verify that both elements are there.
+	assert.Equal(t, 2, am.Len())
+
+	v, ok = am.Get("foo")
+	assert.Equal(t, v.Str(), "bar")
+	assert.True(t, ok)
+
+	v, ok = am.Get("abc")
+	assert.Equal(t, v.Str(), "xyz")
+	assert.True(t, ok)
+}
+
 func TestMap_Clear(t *testing.T) {
 	am := NewMap()
 	assert.Nil(t, *am.getOrig())