Update CHANGELOG.md with entries about null-aware elements and inference using bounds

Change-Id: I47a2d17e8d15028c13fa0319069152323e4920ef
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/424444
Reviewed-by: Erik Ernst <[email protected]>
Reviewed-by: Michael Thomsen <[email protected]>
Commit-Queue: Chloe Stefantsova <[email protected]>

Author: chloestefantsova

CHANGELOG.md

@@ -4,6 +4,39 @@
 
 **Released on:** Unreleased
 
+### Language
+
+Dart 3.8 adds [null-aware elements] to the language. To use them, set
+your package's [SDK constraint][language version] lower bound to 3.8
+or greater (`sdk: '^3.8.0'`).
+
+#### Null-Aware Elements
+
+[null-aware elements]: https://github.com/dart-lang/language/issues/323
+
+The null-aware elements language feature enables a simple syntax for
+including an element into a collection only if the element is not
+null. The syntax is available for list elements, set elements, map
+keys, and map values as described in the
+[null-aware elements specification](https://github.com/dart-lang/language/blob/main/accepted/future-releases/0323-null-aware-elements/feature-specification.md).
+
+The following is an example of a list literal written in both styles,
+without the null-aware elements language feature and with it:
+
+```dart
+var listWithoutNullAwareElements = [
+  if (promotableNullableValue != null) promotableNullableValue,
+  if (nullable.value != null) nullable.value!,
+  if (nullable.value case var value?) value,
+];
+
+var listWithNullAwareElements = [
+  ?promotableNullableValue,
+  ?nullable.value,
+  ?nullable.value,
+];
+```
+
 ### Libraries
 
 #### `dart:core`
@@ -268,9 +301,10 @@ same as it was before.
 
 ### Language
 
-Dart 3.7 adds [wildcard variables] to the language. To use them, set your
-package's [SDK constraint][language version] lower bound to 3.7 or greater
-(`sdk: '^3.7.0'`).
+Dart 3.7 adds [wildcard variables] and [inference using
+bounds][inference using bounds specification] to the language. To use
+them, set your package's [SDK constraint][language version] lower
+bound to 3.7 or greater (`sdk: '^3.7.0'`).
 
 #### Wildcard Variables
 
@@ -297,6 +331,43 @@ main() {
 }
 ```
 
+#### Inference Using Bounds
+
+[inference using bounds specification]: https://github.com/dart-lang/language/blob/main/accepted/future-releases/3009-inference-using-bounds/design-document.md
+
+With the inference using bounds feature, Dart's type inference
+algorithm generates constraints by combining existing constraints with
+the declared type bounds, not just best-effort approximations.
+
+This is especially important for F-bounded types, where inference
+using bounds correctly infers that, in the example below, `X` can be
+bound to `B`. Without the feature, the type argument must be specified
+explicitly: `f<B>(C())`:
+
+
+```dart
+class A<X extends A<X>> {}
+
+class B extends A<B> {}
+
+class C extends B {}
+
+void f<X extends A<X>>(X x) {}
+
+void main() {
+  f(B()); // OK.
+
+  // OK with this feature. Without it, inference fails after detecting
+  // that C is not a subtype of A<C>.
+  f(C());
+
+  f<B>(C()); // OK.
+}
+```
+
+The feature is described in more details in the
+[inference using bounds specification][].
+
 #### Other Language Changes
 
 - **Breaking Change** [#56893][]: If a field is promoted to the type `Null`