Kotlin v1.5RC released, JVM-based programming language
Kotlin is a statically typed, cross-platform, general-purpose programming language with type inference. Kotlin is designed to interoperate fully with Java, and the JVM version of its standard library depends on the Java Class Library, but type inference allows its syntax to be more concise. Kotlin mainly targets the JVM but also compiles to JavaScript or native code (via LLVM). Kotlin is sponsored by JetBrains, a software development company based in Prague, and is also backed by Google under the Kotlin Foundation.
Kotlin is officially supported by Google for mobile development on Android. Since the release of Android Studio 3.0 in October 2017, Kotlin is included as an alternative to the standard Java compiler. The Android Kotlin compiler lets the user choose between targeting Java 6 or Java 8 compatible bytecode.

Changelog v1.5RC
Compiler
New Features
KT-28791
Kotlin serialization with inline classesKT-43920
Support loading binary Java annotations on fieldsPerformance Improvements
KT-44153
NI: Low Memory and IntelliJ hangs when quotes in split() are missedKT-45410
JVM / IR: Extreme performance regression on arithmetic operations inside a loopFixes
KT-35224
It’s possible to pass non-spread arrays after arguments with SAM-conversionKT-36853
IR: UninitializedPropertyAccessException on tailrec with object expression in default argumentKT-41056
Increase stub version due to new “contract” keywordKT-43887
Problem with FunctionReferenceLowering$FunctionReferenceBuilder in kotlin nativeKT-44210
KJS / IR: “AssertionError: Undefined parameter referenced: defined” caused by plus assign operators in build blocksKT-44947
Sealed interfaces: Sealed fun interface leads to “NoWhenBranchMatchedException”KT-44993
JVM IR: VerifyError on getfield with Kotlin generic field and elvis operatorKT-45139
Inline class: AssertionError: Expected top level inline classKT-45195
JVM IR: annotation methods are generated as default interface methods ifallopen
is usedKT-45446
JVM / IR: NullPointerException caused by unreachable code and comparisonKT-45721
JVM / IR: “Unbound symbols not allowed” caused by class reference in sequence lambdaKT-45853
JVM / IR: “Accidental override” caused by inheriting Throwable.getCause from Java interfaceKT-45861
Turning warnings into errors for calls with type parameters annotated by @OnlyInputTypesKT-45868
JVM IR: ClassCastException with SAM function in init block when SAM is generated via invokedynamicKT-45920
JVM IR: “Accidental override” on redefiningget()
in custom Map classKT-45963
JVM / IR: “AbstractMethodError: Receiver class does not define or inherit an implementation of the resolved method” in Dokka testsKT-45967
JVM IR: “IllegalAccessError” with invokedynamic to Java SAM over callable reference to private functionKT-45982
Wrong subtyping result on captured types with postponed type variablesIDE. Inspections and Intentions
KT-38155
Lift assignment out of ‘if’ produces type mismatch without manually adding a semicolonJavaScript
KT-44796
KJS / IR: default parameter of function with @JsName leads to “RangeError: Maximum call stack size exceeded”Libraries
KT-39177
Make CharCategory available in common multiplatform codeKT-43772
Kotlin/Native unfinished workers detected.Tools. Gradle
KT-43605
Kotlin Gradle Plugin 1.4.20 undeclared system property reads cause problems with Gradle configuration cache enabledKT-44462
Kotlin Gradle plugin createscompile
configuration with Gradle 7.0KT-44949
Compatibility with Gradle 7.0KT-44957
gradle – target.compilations seems to be deprecatedKT-45340
Update minimal supported version of Kotlin Gradle Plugin to 6.1Tools. Gradle. Multiplatform
KT-44900
Support gradle configuration cache with kotlin.multiplatform pluginTools. kapt