Better diagnostics for non-exhaustive whens, relevant test #KT-10295 Fixed

idea/testData/checker/WhenNonExhaustive.kt

@@ -0,0 +1,47 @@
+fun nonExhaustiveInt(x: Int) = <error descr="[NO_ELSE_IN_WHEN] when expression must be exhaustive, add necessary 'else' branch">when</error>(x) {
+    0 -> false
+}
+
+fun nonExhaustiveBoolean(b: Boolean) = <error descr="[NO_ELSE_IN_WHEN] when expression must be exhaustive, add necessary 'true' branch or 'else' branch instead">when</error>(b) {
+    false -> 0
+}
+
+enum class Color { 
+    RED,
+    GREEN,
+    BLUE
+}
+
+fun nonExhaustiveEnum(c: Color) = <error descr="[NO_ELSE_IN_WHEN] when expression must be exhaustive, add necessary 'RED', 'BLUE' branches or 'else' branch instead">when</error>(c) {
+    Color.GREEN -> 0xff00
+}
+
+fun nonExhaustiveNullable(c: Color?) = <error descr="[NO_ELSE_IN_WHEN] when expression must be exhaustive, add necessary 'GREEN', 'null' branches or 'else' branch instead">when</error>(c) {
+    Color.RED -> 0xff
+    Color.BLUE -> 0xff0000
+}
+
+fun whenOnEnum(c: Color) {
+    <warning descr="[NON_EXHAUSTIVE_WHEN] when expression on enum is recommended to be exhaustive, add 'RED' branch or 'else' branch instead">when</warning>(c) {
+        Color.BLUE -> {}
+        Color.GREEN -> {}
+    }
+}
+
+sealed class Variant {
+    object Singleton : Variant()
+   
+    class Something : Variant()
+
+    object Another : Variant()
+}
+
+fun nonExhaustiveSealed(v: Variant) = <error descr="[NO_ELSE_IN_WHEN] when expression must be exhaustive, add necessary 'is Something', 'Another' branches or 'else' branch instead">when</error>(v) {
+    Variant.Singleton -> false
+}
+
+sealed class Empty
+
+fun nonExhaustiveEmpty(e: Empty) = <error descr="[NO_ELSE_IN_WHEN] when expression must be exhaustive, add necessary 'else' branch">when</error>(<warning>e</warning>) {}
+
+fun nonExhaustiveNullableEmpty(e: Empty?) = <error descr="[NO_ELSE_IN_WHEN] when expression must be exhaustive, add necessary 'else' branch">when</error>(<warning>e</warning>) {}