Drop KFunction.isTailrec

The fate of this modifier seems unclear, and there doesn't seem to be any
valuable use cases for it in reflection

compiler/testData/codegen/box/reflection/modifiers/functions.kt

@@ -10,7 +10,6 @@ inline fun inline() {}
 class External { external fun external() }
 operator fun Unit.invoke() {}
 infix fun Unit.infix(unit: Unit) {}
-tailrec fun tailrec() { tailrec() }
 class Suspend { suspend fun suspend(c: Continuation<Unit>) {} }
 
 val externalGetter = Unit
@@ -25,42 +24,30 @@ fun box(): String {
     assertFalse(::inline.isExternal)
     assertFalse(::inline.isOperator)
     assertFalse(::inline.isInfix)
-    assertFalse(::inline.isTailrec)
     assertFalse(::inline.isSuspend)
 
     assertFalse(External::external.isInline)
     assertTrue(External::external.isExternal)
     assertFalse(External::external.isOperator)
     assertFalse(External::external.isInfix)
-    assertFalse(External::external.isTailrec)
     assertFalse(External::external.isSuspend)
 
     assertFalse(Unit::invoke.isInline)
     assertFalse(Unit::invoke.isExternal)
     assertTrue(Unit::invoke.isOperator)
     assertFalse(Unit::invoke.isInfix)
-    assertFalse(Unit::invoke.isTailrec)
     assertFalse(Unit::invoke.isSuspend)
 
     assertFalse(Unit::infix.isInline)
     assertFalse(Unit::infix.isExternal)
     assertFalse(Unit::infix.isOperator)
     assertTrue(Unit::infix.isInfix)
-    assertFalse(Unit::infix.isTailrec)
     assertFalse(Unit::infix.isSuspend)
 
-    assertFalse(::tailrec.isInline)
-    assertFalse(::tailrec.isExternal)
-    assertFalse(::tailrec.isOperator)
-    assertFalse(::tailrec.isInfix)
-    assertTrue(::tailrec.isTailrec)
-    assertFalse(::tailrec.isSuspend)
-
     assertFalse(Suspend::suspend.isInline)
     assertFalse(Suspend::suspend.isExternal)
     assertFalse(Suspend::suspend.isOperator)
     assertFalse(Suspend::suspend.isInfix)
-    assertFalse(Suspend::suspend.isTailrec)
     assertTrue(Suspend::suspend.isSuspend)
 
     assertTrue(::externalGetter.getter.isExternal)

core/builtins/src/kotlin/reflect/KFunction.kt

@@ -52,14 +52,6 @@ public interface KFunction<out R> : KCallable<R>, Function<R> {
     @SinceKotlin("1.1")
     public val isInfix: Boolean
 
-    /**
-     * `true` if this function is `tailrec`.
-     * See the [Kotlin language documentation](https://kotlinlang.org/docs/reference/functions.html#tail-recursive-functions)
-     * for more information.
-     */
-    @SinceKotlin("1.1")
-    public val isTailrec: Boolean
-
     /**
      * `true` if this is a suspending function.
      */

core/reflection.jvm/src/kotlin/reflect/jvm/internal/KFunctionImpl.kt

@@ -135,9 +135,6 @@ internal class KFunctionImpl private constructor(
     override val isInfix: Boolean
         get() = descriptor.isInfix
 
-    override val isTailrec: Boolean
-        get() = descriptor.isTailrec
-
     override val isSuspend: Boolean
         get() = descriptor.isSuspend
 

core/reflection.jvm/src/kotlin/reflect/jvm/internal/KPropertyImpl.kt

@@ -118,7 +118,6 @@ internal abstract class KPropertyImpl<out R> private constructor(
         override val isExternal: Boolean get() = descriptor.isExternal
         override val isOperator: Boolean get() = descriptor.isOperator
         override val isInfix: Boolean get() = descriptor.isInfix
-        override val isTailrec: Boolean get() = descriptor.isTailrec
         override val isSuspend: Boolean get() = descriptor.isSuspend
     }
 

core/runtime.jvm/src/kotlin/jvm/internal/FunctionReference.java

@@ -61,11 +61,6 @@ public class FunctionReference extends CallableReference implements FunctionImpl
         return getReflected().isInfix();
     }
 
-    @Override
-    public boolean isTailrec() {
-        return getReflected().isTailrec();
-    }
-
     @Override
     public boolean isSuspend() {
         return getReflected().isSuspend();

libraries/tools/binary-compatibility-validator/reference-public-api/kotlin-runtime.txt

@@ -509,7 +509,6 @@ public class kotlin/jvm/internal/FunctionReference : kotlin/jvm/internal/Callabl
 	public fun isInline ()Z
 	public fun isOperator ()Z
 	public fun isSuspend ()Z
-	public fun isTailrec ()Z
 	public fun toString ()Ljava/lang/String;
 }
 
@@ -1156,7 +1155,6 @@ public abstract interface class kotlin/reflect/KFunction : kotlin/Function, kotl
 	public abstract fun isInline ()Z
 	public abstract fun isOperator ()Z
 	public abstract fun isSuspend ()Z
-	public abstract fun isTailrec ()Z
 }
 
 public abstract interface class kotlin/reflect/KMutableProperty : kotlin/reflect/KProperty {