Temporary workaround to generate functions with optional parameters with bodies in common code.

libraries/stdlib/common/src/generated/_Arrays.kt

@@ -6759,7 +6759,22 @@ public header inline fun <V> CharArray.zip(other: CharArray, transform: (Char, C
  * If the collection could be huge, you can specify a non-negative value of [limit], in which case only the first [limit]
  * elements will be appended, followed by the [truncated] string (which defaults to "...").
  */
-public header fun <T, A : Appendable> Array<out T>.joinTo(buffer: A, separator: CharSequence = ", ", prefix: CharSequence = "", postfix: CharSequence = "", limit: Int = -1, truncated: CharSequence = "...", transform: ((T) -> CharSequence)? = null): A
+public fun <T, A : Appendable> Array<out T>.joinTo(buffer: A, separator: CharSequence = ", ", prefix: CharSequence = "", postfix: CharSequence = "", limit: Int = -1, truncated: CharSequence = "...", transform: ((T) -> CharSequence)? = null): A {
+    buffer.append(prefix)
+    var count = 0
+    for (element in this) {
+        if (++count > 1) buffer.append(separator)
+        if (limit < 0 || count <= limit) {
+            if (transform != null)
+                buffer.append(transform(element))
+            else
+                buffer.append(if (element == null) "null" else element.toString())
+        } else break
+    }
+    if (limit >= 0 && count > limit) buffer.append(truncated)
+    buffer.append(postfix)
+    return buffer
+}
 
 /**
  * Appends the string from all the elements separated using [separator] and using the given [prefix] and [postfix] if supplied.
@@ -6767,7 +6782,22 @@ public header fun <T, A : Appendable> Array<out T>.joinTo(buffer: A, separator:
  * If the collection could be huge, you can specify a non-negative value of [limit], in which case only the first [limit]
  * elements will be appended, followed by the [truncated] string (which defaults to "...").
  */
-public header fun <A : Appendable> ByteArray.joinTo(buffer: A, separator: CharSequence = ", ", prefix: CharSequence = "", postfix: CharSequence = "", limit: Int = -1, truncated: CharSequence = "...", transform: ((Byte) -> CharSequence)? = null): A
+public fun <A : Appendable> ByteArray.joinTo(buffer: A, separator: CharSequence = ", ", prefix: CharSequence = "", postfix: CharSequence = "", limit: Int = -1, truncated: CharSequence = "...", transform: ((Byte) -> CharSequence)? = null): A {
+    buffer.append(prefix)
+    var count = 0
+    for (element in this) {
+        if (++count > 1) buffer.append(separator)
+        if (limit < 0 || count <= limit) {
+            if (transform != null)
+                buffer.append(transform(element))
+            else
+                buffer.append(element.toString())
+        } else break
+    }
+    if (limit >= 0 && count > limit) buffer.append(truncated)
+    buffer.append(postfix)
+    return buffer
+}
 
 /**
  * Appends the string from all the elements separated using [separator] and using the given [prefix] and [postfix] if supplied.
@@ -6775,7 +6805,22 @@ public header fun <A : Appendable> ByteArray.joinTo(buffer: A, separator: CharSe
  * If the collection could be huge, you can specify a non-negative value of [limit], in which case only the first [limit]
  * elements will be appended, followed by the [truncated] string (which defaults to "...").
  */
-public header fun <A : Appendable> ShortArray.joinTo(buffer: A, separator: CharSequence = ", ", prefix: CharSequence = "", postfix: CharSequence = "", limit: Int = -1, truncated: CharSequence = "...", transform: ((Short) -> CharSequence)? = null): A
+public fun <A : Appendable> ShortArray.joinTo(buffer: A, separator: CharSequence = ", ", prefix: CharSequence = "", postfix: CharSequence = "", limit: Int = -1, truncated: CharSequence = "...", transform: ((Short) -> CharSequence)? = null): A {
+    buffer.append(prefix)
+    var count = 0
+    for (element in this) {
+        if (++count > 1) buffer.append(separator)
+        if (limit < 0 || count <= limit) {
+            if (transform != null)
+                buffer.append(transform(element))
+            else
+                buffer.append(element.toString())
+        } else break
+    }
+    if (limit >= 0 && count > limit) buffer.append(truncated)
+    buffer.append(postfix)
+    return buffer
+}
 
 /**
  * Appends the string from all the elements separated using [separator] and using the given [prefix] and [postfix] if supplied.
@@ -6783,7 +6828,22 @@ public header fun <A : Appendable> ShortArray.joinTo(buffer: A, separator: CharS
  * If the collection could be huge, you can specify a non-negative value of [limit], in which case only the first [limit]
  * elements will be appended, followed by the [truncated] string (which defaults to "...").
  */
-public header fun <A : Appendable> IntArray.joinTo(buffer: A, separator: CharSequence = ", ", prefix: CharSequence = "", postfix: CharSequence = "", limit: Int = -1, truncated: CharSequence = "...", transform: ((Int) -> CharSequence)? = null): A
+public fun <A : Appendable> IntArray.joinTo(buffer: A, separator: CharSequence = ", ", prefix: CharSequence = "", postfix: CharSequence = "", limit: Int = -1, truncated: CharSequence = "...", transform: ((Int) -> CharSequence)? = null): A {
+    buffer.append(prefix)
+    var count = 0
+    for (element in this) {
+        if (++count > 1) buffer.append(separator)
+        if (limit < 0 || count <= limit) {
+            if (transform != null)
+                buffer.append(transform(element))
+            else
+                buffer.append(element.toString())
+        } else break
+    }
+    if (limit >= 0 && count > limit) buffer.append(truncated)
+    buffer.append(postfix)
+    return buffer
+}
 
 /**
  * Appends the string from all the elements separated using [separator] and using the given [prefix] and [postfix] if supplied.
@@ -6791,7 +6851,22 @@ public header fun <A : Appendable> IntArray.joinTo(buffer: A, separator: CharSeq
  * If the collection could be huge, you can specify a non-negative value of [limit], in which case only the first [limit]
  * elements will be appended, followed by the [truncated] string (which defaults to "...").
  */
-public header fun <A : Appendable> LongArray.joinTo(buffer: A, separator: CharSequence = ", ", prefix: CharSequence = "", postfix: CharSequence = "", limit: Int = -1, truncated: CharSequence = "...", transform: ((Long) -> CharSequence)? = null): A
+public fun <A : Appendable> LongArray.joinTo(buffer: A, separator: CharSequence = ", ", prefix: CharSequence = "", postfix: CharSequence = "", limit: Int = -1, truncated: CharSequence = "...", transform: ((Long) -> CharSequence)? = null): A {
+    buffer.append(prefix)
+    var count = 0
+    for (element in this) {
+        if (++count > 1) buffer.append(separator)
+        if (limit < 0 || count <= limit) {
+            if (transform != null)
+                buffer.append(transform(element))
+            else
+                buffer.append(element.toString())
+        } else break
+    }
+    if (limit >= 0 && count > limit) buffer.append(truncated)
+    buffer.append(postfix)
+    return buffer
+}
 
 /**
  * Appends the string from all the elements separated using [separator] and using the given [prefix] and [postfix] if supplied.
@@ -6799,7 +6874,22 @@ public header fun <A : Appendable> LongArray.joinTo(buffer: A, separator: CharSe
  * If the collection could be huge, you can specify a non-negative value of [limit], in which case only the first [limit]
  * elements will be appended, followed by the [truncated] string (which defaults to "...").
  */
-public header fun <A : Appendable> FloatArray.joinTo(buffer: A, separator: CharSequence = ", ", prefix: CharSequence = "", postfix: CharSequence = "", limit: Int = -1, truncated: CharSequence = "...", transform: ((Float) -> CharSequence)? = null): A
+public fun <A : Appendable> FloatArray.joinTo(buffer: A, separator: CharSequence = ", ", prefix: CharSequence = "", postfix: CharSequence = "", limit: Int = -1, truncated: CharSequence = "...", transform: ((Float) -> CharSequence)? = null): A {
+    buffer.append(prefix)
+    var count = 0
+    for (element in this) {
+        if (++count > 1) buffer.append(separator)
+        if (limit < 0 || count <= limit) {
+            if (transform != null)
+                buffer.append(transform(element))
+            else
+                buffer.append(element.toString())
+        } else break
+    }
+    if (limit >= 0 && count > limit) buffer.append(truncated)
+    buffer.append(postfix)
+    return buffer
+}
 
 /**
  * Appends the string from all the elements separated using [separator] and using the given [prefix] and [postfix] if supplied.
@@ -6807,7 +6897,22 @@ public header fun <A : Appendable> FloatArray.joinTo(buffer: A, separator: CharS
  * If the collection could be huge, you can specify a non-negative value of [limit], in which case only the first [limit]
  * elements will be appended, followed by the [truncated] string (which defaults to "...").
  */
-public header fun <A : Appendable> DoubleArray.joinTo(buffer: A, separator: CharSequence = ", ", prefix: CharSequence = "", postfix: CharSequence = "", limit: Int = -1, truncated: CharSequence = "...", transform: ((Double) -> CharSequence)? = null): A
+public fun <A : Appendable> DoubleArray.joinTo(buffer: A, separator: CharSequence = ", ", prefix: CharSequence = "", postfix: CharSequence = "", limit: Int = -1, truncated: CharSequence = "...", transform: ((Double) -> CharSequence)? = null): A {
+    buffer.append(prefix)
+    var count = 0
+    for (element in this) {
+        if (++count > 1) buffer.append(separator)
+        if (limit < 0 || count <= limit) {
+            if (transform != null)
+                buffer.append(transform(element))
+            else
+                buffer.append(element.toString())
+        } else break
+    }
+    if (limit >= 0 && count > limit) buffer.append(truncated)
+    buffer.append(postfix)
+    return buffer
+}
 
 /**
  * Appends the string from all the elements separated using [separator] and using the given [prefix] and [postfix] if supplied.
@@ -6815,7 +6920,22 @@ public header fun <A : Appendable> DoubleArray.joinTo(buffer: A, separator: Char
  * If the collection could be huge, you can specify a non-negative value of [limit], in which case only the first [limit]
  * elements will be appended, followed by the [truncated] string (which defaults to "...").
  */
-public header fun <A : Appendable> BooleanArray.joinTo(buffer: A, separator: CharSequence = ", ", prefix: CharSequence = "", postfix: CharSequence = "", limit: Int = -1, truncated: CharSequence = "...", transform: ((Boolean) -> CharSequence)? = null): A
+public fun <A : Appendable> BooleanArray.joinTo(buffer: A, separator: CharSequence = ", ", prefix: CharSequence = "", postfix: CharSequence = "", limit: Int = -1, truncated: CharSequence = "...", transform: ((Boolean) -> CharSequence)? = null): A {
+    buffer.append(prefix)
+    var count = 0
+    for (element in this) {
+        if (++count > 1) buffer.append(separator)
+        if (limit < 0 || count <= limit) {
+            if (transform != null)
+                buffer.append(transform(element))
+            else
+                buffer.append(element.toString())
+        } else break
+    }
+    if (limit >= 0 && count > limit) buffer.append(truncated)
+    buffer.append(postfix)
+    return buffer
+}
 
 /**
  * Appends the string from all the elements separated using [separator] and using the given [prefix] and [postfix] if supplied.
@@ -6823,7 +6943,22 @@ public header fun <A : Appendable> BooleanArray.joinTo(buffer: A, separator: Cha
  * If the collection could be huge, you can specify a non-negative value of [limit], in which case only the first [limit]
  * elements will be appended, followed by the [truncated] string (which defaults to "...").
  */
-public header fun <A : Appendable> CharArray.joinTo(buffer: A, separator: CharSequence = ", ", prefix: CharSequence = "", postfix: CharSequence = "", limit: Int = -1, truncated: CharSequence = "...", transform: ((Char) -> CharSequence)? = null): A
+public fun <A : Appendable> CharArray.joinTo(buffer: A, separator: CharSequence = ", ", prefix: CharSequence = "", postfix: CharSequence = "", limit: Int = -1, truncated: CharSequence = "...", transform: ((Char) -> CharSequence)? = null): A {
+    buffer.append(prefix)
+    var count = 0
+    for (element in this) {
+        if (++count > 1) buffer.append(separator)
+        if (limit < 0 || count <= limit) {
+            if (transform != null)
+                buffer.append(transform(element))
+            else
+                buffer.append(element.toString())
+        } else break
+    }
+    if (limit >= 0 && count > limit) buffer.append(truncated)
+    buffer.append(postfix)
+    return buffer
+}
 
 /**
  * Creates a string from all the elements separated using [separator] and using the given [prefix] and [postfix] if supplied.
@@ -6831,7 +6966,9 @@ public header fun <A : Appendable> CharArray.joinTo(buffer: A, separator: CharSe
  * If the collection could be huge, you can specify a non-negative value of [limit], in which case only the first [limit]
  * elements will be appended, followed by the [truncated] string (which defaults to "...").
  */
-public header fun <T> Array<out T>.joinToString(separator: CharSequence = ", ", prefix: CharSequence = "", postfix: CharSequence = "", limit: Int = -1, truncated: CharSequence = "...", transform: ((T) -> CharSequence)? = null): String
+public fun <T> Array<out T>.joinToString(separator: CharSequence = ", ", prefix: CharSequence = "", postfix: CharSequence = "", limit: Int = -1, truncated: CharSequence = "...", transform: ((T) -> CharSequence)? = null): String {
+    return joinTo(StringBuilder(), separator, prefix, postfix, limit, truncated, transform).toString()
+}
 
 /**
  * Creates a string from all the elements separated using [separator] and using the given [prefix] and [postfix] if supplied.
@@ -6839,7 +6976,9 @@ public header fun <T> Array<out T>.joinToString(separator: CharSequence = ", ",
  * If the collection could be huge, you can specify a non-negative value of [limit], in which case only the first [limit]
  * elements will be appended, followed by the [truncated] string (which defaults to "...").
  */
-public header fun ByteArray.joinToString(separator: CharSequence = ", ", prefix: CharSequence = "", postfix: CharSequence = "", limit: Int = -1, truncated: CharSequence = "...", transform: ((Byte) -> CharSequence)? = null): String
+public fun ByteArray.joinToString(separator: CharSequence = ", ", prefix: CharSequence = "", postfix: CharSequence = "", limit: Int = -1, truncated: CharSequence = "...", transform: ((Byte) -> CharSequence)? = null): String {
+    return joinTo(StringBuilder(), separator, prefix, postfix, limit, truncated, transform).toString()
+}
 
 /**
  * Creates a string from all the elements separated using [separator] and using the given [prefix] and [postfix] if supplied.
@@ -6847,7 +6986,9 @@ public header fun ByteArray.joinToString(separator: CharSequence = ", ", prefix:
  * If the collection could be huge, you can specify a non-negative value of [limit], in which case only the first [limit]
  * elements will be appended, followed by the [truncated] string (which defaults to "...").
  */
-public header fun ShortArray.joinToString(separator: CharSequence = ", ", prefix: CharSequence = "", postfix: CharSequence = "", limit: Int = -1, truncated: CharSequence = "...", transform: ((Short) -> CharSequence)? = null): String
+public fun ShortArray.joinToString(separator: CharSequence = ", ", prefix: CharSequence = "", postfix: CharSequence = "", limit: Int = -1, truncated: CharSequence = "...", transform: ((Short) -> CharSequence)? = null): String {
+    return joinTo(StringBuilder(), separator, prefix, postfix, limit, truncated, transform).toString()
+}
 
 /**
  * Creates a string from all the elements separated using [separator] and using the given [prefix] and [postfix] if supplied.
@@ -6855,7 +6996,9 @@ public header fun ShortArray.joinToString(separator: CharSequence = ", ", prefix
  * If the collection could be huge, you can specify a non-negative value of [limit], in which case only the first [limit]
  * elements will be appended, followed by the [truncated] string (which defaults to "...").
  */
-public header fun IntArray.joinToString(separator: CharSequence = ", ", prefix: CharSequence = "", postfix: CharSequence = "", limit: Int = -1, truncated: CharSequence = "...", transform: ((Int) -> CharSequence)? = null): String
+public fun IntArray.joinToString(separator: CharSequence = ", ", prefix: CharSequence = "", postfix: CharSequence = "", limit: Int = -1, truncated: CharSequence = "...", transform: ((Int) -> CharSequence)? = null): String {
+    return joinTo(StringBuilder(), separator, prefix, postfix, limit, truncated, transform).toString()
+}
 
 /**
  * Creates a string from all the elements separated using [separator] and using the given [prefix] and [postfix] if supplied.
@@ -6863,7 +7006,9 @@ public header fun IntArray.joinToString(separator: CharSequence = ", ", prefix:
  * If the collection could be huge, you can specify a non-negative value of [limit], in which case only the first [limit]
  * elements will be appended, followed by the [truncated] string (which defaults to "...").
  */
-public header fun LongArray.joinToString(separator: CharSequence = ", ", prefix: CharSequence = "", postfix: CharSequence = "", limit: Int = -1, truncated: CharSequence = "...", transform: ((Long) -> CharSequence)? = null): String
+public fun LongArray.joinToString(separator: CharSequence = ", ", prefix: CharSequence = "", postfix: CharSequence = "", limit: Int = -1, truncated: CharSequence = "...", transform: ((Long) -> CharSequence)? = null): String {
+    return joinTo(StringBuilder(), separator, prefix, postfix, limit, truncated, transform).toString()
+}
 
 /**
  * Creates a string from all the elements separated using [separator] and using the given [prefix] and [postfix] if supplied.
@@ -6871,7 +7016,9 @@ public header fun LongArray.joinToString(separator: CharSequence = ", ", prefix:
  * If the collection could be huge, you can specify a non-negative value of [limit], in which case only the first [limit]
  * elements will be appended, followed by the [truncated] string (which defaults to "...").
  */
-public header fun FloatArray.joinToString(separator: CharSequence = ", ", prefix: CharSequence = "", postfix: CharSequence = "", limit: Int = -1, truncated: CharSequence = "...", transform: ((Float) -> CharSequence)? = null): String
+public fun FloatArray.joinToString(separator: CharSequence = ", ", prefix: CharSequence = "", postfix: CharSequence = "", limit: Int = -1, truncated: CharSequence = "...", transform: ((Float) -> CharSequence)? = null): String {
+    return joinTo(StringBuilder(), separator, prefix, postfix, limit, truncated, transform).toString()
+}
 
 /**
  * Creates a string from all the elements separated using [separator] and using the given [prefix] and [postfix] if supplied.
@@ -6879,7 +7026,9 @@ public header fun FloatArray.joinToString(separator: CharSequence = ", ", prefix
  * If the collection could be huge, you can specify a non-negative value of [limit], in which case only the first [limit]
  * elements will be appended, followed by the [truncated] string (which defaults to "...").
  */
-public header fun DoubleArray.joinToString(separator: CharSequence = ", ", prefix: CharSequence = "", postfix: CharSequence = "", limit: Int = -1, truncated: CharSequence = "...", transform: ((Double) -> CharSequence)? = null): String
+public fun DoubleArray.joinToString(separator: CharSequence = ", ", prefix: CharSequence = "", postfix: CharSequence = "", limit: Int = -1, truncated: CharSequence = "...", transform: ((Double) -> CharSequence)? = null): String {
+    return joinTo(StringBuilder(), separator, prefix, postfix, limit, truncated, transform).toString()
+}
 
 /**
  * Creates a string from all the elements separated using [separator] and using the given [prefix] and [postfix] if supplied.
@@ -6887,7 +7036,9 @@ public header fun DoubleArray.joinToString(separator: CharSequence = ", ", prefi
  * If the collection could be huge, you can specify a non-negative value of [limit], in which case only the first [limit]
  * elements will be appended, followed by the [truncated] string (which defaults to "...").
  */
-public header fun BooleanArray.joinToString(separator: CharSequence = ", ", prefix: CharSequence = "", postfix: CharSequence = "", limit: Int = -1, truncated: CharSequence = "...", transform: ((Boolean) -> CharSequence)? = null): String
+public fun BooleanArray.joinToString(separator: CharSequence = ", ", prefix: CharSequence = "", postfix: CharSequence = "", limit: Int = -1, truncated: CharSequence = "...", transform: ((Boolean) -> CharSequence)? = null): String {
+    return joinTo(StringBuilder(), separator, prefix, postfix, limit, truncated, transform).toString()
+}
 
 /**
  * Creates a string from all the elements separated using [separator] and using the given [prefix] and [postfix] if supplied.
@@ -6895,7 +7046,9 @@ public header fun BooleanArray.joinToString(separator: CharSequence = ", ", pref
  * If the collection could be huge, you can specify a non-negative value of [limit], in which case only the first [limit]
  * elements will be appended, followed by the [truncated] string (which defaults to "...").
  */
-public header fun CharArray.joinToString(separator: CharSequence = ", ", prefix: CharSequence = "", postfix: CharSequence = "", limit: Int = -1, truncated: CharSequence = "...", transform: ((Char) -> CharSequence)? = null): String
+public fun CharArray.joinToString(separator: CharSequence = ", ", prefix: CharSequence = "", postfix: CharSequence = "", limit: Int = -1, truncated: CharSequence = "...", transform: ((Char) -> CharSequence)? = null): String {
+    return joinTo(StringBuilder(), separator, prefix, postfix, limit, truncated, transform).toString()
+}
 
 /**
  * Creates an [Iterable] instance that wraps the original array returning its elements when being iterated.

libraries/stdlib/common/src/generated/_Collections.kt

@@ -968,7 +968,22 @@ public header inline fun <T, R, V> Iterable<T>.zip(other: Iterable<R>, transform
  * If the collection could be huge, you can specify a non-negative value of [limit], in which case only the first [limit]
  * elements will be appended, followed by the [truncated] string (which defaults to "...").
  */
-public header fun <T, A : Appendable> Iterable<T>.joinTo(buffer: A, separator: CharSequence = ", ", prefix: CharSequence = "", postfix: CharSequence = "", limit: Int = -1, truncated: CharSequence = "...", transform: ((T) -> CharSequence)? = null): A
+public fun <T, A : Appendable> Iterable<T>.joinTo(buffer: A, separator: CharSequence = ", ", prefix: CharSequence = "", postfix: CharSequence = "", limit: Int = -1, truncated: CharSequence = "...", transform: ((T) -> CharSequence)? = null): A {
+    buffer.append(prefix)
+    var count = 0
+    for (element in this) {
+        if (++count > 1) buffer.append(separator)
+        if (limit < 0 || count <= limit) {
+            if (transform != null)
+                buffer.append(transform(element))
+            else
+                buffer.append(if (element == null) "null" else element.toString())
+        } else break
+    }
+    if (limit >= 0 && count > limit) buffer.append(truncated)
+    buffer.append(postfix)
+    return buffer
+}
 
 /**
  * Creates a string from all the elements separated using [separator] and using the given [prefix] and [postfix] if supplied.
@@ -976,7 +991,9 @@ public header fun <T, A : Appendable> Iterable<T>.joinTo(buffer: A, separator: C
  * If the collection could be huge, you can specify a non-negative value of [limit], in which case only the first [limit]
  * elements will be appended, followed by the [truncated] string (which defaults to "...").
  */
-public header fun <T> Iterable<T>.joinToString(separator: CharSequence = ", ", prefix: CharSequence = "", postfix: CharSequence = "", limit: Int = -1, truncated: CharSequence = "...", transform: ((T) -> CharSequence)? = null): String
+public fun <T> Iterable<T>.joinToString(separator: CharSequence = ", ", prefix: CharSequence = "", postfix: CharSequence = "", limit: Int = -1, truncated: CharSequence = "...", transform: ((T) -> CharSequence)? = null): String {
+    return joinTo(StringBuilder(), separator, prefix, postfix, limit, truncated, transform).toString()
+}
 
 /**
  * Returns this collection as an [Iterable].

libraries/stdlib/common/src/generated/_Sequences.kt

@@ -660,7 +660,22 @@ public header fun <T, R, V> Sequence<T>.zip(other: Sequence<R>, transform: (T, R
  * If the collection could be huge, you can specify a non-negative value of [limit], in which case only the first [limit]
  * elements will be appended, followed by the [truncated] string (which defaults to "...").
  */
-public header fun <T, A : Appendable> Sequence<T>.joinTo(buffer: A, separator: CharSequence = ", ", prefix: CharSequence = "", postfix: CharSequence = "", limit: Int = -1, truncated: CharSequence = "...", transform: ((T) -> CharSequence)? = null): A
+public fun <T, A : Appendable> Sequence<T>.joinTo(buffer: A, separator: CharSequence = ", ", prefix: CharSequence = "", postfix: CharSequence = "", limit: Int = -1, truncated: CharSequence = "...", transform: ((T) -> CharSequence)? = null): A {
+    buffer.append(prefix)
+    var count = 0
+    for (element in this) {
+        if (++count > 1) buffer.append(separator)
+        if (limit < 0 || count <= limit) {
+            if (transform != null)
+                buffer.append(transform(element))
+            else
+                buffer.append(if (element == null) "null" else element.toString())
+        } else break
+    }
+    if (limit >= 0 && count > limit) buffer.append(truncated)
+    buffer.append(postfix)
+    return buffer
+}
 
 /**
  * Creates a string from all the elements separated using [separator] and using the given [prefix] and [postfix] if supplied.
@@ -668,7 +683,9 @@ public header fun <T, A : Appendable> Sequence<T>.joinTo(buffer: A, separator: C
  * If the collection could be huge, you can specify a non-negative value of [limit], in which case only the first [limit]
  * elements will be appended, followed by the [truncated] string (which defaults to "...").
  */
-public header fun <T> Sequence<T>.joinToString(separator: CharSequence = ", ", prefix: CharSequence = "", postfix: CharSequence = "", limit: Int = -1, truncated: CharSequence = "...", transform: ((T) -> CharSequence)? = null): String
+public fun <T> Sequence<T>.joinToString(separator: CharSequence = ", ", prefix: CharSequence = "", postfix: CharSequence = "", limit: Int = -1, truncated: CharSequence = "...", transform: ((T) -> CharSequence)? = null): String {
+    return joinTo(StringBuilder(), separator, prefix, postfix, limit, truncated, transform).toString()
+}
 
 /**
  * Creates an [Iterable] instance that wraps the original sequence returning its elements when being iterated.

libraries/tools/kotlin-stdlib-gen/src/templates/engine/Engine.kt

@@ -318,6 +318,7 @@ class GenericFunction(val signature: String, val keyword: String = "fun") {
 
     fun build(builder: Appendable, f: Family, primitive: PrimitiveType?, platform: Platform) {
         val headerOnly: Boolean = platform == Platform.Common
+        val hasOptionalParams = (customSignature[platform, f] ?: signature).contains("=")
         val returnType = returns[platform, f] ?: throw RuntimeException("No return type specified for $signature")
 
         fun renderType(expression: String, receiver: String, self: String): String {
@@ -473,7 +474,7 @@ class GenericFunction(val signature: String, val keyword: String = "fun") {
         }
 
         builder.append(visibility[f] ?: "public").append(' ')
-        if (headerOnly) {
+        if (headerOnly && !hasOptionalParams) {
             builder.append("header ")
         }
         if (external[platform, f] == true)
@@ -498,7 +499,7 @@ class GenericFunction(val signature: String, val keyword: String = "fun") {
         if (receiverType.isNotEmpty()) builder.append('.')
         builder.append("${(customSignature[platform, f] ?: signature).renderType()}: ${returnType.renderType()}")
 
-        if (headerOnly) {
+        if (headerOnly && !hasOptionalParams) {
             builder.append("\n\n")
             return
         }