Frontend support for function as expression

compiler/testData/diagnostics/tests/functionAsExpression/WithOuterGeneric.kt

@@ -0,0 +1,31 @@
+// !DIAGNOSTICS: -UNUSED_PARAMETER -UNUSED_VARIABLE
+
+fun <T> parameter() = fun (t: T) = t
+fun <T> receiver() = fun T.() = this
+fun <T> returnType() = fun (): T = null!!
+
+val <T> T.fromVal: () -> T get() = fun (): T = this@fromVal
+
+fun devNull(a: Any?){}
+
+fun <O> outer() {
+    fun <T> parameter() = fun (t: T) = t
+    fun <T> receiver() = fun T.() = this
+    fun <T> returnType() = fun (): T = null!!
+
+    devNull(fun (t: O) = t)
+    devNull(fun O.() = this)
+    devNull(fun (): O = null!!)
+}
+
+class Outer<O> {
+    fun <T> parameter() = fun (t: T) = t
+    fun <T> receiver() = fun T.() = this
+    fun <T> returnType() = fun (): T = null!!
+
+    init {
+        devNull(fun (t: O) = t)
+        devNull(fun O.() = this)
+        devNull(fun (): O = null!!)
+    }
+}