Diagnostics on 'infix' (declaration&use site)

compiler/testData/diagnostics/tests/InfixModifierApplicability.kt

@@ -0,0 +1,21 @@
+// !DIAGNOSTICS: -UNUSED_PARAMETER
+
+class Pair<A, B>(val a: A, val b: B)
+infix fun <A, B> A.to(that: B): Pair<A, B> = Pair(this, that)
+
+infix fun String.o1(o: String) = o
+infix fun String.o2(o: String, o2: String? = null) = o
+
+<!INAPPLICABLE_INFIX_MODIFIER!>infix<!> fun w1() {}
+<!INAPPLICABLE_INFIX_MODIFIER!>infix<!> fun w2(s: String) {}
+<!INAPPLICABLE_INFIX_MODIFIER!>infix<!> fun String.w3() {}
+<!INAPPLICABLE_INFIX_MODIFIER!>infix<!> fun String.w4(a: Int, b: Int) {}
+<!INAPPLICABLE_INFIX_MODIFIER!>infix<!> fun w5(a: Int, b: Int) {}
+
+class Example {
+    infix fun c1(s: String) {}
+    infix fun c2(s: String, a: Int = 0) {}
+
+    <!INAPPLICABLE_INFIX_MODIFIER!>infix<!> fun cw1(s: String, a: Int) {}
+    <!INAPPLICABLE_INFIX_MODIFIER!>infix<!> fun sw2() {}
+}