[Assign plugin] Add a compiler plugin for overloading assign ('=') operator

plugins/assign-plugin/testData/diagnostics/plusAssignPrecedence.kt

@@ -0,0 +1,104 @@
+annotation class ValueContainer
+
+abstract class AbstractStringProperty(protected var v: String) {
+    fun get(): String {
+        return v
+    }
+}
+
+@ValueContainer
+class StringProperty(v: String) : AbstractStringProperty(v) {
+    fun assign(v: String) {
+        this.v = v
+    }
+
+    fun assign(v: StringProperty) {
+        this.v = v.get()
+    }
+}
+
+@ValueContainer
+class StringPropertyWithPlus(v: String) : AbstractStringProperty(v) {
+    fun assign(v: String) {
+        this.v = v
+    }
+
+    fun assign(o: StringPropertyWithPlus) {
+        this.v = o.get()
+    }
+
+    operator fun plus(v: String) =
+        StringPropertyWithPlus(this.v + v)
+}
+
+@ValueContainer
+class StringPropertyWithPlusAssign(v: String) : AbstractStringProperty(v) {
+    fun assign(v: String) {
+        this.v = v
+    }
+
+    fun assign(o: StringPropertyWithPlusAssign) {
+        this.v = o.get()
+    }
+
+    operator fun plusAssign(v: String) {
+        this.v += v
+    }
+}
+
+@ValueContainer
+class StringPropertyWithPlusAndPlusAssign(v: String) : AbstractStringProperty(v) {
+    fun assign(v: String) {
+        this.v = v
+    }
+
+    fun assign(o: StringPropertyWithPlusAndPlusAssign) {
+        this.v = o.get()
+    }
+
+    operator fun plus(v: String) =
+        StringPropertyWithPlusAndPlusAssign(this.v + v)
+
+    operator fun plusAssign(v: String) {
+        this.v += v
+    }
+}
+
+data class Task(
+    val valInput: StringProperty,
+    var varInput: StringProperty,
+
+    val valInputWithPlus: StringPropertyWithPlus,
+    var varInputWithPlus: StringPropertyWithPlus,
+
+    val valInputWithPlusAssign: StringPropertyWithPlusAssign,
+    var varInputWithPlusAssign: StringPropertyWithPlusAssign,
+
+    val valInputWithPlusAndPlusAssign: StringPropertyWithPlusAndPlusAssign,
+    var varInputWithPlusAndPlusAssign: StringPropertyWithPlusAndPlusAssign,
+)
+
+fun box(): String {
+    val task = Task(
+        StringProperty("O"),
+        StringProperty("O"),
+
+        StringPropertyWithPlus("O"),
+        StringPropertyWithPlus("O"),
+
+        StringPropertyWithPlusAssign("O"),
+        StringPropertyWithPlusAssign("O"),
+
+        StringPropertyWithPlusAndPlusAssign("O"),
+        StringPropertyWithPlusAndPlusAssign("O")
+    )
+
+    task.valInput <!UNRESOLVED_REFERENCE_WRONG_RECEIVER!>+=<!> "K"
+    task.varInput <!UNRESOLVED_REFERENCE_WRONG_RECEIVER!>+=<!> "K"
+
+    <!VAL_REASSIGNMENT!>task.valInputWithPlus<!> += "K"
+
+    task.varInputWithPlusAndPlusAssign <!ASSIGN_OPERATOR_AMBIGUITY!>+=<!> "K"
+
+    return "OK"
+}