IR text tests: New tests specifically for main functions mangling

^KT-57755

compiler/testData/ir/irText/declarations/mainFunctionMangling.kt

@@ -0,0 +1,78 @@
+// FIR_IDENTICAL
+// WITH_STDLIB
+
+// MUTE_SIGNATURE_COMPARISON_K2: JVM_IR
+// ^^^ JVM K2 eagerly mangles all the functions with `main` name, which is not so in JVM K1. That's the difference that, however,
+//     does not cause problems when switching between K1 and K2 compilers, since signatures are not serialized in JARs.
+
+// FILE: a.kt
+fun main() {
+    println("main()")
+}
+
+// Looks like `main` but is not a main function.
+fun <T> main(t: T): T {
+    println("main(T): T")
+    return t
+}
+
+class C {
+    fun main() {
+        println("C.main()")
+    }
+
+    // Looks like `main` but is not a main function.
+    fun <T> main(t: T): T {
+        println("C.main(T): T")
+        return t
+    }
+}
+
+object O {
+    fun main() {
+        println("O.main()")
+    }
+
+    // Looks like `main` but is not a main function.
+    fun <T> main(t: T): T {
+        println("O.main(T): T")
+        return t
+    }
+}
+
+// FILE: b.kt
+package foo
+
+fun main() {
+    println("foo.main()")
+}
+
+// Looks like `main` but is not a main function.
+fun <T> main(t: T): T {
+    println("foo.main(T): T")
+    return t
+}
+
+class C {
+    fun main() {
+        println("foo.C.main()")
+    }
+
+    // Looks like `main` but is not a main function.
+    fun <T> main(t: T): T {
+        println("foo.C.main(T): T")
+        return t
+    }
+}
+
+object O {
+    fun main() {
+        println("foo.O.main()")
+    }
+
+    // Looks like `main` but is not a main function.
+    fun <T> main(t: T): T {
+        println("foo.O.main(T): T")
+        return t
+    }
+}