FIR2IR: Avoid generation of incorrect suspend adapter for custom implementation

^KT-82590 Fixed

Author: dzharkov

compiler/fir/fir2ir/src/org/jetbrains/kotlin/fir/backend/generators/AdapterGenerator.kt

@@ -551,6 +551,11 @@ class AdapterGenerator(
             return this
         }
 
+        val preparedArgumentType = prepareArgumentTypeForSuspendConversion(argument)
+        // No conversion should happen if an argument already satisfies the expected type requirements
+        // NB: It's not just a fast path, but sometimes the presence adapter generation is incorrect (see KT-82590)
+        if (preparedArgumentType.isSubtypeOf(expectedType, session)) return this
+
         val unwrappedExpectedType = getFunctionTypeForPossibleSamType(expectedType) ?: expectedType
 
         // Expect the expected type to be a suspend functional type.
@@ -559,7 +564,6 @@ class AdapterGenerator(
         }
         val expectedFunctionalType = unwrappedExpectedType.customFunctionTypeToSimpleFunctionType(session)
 
-        val preparedArgumentType = prepareArgumentTypeForSuspendConversion(argument)
         val invokeSymbol = findInvokeSymbol(expectedFunctionalType, preparedArgumentType) ?: return this
         val suspendConvertedType = unwrappedExpectedType.toIrType() as IrSimpleType
         return argument.convertWithOffsets { startOffset, endOffset ->

compiler/testData/codegen/box/funInterface/noConversionForSubtype.kt

@@ -1,6 +1,5 @@
 // IGNORE_BACKEND: JS_IR, JS_IR_ES6
 // IGNORE_IR_DESERIALIZATION_TEST: JS_IR, JS_IR_ES6
-// IGNORE_BACKEND_K2: ANY
 // ISSUE: KT-82590
 
 interface MyInterface

compiler/testData/codegen/box/funInterface/noConversionForSubtypeGeneric.kt

@@ -1,6 +1,5 @@
 // IGNORE_BACKEND: JS_IR, JS_IR_ES6
 // IGNORE_IR_DESERIALIZATION_TEST: JS_IR, JS_IR_ES6
-// IGNORE_BACKEND_K2: ANY
 // ISSUE: KT-82590
 
 interface MyInterface

compiler/testData/ir/irText/expressions/funInterface/noConversionForSubtype.fir.ir.txt

@@ -1,3 +1,4 @@
+// FIR_IDENTICAL
 // DONT_TARGET_EXACT_BACKEND: JS_IR
 // ISSUE: KT-82590