Add @Deprecated annotation to a synthetic $serializer class

in K2 so it matches K1 behavior.

Deprecation is required, so the declaration will not be visible to user in completion in the IDE.

#KT-65757 Fixed

plugins/kotlinx-serialization/testData/diagnostics/GeneratedSerializerInaccessible.kt

@@ -0,0 +1,14 @@
+// FIR_IDENTICAL
+// WITH_STDLIB
+// SKIP_TXT
+
+import kotlinx.serialization.*
+
+@Serializable
+class A
+
+fun foo() {
+    A.<!DEPRECATION_ERROR!>`$serializer`<!>
+    A.<!DEPRECATION_ERROR!>`$serializer`<!>.descriptor
+    A(<!TOO_MANY_ARGUMENTS!>0<!>, <!TOO_MANY_ARGUMENTS!>null<!>)
+}

plugins/kotlinx-serialization/testData/firMembers/abstractAndSealed.fir.txt

@@ -70,7 +70,7 @@ FILE: abstractAndSealed.kt
 
         }
 
-        public final object $serializer : R|kotlinx/serialization/internal/GeneratedSerializer<Bottom>| {
+        @R|kotlin/Deprecated|(message = String(This synthesized declaration should not be used directly), level = Q|kotlin/DeprecationLevel|.R|kotlin/DeprecationLevel.HIDDEN|) public final object $serializer : R|kotlinx/serialization/internal/GeneratedSerializer<Bottom>| {
             public final override fun serialize(encoder: R|kotlinx/serialization/encoding/Encoder|, value: R|Bottom|): R|kotlin/Unit|
 
             public final override fun deserialize(decoder: R|kotlinx/serialization/encoding/Decoder|): R|Bottom|

plugins/kotlinx-serialization/testData/firMembers/classWithCompanionObject.fir.txt

@@ -16,7 +16,7 @@ FILE: classWithCompanionObject.kt
 
         }
 
-        public final object $serializer : R|kotlinx/serialization/internal/GeneratedSerializer<SomeClass>| {
+        @R|kotlin/Deprecated|(message = String(This synthesized declaration should not be used directly), level = Q|kotlin/DeprecationLevel|.R|kotlin/DeprecationLevel.HIDDEN|) public final object $serializer : R|kotlinx/serialization/internal/GeneratedSerializer<SomeClass>| {
             public final override fun serialize(encoder: R|kotlinx/serialization/encoding/Encoder|, value: R|SomeClass|): R|kotlin/Unit|
 
             public final override fun deserialize(decoder: R|kotlinx/serialization/encoding/Decoder|): R|SomeClass|

plugins/kotlinx-serialization/testData/firMembers/classWithGenericParameters.fir.txt

@@ -22,7 +22,7 @@ FILE: classWithGenericParameters.kt
 
         }
 
-        public final class $serializer<T, V> : R|kotlinx/serialization/internal/GeneratedSerializer<GenericBox<T, V>>| {
+        @R|kotlin/Deprecated|(message = String(This synthesized declaration should not be used directly), level = Q|kotlin/DeprecationLevel|.R|kotlin/DeprecationLevel.HIDDEN|) public final class $serializer<T, V> : R|kotlinx/serialization/internal/GeneratedSerializer<GenericBox<T, V>>| {
             public final override fun serialize(encoder: R|kotlinx/serialization/encoding/Encoder|, value: R|GenericBox<T, V>|): R|kotlin/Unit|
 
             public final override fun deserialize(decoder: R|kotlinx/serialization/encoding/Decoder|): R|GenericBox<T, V>|

plugins/kotlinx-serialization/testData/firMembers/defaultProperties.fir.txt

@@ -33,7 +33,7 @@ FILE: defaultProperties.kt
 
         }
 
-        public final object $serializer : R|kotlinx/serialization/internal/GeneratedSerializer<SomeClass>| {
+        @R|kotlin/Deprecated|(message = String(This synthesized declaration should not be used directly), level = Q|kotlin/DeprecationLevel|.R|kotlin/DeprecationLevel.HIDDEN|) public final object $serializer : R|kotlinx/serialization/internal/GeneratedSerializer<SomeClass>| {
             public final override fun serialize(encoder: R|kotlinx/serialization/encoding/Encoder|, value: R|SomeClass|): R|kotlin/Unit|
 
             public final override fun deserialize(decoder: R|kotlinx/serialization/encoding/Decoder|): R|SomeClass|

plugins/kotlinx-serialization/testData/firMembers/enums.fir.txt

@@ -74,7 +74,7 @@ FILE: enums.kt
 
         }
 
-        public final object $serializer : R|kotlinx/serialization/internal/GeneratedSerializer<Holder>| {
+        @R|kotlin/Deprecated|(message = String(This synthesized declaration should not be used directly), level = Q|kotlin/DeprecationLevel|.R|kotlin/DeprecationLevel.HIDDEN|) public final object $serializer : R|kotlinx/serialization/internal/GeneratedSerializer<Holder>| {
             public final override fun serialize(encoder: R|kotlinx/serialization/encoding/Encoder|, value: R|Holder|): R|kotlin/Unit|
 
             public final override fun deserialize(decoder: R|kotlinx/serialization/encoding/Decoder|): R|Holder|

plugins/kotlinx-serialization/testData/firMembers/inlineClasses.fir.txt

@@ -16,7 +16,7 @@ FILE: inlineClasses.kt
 
         }
 
-        public final object $serializer : R|kotlinx/serialization/internal/GeneratedSerializer<Foo>| {
+        @R|kotlin/Deprecated|(message = String(This synthesized declaration should not be used directly), level = Q|kotlin/DeprecationLevel|.R|kotlin/DeprecationLevel.HIDDEN|) public final object $serializer : R|kotlinx/serialization/internal/GeneratedSerializer<Foo>| {
             public final override fun serialize(encoder: R|kotlinx/serialization/encoding/Encoder|, value: R|Foo|): R|kotlin/Unit|
 
             public final override fun deserialize(decoder: R|kotlinx/serialization/encoding/Decoder|): R|Foo|
@@ -50,7 +50,7 @@ FILE: inlineClasses.kt
 
         }
 
-        public final object $serializer : R|kotlinx/serialization/internal/GeneratedSerializer<Holder>| {
+        @R|kotlin/Deprecated|(message = String(This synthesized declaration should not be used directly), level = Q|kotlin/DeprecationLevel|.R|kotlin/DeprecationLevel.HIDDEN|) public final object $serializer : R|kotlinx/serialization/internal/GeneratedSerializer<Holder>| {
             public final override fun serialize(encoder: R|kotlinx/serialization/encoding/Encoder|, value: R|Holder|): R|kotlin/Unit|
 
             public final override fun deserialize(decoder: R|kotlinx/serialization/encoding/Decoder|): R|Holder|

plugins/kotlinx-serialization/testData/firMembers/metaSerializable.fir.txt

@@ -37,7 +37,7 @@ FILE: metaSerializable.kt
 
         }
 
-        public final object $serializer : R|kotlinx/serialization/internal/GeneratedSerializer<Project1>| {
+        @R|kotlin/Deprecated|(message = String(This synthesized declaration should not be used directly), level = Q|kotlin/DeprecationLevel|.R|kotlin/DeprecationLevel.HIDDEN|) public final object $serializer : R|kotlinx/serialization/internal/GeneratedSerializer<Project1>| {
             public final override fun serialize(encoder: R|kotlinx/serialization/encoding/Encoder|, value: R|Project1|): R|kotlin/Unit|
 
             public final override fun deserialize(decoder: R|kotlinx/serialization/encoding/Decoder|): R|Project1|
@@ -74,7 +74,7 @@ FILE: metaSerializable.kt
 
         }
 
-        public final object $serializer : R|kotlinx/serialization/internal/GeneratedSerializer<Project2>| {
+        @R|kotlin/Deprecated|(message = String(This synthesized declaration should not be used directly), level = Q|kotlin/DeprecationLevel|.R|kotlin/DeprecationLevel.HIDDEN|) public final object $serializer : R|kotlinx/serialization/internal/GeneratedSerializer<Project2>| {
             public final override fun serialize(encoder: R|kotlinx/serialization/encoding/Encoder|, value: R|Project2|): R|kotlin/Unit|
 
             public final override fun deserialize(decoder: R|kotlinx/serialization/encoding/Decoder|): R|Project2|
@@ -108,7 +108,7 @@ FILE: metaSerializable.kt
 
         }
 
-        public final object $serializer : R|kotlinx/serialization/internal/GeneratedSerializer<Wrapper>| {
+        @R|kotlin/Deprecated|(message = String(This synthesized declaration should not be used directly), level = Q|kotlin/DeprecationLevel|.R|kotlin/DeprecationLevel.HIDDEN|) public final object $serializer : R|kotlinx/serialization/internal/GeneratedSerializer<Wrapper>| {
             public final override fun serialize(encoder: R|kotlinx/serialization/encoding/Encoder|, value: R|Wrapper|): R|kotlin/Unit|
 
             public final override fun deserialize(decoder: R|kotlinx/serialization/encoding/Decoder|): R|Wrapper|
@@ -145,7 +145,7 @@ FILE: metaSerializable.kt
 
         }
 
-        public final object $serializer : R|kotlinx/serialization/internal/GeneratedSerializer<Project3>| {
+        @R|kotlin/Deprecated|(message = String(This synthesized declaration should not be used directly), level = Q|kotlin/DeprecationLevel|.R|kotlin/DeprecationLevel.HIDDEN|) public final object $serializer : R|kotlinx/serialization/internal/GeneratedSerializer<Project3>| {
             public final override fun serialize(encoder: R|kotlinx/serialization/encoding/Encoder|, value: R|Project3|): R|kotlin/Unit|
 
             public final override fun deserialize(decoder: R|kotlinx/serialization/encoding/Decoder|): R|Project3|
@@ -205,7 +205,7 @@ FILE: metaSerializable.kt
 
             }
 
-            public final object $serializer : R|kotlinx/serialization/internal/GeneratedSerializer<TestSealed.A>| {
+            @R|kotlin/Deprecated|(message = String(This synthesized declaration should not be used directly), level = Q|kotlin/DeprecationLevel|.R|kotlin/DeprecationLevel.HIDDEN|) public final object $serializer : R|kotlinx/serialization/internal/GeneratedSerializer<TestSealed.A>| {
                 public final override fun serialize(encoder: R|kotlinx/serialization/encoding/Encoder|, value: R|TestSealed.A|): R|kotlin/Unit|
 
                 public final override fun deserialize(decoder: R|kotlinx/serialization/encoding/Decoder|): R|TestSealed.A|
@@ -240,7 +240,7 @@ FILE: metaSerializable.kt
 
             }
 
-            public final object $serializer : R|kotlinx/serialization/internal/GeneratedSerializer<TestSealed.B>| {
+            @R|kotlin/Deprecated|(message = String(This synthesized declaration should not be used directly), level = Q|kotlin/DeprecationLevel|.R|kotlin/DeprecationLevel.HIDDEN|) public final object $serializer : R|kotlinx/serialization/internal/GeneratedSerializer<TestSealed.B>| {
                 public final override fun serialize(encoder: R|kotlinx/serialization/encoding/Encoder|, value: R|TestSealed.B|): R|kotlin/Unit|
 
                 public final override fun deserialize(decoder: R|kotlinx/serialization/encoding/Decoder|): R|TestSealed.B|
@@ -290,7 +290,7 @@ FILE: metaSerializable.kt
 
             }
 
-            public final object $serializer : R|kotlinx/serialization/internal/GeneratedSerializer<TestAbstract.A>| {
+            @R|kotlin/Deprecated|(message = String(This synthesized declaration should not be used directly), level = Q|kotlin/DeprecationLevel|.R|kotlin/DeprecationLevel.HIDDEN|) public final object $serializer : R|kotlinx/serialization/internal/GeneratedSerializer<TestAbstract.A>| {
                 public final override fun serialize(encoder: R|kotlinx/serialization/encoding/Encoder|, value: R|TestAbstract.A|): R|kotlin/Unit|
 
                 public final override fun deserialize(decoder: R|kotlinx/serialization/encoding/Decoder|): R|TestAbstract.A|
@@ -325,7 +325,7 @@ FILE: metaSerializable.kt
 
             }
 
-            public final object $serializer : R|kotlinx/serialization/internal/GeneratedSerializer<TestAbstract.B>| {
+            @R|kotlin/Deprecated|(message = String(This synthesized declaration should not be used directly), level = Q|kotlin/DeprecationLevel|.R|kotlin/DeprecationLevel.HIDDEN|) public final object $serializer : R|kotlinx/serialization/internal/GeneratedSerializer<TestAbstract.B>| {
                 public final override fun serialize(encoder: R|kotlinx/serialization/encoding/Encoder|, value: R|TestAbstract.B|): R|kotlin/Unit|
 
                 public final override fun deserialize(decoder: R|kotlinx/serialization/encoding/Decoder|): R|TestAbstract.B|

plugins/kotlinx-serialization/testData/firMembers/multipleProperties.fir.txt

@@ -25,7 +25,7 @@ FILE: multipleProperties.kt
 
         }
 
-        public final object $serializer : R|kotlinx/serialization/internal/GeneratedSerializer<SomeClass>| {
+        @R|kotlin/Deprecated|(message = String(This synthesized declaration should not be used directly), level = Q|kotlin/DeprecationLevel|.R|kotlin/DeprecationLevel.HIDDEN|) public final object $serializer : R|kotlinx/serialization/internal/GeneratedSerializer<SomeClass>| {
             public final override fun serialize(encoder: R|kotlinx/serialization/encoding/Encoder|, value: R|SomeClass|): R|kotlin/Unit|
 
             public final override fun deserialize(decoder: R|kotlinx/serialization/encoding/Decoder|): R|SomeClass|

plugins/kotlinx-serialization/testData/firMembers/privatePropertiesSerialization.fir.txt

@@ -36,7 +36,7 @@ FILE: privatePropertiesSerialization.kt
 
         }
 
-        public final object $serializer : R|kotlinx/serialization/internal/GeneratedSerializer<Parent>| {
+        @R|kotlin/Deprecated|(message = String(This synthesized declaration should not be used directly), level = Q|kotlin/DeprecationLevel|.R|kotlin/DeprecationLevel.HIDDEN|) public final object $serializer : R|kotlinx/serialization/internal/GeneratedSerializer<Parent>| {
             public final override fun serialize(encoder: R|kotlinx/serialization/encoding/Encoder|, value: R|Parent|): R|kotlin/Unit|
 
             public final override fun deserialize(decoder: R|kotlinx/serialization/encoding/Decoder|): R|Parent|
@@ -67,7 +67,7 @@ FILE: privatePropertiesSerialization.kt
 
         }
 
-        public final object $serializer : R|kotlinx/serialization/internal/GeneratedSerializer<Derived>| {
+        @R|kotlin/Deprecated|(message = String(This synthesized declaration should not be used directly), level = Q|kotlin/DeprecationLevel|.R|kotlin/DeprecationLevel.HIDDEN|) public final object $serializer : R|kotlinx/serialization/internal/GeneratedSerializer<Derived>| {
             public final override fun serialize(encoder: R|kotlinx/serialization/encoding/Encoder|, value: R|Derived|): R|kotlin/Unit|
 
             public final override fun deserialize(decoder: R|kotlinx/serialization/encoding/Decoder|): R|Derived|

plugins/kotlinx-serialization/testData/firMembers/serializableWithCompanion.fir.txt

@@ -43,7 +43,7 @@ FILE: serializableWithCompanion.kt
 
         public final fun copy(i: R|kotlin/Int| = this@R|com/example/WithCompanion|.R|com/example/WithCompanion.i|): R|com/example/WithCompanion|
 
-        public final object $serializer : R|kotlinx/serialization/internal/GeneratedSerializer<com/example/WithCompanion>| {
+        @R|kotlin/Deprecated|(message = String(This synthesized declaration should not be used directly), level = Q|kotlin/DeprecationLevel|.R|kotlin/DeprecationLevel.HIDDEN|) public final object $serializer : R|kotlinx/serialization/internal/GeneratedSerializer<com/example/WithCompanion>| {
             public final override fun serialize(encoder: R|kotlinx/serialization/encoding/Encoder|, value: R|com/example/WithCompanion|): R|kotlin/Unit|
 
             public final override fun deserialize(decoder: R|kotlinx/serialization/encoding/Decoder|): R|com/example/WithCompanion|
@@ -85,7 +85,7 @@ FILE: serializableWithCompanion.kt
 
         public final fun copy(i: R|kotlin/Int| = this@R|com/example/WithNamedCompanion|.R|com/example/WithNamedCompanion.i|): R|com/example/WithNamedCompanion|
 
-        public final object $serializer : R|kotlinx/serialization/internal/GeneratedSerializer<com/example/WithNamedCompanion>| {
+        @R|kotlin/Deprecated|(message = String(This synthesized declaration should not be used directly), level = Q|kotlin/DeprecationLevel|.R|kotlin/DeprecationLevel.HIDDEN|) public final object $serializer : R|kotlinx/serialization/internal/GeneratedSerializer<com/example/WithNamedCompanion>| {
             public final override fun serialize(encoder: R|kotlinx/serialization/encoding/Encoder|, value: R|com/example/WithNamedCompanion|): R|kotlin/Unit|
 
             public final override fun deserialize(decoder: R|kotlinx/serialization/encoding/Decoder|): R|com/example/WithNamedCompanion|

plugins/kotlinx-serialization/testData/firMembers/serializerInLocalClass.fir.txt

@@ -21,7 +21,7 @@ FILE: serializerInLocalClass.kt
 
             }
 
-            public final object $serializer : R|kotlinx/serialization/internal/GeneratedSerializer<<local>/Carrier>| {
+            @R|kotlin/Deprecated|(message = String(This synthesized declaration should not be used directly), level = Q|kotlin/DeprecationLevel|.R|kotlin/DeprecationLevel.HIDDEN|) public final object $serializer : R|kotlinx/serialization/internal/GeneratedSerializer<<local>/Carrier>| {
                 public final override fun serialize(encoder: R|kotlinx/serialization/encoding/Encoder|, value: R|<local>/Carrier|): R|kotlin/Unit|
 
                 public final override fun deserialize(decoder: R|kotlinx/serialization/encoding/Decoder|): R|<local>/Carrier|