From d063db3ce0631c84041c24024d04c134339dc38a Mon Sep 17 00:00:00 2001
From: "Sergey.Shanshin" <sergey.shanshin@jetbrains.com>
Date: Wed, 18 Jan 2023 15:47:26 +0000
Subject: [PATCH] Fixed missing fallback serializer in contextual serializer

Fixes Kotlin/kotlinx.serialization#2158

Merge-request: KT-MR-8338
Merged-by: Sergey Shanshin <Sergey.Shanshin@jetbrains.com>
---
 .../compiler/backend/ir/BaseIrGenerator.kt    |  8 +++++++
 .../testData/boxIr/contextualFallback.kt      | 22 +++++++++++++++++++
 ...SerializationFirBlackBoxTestGenerated.java |  6 +++++
 .../SerializationIrBoxTestGenerated.java      |  6 +++++
 4 files changed, 42 insertions(+)
 create mode 100644 plugins/kotlinx-serialization/testData/boxIr/contextualFallback.kt

diff --git a/plugins/kotlinx-serialization/kotlinx-serialization.backend/src/org/jetbrains/kotlinx/serialization/compiler/backend/ir/BaseIrGenerator.kt b/plugins/kotlinx-serialization/kotlinx-serialization.backend/src/org/jetbrains/kotlinx/serialization/compiler/backend/ir/BaseIrGenerator.kt
index a253c3d5e7f..5b6b49c9cbc 100644
--- a/plugins/kotlinx-serialization/kotlinx-serialization.backend/src/org/jetbrains/kotlinx/serialization/compiler/backend/ir/BaseIrGenerator.kt
+++ b/plugins/kotlinx-serialization/kotlinx-serialization.backend/src/org/jetbrains/kotlinx/serialization/compiler/backend/ir/BaseIrGenerator.kt
@@ -467,6 +467,14 @@ abstract class BaseIrGenerator(private val currentClass: IrClass, final override
                 typeArgs = listOf(kType)
             }
             contextSerializerId -> {
+                // don't create an instance if the serializer is being created for the cache
+                if (genericIndex == null && kType.genericIndex != null) {
+                    // if context serializer parametrized by generic type (kType.genericIndex != null)
+                    // and generic types are not allowed (always genericIndex == null for cache)
+                    // then serializer can't be cached
+                    return null
+                }
+
                 args = listOf(classReference(kType.classOrUpperBound()!!))
                 typeArgs = listOf(kType)
 
diff --git a/plugins/kotlinx-serialization/testData/boxIr/contextualFallback.kt b/plugins/kotlinx-serialization/testData/boxIr/contextualFallback.kt
new file mode 100644
index 00000000000..8046d91b68c
--- /dev/null
+++ b/plugins/kotlinx-serialization/testData/boxIr/contextualFallback.kt
@@ -0,0 +1,22 @@
+// TARGET_BACKEND: JVM_IR
+
+// WITH_STDLIB
+
+import kotlinx.serialization.*
+import kotlinx.serialization.json.*
+import kotlinx.serialization.encoding.*
+
+@Serializable
+data class Holder<T>(
+    val ok: Boolean,
+    @Contextual
+    val result: T?
+)
+
+fun box(): String {
+    val serializer = serializer<Holder<List<String>>>()
+    val instance = Holder(true, listOf("a", "b"))
+    val encoded = Json.encodeToString(serializer, instance)
+    if (encoded != """{"ok":true,"result":["a","b"]}""") return encoded
+    return "OK"
+}
diff --git a/plugins/kotlinx-serialization/tests-gen/org/jetbrains/kotlinx/serialization/runners/SerializationFirBlackBoxTestGenerated.java b/plugins/kotlinx-serialization/tests-gen/org/jetbrains/kotlinx/serialization/runners/SerializationFirBlackBoxTestGenerated.java
index 325ab38cb1e..e8be4b91a2e 100644
--- a/plugins/kotlinx-serialization/tests-gen/org/jetbrains/kotlinx/serialization/runners/SerializationFirBlackBoxTestGenerated.java
+++ b/plugins/kotlinx-serialization/tests-gen/org/jetbrains/kotlinx/serialization/runners/SerializationFirBlackBoxTestGenerated.java
@@ -51,6 +51,12 @@ public class SerializationFirBlackBoxTestGenerated extends AbstractSerialization
             runTest("plugins/kotlinx-serialization/testData/boxIr/contextualByDefault.kt");
         }
 
+        @Test
+        @TestMetadata("contextualFallback.kt")
+        public void testContextualFallback() throws Exception {
+            runTest("plugins/kotlinx-serialization/testData/boxIr/contextualFallback.kt");
+        }
+
         @Test
         @TestMetadata("enumsAreCached.kt")
         public void testEnumsAreCached() throws Exception {
diff --git a/plugins/kotlinx-serialization/tests-gen/org/jetbrains/kotlinx/serialization/runners/SerializationIrBoxTestGenerated.java b/plugins/kotlinx-serialization/tests-gen/org/jetbrains/kotlinx/serialization/runners/SerializationIrBoxTestGenerated.java
index ac76e285de4..bce8b071d53 100644
--- a/plugins/kotlinx-serialization/tests-gen/org/jetbrains/kotlinx/serialization/runners/SerializationIrBoxTestGenerated.java
+++ b/plugins/kotlinx-serialization/tests-gen/org/jetbrains/kotlinx/serialization/runners/SerializationIrBoxTestGenerated.java
@@ -49,6 +49,12 @@ public class SerializationIrBoxTestGenerated extends AbstractSerializationIrBoxT
         runTest("plugins/kotlinx-serialization/testData/boxIr/contextualByDefault.kt");
     }
 
+    @Test
+    @TestMetadata("contextualFallback.kt")
+    public void testContextualFallback() throws Exception {
+        runTest("plugins/kotlinx-serialization/testData/boxIr/contextualFallback.kt");
+    }
+
     @Test
     @TestMetadata("enumsAreCached.kt")
     public void testEnumsAreCached() throws Exception {