From 247efb220cbaf08e07b1810c0129eb9a5d76b384 Mon Sep 17 00:00:00 2001
From: Alexander Udalov <alexander.udalov@jetbrains.com>
Date: Mon, 8 Mar 2021 19:40:40 +0100
Subject: [PATCH] Do not require backing fields for extension properties

This has no effect on correct code because extension properties cannot
have a backing field anyway and that is checked separately. But this
function is used in psi2ir to determine whether or not to create a
backing field for a property, and in case the code where the property is
declared is unreachable like in KT-44496 and has no explicit getter or
setter, it would previously return true for extension properties, which
on JVM would result in an actual field in the class file, which made no
sense.

After this change, the compiler will actually crash with an exception in
the IR validaton step because the symbol for the field is unbound. That
is a bit better than proceeding to generate potentially invalid
bytecode, but of course a proper fix would be to report an error in the
frontend.

 #KT-44496
---
 .../src/org/jetbrains/kotlin/resolve/resolveUtil.kt    |  1 +
 .../source.kt                                          |  7 +++++++
 .../source.kt                                          |  8 ++++++++
 .../compiler/CompileKotlinAgainstCustomBinariesTest.kt | 10 ++++++++++
 4 files changed, 26 insertions(+)
 create mode 100644 compiler/testData/compileKotlinAgainstCustomBinaries/unreachableExtensionValPropertyDeclaration/source.kt
 create mode 100644 compiler/testData/compileKotlinAgainstCustomBinaries/unreachableExtensionVarPropertyDeclaration/source.kt

diff --git a/compiler/frontend/src/org/jetbrains/kotlin/resolve/resolveUtil.kt b/compiler/frontend/src/org/jetbrains/kotlin/resolve/resolveUtil.kt
index a3662f9d578..ce92e779851 100644
--- a/compiler/frontend/src/org/jetbrains/kotlin/resolve/resolveUtil.kt
+++ b/compiler/frontend/src/org/jetbrains/kotlin/resolve/resolveUtil.kt
@@ -11,6 +11,7 @@ import org.jetbrains.kotlin.resolve.source.KotlinSourceElement
 
 fun PropertyDescriptor.hasBackingField(bindingContext: BindingContext?): Boolean = when {
     kind == CallableMemberDescriptor.Kind.FAKE_OVERRIDE -> overriddenDescriptors.any { it.hasBackingField(bindingContext) }
+    extensionReceiverParameter != null -> false
     source is KotlinSourceElement && bindingContext != null -> bindingContext.get(BindingContext.BACKING_FIELD_REQUIRED, this) ?: false
     compileTimeInitializer != null -> true
 //    backingField != null -> true // TODO: in case of DeserializedPropetyDescriptor this function returns incorrect result for FO field
diff --git a/compiler/testData/compileKotlinAgainstCustomBinaries/unreachableExtensionValPropertyDeclaration/source.kt b/compiler/testData/compileKotlinAgainstCustomBinaries/unreachableExtensionValPropertyDeclaration/source.kt
new file mode 100644
index 00000000000..eb7ad43b6ad
--- /dev/null
+++ b/compiler/testData/compileKotlinAgainstCustomBinaries/unreachableExtensionValPropertyDeclaration/source.kt
@@ -0,0 +1,7 @@
+// KT-44496
+
+class C {
+    val todo: String = TODO()
+
+    val String.noGetterExtensionProperty: Int
+}
diff --git a/compiler/testData/compileKotlinAgainstCustomBinaries/unreachableExtensionVarPropertyDeclaration/source.kt b/compiler/testData/compileKotlinAgainstCustomBinaries/unreachableExtensionVarPropertyDeclaration/source.kt
new file mode 100644
index 00000000000..569482f6fb8
--- /dev/null
+++ b/compiler/testData/compileKotlinAgainstCustomBinaries/unreachableExtensionVarPropertyDeclaration/source.kt
@@ -0,0 +1,8 @@
+// KT-44496
+
+class C {
+    val todo: String = TODO()
+
+    var String.noSetterExtensionProperty: Int
+        get() = 42
+}
diff --git a/compiler/tests/org/jetbrains/kotlin/jvm/compiler/CompileKotlinAgainstCustomBinariesTest.kt b/compiler/tests/org/jetbrains/kotlin/jvm/compiler/CompileKotlinAgainstCustomBinariesTest.kt
index 20cd32ce46f..c417879f652 100644
--- a/compiler/tests/org/jetbrains/kotlin/jvm/compiler/CompileKotlinAgainstCustomBinariesTest.kt
+++ b/compiler/tests/org/jetbrains/kotlin/jvm/compiler/CompileKotlinAgainstCustomBinariesTest.kt
@@ -696,6 +696,16 @@ class CompileKotlinAgainstCustomBinariesTest : AbstractKotlinCompilerIntegration
         compileKotlin("main.kt", tmpdir, listOf(library), additionalOptions = features)
     }
 
+    fun testUnreachableExtensionVarPropertyDeclaration() {
+        val (output, exitCode) = compileKotlin("source.kt", tmpdir, expectedFileName = null)
+        assertEquals("Output:\n$output", ExitCode.INTERNAL_ERROR, exitCode)
+    }
+
+    fun testUnreachableExtensionValPropertyDeclaration() {
+        val (output, exitCode) = compileKotlin("source.kt", tmpdir, expectedFileName = null)
+        assertEquals("Output:\n$output", ExitCode.INTERNAL_ERROR, exitCode)
+    }
+
     // If this test fails, then bootstrap compiler most likely should be advanced
     fun testPreReleaseFlagIsConsistentBetweenBootstrapAndCurrentCompiler() {
         val bootstrapCompiler = JarFile(PathUtil.kotlinPathsForCompiler.compilerPath)