From 6cf76e1d07a9ecdc33b57bc0804bc872db7924a1 Mon Sep 17 00:00:00 2001
From: Brian Norman <brian.norman@jetbrains.com>
Date: Wed, 1 Nov 2023 13:53:07 -0500
Subject: [PATCH] [FIR] Report no return diagnostic on functions returning
 Nothing

Previously, the NO_RETURN_IN_FUNCTION_WITH_BLOCK_BODY diagnostic was not
reported at all on functions which return Nothing. However, in K1, if
the function returns Nothing but the body is empty or doesn't contain a
Nothing expression, this diagnostic would be reported. The checker in K2
has been updated to report this diagnostic on functions which return
Nothing as well.

^KT-55965 Fixed
---
 .../analysis/checkers/declaration/FirFunctionReturnChecker.kt   | 2 +-
 compiler/testData/diagnostics/tests/FunctionReturnTypes.fir.kt  | 2 ++
 compiler/testData/diagnostics/tests/FunctionReturnTypes.kt      | 2 ++
 compiler/testData/diagnostics/tests/FunctionReturnTypes.txt     | 1 +
 4 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/declaration/FirFunctionReturnChecker.kt b/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/declaration/FirFunctionReturnChecker.kt
index 374471da3d3..dbd34b66f7b 100644
--- a/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/declaration/FirFunctionReturnChecker.kt
+++ b/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/declaration/FirFunctionReturnChecker.kt
@@ -35,7 +35,7 @@ object FirFunctionReturnChecker : FirFunctionChecker() {
         if (declaration is FirConstructor) return
         if (declaration is FirAnonymousFunction && declaration.isLambda) return
         val returnType = declaration.returnTypeRef.coneType.fullyExpandedType(context.session)
-        if (returnType.isUnit || returnType.isNothing) return
+        if (returnType.isUnit) return
         val graph = declaration.controlFlowGraphReference?.controlFlowGraph ?: return
 
         val blockExitNode = graph.exitNode.previousNodes.lastOrNull { it is BlockExitNode } ?: return
diff --git a/compiler/testData/diagnostics/tests/FunctionReturnTypes.fir.kt b/compiler/testData/diagnostics/tests/FunctionReturnTypes.fir.kt
index bc08f5224ee..783b1ace38d 100644
--- a/compiler/testData/diagnostics/tests/FunctionReturnTypes.fir.kt
+++ b/compiler/testData/diagnostics/tests/FunctionReturnTypes.fir.kt
@@ -158,6 +158,8 @@ fun illegalReturnIf(): Char {
 fun returnNothing(): Nothing {
     throw <!TYPE_MISMATCH!>1<!>
 }
+fun returnNothingEmpty(): Nothing {
+<!NO_RETURN_IN_FUNCTION_WITH_BLOCK_BODY!>}<!>
 fun f(): Int {
     if (1 < 2) { return 1 } else returnNothing()
 }
diff --git a/compiler/testData/diagnostics/tests/FunctionReturnTypes.kt b/compiler/testData/diagnostics/tests/FunctionReturnTypes.kt
index 3b6a8a3cf07..f548c71a02c 100644
--- a/compiler/testData/diagnostics/tests/FunctionReturnTypes.kt
+++ b/compiler/testData/diagnostics/tests/FunctionReturnTypes.kt
@@ -158,6 +158,8 @@ fun illegalReturnIf(): Char {
 fun returnNothing(): Nothing {
     throw <!CONSTANT_EXPECTED_TYPE_MISMATCH!>1<!>
 }
+fun returnNothingEmpty(): Nothing {
+<!NO_RETURN_IN_FUNCTION_WITH_BLOCK_BODY!>}<!>
 fun f(): Int {
     if (1 < 2) { return 1 } else returnNothing()
 }
diff --git a/compiler/testData/diagnostics/tests/FunctionReturnTypes.txt b/compiler/testData/diagnostics/tests/FunctionReturnTypes.txt
index 5af51a4886b..85499c952d7 100644
--- a/compiler/testData/diagnostics/tests/FunctionReturnTypes.txt
+++ b/compiler/testData/diagnostics/tests/FunctionReturnTypes.txt
@@ -47,6 +47,7 @@ public fun nonBlockNoReturnIfUnitInOneBranch(): kotlin.Int
 public fun nonBlockReturnIfEmptyIf(): kotlin.Int
 public fun none(): kotlin.Unit
 public fun returnNothing(): kotlin.Nothing
+public fun returnNothingEmpty(): kotlin.Nothing
 public fun test1(): kotlin.Any
 public fun test2(): kotlin.Any
 public fun test3(): kotlin.Any