From 9851ff1905ae167c81714ed62a6520809c218009 Mon Sep 17 00:00:00 2001
From: Sergej Jaskiewicz <sergej.jaskiewicz@jetbrains.com>
Date: Thu, 14 Mar 2024 16:39:23 +0100
Subject: [PATCH] [FIR] Reproduce KT-66277, KT-66279, KT-66512 and KT-66534

---
 ...CompilerTestFE10TestdataTestGenerated.java |  24 ++++
 ...sticCompilerFE10TestDataTestGenerated.java |  24 ++++
 ...eeOldFrontendDiagnosticsTestGenerated.java |  24 ++++
 ...siOldFrontendDiagnosticsTestGenerated.java |  24 ++++
 .../functionLiterals/return/kt66277.fir.kt    |  93 +++++++++++++
 .../tests/functionLiterals/return/kt66277.kt  |  93 +++++++++++++
 .../functionLiterals/return/kt66279.fir.kt    | 114 ++++++++++++++++
 .../tests/functionLiterals/return/kt66279.kt  | 114 ++++++++++++++++
 .../functionLiterals/return/kt66512.fir.kt    |  20 +++
 .../tests/functionLiterals/return/kt66512.kt  |  20 +++
 .../functionLiterals/return/kt66534.fir.kt    | 125 ++++++++++++++++++
 .../tests/functionLiterals/return/kt66534.kt  | 125 ++++++++++++++++++
 .../test/runners/DiagnosticTestGenerated.java |  24 ++++
 13 files changed, 824 insertions(+)
 create mode 100644 compiler/testData/diagnostics/tests/functionLiterals/return/kt66277.fir.kt
 create mode 100644 compiler/testData/diagnostics/tests/functionLiterals/return/kt66277.kt
 create mode 100644 compiler/testData/diagnostics/tests/functionLiterals/return/kt66279.fir.kt
 create mode 100644 compiler/testData/diagnostics/tests/functionLiterals/return/kt66279.kt
 create mode 100644 compiler/testData/diagnostics/tests/functionLiterals/return/kt66512.fir.kt
 create mode 100644 compiler/testData/diagnostics/tests/functionLiterals/return/kt66512.kt
 create mode 100644 compiler/testData/diagnostics/tests/functionLiterals/return/kt66534.fir.kt
 create mode 100644 compiler/testData/diagnostics/tests/functionLiterals/return/kt66534.kt

diff --git a/analysis/low-level-api-fir/tests/org/jetbrains/kotlin/analysis/low/level/api/fir/diagnostic/compiler/based/DiagnosticCompilerTestFE10TestdataTestGenerated.java b/analysis/low-level-api-fir/tests/org/jetbrains/kotlin/analysis/low/level/api/fir/diagnostic/compiler/based/DiagnosticCompilerTestFE10TestdataTestGenerated.java
index a3b8df9bee0..0377361eb47 100644
--- a/analysis/low-level-api-fir/tests/org/jetbrains/kotlin/analysis/low/level/api/fir/diagnostic/compiler/based/DiagnosticCompilerTestFE10TestdataTestGenerated.java
+++ b/analysis/low-level-api-fir/tests/org/jetbrains/kotlin/analysis/low/level/api/fir/diagnostic/compiler/based/DiagnosticCompilerTestFE10TestdataTestGenerated.java
@@ -14199,6 +14199,30 @@ public class DiagnosticCompilerTestFE10TestdataTestGenerated extends AbstractDia
           runTest("compiler/testData/diagnostics/tests/functionLiterals/return/IfWithoutElseWithExplicitType.kt");
         }
 
+        @Test
+        @TestMetadata("kt66277.kt")
+        public void testKt66277() {
+          runTest("compiler/testData/diagnostics/tests/functionLiterals/return/kt66277.kt");
+        }
+
+        @Test
+        @TestMetadata("kt66279.kt")
+        public void testKt66279() {
+          runTest("compiler/testData/diagnostics/tests/functionLiterals/return/kt66279.kt");
+        }
+
+        @Test
+        @TestMetadata("kt66512.kt")
+        public void testKt66512() {
+          runTest("compiler/testData/diagnostics/tests/functionLiterals/return/kt66512.kt");
+        }
+
+        @Test
+        @TestMetadata("kt66534.kt")
+        public void testKt66534() {
+          runTest("compiler/testData/diagnostics/tests/functionLiterals/return/kt66534.kt");
+        }
+
         @Test
         @TestMetadata("LambdaReturnTypeIsUnitIfImplicitReturnExists.kt")
         public void testLambdaReturnTypeIsUnitIfImplicitReturnExists() {
diff --git a/analysis/low-level-api-fir/tests/org/jetbrains/kotlin/analysis/low/level/api/fir/diagnostic/compiler/based/LLFirPreresolvedReversedDiagnosticCompilerFE10TestDataTestGenerated.java b/analysis/low-level-api-fir/tests/org/jetbrains/kotlin/analysis/low/level/api/fir/diagnostic/compiler/based/LLFirPreresolvedReversedDiagnosticCompilerFE10TestDataTestGenerated.java
index e8afba3848b..cdf6201028a 100644
--- a/analysis/low-level-api-fir/tests/org/jetbrains/kotlin/analysis/low/level/api/fir/diagnostic/compiler/based/LLFirPreresolvedReversedDiagnosticCompilerFE10TestDataTestGenerated.java
+++ b/analysis/low-level-api-fir/tests/org/jetbrains/kotlin/analysis/low/level/api/fir/diagnostic/compiler/based/LLFirPreresolvedReversedDiagnosticCompilerFE10TestDataTestGenerated.java
@@ -14199,6 +14199,30 @@ public class LLFirPreresolvedReversedDiagnosticCompilerFE10TestDataTestGenerated
           runTest("compiler/testData/diagnostics/tests/functionLiterals/return/IfWithoutElseWithExplicitType.kt");
         }
 
+        @Test
+        @TestMetadata("kt66277.kt")
+        public void testKt66277() {
+          runTest("compiler/testData/diagnostics/tests/functionLiterals/return/kt66277.kt");
+        }
+
+        @Test
+        @TestMetadata("kt66279.kt")
+        public void testKt66279() {
+          runTest("compiler/testData/diagnostics/tests/functionLiterals/return/kt66279.kt");
+        }
+
+        @Test
+        @TestMetadata("kt66512.kt")
+        public void testKt66512() {
+          runTest("compiler/testData/diagnostics/tests/functionLiterals/return/kt66512.kt");
+        }
+
+        @Test
+        @TestMetadata("kt66534.kt")
+        public void testKt66534() {
+          runTest("compiler/testData/diagnostics/tests/functionLiterals/return/kt66534.kt");
+        }
+
         @Test
         @TestMetadata("LambdaReturnTypeIsUnitIfImplicitReturnExists.kt")
         public void testLambdaReturnTypeIsUnitIfImplicitReturnExists() {
diff --git a/compiler/fir/analysis-tests/tests-gen/org/jetbrains/kotlin/test/runners/FirLightTreeOldFrontendDiagnosticsTestGenerated.java b/compiler/fir/analysis-tests/tests-gen/org/jetbrains/kotlin/test/runners/FirLightTreeOldFrontendDiagnosticsTestGenerated.java
index 1f0c194bba4..d9ab9ccf5d2 100644
--- a/compiler/fir/analysis-tests/tests-gen/org/jetbrains/kotlin/test/runners/FirLightTreeOldFrontendDiagnosticsTestGenerated.java
+++ b/compiler/fir/analysis-tests/tests-gen/org/jetbrains/kotlin/test/runners/FirLightTreeOldFrontendDiagnosticsTestGenerated.java
@@ -14193,6 +14193,30 @@ public class FirLightTreeOldFrontendDiagnosticsTestGenerated extends AbstractFir
           runTest("compiler/testData/diagnostics/tests/functionLiterals/return/IfWithoutElseWithExplicitType.kt");
         }
 
+        @Test
+        @TestMetadata("kt66277.kt")
+        public void testKt66277() {
+          runTest("compiler/testData/diagnostics/tests/functionLiterals/return/kt66277.kt");
+        }
+
+        @Test
+        @TestMetadata("kt66279.kt")
+        public void testKt66279() {
+          runTest("compiler/testData/diagnostics/tests/functionLiterals/return/kt66279.kt");
+        }
+
+        @Test
+        @TestMetadata("kt66512.kt")
+        public void testKt66512() {
+          runTest("compiler/testData/diagnostics/tests/functionLiterals/return/kt66512.kt");
+        }
+
+        @Test
+        @TestMetadata("kt66534.kt")
+        public void testKt66534() {
+          runTest("compiler/testData/diagnostics/tests/functionLiterals/return/kt66534.kt");
+        }
+
         @Test
         @TestMetadata("LambdaReturnTypeIsUnitIfImplicitReturnExists.kt")
         public void testLambdaReturnTypeIsUnitIfImplicitReturnExists() {
diff --git a/compiler/fir/analysis-tests/tests-gen/org/jetbrains/kotlin/test/runners/FirPsiOldFrontendDiagnosticsTestGenerated.java b/compiler/fir/analysis-tests/tests-gen/org/jetbrains/kotlin/test/runners/FirPsiOldFrontendDiagnosticsTestGenerated.java
index 7f5588c8cab..42c3c675e14 100644
--- a/compiler/fir/analysis-tests/tests-gen/org/jetbrains/kotlin/test/runners/FirPsiOldFrontendDiagnosticsTestGenerated.java
+++ b/compiler/fir/analysis-tests/tests-gen/org/jetbrains/kotlin/test/runners/FirPsiOldFrontendDiagnosticsTestGenerated.java
@@ -14199,6 +14199,30 @@ public class FirPsiOldFrontendDiagnosticsTestGenerated extends AbstractFirPsiDia
           runTest("compiler/testData/diagnostics/tests/functionLiterals/return/IfWithoutElseWithExplicitType.kt");
         }
 
+        @Test
+        @TestMetadata("kt66277.kt")
+        public void testKt66277() {
+          runTest("compiler/testData/diagnostics/tests/functionLiterals/return/kt66277.kt");
+        }
+
+        @Test
+        @TestMetadata("kt66279.kt")
+        public void testKt66279() {
+          runTest("compiler/testData/diagnostics/tests/functionLiterals/return/kt66279.kt");
+        }
+
+        @Test
+        @TestMetadata("kt66512.kt")
+        public void testKt66512() {
+          runTest("compiler/testData/diagnostics/tests/functionLiterals/return/kt66512.kt");
+        }
+
+        @Test
+        @TestMetadata("kt66534.kt")
+        public void testKt66534() {
+          runTest("compiler/testData/diagnostics/tests/functionLiterals/return/kt66534.kt");
+        }
+
         @Test
         @TestMetadata("LambdaReturnTypeIsUnitIfImplicitReturnExists.kt")
         public void testLambdaReturnTypeIsUnitIfImplicitReturnExists() {
diff --git a/compiler/testData/diagnostics/tests/functionLiterals/return/kt66277.fir.kt b/compiler/testData/diagnostics/tests/functionLiterals/return/kt66277.fir.kt
new file mode 100644
index 00000000000..ec2e8a86332
--- /dev/null
+++ b/compiler/testData/diagnostics/tests/functionLiterals/return/kt66277.fir.kt
@@ -0,0 +1,93 @@
+// ISSUE: KT-66277
+
+fun foo() {}
+typealias MyUnit = Unit
+
+// Note that resolution works differently for lambdas passed as function arguments and lambdas assigned to variables,
+// thus we need to test both cases.
+
+// ================= Lambdas assigned to a variable =================
+
+val expectedAnyEmptyReturnAndString: () -> Any = l@ {
+    if ("0".hashCode() == 42) return@l
+    ""
+}
+
+val expectedAnyExplicitReturnUnitAndString: () -> Any = l@ {
+    if ("0".hashCode() == 42) return@l Unit
+    ""
+}
+
+val expectedAnyExplicitReturnMyUnitAndString: () -> Any = l@ {
+    if ("0".hashCode() == 42) return@l MyUnit
+    ""
+}
+
+val expectedAnyExplicitReturnFooAndString: () -> Any = l@ {
+    if ("0".hashCode() == 42) return@l foo()
+    ""
+}
+
+val expectedAnyEmptyReturnOnly: () -> Any = l@ {
+    if ("0".hashCode() == 42) return@l
+    return@l
+}
+
+val expectedAnyImplicitAndExplicitReturnUnit: () -> Any = l@ {
+    if ("0".hashCode() == 42) return@l
+    return@l Unit
+}
+
+val expectedAnyEmptyReturnAndExplicitReturnMyUnit: () -> Any = l@ {
+    if ("0".hashCode() == 42) return@l
+    return@l MyUnit
+}
+
+val expectedAnyEmptyReturnAndExplicitReturnFoo: () -> Any = l@ {
+    if ("0".hashCode() == 42) return@l
+    return@l foo()
+}
+
+// ============== Lambdas passed as function argument ===============
+
+fun test() {
+    run<Any> l@ {
+        if ("0".hashCode() == 42) return@l
+        ""
+    }
+
+    run<Any> l@ {
+        if ("0".hashCode() == 42) return@l Unit
+        ""
+    }
+
+    run<Any> l@ {
+        if ("0".hashCode() == 42) return@l MyUnit
+        ""
+    }
+
+    run<Any> l@ {
+        if ("0".hashCode() == 42) return@l foo()
+        ""
+    }
+
+    run<Any> l@ {
+        if ("0".hashCode() == 42) return@l
+        return@l
+    }
+
+    run<Any> l@ {
+        if ("0".hashCode() == 42) return@l
+        return@l Unit
+    }
+
+    run<Any> l@ {
+        if ("0".hashCode() == 42) return@l
+        return@l MyUnit
+    }
+
+    run<Any> l@ {
+        if ("0".hashCode() == 42) return@l
+        return@l foo()
+    }
+}
diff --git a/compiler/testData/diagnostics/tests/functionLiterals/return/kt66277.kt b/compiler/testData/diagnostics/tests/functionLiterals/return/kt66277.kt
new file mode 100644
index 00000000000..d3be1cefc6d
--- /dev/null
+++ b/compiler/testData/diagnostics/tests/functionLiterals/return/kt66277.kt
@@ -0,0 +1,93 @@
+// ISSUE: KT-66277
+
+fun foo() {}
+typealias MyUnit = Unit
+
+// Note that resolution works differently for lambdas passed as function arguments and lambdas assigned to variables,
+// thus we need to test both cases.
+
+// ================= Lambdas assigned to a variable =================
+
+val expectedAnyEmptyReturnAndString: () -> Any = l@ {
+    if ("0".hashCode() == 42) <!RETURN_TYPE_MISMATCH!>return@l<!>
+    ""
+}
+
+val expectedAnyExplicitReturnUnitAndString: () -> Any = l@ {
+    if ("0".hashCode() == 42) return@l Unit
+    ""
+}
+
+val expectedAnyExplicitReturnMyUnitAndString: () -> Any = l@ {
+    if ("0".hashCode() == 42) return@l MyUnit
+    ""
+}
+
+val expectedAnyExplicitReturnFooAndString: () -> Any = l@ {
+    if ("0".hashCode() == 42) return@l foo()
+    ""
+}
+
+val expectedAnyEmptyReturnOnly: () -> Any = l@ {
+    if ("0".hashCode() == 42) <!RETURN_TYPE_MISMATCH!>return@l<!>
+    <!RETURN_TYPE_MISMATCH!>return@l<!>
+}
+
+val expectedAnyImplicitAndExplicitReturnUnit: () -> Any = l@ {
+    if ("0".hashCode() == 42) <!RETURN_TYPE_MISMATCH!>return@l<!>
+    return@l Unit
+}
+
+val expectedAnyEmptyReturnAndExplicitReturnMyUnit: () -> Any = l@ {
+    if ("0".hashCode() == 42) <!RETURN_TYPE_MISMATCH!>return@l<!>
+    return@l MyUnit
+}
+
+val expectedAnyEmptyReturnAndExplicitReturnFoo: () -> Any = l@ {
+    if ("0".hashCode() == 42) <!RETURN_TYPE_MISMATCH!>return@l<!>
+    return@l foo()
+}
+
+// ============== Lambdas passed as function argument ===============
+
+fun test() {
+    run<Any> l@ {
+        if ("0".hashCode() == 42) return@l
+        ""
+    }
+
+    run<Any> l@ {
+        if ("0".hashCode() == 42) return@l Unit
+        ""
+    }
+
+    run<Any> l@ {
+        if ("0".hashCode() == 42) return@l MyUnit
+        ""
+    }
+
+    run<Any> l@ {
+        if ("0".hashCode() == 42) return@l foo()
+        ""
+    }
+
+    run<Any> l@ {
+        if ("0".hashCode() == 42) return@l
+        return@l
+    }
+
+    run<Any> l@ {
+        if ("0".hashCode() == 42) return@l
+        return@l Unit
+    }
+
+    run<Any> l@ {
+        if ("0".hashCode() == 42) return@l
+        return@l MyUnit
+    }
+
+    run<Any> l@ {
+        if ("0".hashCode() == 42) return@l
+        return@l foo()
+    }
+}
diff --git a/compiler/testData/diagnostics/tests/functionLiterals/return/kt66279.fir.kt b/compiler/testData/diagnostics/tests/functionLiterals/return/kt66279.fir.kt
new file mode 100644
index 00000000000..6ca002b9e2b
--- /dev/null
+++ b/compiler/testData/diagnostics/tests/functionLiterals/return/kt66279.fir.kt
@@ -0,0 +1,114 @@
+// ISSUE: KT-66279
+
+fun foo() {}
+
+typealias MyUnit = Unit
+
+// Note that resolution works differently for lambdas passed as function arguments and lambdas assigned to variables,
+// thus we need to test both cases.
+
+// ================= Lambdas assigned to a variable =================
+
+val expectedUnitEmptyReturnUnitAndString: () -> Unit = l@ {
+    if ("0".hashCode() == 42) return@l
+    ""
+}
+
+val expectedMyUnitEmptyReturnUnitAndString: () -> Unit = l@ {
+    if ("0".hashCode() == 42) return@l
+    ""
+}
+
+val expectedUnitExplicitReturnUnitAndString: () -> Unit = <!INITIALIZER_TYPE_MISMATCH!>l@ {
+    if ("0".hashCode() == 42) return@l Unit
+    ""
+}<!>
+
+val expectedUnitExplicitReturnMyUniAndString: () -> Unit = <!INITIALIZER_TYPE_MISMATCH!>l@ {
+    if ("0".hashCode() == 42) return@l MyUnit
+    ""
+}<!>
+
+val expectedUnitExplicitReturnFooAndString: () -> Unit = <!INITIALIZER_TYPE_MISMATCH!>l@ {
+    if ("0".hashCode() == 42) return@l foo()
+    ""
+}<!>
+
+val expectedUnitEmptyReturnOnly: () -> Unit = l@ {
+    if ("0".hashCode() == 42) return@l
+    return@l
+}
+
+val expectedUnitEmptyReturnAndExplicitReturnUnit: () -> Unit = l@ {
+    if ("0".hashCode() == 42) return@l
+    return@l Unit
+}
+
+val expectedUnitEmptyReturnAndExplicitReturnFoo: () -> Unit = l@ {
+    if ("0".hashCode() == 42) return@l
+    return@l foo()
+}
+
+val expectedMyUnitEmptyReturnOnly: () -> MyUnit = l@ {
+    if ("0".hashCode() == 42) return@l
+    return@l
+}
+
+val expectedMyUnitEmptyReturnAndExplicitReturnMyUnit: () -> MyUnit = l@ {
+    if ("0".hashCode() == 42) return@l
+    return@l Unit
+}
+
+// ============== Lambdas passed as function argument ===============
+
+fun test() {
+    run<Unit> l@ {
+        if ("0".hashCode() == 42) return@l
+        ""
+    }
+
+    run<MyUnit> l@ {
+        if ("0".hashCode() == 42) return@l
+        ""
+    }
+
+    run<Unit> l@ {
+        if ("0".hashCode() == 42) return@l Unit
+        ""
+    }
+
+    run<Unit> l@ {
+        if ("0".hashCode() == 42) return@l MyUnit
+        ""
+    }
+
+    run<Unit> l@ {
+        if ("0".hashCode() == 42) return@l foo()
+        ""
+    }
+
+    run<Unit> l@ {
+        if ("0".hashCode() == 42) return@l
+        return@l
+    }
+
+    run<Unit> l@ {
+        if ("0".hashCode() == 42) return@l
+        return@l Unit
+    }
+
+    run<Unit> l@ {
+        if ("0".hashCode() == 42) return@l
+        return@l foo()
+    }
+
+    run<MyUnit> l@ {
+        if ("0".hashCode() == 42) return@l
+        return@l
+    }
+
+    run<MyUnit> l@ {
+        if ("0".hashCode() == 42) return@l
+        return@l Unit
+    }
+}
diff --git a/compiler/testData/diagnostics/tests/functionLiterals/return/kt66279.kt b/compiler/testData/diagnostics/tests/functionLiterals/return/kt66279.kt
new file mode 100644
index 00000000000..882925cfeec
--- /dev/null
+++ b/compiler/testData/diagnostics/tests/functionLiterals/return/kt66279.kt
@@ -0,0 +1,114 @@
+// ISSUE: KT-66279
+
+fun foo() {}
+
+typealias MyUnit = Unit
+
+// Note that resolution works differently for lambdas passed as function arguments and lambdas assigned to variables,
+// thus we need to test both cases.
+
+// ================= Lambdas assigned to a variable =================
+
+val expectedUnitEmptyReturnUnitAndString: () -> Unit = l@ {
+    if ("0".hashCode() == 42) return@l
+    ""
+}
+
+val expectedMyUnitEmptyReturnUnitAndString: () -> Unit = l@ {
+    if ("0".hashCode() == 42) return@l
+    ""
+}
+
+val expectedUnitExplicitReturnUnitAndString: () -> Unit = l@ {
+    if ("0".hashCode() == 42) return@l Unit
+    ""
+}
+
+val expectedUnitExplicitReturnMyUniAndString: () -> Unit = l@ {
+    if ("0".hashCode() == 42) return@l MyUnit
+    ""
+}
+
+val expectedUnitExplicitReturnFooAndString: () -> Unit = l@ {
+    if ("0".hashCode() == 42) return@l foo()
+    ""
+}
+
+val expectedUnitEmptyReturnOnly: () -> Unit = l@ {
+    if ("0".hashCode() == 42) return@l
+    return@l
+}
+
+val expectedUnitEmptyReturnAndExplicitReturnUnit: () -> Unit = l@ {
+    if ("0".hashCode() == 42) return@l
+    return@l Unit
+}
+
+val expectedUnitEmptyReturnAndExplicitReturnFoo: () -> Unit = l@ {
+    if ("0".hashCode() == 42) return@l
+    return@l foo()
+}
+
+val expectedMyUnitEmptyReturnOnly: () -> MyUnit = l@ {
+    if ("0".hashCode() == 42) return@l
+    return@l
+}
+
+val expectedMyUnitEmptyReturnAndExplicitReturnMyUnit: () -> MyUnit = l@ {
+    if ("0".hashCode() == 42) return@l
+    return@l Unit
+}
+
+// ============== Lambdas passed as function argument ===============
+
+fun test() {
+    run<Unit> l@ {
+        if ("0".hashCode() == 42) return@l
+        ""
+    }
+
+    run<MyUnit> l@ {
+        if ("0".hashCode() == 42) return@l
+        ""
+    }
+
+    run<Unit> l@ {
+        if ("0".hashCode() == 42) return@l Unit
+        ""
+    }
+
+    run<Unit> l@ {
+        if ("0".hashCode() == 42) return@l MyUnit
+        ""
+    }
+
+    run<Unit> l@ {
+        if ("0".hashCode() == 42) return@l foo()
+        ""
+    }
+
+    run<Unit> l@ {
+        if ("0".hashCode() == 42) return@l
+        return@l
+    }
+
+    run<Unit> l@ {
+        if ("0".hashCode() == 42) return@l
+        return@l Unit
+    }
+
+    run<Unit> l@ {
+        if ("0".hashCode() == 42) return@l
+        return@l foo()
+    }
+
+    run<MyUnit> l@ {
+        if ("0".hashCode() == 42) return@l
+        return@l
+    }
+
+    run<MyUnit> l@ {
+        if ("0".hashCode() == 42) return@l
+        return@l Unit
+    }
+}
diff --git a/compiler/testData/diagnostics/tests/functionLiterals/return/kt66512.fir.kt b/compiler/testData/diagnostics/tests/functionLiterals/return/kt66512.fir.kt
new file mode 100644
index 00000000000..808fd85d517
--- /dev/null
+++ b/compiler/testData/diagnostics/tests/functionLiterals/return/kt66512.fir.kt
@@ -0,0 +1,20 @@
+// ISSUE: KT-66512
+
+typealias MyUnit = Unit
+
+// Note that resolution works differently for lambdas passed as function arguments and lambdas assigned to variables,
+// thus we need to test both cases.
+
+// ================= Lambdas assigned to a variable =================
+
+val expectedMyUnitExplicitReturnString: () -> MyUnit = <!INITIALIZER_TYPE_MISMATCH!>l@ {
+    return@l ""
+}<!>
+
+// ============== Lambdas passed as function argument ===============
+
+fun test() {
+    run<MyUnit> l@ {
+        return@l <!ARGUMENT_TYPE_MISMATCH, RETURN_TYPE_MISMATCH!>""<!>
+    }
+}
diff --git a/compiler/testData/diagnostics/tests/functionLiterals/return/kt66512.kt b/compiler/testData/diagnostics/tests/functionLiterals/return/kt66512.kt
new file mode 100644
index 00000000000..efb83f99aa1
--- /dev/null
+++ b/compiler/testData/diagnostics/tests/functionLiterals/return/kt66512.kt
@@ -0,0 +1,20 @@
+// ISSUE: KT-66512
+
+typealias MyUnit = Unit
+
+// Note that resolution works differently for lambdas passed as function arguments and lambdas assigned to variables,
+// thus we need to test both cases.
+
+// ================= Lambdas assigned to a variable =================
+
+val expectedMyUnitExplicitReturnString: () -> MyUnit = l@ {
+    return@l <!TYPE_MISMATCH!>""<!>
+}
+
+// ============== Lambdas passed as function argument ===============
+
+fun test() {
+    run<MyUnit> l@ {
+        return@l <!TYPE_MISMATCH, TYPE_MISMATCH!>""<!>
+    }
+}
diff --git a/compiler/testData/diagnostics/tests/functionLiterals/return/kt66534.fir.kt b/compiler/testData/diagnostics/tests/functionLiterals/return/kt66534.fir.kt
new file mode 100644
index 00000000000..319567557b4
--- /dev/null
+++ b/compiler/testData/diagnostics/tests/functionLiterals/return/kt66534.fir.kt
@@ -0,0 +1,125 @@
+// ISSUE: KT-66534
+// WITH_STDLIB
+
+// FILE: A.java
+import org.jetbrains.annotations.NotNull;
+import kotlin.jvm.functions.Function0;
+import kotlin.Unit;
+
+public class A {
+    public static @NotNull Function0<Unit> foo;
+    public static void run(@NotNull Function0<Unit> foo) {}
+}
+
+// FILE: main.kt
+
+// Note that resolution works differently for lambdas passed as function arguments and lambdas assigned to variables,
+// thus we need to test both cases.
+
+// ================= Lambdas assigned to a variable =================
+
+val expectedNullableUnitEmptyReturnAndString: () -> Unit? = l@ {
+    if ("0".hashCode() == 42) return@l
+    ""
+}
+
+fun expectedFlexibleUnitEmptyReturnAndString() {
+    A.foo = l@ {
+        if ("0".hashCode() == 42) return@l
+        ""
+    }
+}
+
+val expectedNullableUnitEmptyReturnAndExplicitReturnNull: () -> Unit? = l@ {
+    if ("0".hashCode() == 42) return@l
+    return@l <!NULL_FOR_NONNULL_TYPE!>null<!>
+}
+
+fun expectedFlexibleUnitEmptyReturnAndExplicitReturnNull() {
+    A.foo = l@ {
+        if ("0".hashCode() == 42) return@l
+        return@l <!NULL_FOR_NONNULL_TYPE!>null<!>
+    }
+}
+
+val expectedNullableUnitExplicitReturnUnitAndString: () -> Unit? = <!INITIALIZER_TYPE_MISMATCH!>l@ {
+    if ("0".hashCode() == 42) return@l Unit
+    ""
+}<!>
+
+fun expectedFlexibleUnitExplicitReturnUnitAndString() {
+    A.foo = l@ <!ASSIGNMENT_TYPE_MISMATCH!>{
+        if ("0".hashCode() == 42) return@l Unit
+        ""
+    }<!>
+}
+
+val expectedNullableUnitExplicitReturnString: () -> Unit? = <!INITIALIZER_TYPE_MISMATCH!>l@ {
+    return@l ""
+}<!>
+
+fun expectedFlexibleUnitExplicitReturnString() {
+    A.foo = l@ <!ASSIGNMENT_TYPE_MISMATCH!>{
+        return@l ""
+    }<!>
+}
+
+val expectedNullableUnitExplicitReturnNull: () -> Unit? = l@ {
+    return@l null
+}
+
+fun expectedFlexibleUnitExplicitReturnNull() {
+    A.foo = l@ {
+        return@l null
+    }
+}
+
+// ============== Lambdas passed as function argument ===============
+
+fun test() {
+    run<Unit?> l@ {
+        if ("0".hashCode() == 42) return@l
+        ""
+    }
+
+    A.run l@ {
+        if ("0".hashCode() == 42) return@l
+        ""
+    }
+
+    run<Unit?> l@ {
+        if ("0".hashCode() == 42) return@l
+        return@l <!NULL_FOR_NONNULL_TYPE!>null<!>
+    }
+
+    A.run l@ {
+        if ("0".hashCode() == 42) return@l
+        return@l null
+    }
+
+    run<Unit?> l@ {
+        if ("0".hashCode() == 42) return@l Unit
+        <!ARGUMENT_TYPE_MISMATCH!>""<!>
+    }
+
+    A.run l@ {
+        if ("0".hashCode() == 42) return@l Unit
+        ""
+    }
+
+    run<Unit?> l@ {
+        return@l <!ARGUMENT_TYPE_MISMATCH, RETURN_TYPE_MISMATCH!>""<!>
+    }
+
+    A.run l@ {
+        return@l <!ARGUMENT_TYPE_MISMATCH, RETURN_TYPE_MISMATCH!>""<!>
+    }
+
+    run<Unit?> l@ {
+        return@l null
+    }
+
+    A.run l@ {
+        return@l null
+    }
+}
diff --git a/compiler/testData/diagnostics/tests/functionLiterals/return/kt66534.kt b/compiler/testData/diagnostics/tests/functionLiterals/return/kt66534.kt
new file mode 100644
index 00000000000..2ab352542c7
--- /dev/null
+++ b/compiler/testData/diagnostics/tests/functionLiterals/return/kt66534.kt
@@ -0,0 +1,125 @@
+// ISSUE: KT-66534
+// WITH_STDLIB
+
+// FILE: A.java
+import org.jetbrains.annotations.NotNull;
+import kotlin.jvm.functions.Function0;
+import kotlin.Unit;
+
+public class A {
+    public static @NotNull Function0<Unit> foo;
+    public static void run(@NotNull Function0<Unit> foo) {}
+}
+
+// FILE: main.kt
+
+// Note that resolution works differently for lambdas passed as function arguments and lambdas assigned to variables,
+// thus we need to test both cases.
+
+// ================= Lambdas assigned to a variable =================
+
+val expectedNullableUnitEmptyReturnAndString: () -> Unit? = l@ {
+    if ("0".hashCode() == 42) <!RETURN_TYPE_MISMATCH!>return@l<!>
+    <!TYPE_MISMATCH!>""<!>
+}
+
+fun expectedFlexibleUnitEmptyReturnAndString() {
+    A.foo = l@ {
+        if ("0".hashCode() == 42) return@l
+        ""
+    }
+}
+
+val expectedNullableUnitEmptyReturnAndExplicitReturnNull: () -> Unit? = l@ {
+    if ("0".hashCode() == 42) <!RETURN_TYPE_MISMATCH!>return@l<!>
+    return@l <!RETURN_TYPE_MISMATCH!>null<!>
+}
+
+fun expectedFlexibleUnitEmptyReturnAndExplicitReturnNull() {
+    A.foo = l@ {
+        if ("0".hashCode() == 42) return@l
+        return@l <!RETURN_TYPE_MISMATCH!>null<!>
+    }
+}
+
+val expectedNullableUnitExplicitReturnUnitAndString: () -> Unit? = l@ {
+    if ("0".hashCode() == 42) return@l Unit
+    <!TYPE_MISMATCH!>""<!>
+}
+
+fun expectedFlexibleUnitExplicitReturnUnitAndString() {
+    A.foo = l@ {
+        if ("0".hashCode() == 42) return@l Unit
+        ""
+    }
+}
+
+val expectedNullableUnitExplicitReturnString: () -> Unit? = l@ {
+    return@l <!TYPE_MISMATCH!>""<!>
+}
+
+fun expectedFlexibleUnitExplicitReturnString() {
+    A.foo = l@ {
+        return@l <!TYPE_MISMATCH!>""<!>
+    }
+}
+
+val expectedNullableUnitExplicitReturnNull: () -> Unit? = l@ {
+    return@l null
+}
+
+fun expectedFlexibleUnitExplicitReturnNull() {
+    A.foo = l@ {
+        return@l null
+    }
+}
+
+// ============== Lambdas passed as function argument ===============
+
+fun test() {
+    run<Unit?> l@ {
+        if ("0".hashCode() == 42) return@l
+        ""
+    }
+
+    A.run l@ {
+        if ("0".hashCode() == 42) return@l
+        ""
+    }
+
+    run<Unit?> l@ {
+        if ("0".hashCode() == 42) return@l
+        return@l <!RETURN_TYPE_MISMATCH!>null<!>
+    }
+
+    A.run l@ {
+        if ("0".hashCode() == 42) return@l
+        return@l <!RETURN_TYPE_MISMATCH!>null<!>
+    }
+
+    run<Unit?> l@ {
+        if ("0".hashCode() == 42) return@l Unit
+        <!TYPE_MISMATCH!>""<!>
+    }
+
+    A.run l@ {
+        if ("0".hashCode() == 42) return@l Unit
+        ""
+    }
+
+    run<Unit?> l@ {
+        return@l <!TYPE_MISMATCH!>""<!>
+    }
+
+    A.run l@ {
+        return@l <!TYPE_MISMATCH, TYPE_MISMATCH!>""<!>
+    }
+
+    run<Unit?> l@ {
+        return@l null
+    }
+
+    A.run l@ {
+        return@l null
+    }
+}
diff --git a/compiler/tests-common-new/tests-gen/org/jetbrains/kotlin/test/runners/DiagnosticTestGenerated.java b/compiler/tests-common-new/tests-gen/org/jetbrains/kotlin/test/runners/DiagnosticTestGenerated.java
index 360998de346..3f3a18b36d0 100644
--- a/compiler/tests-common-new/tests-gen/org/jetbrains/kotlin/test/runners/DiagnosticTestGenerated.java
+++ b/compiler/tests-common-new/tests-gen/org/jetbrains/kotlin/test/runners/DiagnosticTestGenerated.java
@@ -14199,6 +14199,30 @@ public class DiagnosticTestGenerated extends AbstractDiagnosticTest {
           runTest("compiler/testData/diagnostics/tests/functionLiterals/return/IfWithoutElseWithExplicitType.kt");
         }
 
+        @Test
+        @TestMetadata("kt66277.kt")
+        public void testKt66277() {
+          runTest("compiler/testData/diagnostics/tests/functionLiterals/return/kt66277.kt");
+        }
+
+        @Test
+        @TestMetadata("kt66279.kt")
+        public void testKt66279() {
+          runTest("compiler/testData/diagnostics/tests/functionLiterals/return/kt66279.kt");
+        }
+
+        @Test
+        @TestMetadata("kt66512.kt")
+        public void testKt66512() {
+          runTest("compiler/testData/diagnostics/tests/functionLiterals/return/kt66512.kt");
+        }
+
+        @Test
+        @TestMetadata("kt66534.kt")
+        public void testKt66534() {
+          runTest("compiler/testData/diagnostics/tests/functionLiterals/return/kt66534.kt");
+        }
+
         @Test
         @TestMetadata("LambdaReturnTypeIsUnitIfImplicitReturnExists.kt")
         public void testLambdaReturnTypeIsUnitIfImplicitReturnExists() {