JVM_IR: remove an assertion that triggers due to a frontend bug

compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/codegen/ExpressionCodegen.kt

@@ -590,9 +590,6 @@ class ExpressionCodegen(
 
         val endLabel = Label()
         val exhaustive = expression.branches.any { it.condition.isTrueConst() }
-        assert(exhaustive || expression.type.isUnit() || expression.type.isNothing()) {
-            "non-exhaustive conditional should return Unit: ${expression.dump()}"
-        }
         for (branch in expression.branches) {
             val elseLabel = Label()
             if (branch.condition.isFalseConst() || branch.condition.isTrueConst()) {
@@ -619,6 +616,14 @@ class ExpressionCodegen(
             mv.mark(elseLabel)
         }
         mv.mark(endLabel)
+        // NOTE: using a non-exhaustive if/when as an expression is invalid, so it should theoretically
+        //       always return Unit. However, with the current frontend this is not always the case.
+        //       Most notably, 1. when all branches return/break/continue, the type is Nothing;
+        //       2. the frontend may sometimes infer Any instead of Unit, probably due to a bug
+        //       (see compiler/testData/codegen/box/controlStructures/ifIncompatibleBranches.kt).
+        //       It should still be safe to produce a soon-to-be-discarded Unit. (What is not ok is
+        //       inserting *any* code here, though, as its line number will be that of the last line
+        //       of the last branch.)
         return immaterialUnitValue
     }
 

compiler/testData/codegen/box/controlStructures/ifIncompatibleBranches.kt

@@ -0,0 +1,10 @@
+fun box(): String {
+    var s = "2"
+    var res = "Fail"
+    if (s == "1") {
+        false
+    } else if (s == "2") {
+        res = "OK"
+    }
+    return res
+}

compiler/tests/org/jetbrains/kotlin/codegen/BlackBoxCodegenTestGenerated.java

@@ -4838,6 +4838,11 @@ public class BlackBoxCodegenTestGenerated extends AbstractBlackBoxCodegenTest {
             runTest("compiler/testData/codegen/box/controlStructures/ifConst2.kt");
         }
 
+        @TestMetadata("ifIncompatibleBranches.kt")
+        public void testIfIncompatibleBranches() throws Exception {
+            runTest("compiler/testData/codegen/box/controlStructures/ifIncompatibleBranches.kt");
+        }
+
         @TestMetadata("inRangeConditionsInWhen.kt")
         public void testInRangeConditionsInWhen() throws Exception {
             runTest("compiler/testData/codegen/box/controlStructures/inRangeConditionsInWhen.kt");

compiler/tests/org/jetbrains/kotlin/codegen/LightAnalysisModeTestGenerated.java

@@ -4838,6 +4838,11 @@ public class LightAnalysisModeTestGenerated extends AbstractLightAnalysisModeTes
             runTest("compiler/testData/codegen/box/controlStructures/ifConst2.kt");
         }
 
+        @TestMetadata("ifIncompatibleBranches.kt")
+        public void testIfIncompatibleBranches() throws Exception {
+            runTest("compiler/testData/codegen/box/controlStructures/ifIncompatibleBranches.kt");
+        }
+
         @TestMetadata("inRangeConditionsInWhen.kt")
         public void testInRangeConditionsInWhen() throws Exception {
             runTest("compiler/testData/codegen/box/controlStructures/inRangeConditionsInWhen.kt");

compiler/tests/org/jetbrains/kotlin/codegen/ir/IrBlackBoxCodegenTestGenerated.java

@@ -4808,6 +4808,11 @@ public class IrBlackBoxCodegenTestGenerated extends AbstractIrBlackBoxCodegenTes
             runTest("compiler/testData/codegen/box/controlStructures/ifConst2.kt");
         }
 
+        @TestMetadata("ifIncompatibleBranches.kt")
+        public void testIfIncompatibleBranches() throws Exception {
+            runTest("compiler/testData/codegen/box/controlStructures/ifIncompatibleBranches.kt");
+        }
+
         @TestMetadata("inRangeConditionsInWhen.kt")
         public void testInRangeConditionsInWhen() throws Exception {
             runTest("compiler/testData/codegen/box/controlStructures/inRangeConditionsInWhen.kt");

js/js.tests/test/org/jetbrains/kotlin/js/test/ir/semantics/IrJsCodegenBoxTestGenerated.java

@@ -3963,6 +3963,11 @@ public class IrJsCodegenBoxTestGenerated extends AbstractIrJsCodegenBoxTest {
             runTest("compiler/testData/codegen/box/controlStructures/ifConst2.kt");
         }
 
+        @TestMetadata("ifIncompatibleBranches.kt")
+        public void testIfIncompatibleBranches() throws Exception {
+            runTest("compiler/testData/codegen/box/controlStructures/ifIncompatibleBranches.kt");
+        }
+
         @TestMetadata("inRangeConditionsInWhen.kt")
         public void testInRangeConditionsInWhen() throws Exception {
             runTest("compiler/testData/codegen/box/controlStructures/inRangeConditionsInWhen.kt");

js/js.tests/test/org/jetbrains/kotlin/js/test/semantics/JsCodegenBoxTestGenerated.java

@@ -3973,6 +3973,11 @@ public class JsCodegenBoxTestGenerated extends AbstractJsCodegenBoxTest {
             runTest("compiler/testData/codegen/box/controlStructures/ifConst2.kt");
         }
 
+        @TestMetadata("ifIncompatibleBranches.kt")
+        public void testIfIncompatibleBranches() throws Exception {
+            runTest("compiler/testData/codegen/box/controlStructures/ifIncompatibleBranches.kt");
+        }
+
         @TestMetadata("inRangeConditionsInWhen.kt")
         public void testInRangeConditionsInWhen() throws Exception {
             runTest("compiler/testData/codegen/box/controlStructures/inRangeConditionsInWhen.kt");