Error on 'if' without an 'else' branch when used as an expression

compiler/conditional-preprocessor/src/org.jetbrains.kotlin.preprocessor/logging.kt

@@ -27,7 +27,9 @@ public object SystemOutLogger : Logger {
     private fun out(level: String, msg: CharSequence) = println("[$level] $msg")
 
     public var isDebugEnabled: Boolean = true
-    override fun debug(msg: CharSequence) = if (isDebugEnabled) out("DEBUG", msg)
+    override fun debug(msg: CharSequence) {
+        if (isDebugEnabled) out("DEBUG", msg)
+    }
     override fun info(msg: CharSequence) = out("INFO", msg)
     override fun warn(msg: CharSequence) = out("WARN", msg)
     override fun error(msg: CharSequence) = out("ERROR", msg)

compiler/frontend/src/org/jetbrains/kotlin/diagnostics/Errors.java

@@ -610,6 +610,8 @@ public interface Errors {
 
     DiagnosticFactory0<JetElement> SENSELESS_NULL_IN_WHEN = DiagnosticFactory0.create(WARNING);
 
+    DiagnosticFactory0<JetIfExpression> INVALID_IF_AS_EXPRESSION = DiagnosticFactory0.create(ERROR);
+
     // Nullability
 
     DiagnosticFactory1<PsiElement, JetType> UNSAFE_CALL = DiagnosticFactory1.create(ERROR);

compiler/frontend/src/org/jetbrains/kotlin/diagnostics/rendering/DefaultErrorMessages.java

@@ -537,6 +537,8 @@ public class DefaultErrorMessages {
         MAP.put(SENSELESS_COMPARISON, "Condition ''{0}'' is always ''{1}''", ELEMENT_TEXT, TO_STRING);
         MAP.put(SENSELESS_NULL_IN_WHEN, "Expression under 'when' is never equal to null");
 
+        MAP.put(INVALID_IF_AS_EXPRESSION, "'if' must have both main and 'else' branches if used as an expression");
+
         MAP.put(OVERRIDING_FINAL_MEMBER, "''{0}'' in ''{1}'' is final and cannot be overridden", NAME, NAME);
         MAP.put(CANNOT_WEAKEN_ACCESS_PRIVILEGE, "Cannot weaken access privilege ''{0}'' for ''{1}'' in ''{2}''", TO_STRING, NAME, NAME);
         MAP.put(CANNOT_CHANGE_ACCESS_PRIVILEGE, "Cannot change access privilege ''{0}'' for ''{1}'' in ''{2}''", TO_STRING, NAME, NAME);

compiler/frontend/src/org/jetbrains/kotlin/resolve/calls/CandidateResolver.kt

@@ -504,8 +504,11 @@ public class CandidateResolver(
     private fun <D : CallableDescriptor> CallCandidateResolutionContext<D>.shouldContinue() =
             candidateResolveMode == CandidateResolveMode.FULLY || candidateCall.getStatus().possibleTransformToSuccess()
 
-    private inline fun <D : CallableDescriptor> CallCandidateResolutionContext<D>
-            .check(checker: CallCandidateResolutionContext<D>.() -> Unit): Unit = if (shouldContinue()) checker()
+    private inline fun <D : CallableDescriptor> CallCandidateResolutionContext<D>.check(
+            checker: CallCandidateResolutionContext<D>.() -> Unit
+    ) {
+        if (shouldContinue()) checker()
+    }
 
     private inline fun <D : CallableDescriptor> CallCandidateResolutionContext<D>.
             checkAndReport(checker: CallCandidateResolutionContext<D>.() -> ResolutionStatus) {

compiler/frontend/src/org/jetbrains/kotlin/types/expressions/DataFlowAnalyzer.java

@@ -256,10 +256,21 @@ public class DataFlowAnalyzer {
 
     @Nullable
     public JetType checkImplicitCast(@Nullable JetType expressionType, @NotNull JetExpression expression, @NotNull ResolutionContext context, boolean isStatement) {
-        if (expressionType != null && context.expectedType == NO_EXPECTED_TYPE && context.contextDependency == INDEPENDENT && !isStatement
+        boolean isIfExpression = expression instanceof JetIfExpression;
+        if (expressionType != null && (context.expectedType == NO_EXPECTED_TYPE || isIfExpression)
+                && context.contextDependency == INDEPENDENT && !isStatement
                 && (KotlinBuiltIns.isUnit(expressionType) || KotlinBuiltIns.isAnyOrNullableAny(expressionType))
                 && !DynamicTypesKt.isDynamic(expressionType)) {
-            context.trace.report(IMPLICIT_CAST_TO_UNIT_OR_ANY.on(expression, expressionType));
+            if (isIfExpression && KotlinBuiltIns.isUnit(expressionType)) {
+                JetIfExpression ifExpression = (JetIfExpression) expression;
+                if (ifExpression.getThen() == null || ifExpression.getElse() == null) {
+                    context.trace.report(INVALID_IF_AS_EXPRESSION.on((JetIfExpression) expression));
+                    return expressionType;
+                }
+            }
+            else {
+                context.trace.report(IMPLICIT_CAST_TO_UNIT_OR_ANY.on(expression, expressionType));
+            }
         }
         return expressionType;
     }

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

@@ -1,12 +0,0 @@
-fun box(): String {
-    if (true);
-    if (false);
-    val iftrue = if (true);
-    val iffalse = if (false);
-
-    var state = 0
-    val k = if (state++==1);
-    if (state != 1) return "Fail: $state"
-
-    return "OK"
-}

compiler/testData/codegen/box/controlStructures/kt2062.kt

@@ -1,5 +0,0 @@
-fun box(): String {
-  val a = if(true) {
-  }
-  return if (a.toString() == "kotlin.Unit") "OK" else "fail"
-}

compiler/testData/codegen/box/controlStructures/kt2598.kt

@@ -1,9 +0,0 @@
-fun foo(condition: Boolean): String {
-    val u = if (condition) {
-        "OK"
-    } else {
-    }
-    return u.toString()
-}
-
-fun box() = foo(true)

compiler/testData/codegen/box/finally/notChainCatch.kt

@@ -1,5 +1,10 @@
-fun unsupportedEx() = if (true) throw UnsupportedOperationException()
-fun runtimeEx() = if (true) throw RuntimeException()
+fun unsupportedEx() {
+    if (true) throw UnsupportedOperationException()
+}
+
+fun runtimeEx() {
+    if (true) throw RuntimeException()
+}
 
 fun test1() : String {
     var s = "";

compiler/testData/codegen/box/finally/tryFinally.kt

@@ -1,5 +1,10 @@
-fun unsupportedEx() = if (true) throw UnsupportedOperationException()
-fun runtimeEx() = if (true) throw RuntimeException()
+fun unsupportedEx() {
+    if (true) throw UnsupportedOperationException()
+}
+
+fun runtimeEx() {
+    if (true) throw RuntimeException()
+}
 
 fun test1WithFinally() : String {
     var s = "";

compiler/testData/codegen/box/primitiveTypes/comparisonWithNaN.kt

@@ -1,7 +1,8 @@
 // This test checks that our bytecode is consistent with javac bytecode
 
-fun _assert(condition: Boolean): Unit =
+fun _assert(condition: Boolean) {
     if (!condition) throw AssertionError("Fail")
+}
 
 fun _assertFalse(condition: Boolean) = _assert(!condition)
 

compiler/testData/codegen/box/unit/ifElse.kt

@@ -4,9 +4,9 @@ class A (val p: String, p1: String, p2: String) {
 
     var cond2: String = ""
 
-    val prop1 = if (cond1(p)) p1
+    val prop1 = if (cond1(p)) p1 else null
 
-    val prop2 = if (cond2(p)) else;
+    val prop2 = if (cond2(p)) p2 else null;
 
 
     fun cond1(p: String): Boolean {

compiler/testData/codegen/boxWithStdlib/lazyCodegen/ifElse.kt

@@ -6,9 +6,9 @@ class A (val p: String, p1: String, p2: String) {
 
     val prop: String = if (p == "test") p1 else p2
 
-    val prop1 = if (cond1(p)) p1
+    val prop1 = if (cond1(p)) p1 else false
 
-    val prop2 = if (cond2(p)) else;
+    val prop2 = if (cond2(p)) true else false
 
     fun cond1(p: String): Boolean {
         cond1 = "cond1"

compiler/testData/diagnostics/tests/FunctionReturnTypes.kt

@@ -69,10 +69,10 @@ fun blockReturnValueTypeMatch1() : Int {
   return if (1 > 2) <!CONSTANT_EXPECTED_TYPE_MISMATCH!>1.0<!> else <!CONSTANT_EXPECTED_TYPE_MISMATCH!>2.0<!>
 }
 fun blockReturnValueTypeMatch2() : Int {
-  return <!TYPE_MISMATCH!>if (1 > 2) 1<!>
+  return <!TYPE_MISMATCH, INVALID_IF_AS_EXPRESSION!>if (1 > 2) 1<!>
 }
 fun blockReturnValueTypeMatch3() : Int {
-  return <!TYPE_MISMATCH!>if (1 > 2) else 1<!>
+  return <!TYPE_MISMATCH, INVALID_IF_AS_EXPRESSION!>if (1 > 2) else 1<!>
 }
 fun blockReturnValueTypeMatch4() : Int {
   if (1 > 2)
@@ -105,7 +105,7 @@ fun blockReturnValueTypeMatch9() : Int {
     <!UNUSED_EXPRESSION!>1.0<!>
 <!NO_RETURN_IN_FUNCTION_WITH_BLOCK_BODY!>}<!>
 fun blockReturnValueTypeMatch10() : Int {
-  return <!TYPE_MISMATCH!>if (1 > 2)
+  return <!TYPE_MISMATCH, INVALID_IF_AS_EXPRESSION!>if (1 > 2)
     1<!>
 }
 fun blockReturnValueTypeMatch11() : Int {

compiler/testData/diagnostics/tests/controlStructures/emptyIf.kt

@@ -4,13 +4,13 @@ fun test() {
     if (false);
     if (true);
 
-    val x = <!IMPLICIT_CAST_TO_UNIT_OR_ANY!>if (false)<!>;
+    val x = <!INVALID_IF_AS_EXPRESSION!>if (false)<!>;
     foo(x)
 
-    val y: Unit = if (false);
+    val y: Unit = <!INVALID_IF_AS_EXPRESSION!>if (false)<!>;
     foo(y)
 
     foo({if (1==1);}())
 
-    return if (true);
+    return <!INVALID_IF_AS_EXPRESSION!>if (true)<!>;
 }

compiler/testData/diagnostics/tests/controlStructures/improperElseInExpression.kt

@@ -0,0 +1,33 @@
+// !DIAGNOSTICS: -UNUSED_VARIABLE
+
+fun example() {
+    val a = if (true) true else false
+    val b = <!INVALID_IF_AS_EXPRESSION!>if (true) else false<!>
+    val c = <!INVALID_IF_AS_EXPRESSION!>if (true) true<!>
+    val d = <!INVALID_IF_AS_EXPRESSION!>if (true) true else<!>;
+    val e = <!IMPLICIT_CAST_TO_UNIT_OR_ANY!>if (true) {} else false<!>
+    val f = <!IMPLICIT_CAST_TO_UNIT_OR_ANY!>if (true) true else {}<!>
+
+    {
+        if (true) <!UNUSED_EXPRESSION!>true<!>
+    }();
+
+    {
+        if (true) true else false
+    }();
+
+    {
+        if (true) {} else false
+    }();
+
+
+    {
+        if (true) true else {}
+    }()
+
+    fun t(): Boolean {
+        return <!TYPE_MISMATCH, INVALID_IF_AS_EXPRESSION!>if (true) true<!>
+    }
+
+    return if (true) <!CONSTANT_EXPECTED_TYPE_MISMATCH!>true<!> else {}
+}

compiler/testData/diagnostics/tests/controlStructures/improperElseInExpression.txt

@@ -0,0 +1,3 @@
+package
+
+public fun example(): kotlin.Unit

compiler/testData/diagnostics/tests/controlStructures/kt4310.kt

@@ -7,5 +7,5 @@ fun test(a: Boolean, b: Boolean): Int {
         <!TYPE_MISMATCH!>if (b) {
             3
         }<!>
-    }    // no error, but must be
+    }
 }

compiler/testData/diagnostics/tests/controlStructures/kt770.kt351.kt735_StatementType.kt

@@ -34,7 +34,7 @@ fun foo() {
 fun box() : Int {
     val d = 2
     var z = 0
-        when(d) {
+    when(d) {
         5, 3 -> z++
         else -> z = -1000
     }
@@ -100,10 +100,10 @@ fun testImplicitCoercion() {
         else -> <!UNUSED_CHANGED_VALUE!>z--<!>
     }<!>
 
-    var <!UNUSED_VARIABLE!>iff<!> = <!IMPLICIT_CAST_TO_UNIT_OR_ANY!>if (true) {
+    var <!UNUSED_VARIABLE!>iff<!> = <!INVALID_IF_AS_EXPRESSION!>if (true) {
         <!UNUSED_VALUE!>z =<!> 34
     }<!>
-    val <!UNUSED_VARIABLE!>g<!> = <!IMPLICIT_CAST_TO_UNIT_OR_ANY!>if (true) 4<!>
+    val <!UNUSED_VARIABLE!>g<!> = <!INVALID_IF_AS_EXPRESSION!>if (true) 4<!>
     val <!UNUSED_VARIABLE!>h<!> = <!IMPLICIT_CAST_TO_UNIT_OR_ANY!>if (false) 4 else {}<!>
 
     bar(if (true) {

compiler/testData/diagnostics/tests/dataFlow/EmptyIf.kt

@@ -18,7 +18,7 @@ fun f3(s: Number?) {
 }
 
 fun f4(s: Int?) {
-    var u = <!IMPLICIT_CAST_TO_UNIT_OR_ANY!>if (s!! == 42)<!>;
-    if (u == Unit) u = if (s == 239);
+    var u = <!INVALID_IF_AS_EXPRESSION!>if (s!! == 42)<!>;
+    if (u == Unit) u = <!INVALID_IF_AS_EXPRESSION!>if (s == 239)<!>;
     return u
-}
+}

compiler/testData/diagnostics/tests/functionLiterals/return/IfWithoutElse.kt

@@ -1,7 +1,7 @@
 val flag = true
 
 // type of a was checked by txt
-val a/*: () -> Any*/ = l@ { // commonSupertype(Int, Unit) = Any
+val a/*: () -> Any*/ = l@ {
     if (flag) return@l 4
 }
 

compiler/testData/lineNumber/custom/ifThen.kt

@@ -2,10 +2,6 @@ fun foo() {
     if (0 < 1) {
         return
     }
-    
-    val u: Unit = if (0 < 1) {
-        return
-    }
 }
 
-// 2 3 6 7 6 9
+// 2 3 5

compiler/tests/org/jetbrains/kotlin/checkers/JetDiagnosticsTestGenerated.java

@@ -3258,6 +3258,12 @@ public class JetDiagnosticsTestGenerated extends AbstractJetDiagnosticsTest {
                 doTest(fileName);
             }
 
+            @TestMetadata("improperElseInExpression.kt")
+            public void testImproperElseInExpression() throws Exception {
+                String fileName = JetTestUtils.navigationMetadata("compiler/testData/diagnostics/tests/controlStructures/improperElseInExpression.kt");
+                doTest(fileName);
+            }
+
             @TestMetadata("jumpAcrossFunctionBoundary.kt")
             public void testJumpAcrossFunctionBoundary() throws Exception {
                 String fileName = JetTestUtils.navigationMetadata("compiler/testData/diagnostics/tests/controlStructures/jumpAcrossFunctionBoundary.kt");

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

@@ -2053,12 +2053,6 @@ public class BlackBoxCodegenTestGenerated extends AbstractBlackBoxCodegenTest {
             doTest(fileName);
         }
 
-        @TestMetadata("emptyIf.kt")
-        public void testEmptyIf() throws Exception {
-            String fileName = JetTestUtils.navigationMetadata("compiler/testData/codegen/box/controlStructures/emptyIf.kt");
-            doTest(fileName);
-        }
-
         @TestMetadata("emptyWhile.kt")
         public void testEmptyWhile() throws Exception {
             String fileName = JetTestUtils.navigationMetadata("compiler/testData/codegen/box/controlStructures/emptyWhile.kt");
@@ -2149,12 +2143,6 @@ public class BlackBoxCodegenTestGenerated extends AbstractBlackBoxCodegenTest {
             doTest(fileName);
         }
 
-        @TestMetadata("kt2062.kt")
-        public void testKt2062() throws Exception {
-            String fileName = JetTestUtils.navigationMetadata("compiler/testData/codegen/box/controlStructures/kt2062.kt");
-            doTest(fileName);
-        }
-
         @TestMetadata("kt2147.kt")
         public void testKt2147() throws Exception {
             String fileName = JetTestUtils.navigationMetadata("compiler/testData/codegen/box/controlStructures/kt2147.kt");
@@ -2197,12 +2185,6 @@ public class BlackBoxCodegenTestGenerated extends AbstractBlackBoxCodegenTest {
             doTest(fileName);
         }
 
-        @TestMetadata("kt2598.kt")
-        public void testKt2598() throws Exception {
-            String fileName = JetTestUtils.navigationMetadata("compiler/testData/codegen/box/controlStructures/kt2598.kt");
-            doTest(fileName);
-        }
-
         @TestMetadata("kt299.kt")
         public void testKt299() throws Exception {
             String fileName = JetTestUtils.navigationMetadata("compiler/testData/codegen/box/controlStructures/kt299.kt");

generators/src/org/jetbrains/kotlin/generators/builtins/generateBuiltIns.kt

@@ -28,8 +28,9 @@ import org.jetbrains.kotlin.generators.builtins.ranges.GenerateRanges
 import java.io.File
 import java.io.PrintWriter
 
-fun assertExists(file: File): Unit =
-        if (!file.exists()) error("Output dir does not exist: ${file.getAbsolutePath()}")
+fun assertExists(file: File) {
+    if (!file.exists()) error("Output dir does not exist: ${file.getAbsolutePath()}")
+}
 
 val BUILT_INS_NATIVE_DIR = File("core/builtins/native/")
 val BUILT_INS_SRC_DIR = File("core/builtins/src/")

idea/testData/intentions/swapBinaryExpression/is.kt

@@ -1,4 +1,5 @@
 // IS_APPLICABLE: false
+// ERROR: 'if' must have both main and 'else' branches if used as an expression
 // ERROR: Expression 'if "test" is String' of type 'kotlin.Unit' cannot be invoked as a function. The function invoke() is not found
 
 fun doSomething<T>(a: T) {}

jps-plugin/src/org/jetbrains/kotlin/jps/build/KotlinBuilder.kt

@@ -320,7 +320,9 @@ public class KotlinBuilder : ModuleLevelBuilder(BuilderCategory.SOURCE_PROCESSOR
         val compilerServices = Services.Builder()
                 .register(javaClass<IncrementalCompilationComponents>(), IncrementalCompilationComponentsImpl(incrementalCaches, lookupTracker))
                 .register(javaClass<CompilationCanceledStatus>(), object : CompilationCanceledStatus {
-                    override fun checkCanceled(): Unit = if (context.getCancelStatus().isCanceled()) throw CompilationCanceledException()
+                    override fun checkCanceled() {
+                        if (context.getCancelStatus().isCanceled()) throw CompilationCanceledException()
+                    }
                 })
                 .build()
 

js/js.parser/src/org/jetbrains/kotlin/js/parser/parserUtils.kt

@@ -42,19 +42,20 @@ public fun parseFunction(code: String, offset: Int, reporter: ErrorReporter, sco
 private class FunctionParsingObserver : Observer {
     var functionsStarted = 0
 
-    override fun update(o: Observable?, arg: Any?): Unit =
-            when (arg) {
-                is ParserEvents.OnFunctionParsingStart -> {
-                    functionsStarted++
-                }
-                is ParserEvents.OnFunctionParsingEnd -> {
-                    functionsStarted--
+    override fun update(o: Observable?, arg: Any?) {
+        when (arg) {
+            is ParserEvents.OnFunctionParsingStart -> {
+                functionsStarted++
+            }
+            is ParserEvents.OnFunctionParsingEnd -> {
+                functionsStarted--
 
-                    if (functionsStarted == 0) {
-                        arg.tokenStream.ungetToken(TokenStream.EOF)
-                    }
+                if (functionsStarted == 0) {
+                    arg.tokenStream.ungetToken(TokenStream.EOF)
                 }
             }
+        }
+    }
 }
 
 inline

js/js.translator/testData/expression/evaluationOrder/cases/orOrWithSideEffect.kt

@@ -8,7 +8,7 @@ fun bar(s: String, value: Boolean): Boolean {
 }
 
 fun box(): String {
-    val a =  if (true || if(bar("A", false)) {2} else {3} == 0) { }
+    val a =  if (true || if(bar("A", false)) {2} else {3} == 0) true else false
     assertEquals("", global)
 
     true || if(bar("A", false)) {2} else {3} == 0