[FIR] Implement checker for exhaustive when's in expression position

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

@@ -1,16 +0,0 @@
-fun foo(x: Unit) = x
-
-fun test() {
-    if (false);
-    if (true);
-
-    val x = if (false);
-    foo(x)
-
-    val y: Unit = if (false);
-    foo(y)
-
-    foo({if (1==1);}())
-
-    return if (true);
-}

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

@@ -1,3 +1,4 @@
+// FIR_IDENTICAL
 fun foo(x: Unit) = x
 
 fun test() {

compiler/testData/diagnostics/tests/controlStructures/ifWhenToAnyComplexExpressions.fir.kt

@@ -11,7 +11,7 @@ fun testMixedIfAndWhen() =
                 else 1
                     true -> if (true) 42
                 else println()
-                else -> if (true) println()
+                else -> <!INVALID_IF_AS_EXPRESSION!>if<!> (true) println()
             }
         else println()
 
@@ -28,4 +28,4 @@ fun testWrappedExpressions() =
         }
         else {
             (((((42)) + 1)))
-        }
+        }

compiler/testData/diagnostics/tests/controlStructures/ifWhenWithoutElse.fir.kt

@@ -11,21 +11,21 @@ val mlist = MList()
 
 fun work() {}
 
-val xx1 = if (true) 42
-val xx2: Unit = if (true) 42
-val xx3 = idAny(if (true) 42)
-val xx4 = id(if (true) 42)
-val xx5 = idUnit(if (true) 42)
-val xx6 = null ?: if (true) 42
-val xx7 = "" + if (true) 42
+val xx1 = <!INVALID_IF_AS_EXPRESSION!>if<!> (true) 42
+val xx2: Unit = <!INVALID_IF_AS_EXPRESSION!>if<!> (true) 42
+val xx3 = idAny(<!INVALID_IF_AS_EXPRESSION!>if<!> (true) 42)
+val xx4 = id(<!INVALID_IF_AS_EXPRESSION!>if<!> (true) 42)
+val xx5 = idUnit(<!INVALID_IF_AS_EXPRESSION!>if<!> (true) 42)
+val xx6 = null ?: <!INVALID_IF_AS_EXPRESSION!>if<!> (true) 42
+val xx7 = "" + <!INVALID_IF_AS_EXPRESSION!>if<!> (true) 42
 
-val wxx1 = when { true -> 42 }
-val wxx2: Unit = when { true -> 42 }
-val wxx3 = idAny(when { true -> 42 })
-val wxx4 = id(when { true -> 42 })
-val wxx5 = idUnit(when { true -> 42 })
-val wxx6 = null ?: when { true -> 42 }
-val wxx7 = "" + when { true -> 42 }
+val wxx1 = <!NO_ELSE_IN_WHEN!>when<!> { true -> 42 }
+val wxx2: Unit = <!NO_ELSE_IN_WHEN!>when<!> { true -> 42 }
+val wxx3 = idAny(<!NO_ELSE_IN_WHEN!>when<!> { true -> 42 })
+val wxx4 = id(<!NO_ELSE_IN_WHEN!>when<!> { true -> 42 })
+val wxx5 = idUnit(<!NO_ELSE_IN_WHEN!>when<!> { true -> 42 })
+val wxx6 = null ?: <!NO_ELSE_IN_WHEN!>when<!> { true -> 42 }
+val wxx7 = "" + <!NO_ELSE_IN_WHEN!>when<!> { true -> 42 }
 
 val fn1 = { if (true) 42 }
 val fn2 = { if (true) mlist.add() }
@@ -41,24 +41,24 @@ val ufn4: () -> Unit = { when { true -> 42 } }
 val ufn5: () -> Unit = { when { true -> mlist.add() } }
 val ufn6: () -> Unit = { when { true -> work() } }
 
-fun f1() = if (true) work()
-fun f2() = if (true) mlist.add()
-fun f3() = if (true) 42
-fun f4(): Unit = if (true) work()
-fun f5(): Unit = if (true) mlist.add()
-fun f6(): Unit = if (true) 42
-fun g1() = when { true -> work() }
-fun g2() = when { true -> mlist.add() }
-fun g3() = when { true -> 42 }
-fun g4(): Unit = when { true -> work() }
-fun g5(): Unit = when { true -> mlist.add() }
-fun g6(): Unit = when { true -> 42 }
+fun f1() = <!INVALID_IF_AS_EXPRESSION!>if<!> (true) work()
+fun f2() = <!INVALID_IF_AS_EXPRESSION!>if<!> (true) mlist.add()
+fun f3() = <!INVALID_IF_AS_EXPRESSION!>if<!> (true) 42
+fun f4(): Unit = <!INVALID_IF_AS_EXPRESSION!>if<!> (true) work()
+fun f5(): Unit = <!INVALID_IF_AS_EXPRESSION!>if<!> (true) mlist.add()
+fun f6(): Unit = <!INVALID_IF_AS_EXPRESSION!>if<!> (true) 42
+fun g1() = <!NO_ELSE_IN_WHEN!>when<!> { true -> work() }
+fun g2() = <!NO_ELSE_IN_WHEN!>when<!> { true -> mlist.add() }
+fun g3() = <!NO_ELSE_IN_WHEN!>when<!> { true -> 42 }
+fun g4(): Unit = <!NO_ELSE_IN_WHEN!>when<!> { true -> work() }
+fun g5(): Unit = <!NO_ELSE_IN_WHEN!>when<!> { true -> mlist.add() }
+fun g6(): Unit = <!NO_ELSE_IN_WHEN!>when<!> { true -> 42 }
 
 fun foo1(x: String?) {
-    "" + if (true) 42
+    "" + <!INVALID_IF_AS_EXPRESSION!>if<!> (true) 42
     w@while (true) {
-        x ?: if (true) break
-        x ?: when { true -> break@w }
+        x ?: <!INVALID_IF_AS_EXPRESSION!>if<!> (true) break
+        x ?: <!NO_ELSE_IN_WHEN!>when<!> { true -> break@w }
     }
 }
 

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

@@ -4,7 +4,7 @@
 fun example() {
     val a = if (true) true else false
     val b = if (true) else false
-    val c = if (true) true
+    val c = <!INVALID_IF_AS_EXPRESSION!>if<!> (true) true
     val d = if (true) true else;
     val e = if (true) {} else false
     val f = if (true) true else {}
@@ -27,7 +27,7 @@ fun example() {
     }()
 
     fun t(): Boolean {
-        return if (true) true
+        return <!INVALID_IF_AS_EXPRESSION!>if<!> (true) true
     }
 
     return if (true) true else {}

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

@@ -99,10 +99,10 @@ fun testImplicitCoercion() {
         else -> z--
     }
 
-    var iff = if (true) {
+    var iff = <!INVALID_IF_AS_EXPRESSION!>if<!> (true) {
         z = 34
     }
-    val g = if (true) 4
+    val g = <!INVALID_IF_AS_EXPRESSION!>if<!> (true) 4
     val h = if (false) 4 else {}
 
     <!INAPPLICABLE_CANDIDATE!>bar<!>(if (true) {

compiler/testData/diagnostics/tests/controlStructures/when.kt234.kt973.fir.kt

@@ -25,7 +25,7 @@ fun t1(x: Int) = when(x) {
     else -> 1
 }
 
-fun t5(x: Int) = when (x) {
+fun t5(x: Int) = <!NO_ELSE_IN_WHEN!>when<!> (x) {
     is Int -> 1
     2 -> 2
 }