PatternMatchingTypingVisitor:

rewrite type inference for 'when' using special constructs.
This fixes several type inference issues for 'when':
KT-9929, KT-9972, KT-10439, KT-10463
along with some other diagnostics-related issues.

compiler/testData/diagnostics/tests/when/WhenTypeDisjunctions.kt

@@ -1,11 +1,11 @@
 fun foo(s: Any): String {
     val x = when (s) {
-        is String -> s
+        is String -> <!DEBUG_INFO_SMARTCAST!>s<!>
         is Int -> "$s"
         else -> return ""
     }
 
-    val y: String = <!DEBUG_INFO_SMARTCAST!>x<!> // should be Ok
+    val y: String = x // should be Ok
     return y
 }
 

compiler/testData/diagnostics/tests/when/kt10439.kt

@@ -0,0 +1,12 @@
+fun foo(x: Int) = x
+
+fun test0(flag: Boolean) {
+    foo(if (flag) <!CONSTANT_EXPECTED_TYPE_MISMATCH!>true<!> else <!TYPE_MISMATCH!>""<!>)
+}
+
+fun test1(flag: Boolean) {
+    foo(when (flag) {
+        true -> <!CONSTANT_EXPECTED_TYPE_MISMATCH!>true<!>
+        else -> <!TYPE_MISMATCH!>""<!>
+    })
+}

compiler/testData/diagnostics/tests/when/kt10439.txt

@@ -0,0 +1,5 @@
+package
+
+public fun foo(/*0*/ x: kotlin.Int): kotlin.Int
+public fun test0(/*0*/ flag: kotlin.Boolean): kotlin.Unit
+public fun test1(/*0*/ flag: kotlin.Boolean): kotlin.Unit

compiler/testData/diagnostics/tests/when/kt9929.kt

@@ -0,0 +1,9 @@
+val test: Int = if (true) {
+    when (2) {
+        1 -> 1
+        else -> <!NULL_FOR_NONNULL_TYPE!>null<!>
+    }
+}
+else {
+    2
+}

compiler/testData/diagnostics/tests/when/kt9929.txt

@@ -0,0 +1,3 @@
+package
+
+public val test: kotlin.Int

compiler/testData/diagnostics/tests/when/kt9972.kt

@@ -0,0 +1,17 @@
+fun test1(): Int {
+    val x: String = if (true) {
+        when {
+            true -> <!TYPE_MISMATCH!>Any()<!>
+            else -> <!NULL_FOR_NONNULL_TYPE!>null<!>
+        }
+    } else ""
+    return x.hashCode()
+}
+
+fun test2(): Int {
+    val x: String = when {
+                        true -> <!TYPE_MISMATCH!>Any()<!>
+                        else -> null
+                    } ?: return 0
+    return x.hashCode()
+}

compiler/testData/diagnostics/tests/when/kt9972.txt

@@ -0,0 +1,4 @@
+package
+
+public fun test1(): kotlin.Int
+public fun test2(): kotlin.Int