Eleven new tests about smart casts and value / variable null safety.

At this moment 5/11 are passed successfully.
Related issues: KT-3175 (active), KT-3993 (fixed at M11), KT-5427 (fixed at M11), KT-4450, KT-5840, KT-5907, KT-6819.

Author: mglukhikh

compiler/testData/diagnostics/tests/smartCasts/varnotnull/false01.kt

@@ -0,0 +1,9 @@
+public fun foo() {
+    var i: Int? = 1
+    if (i != null) {
+        while (i != 10) {
+            <!UNUSED_CHANGED_VALUE!>i<!UNSAFE_CALL!>++<!><!>      // Here smart cast should not be performed due to a successor
+            i = null
+        }
+    }
+}

compiler/testData/diagnostics/tests/smartCasts/varnotnull/false01.txt

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

compiler/testData/diagnostics/tests/smartCasts/varnotnull/false03.kt

@@ -0,0 +1,17 @@
+public fun foo() {
+    var s: String? = ""
+    fun closure(): Int {
+        if (s == "") {
+            s = null
+            return -1
+        } else if (s == null) {
+            return -2
+        } else {
+            return s<!UNSAFE_CALL!>.<!>length() // Here smartcast is possible, at least in principle
+        }
+    }
+    if (s != null) {
+        System.out.println(closure())
+        System.out.println(s<!UNSAFE_CALL!>.<!>length())   // Here smartcast is not possible due to a closure predecessor
+    }
+}

compiler/testData/diagnostics/tests/smartCasts/varnotnull/false03.txt

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

compiler/testData/diagnostics/tests/smartCasts/varnotnull/false05.kt

@@ -0,0 +1,26 @@
+// FILE: a.kt
+
+package a
+
+public class X {
+    public val x : String? = null
+    public fun fn(): Int {
+        if (x != null)
+            return <!DEBUG_INFO_SMARTCAST!>x<!>.length() // bogus error here
+        else
+            return 0
+    }
+}
+
+// FILE: b.kt
+
+package b
+
+import a.X
+
+public fun X.gav(): Int {
+    if (x != null)
+        return x<!UNSAFE_CALL!>.<!>length() // bogus error here
+    else
+        return 0
+}

compiler/testData/diagnostics/tests/smartCasts/varnotnull/false05.txt

@@ -0,0 +1,17 @@
+package
+
+package a {
+
+    public final class X {
+        public constructor X()
+        public final val x: kotlin.String? = null
+        public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+        public final fun fn(): kotlin.Int
+        public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+        public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+    }
+}
+
+package b {
+    public fun a.X.gav(): kotlin.Int
+}

compiler/testData/diagnostics/tests/smartCasts/varnotnull/kt3175a.kt

@@ -0,0 +1,9 @@
+public fun fooNotNull(s: String) {
+    System.out.println("Length of $s is ${s.length()}")
+}
+
+public fun foo() {
+    var s: String? = "not null"
+    if (s != null)
+        fooNotNull(<!DEBUG_INFO_SMARTCAST!>s<!>)
+}

compiler/testData/diagnostics/tests/smartCasts/varnotnull/kt3175a.txt

@@ -0,0 +1,4 @@
+package
+
+public fun foo(): kotlin.Unit
+public fun fooNotNull(/*0*/ s: kotlin.String): kotlin.Unit

compiler/testData/diagnostics/tests/smartCasts/varnotnull/kt3175b.kt

@@ -0,0 +1,12 @@
+public fun fooNotNull(s: String) {
+    System.out.println("Length of $s is ${s.length()}")
+}
+
+public fun foo() {
+    var s: String? = "not null"
+    if (s == null) {
+        // Coming soon
+    } else {
+        fooNotNull(<!DEBUG_INFO_SMARTCAST!>s<!>)
+    }
+}

compiler/testData/diagnostics/tests/smartCasts/varnotnull/kt3175b.txt

@@ -0,0 +1,4 @@
+package
+
+public fun foo(): kotlin.Unit
+public fun fooNotNull(/*0*/ s: kotlin.String): kotlin.Unit

compiler/testData/diagnostics/tests/smartCasts/varnotnull/kt3175c.kt

@@ -0,0 +1,11 @@
+public fun fooNotNull(s: String) {
+    System.out.println("Length of $s is ${s.length()}")
+}
+
+public fun foo() {
+    var s: String? = "not null"
+    if (s == null) {
+        return
+    }
+    fooNotNull(<!DEBUG_INFO_SMARTCAST!>s<!>)
+}

compiler/testData/diagnostics/tests/smartCasts/varnotnull/kt3175c.txt

@@ -0,0 +1,4 @@
+package
+
+public fun foo(): kotlin.Unit
+public fun fooNotNull(/*0*/ s: kotlin.String): kotlin.Unit

compiler/testData/diagnostics/tests/smartCasts/varnotnull/kt5840.kt

@@ -0,0 +1,3 @@
+fun calc(x: List<String>?) {
+    x?.get(<!DEBUG_INFO_SMARTCAST!>x<!>.size() - 1) // x should be non-null in arguments list
+}

compiler/testData/diagnostics/tests/smartCasts/varnotnull/kt5840.txt

@@ -0,0 +1,3 @@
+package
+
+internal fun calc(/*0*/ x: kotlin.List<kotlin.String>?): kotlin.Unit