Properly check whether nullability of receiver argument fits to parameter's nullability

It's should behave like we check isSubtype(receiverType, parameterType) + use nullability info from smart cast

 #KT-1090 Fixed

compiler/testData/diagnostics/tests/generics/nullability/smartCasts.kt

@@ -0,0 +1,45 @@
+// !DIAGNOSTICS: -UNUSED_EXPRESSION,-UNUSED_VARIABLE
+
+fun <T : CharSequence?> T.bar1() {}
+fun CharSequence?.bar2() {}
+
+fun <T : CharSequence> T.bar3() {}
+fun CharSequence.bar4() {}
+
+fun <T : CharSequence?> foo(x: T) {
+
+    if (x != null) {
+        if (<!SENSELESS_COMPARISON!>x != null<!>) {}
+
+        <!DEBUG_INFO_SMARTCAST!>x<!>.length()
+        x<!UNNECESSARY_SAFE_CALL!>?.<!>length()
+
+        x.bar1()
+        x.bar2()
+        x.<!TYPE_INFERENCE_UPPER_BOUND_VIOLATED!>bar3<!>()
+        <!DEBUG_INFO_SMARTCAST!>x<!>.bar4()
+
+
+        x<!UNNECESSARY_SAFE_CALL!>?.<!>bar1()
+    }
+
+    x<!UNSAFE_CALL!>.<!>length()
+
+    if (x is String) {
+        <!DEBUG_INFO_SMARTCAST!>x<!>.length()
+        <!DEBUG_INFO_SMARTCAST!>x<!><!UNNECESSARY_SAFE_CALL!>?.<!>length()
+
+        <!DEBUG_INFO_SMARTCAST!>x<!>.bar1()
+        x.bar2()
+        <!DEBUG_INFO_SMARTCAST!>x<!>.bar3()
+    }
+
+    if (x is CharSequence) {
+        <!DEBUG_INFO_SMARTCAST!>x<!>.length()
+        x<!UNNECESSARY_SAFE_CALL!>?.<!>length()
+
+        <!DEBUG_INFO_SMARTCAST!>x<!>.bar1()
+        x.bar2()
+        <!DEBUG_INFO_SMARTCAST!>x<!>.bar3()
+    }
+}

compiler/testData/diagnostics/tests/generics/nullability/smartCasts.txt

@@ -0,0 +1,7 @@
+package
+
+internal fun </*0*/ T : kotlin.CharSequence?> foo(/*0*/ x: T): kotlin.Unit
+internal fun </*0*/ T : kotlin.CharSequence?> T.bar1(): kotlin.Unit
+internal fun kotlin.CharSequence?.bar2(): kotlin.Unit
+internal fun </*0*/ T : kotlin.CharSequence> T.bar3(): kotlin.Unit
+internal fun kotlin.CharSequence.bar4(): kotlin.Unit

compiler/testData/diagnostics/tests/generics/nullability/smartCastsOnThis.kt

@@ -0,0 +1,35 @@
+// !DIAGNOSTICS: -UNUSED_EXPRESSION,-UNUSED_VARIABLE
+
+fun <T : CharSequence?> T.bar1() {}
+fun CharSequence?.bar2() {}
+
+fun <T : CharSequence> T.bar3() {}
+fun CharSequence.bar4() {}
+
+fun <T : String?> T.foo() {
+    if (this != null) {
+        if (<!SENSELESS_COMPARISON!>this != null<!>) {}
+
+        length()
+        this<!UNNECESSARY_SAFE_CALL!>?.<!>length()
+
+        bar1()
+        bar2()
+        <!TYPE_INFERENCE_UPPER_BOUND_VIOLATED!>bar3<!>()
+        bar4()
+
+
+        this<!UNNECESSARY_SAFE_CALL!>?.<!>bar1()
+    }
+
+    <!UNSAFE_CALL!>length<!>()
+
+    if (this is String) {
+        length()
+        this<!UNNECESSARY_SAFE_CALL!>?.<!>length()
+
+        bar1()
+        bar2()
+        <!TYPE_INFERENCE_UPPER_BOUND_VIOLATED!>bar3<!>()
+    }
+}

compiler/testData/diagnostics/tests/generics/nullability/smartCastsOnThis.txt

@@ -0,0 +1,7 @@
+package
+
+internal fun </*0*/ T : kotlin.CharSequence?> T.bar1(): kotlin.Unit
+internal fun kotlin.CharSequence?.bar2(): kotlin.Unit
+internal fun </*0*/ T : kotlin.CharSequence> T.bar3(): kotlin.Unit
+internal fun kotlin.CharSequence.bar4(): kotlin.Unit
+internal fun </*0*/ T : kotlin.String?> T.foo(): kotlin.Unit

compiler/testData/diagnostics/tests/generics/nullability/tpInBounds.kt

@@ -0,0 +1,40 @@
+// !DIAGNOSTICS: -UNUSED_VALUE,-UNUSED_VARIABLE,-ASSIGNED_BUT_NEVER_ACCESSED_VARIABLE,-BASE_WITH_NULLABLE_UPPER_BOUND,-VARIABLE_WITH_REDUNDANT_INITIALIZER
+
+class A<T : CharSequence?, E1 : T, E2: T?> {
+    fun T.bar() {}
+
+    fun foo(x: E1, y: E2) {
+        x.bar()
+
+        if (1 == 1) {
+            y<!UNSAFE_CALL!>.<!>bar()
+        }
+
+        x?.bar()
+        y?.bar()
+
+
+        var t: T = x
+        var tN: T? = y
+
+        // condition needed to make smart cast on tN impossible
+        if (1 == 1) {
+            tN = x
+        }
+
+        if (1 == 1) {
+            t = <!TYPE_MISMATCH!>tN<!>
+        }
+
+        t = <!TYPE_MISMATCH!>y<!>
+
+        // Could be smart-cast
+        if (y != null) {
+            t = <!TYPE_MISMATCH!>y<!>
+        }
+
+        if (tN != null) {
+            t = <!DEBUG_INFO_SMARTCAST!>tN<!>
+        }
+    }
+}

compiler/testData/diagnostics/tests/generics/nullability/tpInBounds.txt

@@ -0,0 +1,10 @@
+package
+
+internal final class A</*0*/ T : kotlin.CharSequence?, /*1*/ E1 : T, /*2*/ E2 : T?> {
+    public constructor A</*0*/ T : kotlin.CharSequence?, /*1*/ E1 : T, /*2*/ E2 : T?>()
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    internal final fun foo(/*0*/ x: E1, /*1*/ y: E2): kotlin.Unit
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+    internal final fun T.bar(): kotlin.Unit
+}

compiler/testData/diagnostics/tests/generics/nullability/useAsReceiver.kt

@@ -0,0 +1,28 @@
+// !DIAGNOSTICS: -UNUSED_EXPRESSION,-UNUSED_VARIABLE
+
+fun <T : CharSequence?> T.bar1() {}
+fun CharSequence?.bar2() {}
+
+fun <T : CharSequence> T.bar3() {}
+
+fun <T, R> T.let(f: (T) -> R): R = f(this)
+
+fun <T : String?> foo(x: T) {
+    x<!UNSAFE_CALL!>.<!>length()
+    x?.length()
+
+    if (1 == 1) {
+        x!!.length()
+    }
+
+
+    x.bar1()
+    x.bar2()
+
+    x?.bar1()
+    x?.bar2()
+
+    x.<!TYPE_INFERENCE_UPPER_BOUND_VIOLATED!>bar3<!>()
+
+    x?.let { it<!UNSAFE_CALL!>.<!>length() }
+}

compiler/testData/diagnostics/tests/generics/nullability/useAsReceiver.txt

@@ -0,0 +1,7 @@
+package
+
+internal fun </*0*/ T : kotlin.String?> foo(/*0*/ x: T): kotlin.Unit
+internal fun </*0*/ T : kotlin.CharSequence?> T.bar1(): kotlin.Unit
+internal fun kotlin.CharSequence?.bar2(): kotlin.Unit
+internal fun </*0*/ T : kotlin.CharSequence> T.bar3(): kotlin.Unit
+internal fun </*0*/ T, /*1*/ R> T.let(/*0*/ f: (T) -> R): R