[FIR] Add test cases to prove resolution of backlog tickets

^KT-41728 Fixed
^KT-46586 Fixed
^KT-49696 Fixed
^KT-51160 Fixed
^KT-53308 Fixed

compiler/testData/diagnostics/tests/smartCasts/varnotnull/capturedInlineModifiedBefore.fir.kt

@@ -0,0 +1,15 @@
+// WITH_STDLIB
+// ISSUE: KT-46586
+
+inline fun run(block: () -> Unit) = block()
+
+fun test() {
+    var label: String? = null
+    run {
+        label = "zzz"
+    }
+    if (label == null) {
+        label = "zzz"
+    }
+    label.isBlank()
+}

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

@@ -0,0 +1,15 @@
+// WITH_STDLIB
+// ISSUE: KT-46586
+
+inline fun run(block: () -> Unit) = block()
+
+fun test() {
+    var label: String? = null
+    run {
+        label = "zzz"
+    }
+    if (label == null) {
+        label = "zzz"
+    }
+    <!SMARTCAST_IMPOSSIBLE!>label<!>.isBlank()
+}

compiler/testData/diagnostics/tests/smartCasts/varnotnull/equalityAndIdentity.fir.kt

@@ -0,0 +1,39 @@
+// !OPT_IN: kotlin.contracts.ExperimentalContracts
+// WITH_STDLIB
+// ISSUE: KT-53308
+
+import kotlin.contracts.*
+
+fun <E> checkEquality(arg: E?) { contract { returns() implies (arg != null) } }
+fun <E> checkIdentity(arg: E?) { contract { <!ERROR_IN_CONTRACT_DESCRIPTION("NOT_IDENTITY operator call is illegal in contract description")!>returns() implies (arg !== null)<!> } }
+fun checkTrue(statement: Boolean) { contract { returns() implies statement } }
+fun checkFalse(statement: Boolean) { contract { returns() implies !statement } }
+
+fun consume(arg: String) {}
+
+fun test(a: String?) {
+    a.let {
+        checkEquality(it)
+        consume(it)
+    }
+    a.let {
+        checkIdentity(it)
+        consume(<!ARGUMENT_TYPE_MISMATCH!>it<!>)
+    }
+    a.let {
+        checkTrue(it != null)
+        consume(it)
+    }
+    a.let {
+        checkTrue(it !== null)
+        consume(it)
+    }
+    a.let {
+        checkFalse(it == null)
+        consume(it)
+    }
+    a.let {
+        checkFalse(it === null)
+        consume(it)
+    }
+}

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

@@ -0,0 +1,39 @@
+// !OPT_IN: kotlin.contracts.ExperimentalContracts
+// WITH_STDLIB
+// ISSUE: KT-53308
+
+import kotlin.contracts.*
+
+fun <E> checkEquality(arg: E?) { contract { returns() implies (arg != null) } }
+fun <E> checkIdentity(arg: E?) { contract { returns() implies (arg !== null) } }
+fun checkTrue(statement: Boolean) { contract { returns() implies statement } }
+fun checkFalse(statement: Boolean) { contract { returns() implies !statement } }
+
+fun consume(arg: String) {}
+
+fun test(a: String?) {
+    a.let {
+        checkEquality(it)
+        consume(<!DEBUG_INFO_SMARTCAST!>it<!>)
+    }
+    a.let {
+        checkIdentity(it)
+        consume(<!DEBUG_INFO_SMARTCAST!>it<!>)
+    }
+    a.let {
+        checkTrue(it != null)
+        consume(<!DEBUG_INFO_SMARTCAST!>it<!>)
+    }
+    a.let {
+        checkTrue(it !== null)
+        consume(<!TYPE_MISMATCH!>it<!>)
+    }
+    a.let {
+        checkFalse(it == null)
+        consume(<!DEBUG_INFO_SMARTCAST!>it<!>)
+    }
+    a.let {
+        checkFalse(it === null)
+        consume(<!TYPE_MISMATCH!>it<!>)
+    }
+}