Add "Redundant nullable return type" inspection

^KT-19321 Fixed

idea/testData/inspectionsLocal/redundantNullableReturnType/.inspection

@@ -0,0 +1 @@
+org.jetbrains.kotlin.idea.inspections.RedundantNullableReturnTypeInspection

idea/testData/inspectionsLocal/redundantNullableReturnType/function/blockBody.kt

@@ -0,0 +1,5 @@
+// PROBLEM: 'foo' always returns non-null type
+// WITH_RUNTIME
+fun foo(xs: List<Int>): Int?<caret> {
+    return xs.first()
+}

idea/testData/inspectionsLocal/redundantNullableReturnType/function/blockBody.kt.after

@@ -0,0 +1,5 @@
+// PROBLEM: 'foo' always returns non-null type
+// WITH_RUNTIME
+fun foo(xs: List<Int>): Int {
+    return xs.first()
+}

idea/testData/inspectionsLocal/redundantNullableReturnType/function/blockBodyReturnsNullable.kt

@@ -0,0 +1,9 @@
+// PROBLEM: none
+// WITH_RUNTIME
+fun foo(xs: List<Int>, b: Boolean): Int?<caret> {
+    if (b) {
+        return xs.first()
+    } else {
+        return xs.lastOrNull()
+    }
+}

idea/testData/inspectionsLocal/redundantNullableReturnType/function/blockBodyWithSmartCast.kt

@@ -0,0 +1,8 @@
+// PROBLEM: 'foo' always returns non-null type
+fun foo(i: Int?): Int?<caret> {
+    if (i != null) {
+        return i
+    } else {
+        return 0
+    }
+}

idea/testData/inspectionsLocal/redundantNullableReturnType/function/blockBodyWithSmartCast.kt.after

@@ -0,0 +1,8 @@
+// PROBLEM: 'foo' always returns non-null type
+fun foo(i: Int?): Int {
+    if (i != null) {
+        return i
+    } else {
+        return 0
+    }
+}

idea/testData/inspectionsLocal/redundantNullableReturnType/function/notNullableReturnType.kt

@@ -0,0 +1,2 @@
+// PROBLEM: none
+fun foo(): String<caret> = ""

idea/testData/inspectionsLocal/redundantNullableReturnType/function/overridable.kt

@@ -0,0 +1,4 @@
+// PROBLEM: none
+abstract class Foo {
+    open fun foo(): String?<caret> = ""
+}

idea/testData/inspectionsLocal/redundantNullableReturnType/function/singleExpressionBody.kt

@@ -0,0 +1,3 @@
+// PROBLEM: 'foo' always returns non-null type
+// WITH_RUNTIME
+fun foo(xs: List<Int>): Int?<caret> = xs.first()

idea/testData/inspectionsLocal/redundantNullableReturnType/function/singleExpressionBody.kt.after

@@ -0,0 +1,3 @@
+// PROBLEM: 'foo' always returns non-null type
+// WITH_RUNTIME
+fun foo(xs: List<Int>): Int = xs.first()

idea/testData/inspectionsLocal/redundantNullableReturnType/function/singleExpressionBodyReturnsNullable.kt

@@ -0,0 +1,3 @@
+// PROBLEM: none
+// WITH_RUNTIME
+fun foo(xs: List<Int>, b: Boolean): Int?<caret> = if (b) xs.first() else xs.lastOrNull()

idea/testData/inspectionsLocal/redundantNullableReturnType/property/getter.kt

@@ -0,0 +1,3 @@
+// PROBLEM: 'foo' is always non-null type
+val foo: Int?<caret>
+    get() = 1

idea/testData/inspectionsLocal/redundantNullableReturnType/property/getter.kt.after

@@ -0,0 +1,3 @@
+// PROBLEM: 'foo' is always non-null type
+val foo: Int
+    get() = 1

idea/testData/inspectionsLocal/redundantNullableReturnType/property/getterWithBody.kt

@@ -0,0 +1,5 @@
+// PROBLEM: 'foo' is always non-null type
+val foo: Int?<caret>
+    get() {
+        return 1
+    }

idea/testData/inspectionsLocal/redundantNullableReturnType/property/getterWithBody.kt.after

@@ -0,0 +1,5 @@
+// PROBLEM: 'foo' is always non-null type
+val foo: Int
+    get() {
+        return 1
+    }

idea/testData/inspectionsLocal/redundantNullableReturnType/property/initializer.kt

@@ -0,0 +1,2 @@
+// PROBLEM: 'foo' is always non-null type
+val foo: String?<caret> = ""

idea/testData/inspectionsLocal/redundantNullableReturnType/property/initializer.kt.after

@@ -0,0 +1,2 @@
+// PROBLEM: 'foo' is always non-null type
+val foo: String = ""

idea/testData/inspectionsLocal/redundantNullableReturnType/property/var.kt

@@ -0,0 +1,2 @@
+// PROBLEM: none
+var foo: String?<caret> = ""