Refine smart cast check for type parameters

compiler/frontend/src/org/jetbrains/kotlin/types/expressions/DataFlowAnalyzer.java

@@ -226,6 +226,22 @@ public class DataFlowAnalyzer {
             }
         }
 
+        // For cases like:
+        // fun bar(x: Any) {}
+        // fun <T : Any?> foo(x: T) {
+        //      if (x != null) {
+        //          bar(x) // Should be allowed with smart cast
+        //      }
+        // }
+        //
+        // It doesn't handled by upper code with getPossibleTypes because smart cast of T after `x != null` is still has same type T.
+        // But at the same time we're sure that `x` can't be null and just check for such cases manually
+        if (!c.dataFlowInfo.getNullability(dataFlowValue).canBeNull()
+                && JetTypeChecker.DEFAULT.isSubtypeOf(expressionType, TypeUtils.makeNullable(c.expectedType))) {
+            smartCastManager.recordCastOrError(expression, expressionType, c.trace, dataFlowValue.isPredictable(), false);
+            return expressionType;
+        }
+
         return null;
     }
 

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

@@ -0,0 +1,49 @@
+// !DIAGNOSTICS: -UNUSED_EXPRESSION,-UNUSED_VARIABLE,-UNUSED_PARAMETER,-ASSIGNED_BUT_NEVER_ACCESSED_VARIABLE,-UNUSED_VALUE
+
+fun <T : CharSequence> bar1(x: T) {}
+fun bar2(x: CharSequence) {}
+fun bar3(x: String) {}
+
+fun <T : CharSequence?> foo(x: T) {
+    var y1: CharSequence = ""
+    var y2: String = ""
+    if (x != null) {
+        if (<!SENSELESS_COMPARISON!>x != null<!>) {}
+
+        y1 = <!DEBUG_INFO_SMARTCAST!>x<!>
+        y2 = <!TYPE_MISMATCH!>x<!>
+
+        <!TYPE_INFERENCE_UPPER_BOUND_VIOLATED!>bar1<!>(x)
+        bar2(<!DEBUG_INFO_SMARTCAST!>x<!>)
+        bar3(<!TYPE_MISMATCH!>x<!>)
+    }
+
+    if (x is String) {
+        y1 = <!DEBUG_INFO_SMARTCAST!>x<!>
+        y2 = <!DEBUG_INFO_SMARTCAST!>x<!>
+
+        bar1(<!DEBUG_INFO_SMARTCAST!>x<!>)
+        bar2(<!DEBUG_INFO_SMARTCAST!>x<!>)
+        bar3(<!DEBUG_INFO_SMARTCAST!>x<!>)
+    }
+
+    if (x is CharSequence) {
+        y1 = <!DEBUG_INFO_SMARTCAST!>x<!>
+        y2 = <!TYPE_MISMATCH!>x<!>
+
+        bar1(<!DEBUG_INFO_SMARTCAST!>x<!>)
+        bar2(<!DEBUG_INFO_SMARTCAST!>x<!>)
+        bar3(<!TYPE_MISMATCH!>x<!>)
+    }
+
+    if (1 == 1) {
+        val y = x!!
+        <!TYPE_INFERENCE_UPPER_BOUND_VIOLATED!>bar1<!>(x)
+        bar2(<!DEBUG_INFO_SMARTCAST!>x<!>)
+        bar3(<!TYPE_MISMATCH!>x<!>)
+
+        <!TYPE_INFERENCE_UPPER_BOUND_VIOLATED!>bar1<!>(y)
+        bar2(<!DEBUG_INFO_SMARTCAST!>y<!>)
+        bar3(<!TYPE_MISMATCH!>y<!>)
+    }
+}

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

@@ -0,0 +1,6 @@
+package
+
+internal fun </*0*/ T : kotlin.CharSequence> bar1(/*0*/ x: T): kotlin.Unit
+internal fun bar2(/*0*/ x: kotlin.CharSequence): kotlin.Unit
+internal fun bar3(/*0*/ x: kotlin.String): kotlin.Unit
+internal fun </*0*/ T : kotlin.CharSequence?> foo(/*0*/ x: T): kotlin.Unit

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

@@ -28,9 +28,8 @@ class A<T : CharSequence?, E1 : T, E2: T?> {
 
         t = <!TYPE_MISMATCH!>y<!>
 
-        // Could be smart-cast
         if (y != null) {
-            t = <!TYPE_MISMATCH!>y<!>
+            t = <!DEBUG_INFO_SMARTCAST!>y<!>
         }
 
         if (tN != null) {

compiler/tests/org/jetbrains/kotlin/checkers/JetDiagnosticsTestGenerated.java

@@ -6167,6 +6167,12 @@ public class JetDiagnosticsTestGenerated extends AbstractJetDiagnosticsTest {
                     doTest(fileName);
                 }
 
+                @TestMetadata("smartCastsValueArgument.kt")
+                public void testSmartCastsValueArgument() throws Exception {
+                    String fileName = JetTestUtils.navigationMetadata("compiler/testData/diagnostics/tests/generics/nullability/smartCastsValueArgument.kt");
+                    doTest(fileName);
+                }
+
                 @TestMetadata("tpBoundsViolation.kt")
                 public void testTpBoundsViolation() throws Exception {
                     String fileName = JetTestUtils.navigationMetadata("compiler/testData/diagnostics/tests/generics/nullability/tpBoundsViolation.kt");