From 0c0232f42b14b5587c43e5d653a7c9e726b0a1bc Mon Sep 17 00:00:00 2001
From: Alexander Udalov <Alexander.Udalov@jetbrains.com>
Date: Fri, 20 Jul 2012 17:39:09 +0400
Subject: [PATCH] Senseless null in when (KT-2457 frontend part)

---
 .../src/org/jetbrains/jet/lang/diagnostics/Errors.java |  1 +
 .../diagnostics/rendering/DefaultErrorMessages.java    |  1 +
 .../expressions/PatternMatchingTypingVisitor.java      |  5 +++++
 .../nullabilityAndAutoCasts/SenselessNullInWhen.kt     | 10 ++++++++++
 .../jet/checkers/JetDiagnosticsTestGenerated.java      |  5 +++++
 5 files changed, 22 insertions(+)
 create mode 100644 compiler/testData/diagnostics/tests/nullabilityAndAutoCasts/SenselessNullInWhen.kt

diff --git a/compiler/frontend/src/org/jetbrains/jet/lang/diagnostics/Errors.java b/compiler/frontend/src/org/jetbrains/jet/lang/diagnostics/Errors.java
index 2b6f6c33b92..fba88aadc4e 100644
--- a/compiler/frontend/src/org/jetbrains/jet/lang/diagnostics/Errors.java
+++ b/compiler/frontend/src/org/jetbrains/jet/lang/diagnostics/Errors.java
@@ -283,6 +283,7 @@ public interface Errors {
             DiagnosticFactory3.create(ERROR);
 
     DiagnosticFactory2<JetBinaryExpression, JetBinaryExpression, Boolean> SENSELESS_COMPARISON = DiagnosticFactory2.create(WARNING);
+    SimpleDiagnosticFactory<JetElement> SENSELESS_NULL_IN_WHEN = SimpleDiagnosticFactory.create(WARNING);
 
     DiagnosticFactory2<PsiElement, CallableMemberDescriptor, DeclarationDescriptor> OVERRIDING_FINAL_MEMBER = DiagnosticFactory2.create(ERROR);
     DiagnosticFactory3<JetModifierListOwner, Visibility, CallableMemberDescriptor, DeclarationDescriptor> CANNOT_WEAKEN_ACCESS_PRIVILEGE =
diff --git a/compiler/frontend/src/org/jetbrains/jet/lang/diagnostics/rendering/DefaultErrorMessages.java b/compiler/frontend/src/org/jetbrains/jet/lang/diagnostics/rendering/DefaultErrorMessages.java
index 71ebfa2ddea..25522dd56a2 100644
--- a/compiler/frontend/src/org/jetbrains/jet/lang/diagnostics/rendering/DefaultErrorMessages.java
+++ b/compiler/frontend/src/org/jetbrains/jet/lang/diagnostics/rendering/DefaultErrorMessages.java
@@ -345,6 +345,7 @@ public class DefaultErrorMessages {
         }, RENDER_TYPE, RENDER_TYPE);
 
         MAP.put(SENSELESS_COMPARISON, "Condition ''{0}'' is always ''{1}''", ELEMENT_TEXT, TO_STRING);
+        MAP.put(SENSELESS_NULL_IN_WHEN, "Expression under 'when' is never equal to null");
 
         MAP.put(OVERRIDING_FINAL_MEMBER, "''{0}'' in ''{1}'' is final and cannot be overridden", NAME, NAME);
         MAP.put(CANNOT_WEAKEN_ACCESS_PRIVILEGE, "Cannot weaken access privilege ''{0}'' for ''{1}'' in ''{2}''", TO_STRING, NAME, NAME);
diff --git a/compiler/frontend/src/org/jetbrains/jet/lang/types/expressions/PatternMatchingTypingVisitor.java b/compiler/frontend/src/org/jetbrains/jet/lang/types/expressions/PatternMatchingTypingVisitor.java
index f595a08fdc5..550e05fa088 100644
--- a/compiler/frontend/src/org/jetbrains/jet/lang/types/expressions/PatternMatchingTypingVisitor.java
+++ b/compiler/frontend/src/org/jetbrains/jet/lang/types/expressions/PatternMatchingTypingVisitor.java
@@ -330,6 +330,11 @@ public class PatternMatchingTypingVisitor extends ExpressionTypingVisitor {
                     return;
                 }
 
+                // check if the pattern is essentially a 'null' expression
+                if (type == JetStandardClasses.getNullableNothingType() && !subjectType.isNullable()) {
+                    context.trace.report(SENSELESS_NULL_IN_WHEN.on(reportErrorOn));
+                }
+
                 if (BasicExpressionTypingVisitor.isCastErased(subjectType, type, JetTypeChecker.INSTANCE)) {
                     context.trace.report(Errors.CANNOT_CHECK_FOR_ERASED.on(reportErrorOn, type));
                 }
diff --git a/compiler/testData/diagnostics/tests/nullabilityAndAutoCasts/SenselessNullInWhen.kt b/compiler/testData/diagnostics/tests/nullabilityAndAutoCasts/SenselessNullInWhen.kt
new file mode 100644
index 00000000000..8e48d129c13
--- /dev/null
+++ b/compiler/testData/diagnostics/tests/nullabilityAndAutoCasts/SenselessNullInWhen.kt
@@ -0,0 +1,10 @@
+//KT-2457 Verify error when comparing not null value with null in when
+
+package kt2457
+
+fun foo(i: Int) : Int =
+    when (i) {
+        1 -> 1
+        <!SENSELESS_NULL_IN_WHEN!>null<!> -> 1
+        else -> 1
+    }
diff --git a/compiler/tests/org/jetbrains/jet/checkers/JetDiagnosticsTestGenerated.java b/compiler/tests/org/jetbrains/jet/checkers/JetDiagnosticsTestGenerated.java
index ba8d41255e8..a07455b87fd 100644
--- a/compiler/tests/org/jetbrains/jet/checkers/JetDiagnosticsTestGenerated.java
+++ b/compiler/tests/org/jetbrains/jet/checkers/JetDiagnosticsTestGenerated.java
@@ -1481,6 +1481,11 @@ public class JetDiagnosticsTestGenerated extends AbstractDiagnosticsTestWithEage
                 doTest("compiler/testData/diagnostics/tests/nullabilityAndAutoCasts/ReceiverNullability.kt");
             }
             
+            @TestMetadata("SenselessNullInWhen.kt")
+            public void testSenselessNullInWhen() throws Exception {
+                doTest("compiler/testData/diagnostics/tests/nullabilityAndAutoCasts/SenselessNullInWhen.kt");
+            }
+            
         }
         
         @TestMetadata("compiler/testData/diagnostics/tests/objects")