From 6065095e2486d23fbda804f36ccda653104de8ef Mon Sep 17 00:00:00 2001
From: Dmitry Savvinov <dmitry.savvinov@jetbrains.com>
Date: Mon, 24 Sep 2018 18:50:00 +0300
Subject: [PATCH] Fix too aggressive data-flow clearing of loop-assigned vars

This is effectively a revert of
447c127036b9902de4f9f7f4841684a2a40be3b9, which was an (incorrect) fix
for KT-22379.

The bug was that we've cleared data-flow info for assigned variables
*after* knowledge that loop condition if 'false' was applied (we can
claim that if loop has no jump-outs). Therefore, we broke smartcasts in
the innocent code like that:

  var x: Int? = null
  while (x == null) {
      x = readPotentiallyNullableInt()
  }
  // x should be non-null here

Commit reverts that "fix" for 1.3.0 and postpones deprecation until 1.4

KT-22379 Open
KT-27084 Fixed
---
 .../ControlStructureTypingVisitor.java           | 16 ++--------------
 .../loops/whileNullAssignToSomething.kt          |  2 +-
 .../kotlin/config/LanguageVersionSettings.kt     |  3 ++-
 3 files changed, 5 insertions(+), 16 deletions(-)

diff --git a/compiler/frontend/src/org/jetbrains/kotlin/types/expressions/ControlStructureTypingVisitor.java b/compiler/frontend/src/org/jetbrains/kotlin/types/expressions/ControlStructureTypingVisitor.java
index 4c8e3b43c56..212ccd3f53d 100644
--- a/compiler/frontend/src/org/jetbrains/kotlin/types/expressions/ControlStructureTypingVisitor.java
+++ b/compiler/frontend/src/org/jetbrains/kotlin/types/expressions/ControlStructureTypingVisitor.java
@@ -286,16 +286,9 @@ public class ControlStructureTypingVisitor extends ExpressionTypingVisitor {
             dataFlowInfo = dataFlowInfo.and(loopVisitor.clearDataFlowInfoForAssignedLocalVariables(bodyTypeInfo.getJumpFlowInfo(),
                                                                                                    components.languageVersionSettings));
         }
-
-        DataFlowInfo conservativeInfoAfterLoop =
-                components.languageVersionSettings.supportsFeature(LanguageFeature.SoundSmartcastFromLoopConditionForLoopAssignedVariables)
-                ? loopVisitor.clearDataFlowInfoForAssignedLocalVariables(dataFlowInfo, components.languageVersionSettings)
-                : dataFlowInfo;
-
-
         return components.dataFlowAnalyzer
                 .checkType(bodyTypeInfo.replaceType(components.builtIns.getUnitType()), expression, contextWithExpectedType)
-                .replaceDataFlowInfo(conservativeInfoAfterLoop);
+                .replaceDataFlowInfo(dataFlowInfo);
     }
 
     private boolean containsJumpOutOfLoop(@NotNull KtExpression expression, ExpressionTypingContext context) {
@@ -466,14 +459,9 @@ public class ControlStructureTypingVisitor extends ExpressionTypingVisitor {
             bodyTypeInfo = loopRangeInfo;
         }
 
-        DataFlowInfo conservativeInfoAfterLoop =
-                components.languageVersionSettings.supportsFeature(LanguageFeature.SoundSmartcastFromLoopConditionForLoopAssignedVariables)
-                ? loopVisitor.clearDataFlowInfoForAssignedLocalVariables(loopRangeInfo.getDataFlowInfo(), components.languageVersionSettings)
-                : loopRangeInfo.getDataFlowInfo();
-
         return components.dataFlowAnalyzer
                 .checkType(bodyTypeInfo.replaceType(components.builtIns.getUnitType()), expression, contextWithExpectedType)
-                .replaceDataFlowInfo(conservativeInfoAfterLoop);
+                .replaceDataFlowInfo(loopRangeInfo.getDataFlowInfo());
     }
 
     private VariableDescriptor createLoopParameterDescriptor(
diff --git a/compiler/testData/diagnostics/tests/smartCasts/loops/whileNullAssignToSomething.kt b/compiler/testData/diagnostics/tests/smartCasts/loops/whileNullAssignToSomething.kt
index 44bb1f3ef76..ba9432e1dab 100644
--- a/compiler/testData/diagnostics/tests/smartCasts/loops/whileNullAssignToSomething.kt
+++ b/compiler/testData/diagnostics/tests/smartCasts/loops/whileNullAssignToSomething.kt
@@ -5,5 +5,5 @@ fun main(args: Array<String>) {
         if (i == 10) result = "non null"
         else i++
     }
-    result<!UNSAFE_CALL!>.<!>length
+    <!DEBUG_INFO_SMARTCAST!>result<!>.length
 }
\ No newline at end of file
diff --git a/compiler/util/src/org/jetbrains/kotlin/config/LanguageVersionSettings.kt b/compiler/util/src/org/jetbrains/kotlin/config/LanguageVersionSettings.kt
index 69eae3b4ad8..d8a7f5096e0 100644
--- a/compiler/util/src/org/jetbrains/kotlin/config/LanguageVersionSettings.kt
+++ b/compiler/util/src/org/jetbrains/kotlin/config/LanguageVersionSettings.kt
@@ -83,7 +83,6 @@ enum class LanguageFeature(
     NormalizeConstructorCalls(KOTLIN_1_3),
     StrictJavaNullabilityAssertions(KOTLIN_1_3, kind = BUG_FIX),
     SoundSmartcastForEnumEntries(KOTLIN_1_3, kind = BUG_FIX),
-    SoundSmartcastFromLoopConditionForLoopAssignedVariables(KOTLIN_1_3, kind = BUG_FIX),
     DslMarkerOnFunctionTypeReceiver(KOTLIN_1_4, kind = BUG_FIX),
     ProhibitErroneousExpressionsInAnnotationsWithUseSiteTargets(KOTLIN_1_3, kind = BUG_FIX),
     NewCapturedReceiverFieldNamingConvention(KOTLIN_1_3, kind = BUG_FIX),
@@ -94,6 +93,8 @@ enum class LanguageFeature(
     NoConstantValueAttributeForNonConstVals(KOTLIN_1_4, kind = BUG_FIX),
 
     ProperVisibilityForCompanionObjectInstanceField(sinceVersion = null, kind = BUG_FIX),
+    // Temporarily disabled, see KT-27084/KT-22379
+    SoundSmartcastFromLoopConditionForLoopAssignedVariables(sinceVersion = null, kind = BUG_FIX),
 
     ProperIeee754Comparisons(sinceVersion = null, defaultState = State.DISABLED, kind = BUG_FIX),