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.

Actually, KT-22379 implies that we should clear data-flow which we got
from `checkCondition` (it contains information just that condition
expression is executed), while actual fix cleared data-flow after applyng
knowledge that condition should be 'false' after loop is finished.

KT-22379 Open
KT-27084 Fixed

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

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 4c8e3b4..212ccd3 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 @@
             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 @@
             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(

compiler/testData/diagnostics/tests/smartCasts/loops/whileNullAssignToSomething.kt

diff --git a/compiler/testData/diagnostics/tests/smartCasts/loops/whileNullAssignToSomething.kt b/compiler/testData/diagnostics/tests/smartCasts/loops/whileNullAssignToSomething.kt
index 44bb1f3..ba9432e 100644
--- a/compiler/testData/diagnostics/tests/smartCasts/loops/whileNullAssignToSomething.kt
+++ b/compiler/testData/diagnostics/tests/smartCasts/loops/whileNullAssignToSomething.kt
@@ -5,5 +5,5 @@
         if (i == 10) result = "non null"
         else i++
     }
-    result<!UNSAFE_CALL!>.<!>length
+    <!DEBUG_INFO_SMARTCAST!>result<!>.length
 }
\ No newline at end of file

compiler/util/src/org/jetbrains/kotlin/config/LanguageVersionSettings.kt

diff --git a/compiler/util/src/org/jetbrains/kotlin/config/LanguageVersionSettings.kt b/compiler/util/src/org/jetbrains/kotlin/config/LanguageVersionSettings.kt
index d6ee202..c122628 100644
--- a/compiler/util/src/org/jetbrains/kotlin/config/LanguageVersionSettings.kt
+++ b/compiler/util/src/org/jetbrains/kotlin/config/LanguageVersionSettings.kt
@@ -84,7 +84,6 @@
     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 @@
     RestrictReturnStatementTarget(KOTLIN_1_4, kind = BUG_FIX),
     NoConstantValueAttributeForNonConstVals(KOTLIN_1_4, 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),
 
     // Experimental features