From 051ad0f79e5a44095726a727f30b85b3a4e28cb9 Mon Sep 17 00:00:00 2001
From: Dmitry Savvinov <dmitry.savvinov@jetbrains.com>
Date: Wed, 5 Sep 2018 14:30:32 +0300
Subject: [PATCH] Fix unsound smartcast due to returns(null) in safecall

^KT-26382 Fixed
---
 .../contracts/EffectsExtractingVisitor.kt     | 21 +++++++++++++++----
 .../smartcasts/safecallAndReturnsNull.kt      |  2 +-
 2 files changed, 18 insertions(+), 5 deletions(-)

diff --git a/compiler/frontend/src/org/jetbrains/kotlin/contracts/EffectsExtractingVisitor.kt b/compiler/frontend/src/org/jetbrains/kotlin/contracts/EffectsExtractingVisitor.kt
index c4811e108f9..519b73f6987 100644
--- a/compiler/frontend/src/org/jetbrains/kotlin/contracts/EffectsExtractingVisitor.kt
+++ b/compiler/frontend/src/org/jetbrains/kotlin/contracts/EffectsExtractingVisitor.kt
@@ -19,12 +19,11 @@ package org.jetbrains.kotlin.contracts
 import org.jetbrains.kotlin.builtins.DefaultBuiltIns
 import org.jetbrains.kotlin.contracts.interpretation.ContractInterpretationDispatcher
 import org.jetbrains.kotlin.contracts.model.Computation
+import org.jetbrains.kotlin.contracts.model.ConditionalEffect
+import org.jetbrains.kotlin.contracts.model.ESEffect
 import org.jetbrains.kotlin.contracts.model.Functor
 import org.jetbrains.kotlin.contracts.model.functors.*
-import org.jetbrains.kotlin.contracts.model.structure.CallComputation
-import org.jetbrains.kotlin.contracts.model.structure.ESConstant
-import org.jetbrains.kotlin.contracts.model.structure.UNKNOWN_COMPUTATION
-import org.jetbrains.kotlin.contracts.model.structure.lift
+import org.jetbrains.kotlin.contracts.model.structure.*
 import org.jetbrains.kotlin.contracts.parsing.isEqualsDescriptor
 import org.jetbrains.kotlin.descriptors.FunctionDescriptor
 import org.jetbrains.kotlin.descriptors.ModuleDescriptor
@@ -114,6 +113,20 @@ class EffectsExtractingVisitor(
         )
     }
 
+    override fun visitSafeQualifiedExpression(expression: KtSafeQualifiedExpression, data: Unit?): Computation {
+        val computation = super.visitSafeQualifiedExpression(expression, data)
+        if (computation === UNKNOWN_COMPUTATION) return computation
+
+        // For safecall any clauses of form 'returns(null) -> ...' are incorrect, because safecall can return
+        // null bypassing function's contract, so we have to filter them out
+
+        fun ESEffect.containsReturnsNull(): Boolean =
+            this == ESReturns(ESConstant.NULL) || this is ConditionalEffect && this.simpleEffect.containsReturnsNull()
+
+        val effectsWithoutReturnsNull = computation.effects.filter { !it.containsReturnsNull() }
+        return CallComputation(computation.type, effectsWithoutReturnsNull)
+    }
+
     override fun visitBinaryExpression(expression: KtBinaryExpression, data: Unit): Computation {
         val left = extractOrGetCached(expression.left ?: return UNKNOWN_COMPUTATION)
         val right = extractOrGetCached(expression.right ?: return UNKNOWN_COMPUTATION)
diff --git a/compiler/testData/diagnostics/testsWithStdLib/contracts/smartcasts/safecallAndReturnsNull.kt b/compiler/testData/diagnostics/testsWithStdLib/contracts/smartcasts/safecallAndReturnsNull.kt
index cd3cb396769..96916e514e9 100644
--- a/compiler/testData/diagnostics/testsWithStdLib/contracts/smartcasts/safecallAndReturnsNull.kt
+++ b/compiler/testData/diagnostics/testsWithStdLib/contracts/smartcasts/safecallAndReturnsNull.kt
@@ -12,6 +12,6 @@ fun Any.nullWhenString(): Any? {
 
 fun test(x: Int?) {
     if (x?.nullWhenString() == null) {
-        <!DEBUG_INFO_SMARTCAST!>x<!>.length
+        x.<!UNRESOLVED_REFERENCE!>length<!>
     }
 }
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