"Simplify comparison": remove if when possible after applying quickfix

#KT-25995 Fixed

idea/src/org/jetbrains/kotlin/idea/inspections/ConstantConditionIfInspection.kt

@@ -26,13 +26,17 @@ import org.jetbrains.kotlin.resolve.lazy.BodyResolveMode
 class ConstantConditionIfInspection : AbstractKotlinInspection() {
 
     override fun buildVisitor(holder: ProblemsHolder, isOnTheFly: Boolean): PsiElementVisitor {
-        return ifExpressionVisitor(fun(expression) {
-            val condition = expression.condition ?: return
+        return ifExpressionVisitor { expression -> collectFixesAndRegisterProblem(expression, holder) }
+    }
+
+    companion object {
+        private fun collectFixesAndRegisterProblem(expression: KtIfExpression, holder: ProblemsHolder?): List<ConstantConditionIfFix> {
+            val condition = expression.condition ?: return emptyList()
 
             val context = condition.analyze(BodyResolveMode.PARTIAL_WITH_CFA)
-            val constantValue = condition.constantBooleanValue(context) ?: return
+            val constantValue = condition.constantBooleanValue(context) ?: return emptyList()
 
-            val fixes = mutableListOf<LocalQuickFix>()
+            val fixes = mutableListOf<ConstantConditionIfFix>()
 
             if (expression.branch(constantValue) != null) {
                 val keepBraces = expression.isElseIf() && expression.branch(constantValue) is KtBlockExpression
@@ -43,39 +47,57 @@ class ConstantConditionIfInspection : AbstractKotlinInspection() {
                 fixes += RemoveFix()
             }
 
-            holder.registerProblem(condition,
-                                   "Condition is always '$constantValue'",
-                                   *fixes.toTypedArray())
-        })
+            holder?.registerProblem(
+                condition,
+                "Condition is always '$constantValue'",
+                *fixes.toTypedArray()
+            )
+
+            return fixes
+        }
+
+        fun applyFixIfSingle(ifExpression: KtIfExpression) {
+            collectFixesAndRegisterProblem(ifExpression, null).singleOrNull()?.applyFix(ifExpression)
+        }
+    }
+
+    private interface ConstantConditionIfFix : LocalQuickFix {
+        fun applyFix(ifExpression: KtIfExpression)
     }
 
     private class SimplifyFix(
-            private val conditionValue: Boolean,
-            private val isUsedAsExpression: Boolean,
-            private val keepBraces: Boolean
-    ) : LocalQuickFix {
+        private val conditionValue: Boolean,
+        private val isUsedAsExpression: Boolean,
+        private val keepBraces: Boolean
+    ) : ConstantConditionIfFix {
         override fun getFamilyName() = name
 
         override fun getName() = "Simplify expression"
 
         override fun applyFix(project: Project, descriptor: ProblemDescriptor) {
             val ifExpression = descriptor.psiElement.getParentOfType<KtIfExpression>(strict = true) ?: return
+            applyFix(ifExpression)
+        }
 
+        override fun applyFix(ifExpression: KtIfExpression) {
             val branch = ifExpression.branch(conditionValue)?.let {
                 if (keepBraces) it else it.unwrapBlockOrParenthesis()
             } ?: return
-
             ifExpression.replaceWithBranch(branch, isUsedAsExpression, keepBraces)
         }
     }
 
-    private class RemoveFix : LocalQuickFix {
+    private class RemoveFix : ConstantConditionIfFix {
         override fun getFamilyName() = name
 
         override fun getName() = "Delete expression"
 
         override fun applyFix(project: Project, descriptor: ProblemDescriptor) {
             val ifExpression = descriptor.psiElement.getParentOfType<KtIfExpression>(strict = true) ?: return
+            applyFix(ifExpression)
+        }
+
+        override fun applyFix(ifExpression: KtIfExpression) {
             ifExpression.delete()
         }
     }
@@ -103,8 +125,7 @@ fun KtExpression.replaceWithBranch(branch: KtExpression, isUsedAsExpression: Boo
             if (firstChildSibling != lastChild) {
                 if (keepBraces) {
                     parent.addAfter(branch, this)
-                }
-                else {
+                } else {
                     parent.addRangeAfter(firstChildSibling, lastChild.prevSibling, this)
                 }
             }

idea/src/org/jetbrains/kotlin/idea/quickfix/SimplifyComparisonFix.kt

@@ -22,12 +22,11 @@ import com.intellij.openapi.project.Project
 import org.jetbrains.kotlin.diagnostics.Diagnostic
 import org.jetbrains.kotlin.diagnostics.DiagnosticWithParameters2
 import org.jetbrains.kotlin.idea.core.replaced
+import org.jetbrains.kotlin.idea.inspections.ConstantConditionIfInspection
 import org.jetbrains.kotlin.idea.intentions.SimplifyBooleanWithConstantsIntention
-import org.jetbrains.kotlin.psi.KtBinaryExpression
-import org.jetbrains.kotlin.psi.KtExpression
-import org.jetbrains.kotlin.psi.KtFile
-import org.jetbrains.kotlin.psi.KtPsiFactory
+import org.jetbrains.kotlin.psi.*
 import org.jetbrains.kotlin.psi.psiUtil.getNonStrictParentOfType
+import org.jetbrains.kotlin.psi.psiUtil.getStrictParentOfType
 
 class SimplifyComparisonFix(element: KtExpression, val value: Boolean) : KotlinQuickFixAction<KtExpression>(element) {
     override fun getFamilyName() = "Simplify $element to '$value'"
@@ -43,10 +42,12 @@ class SimplifyComparisonFix(element: KtExpression, val value: Boolean) : KotlinQ
         val simplifyIntention = SimplifyBooleanWithConstantsIntention()
         if (booleanExpression != null && simplifyIntention.isApplicableTo(booleanExpression)) {
             simplifyIntention.applyTo(booleanExpression, editor)
-        }
-        else {
+        } else {
             simplifyIntention.removeRedundantAssertion(result)
         }
+
+        val ifExpression = result.getStrictParentOfType<KtIfExpression>()?.takeIf { it.condition == result }
+        if (ifExpression != null) ConstantConditionIfInspection.applyFixIfSingle(ifExpression)
     }
 
     companion object : KotlinSingleIntentionActionFactory() {

idea/testData/quickfix/simplifyComparison/doubleNull.kt

@@ -5,7 +5,9 @@ fun foo(x: String?) {
     }
     else {
         if (<caret>x == null) {
-
+            bar()
         }
     }
-}
+}
+
+fun bar() {}

idea/testData/quickfix/simplifyComparison/doubleNull.kt.after

@@ -4,8 +4,7 @@ fun foo(x: String?) {
 
     }
     else {
-        if (false) {
-
-        }
     }
-}
+}
+
+fun bar() {}

idea/testData/quickfix/simplifyComparison/notNull.kt

@@ -1,6 +1,8 @@
 // "Simplify comparison" "true"
 fun foo(x: Int) {
     if (<caret>x != null) {
-
+        bar()
     }
-}
+}
+
+fun bar() {}

idea/testData/quickfix/simplifyComparison/notNull.kt.after

@@ -1,6 +1,6 @@
 // "Simplify comparison" "true"
 fun foo(x: Int) {
-    if (true) {
+    bar()
+}
 
-    }
-}
+fun bar() {}