Moved shouldUseInputVariable from Transformation to TransformationMatcher and changed its semantics a bit

idea/src/org/jetbrains/kotlin/idea/intentions/loopToCallChain/commonUtils.kt

@@ -116,6 +116,10 @@ fun KtVariableDeclaration.hasWriteUsages(inElement: KtElement): Boolean {
     }
 }
 
+fun KtCallableDeclaration.hasDifferentSetsOfUsages(elements1: Collection<KtElement>, elements2: Collection<KtElement>): Boolean {
+    return countUsages(elements1 - elements2) != countUsages(elements2 - elements1)
+}
+
 fun KtExpressionWithLabel.targetLoop(): KtLoopExpression? {
     val label = getTargetLabel()
     if (label == null) {

idea/src/org/jetbrains/kotlin/idea/intentions/loopToCallChain/interfaces.kt

@@ -60,9 +60,6 @@ interface Transformation {
 
     val chainCallCount: Int
         get() = 1
-
-    val shouldUseInputVariable: Boolean
-        get() = true
 }
 
 /**
@@ -122,6 +119,12 @@ interface TransformationMatcher {
      */
     val indexVariableAllowed: Boolean
 
+    /**
+     * Override with false value if the result of the match should be rejected if the matched part uses neither the input variable nor the index variable.
+     */
+    val shouldUseInputVariables: Boolean
+        get() = true
+
     /**
      * Implementors should return true if they match some constructs with expression-embedded break or continue.
      * In this case they are obliged to deal with them and filter out invalid cases.

idea/src/org/jetbrains/kotlin/idea/intentions/loopToCallChain/matchAndConvert.kt

@@ -87,17 +87,23 @@ fun match(loop: KtForExpression, useLazySequence: Boolean): MatchResult? {
         MatchersLoop@
         for (matcher in MatcherRegistrar.matchers) {
             if (state.indexVariable != null && !matcher.indexVariableAllowed) continue
+            if (matcher.shouldUseInputVariables && !inputVariableUsed && state.indexVariable == null) continue
 
             val match = matcher.match(state)
             if (match != null) {
-                if (!inputVariableUsed && match.allTransformations.any { it.shouldUseInputVariable }) return null
-
                 when (match) {
                     is TransformationMatch.Sequence -> {
                         // check that old input variable is not needed anymore
                         var newState = match.newState
                         if (state.inputVariable != newState.inputVariable && state.inputVariable.hasUsages(newState.statements)) return null
 
+                        if (matcher.shouldUseInputVariables
+                            && !state.inputVariable.hasDifferentSetsOfUsages(state.statements, newState.statements)
+                            && !(state.indexVariable?.hasDifferentSetsOfUsages(state.statements, newState.statements) ?: false)) {
+                            // matched part of the loop uses neither input variable nor index variable
+                            continue@MatchersLoop
+                        }
+
                         if (state.indexVariable != null && match.sequenceTransformations.any { it.affectsIndex }) {
                             // index variable is still needed but index in the new sequence is different
                             if (state.indexVariable!!.hasUsages(newState.statements)) return null

idea/src/org/jetbrains/kotlin/idea/intentions/loopToCallChain/result/CountTransformation.kt

@@ -40,9 +40,6 @@ class CountTransformation(
     override val presentation: String
         get() = "count" + (if (filter != null) "{}" else "()")
 
-    override val shouldUseInputVariable: Boolean
-        get() = false
-
     override fun generateCode(chainedCallGenerator: ChainedCallGenerator): KtExpression {
         val call = if (filter != null) {
             val lambda = generateLambda(inputVariable, filter)
@@ -72,6 +69,9 @@ class CountTransformation(
         override val indexVariableAllowed: Boolean
             get() = false
 
+        override val shouldUseInputVariables: Boolean
+            get() = false
+
         override fun match(state: MatchingState): TransformationMatch.Result? {
             val operand = state.statements.singleOrNull()?.isPlusPlusOf() ?: return null
             val initialization = operand.isVariableInitializedBeforeLoop(state.outerLoop, checkNoOtherUsagesInLoop = true) ?: return null

idea/src/org/jetbrains/kotlin/idea/intentions/loopToCallChain/result/FindTransformationMatcher.kt

@@ -54,6 +54,9 @@ object FindTransformationMatcher : TransformationMatcher {
     override val indexVariableAllowed: Boolean
         get() = false
 
+    override val shouldUseInputVariables: Boolean
+        get() = false
+
     override fun match(state: MatchingState): TransformationMatch.Result? {
         return matchWithFilterBefore(state, null)
     }
@@ -128,9 +131,6 @@ object FindTransformationMatcher : TransformationMatcher {
         override val chainCallCount: Int
             get() = generator.chainCallCount
 
-        override val shouldUseInputVariable: Boolean
-            get() = false
-
         override fun generateCode(chainedCallGenerator: ChainedCallGenerator): KtExpression {
             return generator.generate(chainedCallGenerator)
         }
@@ -157,9 +157,6 @@ object FindTransformationMatcher : TransformationMatcher {
         override val chainCallCount: Int
             get() = generator.chainCallCount
 
-        override val shouldUseInputVariable: Boolean
-            get() = false
-
         override fun generateCode(chainedCallGenerator: ChainedCallGenerator): KtExpression {
             return generator.generate(chainedCallGenerator)
         }

idea/src/org/jetbrains/kotlin/idea/intentions/loopToCallChain/sequence/IntroduceIndexMatcher.kt

@@ -37,6 +37,9 @@ object IntroduceIndexMatcher : TransformationMatcher {
     override val indexVariableAllowed: Boolean
         get() = false // old index variable is still needed - cannot introduce another one
 
+    override val shouldUseInputVariables: Boolean
+        get() = false
+
     override fun match(state: MatchingState): TransformationMatch.Sequence? {
         for (statement in state.statements) {
             val unaryExpressions = statement.collectDescendantsOfType<KtUnaryExpression>(

idea/testData/intentions/loopToCallChain/filter_inputVariableNotUsed.kt

@@ -0,0 +1,12 @@
+// WITH_RUNTIME
+// IS_APPLICABLE: false
+// IS_APPLICABLE_2: false
+import java.util.*
+
+fun foo(list: List<String>) {
+    val random = Random()
+    <caret>for (s in list) {
+        if (random.nextBoolean()) continue
+        print(s)
+    }
+}

idea/tests/org/jetbrains/kotlin/idea/intentions/IntentionTest2Generated.java

@@ -473,6 +473,12 @@ public class IntentionTest2Generated extends AbstractIntentionTest2 {
         doTest(fileName);
     }
 
+    @TestMetadata("filter_inputVariableNotUsed.kt")
+    public void testFilter_inputVariableNotUsed() throws Exception {
+        String fileName = KotlinTestUtils.navigationMetadata("idea/testData/intentions/loopToCallChain/filter_inputVariableNotUsed.kt");
+        doTest(fileName);
+    }
+
     @TestMetadata("filter_mergeMultiple.kt")
     public void testFilter_mergeMultiple() throws Exception {
         String fileName = KotlinTestUtils.navigationMetadata("idea/testData/intentions/loopToCallChain/filter_mergeMultiple.kt");

idea/tests/org/jetbrains/kotlin/idea/intentions/IntentionTestGenerated.java

@@ -7591,6 +7591,12 @@ public class IntentionTestGenerated extends AbstractIntentionTest {
             doTest(fileName);
         }
 
+        @TestMetadata("filter_inputVariableNotUsed.kt")
+        public void testFilter_inputVariableNotUsed() throws Exception {
+            String fileName = KotlinTestUtils.navigationMetadata("idea/testData/intentions/loopToCallChain/filter_inputVariableNotUsed.kt");
+            doTest(fileName);
+        }
+
         @TestMetadata("filter_mergeMultiple.kt")
         public void testFilter_mergeMultiple() throws Exception {
             String fileName = KotlinTestUtils.navigationMetadata("idea/testData/intentions/loopToCallChain/filter_mergeMultiple.kt");