Add multiline-loop to complement multiline-if-else

CHANGELOG.md

@@ -105,7 +105,9 @@ This project adheres to [Semantic Versioning](https://semver.org/).
 
 * Add new experimental rule `function-type-modifier-spacing` rule - [#2216](https://github.com/pinterest/ktlint/pull/2216), by @t-kameyama
 
-* Define `EditorConfigOverride` for dynamically loaded ruleset - [#2194](https://github.com/pinterest/ktlint/pull/2194), by @paul-dingemans  
+* Add new experimental rule `multiline-loop` rule - [#2298](https://github.com/pinterest/ktlint/pull/2298), by @hendraanggrian
+
+* Define `EditorConfigOverride` for dynamically loaded ruleset - [#2194](https://github.com/pinterest/ktlint/pull/2194), by @paul-dingemans
   The `EditorConfigOverride` parameter of the `KtlintRuleEngine` can be defined using the factory method `EditorConfigOverride.from(vararg properties: Pair<EditorConfigProperty<*>, *>)`. This requires the `EditorConfigProperty`'s to be available at compile time. Some common `EditorConfigProperty`'s are defined in `ktlint-rule-engine-core` which is loaded as transitive dependency of `ktlint-rule-engine` and as of that are available at compile.
   If an `EditorConfigProperty` is defined in a `Rule` that is only provided via a runtime dependency, it gets a bit more complicated. The `ktlint-api-consumer` example has now been updated to show how the `EditorConfigProperty` can be retrieved from the `Rule`.
 

documentation/snapshot/docs/rules/experimental.md

@@ -480,3 +480,24 @@ Enforce a single whitespace between the modifier list and the function type.
     ```
 
 Rule id: `function-type-modifier-spacing` (`standard` rule set)
+
+## Multiline loop
+
+Braces required for multiline for, while, and do statements.
+
+=== "[:material-heart:](#) Ktlint"
+
+    ```kotlin
+    for (i in 1..10) {
+        println(i)
+    }
+    ```
+
+=== "[:material-heart-off-outline:](#) Disallowed"
+
+    ```kotlin
+    for (i in 1..10)
+        println(i)
+    ```
+
+Rule id: `multiline-loop` (`standard` rule set)

ktlint-ruleset-standard/api/ktlint-ruleset-standard.api

@@ -397,6 +397,16 @@ public final class com/pinterest/ktlint/ruleset/standard/rules/MultiLineIfElseRu
 	public static final fun getMULTI_LINE_IF_ELSE_RULE_ID ()Lcom/pinterest/ktlint/rule/engine/core/api/RuleId;
 }
 
+public final class com/pinterest/ktlint/ruleset/standard/rules/MultiLineLoopRule : com/pinterest/ktlint/ruleset/standard/StandardRule {
+	public fun <init> ()V
+	public fun beforeFirstNode (Lcom/pinterest/ktlint/rule/engine/core/api/editorconfig/EditorConfig;)V
+	public fun beforeVisitChildNodes (Lorg/jetbrains/kotlin/com/intellij/lang/ASTNode;ZLkotlin/jvm/functions/Function3;)V
+}
+
+public final class com/pinterest/ktlint/ruleset/standard/rules/MultiLineLoopRuleKt {
+	public static final fun getMULTI_LINE_LOOP_RULE_ID ()Lcom/pinterest/ktlint/rule/engine/core/api/RuleId;
+}
+
 public final class com/pinterest/ktlint/ruleset/standard/rules/MultilineExpressionWrappingRule : com/pinterest/ktlint/ruleset/standard/StandardRule, com/pinterest/ktlint/rule/engine/core/api/Rule$OfficialCodeStyle {
 	public fun <init> ()V
 	public fun beforeFirstNode (Lcom/pinterest/ktlint/rule/engine/core/api/editorconfig/EditorConfig;)V

ktlint-ruleset-standard/src/main/kotlin/com/pinterest/ktlint/ruleset/standard/StandardRuleSetProvider.kt

@@ -39,6 +39,7 @@ import com.pinterest.ktlint.ruleset.standard.rules.MaxLineLengthRule
 import com.pinterest.ktlint.ruleset.standard.rules.ModifierListSpacingRule
 import com.pinterest.ktlint.ruleset.standard.rules.ModifierOrderRule
 import com.pinterest.ktlint.ruleset.standard.rules.MultiLineIfElseRule
+import com.pinterest.ktlint.ruleset.standard.rules.MultiLineLoopRule
 import com.pinterest.ktlint.ruleset.standard.rules.MultilineExpressionWrappingRule
 import com.pinterest.ktlint.ruleset.standard.rules.NoBlankLineBeforeRbraceRule
 import com.pinterest.ktlint.ruleset.standard.rules.NoBlankLineInListRule
@@ -129,6 +130,7 @@ public class StandardRuleSetProvider : RuleSetProviderV3(RuleSetId.STANDARD) {
             RuleProvider { ModifierListSpacingRule() },
             RuleProvider { ModifierOrderRule() },
             RuleProvider { MultiLineIfElseRule() },
+            RuleProvider { MultiLineLoopRule() },
             RuleProvider { MultilineExpressionWrappingRule() },
             RuleProvider { NoBlankLineBeforeRbraceRule() },
             RuleProvider { NoBlankLineInListRule() },

ktlint-ruleset-standard/src/main/kotlin/com/pinterest/ktlint/ruleset/standard/rules/MultiLineLoopRule.kt

@@ -0,0 +1,127 @@
+package com.pinterest.ktlint.ruleset.standard.rules
+
+import com.pinterest.ktlint.rule.engine.core.api.ElementType.BLOCK
+import com.pinterest.ktlint.rule.engine.core.api.ElementType.BODY
+import com.pinterest.ktlint.rule.engine.core.api.ElementType.DO_KEYWORD
+import com.pinterest.ktlint.rule.engine.core.api.ElementType.LBRACE
+import com.pinterest.ktlint.rule.engine.core.api.ElementType.RBRACE
+import com.pinterest.ktlint.rule.engine.core.api.ElementType.RPAR
+import com.pinterest.ktlint.rule.engine.core.api.IndentConfig
+import com.pinterest.ktlint.rule.engine.core.api.RuleId
+import com.pinterest.ktlint.rule.engine.core.api.SinceKtlint
+import com.pinterest.ktlint.rule.engine.core.api.SinceKtlint.Status.EXPERIMENTAL
+import com.pinterest.ktlint.rule.engine.core.api.editorconfig.EditorConfig
+import com.pinterest.ktlint.rule.engine.core.api.editorconfig.INDENT_SIZE_PROPERTY
+import com.pinterest.ktlint.rule.engine.core.api.editorconfig.INDENT_STYLE_PROPERTY
+import com.pinterest.ktlint.rule.engine.core.api.indent
+import com.pinterest.ktlint.rule.engine.core.api.isPartOfComment
+import com.pinterest.ktlint.rule.engine.core.api.isWhiteSpace
+import com.pinterest.ktlint.rule.engine.core.api.isWhiteSpaceWithoutNewline
+import com.pinterest.ktlint.rule.engine.core.api.nextSibling
+import com.pinterest.ktlint.rule.engine.core.api.upsertWhitespaceBeforeMe
+import com.pinterest.ktlint.ruleset.standard.StandardRule
+import org.jetbrains.kotlin.com.intellij.lang.ASTNode
+import org.jetbrains.kotlin.com.intellij.psi.impl.source.tree.LeafPsiElement
+import org.jetbrains.kotlin.com.intellij.psi.impl.source.tree.PsiWhiteSpaceImpl
+import org.jetbrains.kotlin.psi.KtBlockExpression
+import org.jetbrains.kotlin.psi.psiUtil.leaves
+
+/**
+ * https://developer.android.com/kotlin/style-guide#braces
+ */
+@SinceKtlint("1.0", EXPERIMENTAL)
+public class MultiLineLoopRule :
+    StandardRule(
+        id = "multiline-loop",
+        usesEditorConfigProperties =
+            setOf(
+                INDENT_SIZE_PROPERTY,
+                INDENT_STYLE_PROPERTY,
+            ),
+    ) {
+    private var indentConfig = IndentConfig.DEFAULT_INDENT_CONFIG
+
+    override fun beforeFirstNode(editorConfig: EditorConfig) {
+        indentConfig =
+            IndentConfig(
+                indentStyle = editorConfig[INDENT_STYLE_PROPERTY],
+                tabWidth = editorConfig[INDENT_SIZE_PROPERTY],
+            )
+    }
+
+    override fun beforeVisitChildNodes(
+        node: ASTNode,
+        autoCorrect: Boolean,
+        emit: (offset: Int, errorMessage: String, canBeAutoCorrected: Boolean) -> Unit,
+    ) {
+        if (node.elementType != BODY) {
+            return
+        }
+
+        // Ignore when already wrapped in a block
+        if (node.firstChildNode?.elementType == BLOCK) {
+            return
+        }
+
+        if (!node.treePrev.textContains('\n')) {
+            if (!node.treeParent.textContains('\n')) {
+                // Allow single line loop statements as long as they are really simple (e.g. do not contain newlines)
+                //    for (...) <statement>
+                //    while (...) <statement>
+                //    do <statement> while (...)
+                return
+            }
+
+            Unit
+        }
+
+        emit(node.firstChildNode.startOffset, "Missing { ... }", true)
+        if (autoCorrect) {
+            autocorrect(node)
+        }
+    }
+
+    private fun autocorrect(node: ASTNode) {
+        val prevLeaves =
+            node
+                .leaves(forward = false)
+                .takeWhile { it.elementType !in listOf(RPAR, DO_KEYWORD) }
+                .toList()
+                .reversed()
+        val nextLeaves =
+            node
+                .leaves(forward = true)
+                .takeWhile { it.isWhiteSpaceWithoutNewline() || it.isPartOfComment() }
+                .toList()
+                .dropLastWhile { it.isWhiteSpaceWithoutNewline() }
+
+        prevLeaves
+            .firstOrNull()
+            .takeIf { it.isWhiteSpace() }
+            ?.let {
+                (it as LeafPsiElement).rawReplaceWithText(" ")
+            }
+        KtBlockExpression(null).apply {
+            val previousChild = node.firstChildNode
+            node.replaceChild(node.firstChildNode, this)
+            addChild(LeafPsiElement(LBRACE, "{"))
+            addChild(PsiWhiteSpaceImpl(indentConfig.childIndentOf(node)))
+            prevLeaves
+                .dropWhile { it.isWhiteSpace() }
+                .forEach(::addChild)
+            addChild(previousChild)
+            nextLeaves.forEach(::addChild)
+            addChild(PsiWhiteSpaceImpl(node.indent()))
+            addChild(LeafPsiElement(RBRACE, "}"))
+        }
+
+        // Make sure while starts on same line as newly inserted right brace
+        if (node.elementType == BODY) {
+            node
+                .nextSibling { !it.isPartOfComment() }
+                ?.upsertWhitespaceBeforeMe(" ")
+        }
+    }
+}
+
+public val MULTI_LINE_LOOP_RULE_ID: RuleId = MultiLineLoopRule().ruleId