From 4e1403e40c2e63a68b20300c2842b83ca761c5ad Mon Sep 17 00:00:00 2001
From: Toshiaki Kameyama <kmymtsak@gmail.com>
Date: Sun, 29 Nov 2020 06:48:05 +0900
Subject: [PATCH] NoSemicolonsRule: don't report semicolon for control flow
 with empty body (#976)

* NoSemicolonsRule: don't report semicolon for control flow with empty body

* Drop a comment

* Add comments pointing to issues

Co-authored-by: Roman Zavarnitsyn <rom4ek93@gmail.com>
---
 .../ruleset/standard/NoSemicolonsRule.kt      | 33 +++++++++--
 .../ruleset/standard/NoSemicolonsRuleTest.kt  | 56 +++++++++++++++++++
 2 files changed, 83 insertions(+), 6 deletions(-)

diff --git a/ktlint-ruleset-standard/src/main/kotlin/com/pinterest/ktlint/ruleset/standard/NoSemicolonsRule.kt b/ktlint-ruleset-standard/src/main/kotlin/com/pinterest/ktlint/ruleset/standard/NoSemicolonsRule.kt
index 21ea5418f6..e063b53c11 100644
--- a/ktlint-ruleset-standard/src/main/kotlin/com/pinterest/ktlint/ruleset/standard/NoSemicolonsRule.kt
+++ b/ktlint-ruleset-standard/src/main/kotlin/com/pinterest/ktlint/ruleset/standard/NoSemicolonsRule.kt
@@ -3,6 +3,7 @@ package com.pinterest.ktlint.ruleset.standard
 import com.pinterest.ktlint.core.Rule
 import com.pinterest.ktlint.core.ast.ElementType.KDOC_TEXT
 import com.pinterest.ktlint.core.ast.ElementType.OBJECT_KEYWORD
+import com.pinterest.ktlint.core.ast.ElementType.SEMICOLON
 import com.pinterest.ktlint.core.ast.isPartOf
 import com.pinterest.ktlint.core.ast.isPartOfComment
 import com.pinterest.ktlint.core.ast.isPartOfString
@@ -20,7 +21,10 @@ import org.jetbrains.kotlin.lexer.KtTokens
 import org.jetbrains.kotlin.psi.KtAnnotationEntry
 import org.jetbrains.kotlin.psi.KtClass
 import org.jetbrains.kotlin.psi.KtClassBody
+import org.jetbrains.kotlin.psi.KtDoWhileExpression
 import org.jetbrains.kotlin.psi.KtEnumEntry
+import org.jetbrains.kotlin.psi.KtIfExpression
+import org.jetbrains.kotlin.psi.KtLoopExpression
 import org.jetbrains.kotlin.psi.psiUtil.getStrictParentOfType
 
 class NoSemicolonsRule : Rule("no-semi") {
@@ -33,13 +37,14 @@ class NoSemicolonsRule : Rule("no-semi") {
         if (node.elementType == KDOC_TEXT) {
             return
         }
-        if (node is LeafPsiElement && node.textMatches(";") && !node.isPartOfString() && !node.isPartOfEnumEntry()) {
+        if (node is LeafPsiElement &&
+            node.elementType == SEMICOLON &&
+            !node.isPartOfString() &&
+            !node.isPartOfEnumEntry()
+        ) {
             val nextLeaf = node.nextLeaf()
-            if (doesNotRequirePreSemi(nextLeaf)) {
-                if (node.prevCodeLeaf()?.elementType == OBJECT_KEYWORD) {
-                    // https://github.com/shyiko/ktlint/issues/281
-                    return
-                }
+            val prevCodeLeaf = node.prevCodeLeaf()
+            if (doesNotRequirePreSemi(nextLeaf) && doesNotRequirePostSemi(prevCodeLeaf)) {
                 emit(node.startOffset, "Unnecessary semicolon", true)
                 if (autoCorrect) {
                     node.treeParent.removeChild(node)
@@ -73,6 +78,22 @@ class NoSemicolonsRule : Rule("no-semi") {
         return nextLeaf == null /* eof */
     }
 
+    private fun doesNotRequirePostSemi(prevLeaf: ASTNode?): Boolean {
+        if (prevLeaf?.elementType == OBJECT_KEYWORD) {
+            // https://github.com/pinterest/ktlint/issues/281
+            return false
+        }
+        val parent = prevLeaf?.treeParent?.psi
+        if (parent is KtLoopExpression && parent !is KtDoWhileExpression && parent.body == null) {
+            // https://github.com/pinterest/ktlint/issues/955
+            return false
+        }
+        if (parent is KtIfExpression && parent.then == null) {
+            return false
+        }
+        return true
+    }
+
     private fun ASTNode.isPartOfEnumEntry(): Boolean {
         if (isPartOf(KtEnumEntry::class)) return true
         val lBrace = prevLeaf { !it.isWhiteSpace() && !it.isPartOfComment() }
diff --git a/ktlint-ruleset-standard/src/test/kotlin/com/pinterest/ktlint/ruleset/standard/NoSemicolonsRuleTest.kt b/ktlint-ruleset-standard/src/test/kotlin/com/pinterest/ktlint/ruleset/standard/NoSemicolonsRuleTest.kt
index df74dcb151..8927825d3d 100644
--- a/ktlint-ruleset-standard/src/test/kotlin/com/pinterest/ktlint/ruleset/standard/NoSemicolonsRuleTest.kt
+++ b/ktlint-ruleset-standard/src/test/kotlin/com/pinterest/ktlint/ruleset/standard/NoSemicolonsRuleTest.kt
@@ -230,4 +230,60 @@ class NoSemicolonsRuleTest {
             )
         )
     }
+
+    @Test
+    fun testForWithEmptyBody() {
+        assertThat(
+            NoSemicolonsRule().lint(
+                """
+                fun test(list: List<Int>) {
+                    for (i in list);
+                }
+                """.trimIndent()
+            )
+        ).isEmpty()
+    }
+
+    @Test
+    fun testWhileWithEmptyBody() {
+        assertThat(
+            NoSemicolonsRule().lint(
+                """
+                fun test() {
+                    while (true);
+                }
+                """.trimIndent()
+            )
+        ).isEmpty()
+    }
+
+    @Test
+    fun testDoWhileWithEmptyBody() {
+        assertThat(
+            NoSemicolonsRule().lint(
+                """
+                fun test() {
+                    do while (true);
+                }
+                """.trimIndent()
+            )
+        ).isEqualTo(
+            listOf(
+                LintError(2, 20, "no-semi", "Unnecessary semicolon")
+            )
+        )
+    }
+
+    @Test
+    fun testIfWithEmptyBranch() {
+        assertThat(
+            NoSemicolonsRule().lint(
+                """
+                fun testIf() {
+                    if (true);
+                }
+                """.trimIndent()
+            )
+        ).isEmpty()
+    }
 }