Trailing spaces should not delete the indent of the next line

In most cases this is probably fixed by the indent rule but at least not
when next line contains a KDoc

Closes pinterest#1334

CHANGELOG.md

@@ -21,6 +21,7 @@ This project adheres to [Semantic Versioning](https://semver.org/).
 - Fix alignment of arrow when trailing comma is missing in when entry (`trailing-comma`) ([#1312](https://github.com/pinterest/ktlint/issues/1312))
 - Fix indent of delegated super type entry (`indent`) ([#1210](https://github.com/pinterest/ktlint/issues/1210))
 - Improve indentation of closing quotes of a multiline raw string literal (`indent`) ([#1262](https://github.com/pinterest/ktlint/pull/1262))
+- Trailing space should not lead to delete of indent of next line (`no-trailing-spaces`) ([#1334](https://github.com/pinterest/ktlint/pull/1334))
 
 ### Changed
 - Update Kotlin version to `1.6.0` release

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

@@ -1,17 +1,16 @@
 package com.pinterest.ktlint.ruleset.standard
 
 import com.pinterest.ktlint.core.Rule
+import com.pinterest.ktlint.core.ast.ElementType.EOL_COMMENT
 import com.pinterest.ktlint.core.ast.ElementType.WHITE_SPACE
 import com.pinterest.ktlint.core.ast.isPartOfComment
 import com.pinterest.ktlint.core.ast.nextLeaf
 import com.pinterest.ktlint.core.ast.parent
 import org.jetbrains.kotlin.com.intellij.lang.ASTNode
-import org.jetbrains.kotlin.com.intellij.psi.PsiWhiteSpace
 import org.jetbrains.kotlin.com.intellij.psi.impl.source.tree.LeafPsiElement
 import org.jetbrains.kotlin.kdoc.psi.api.KDoc
 
 class NoTrailingSpacesRule : Rule("no-trailing-spaces") {
-
     override fun visit(
         node: ASTNode,
         autoCorrect: Boolean,
@@ -28,29 +27,29 @@ class NoTrailingSpacesRule : Rule("no-trailing-spaces") {
             val lines = node.text.split("\n")
             var violated = false
             var violationOffset = node.startOffset
-            lines
-                .head()
-                .forEach { line ->
-                    if (line.hasTrailingSpace()) {
-                        val firstTrailingSpaceOffset = violationOffset + line.trimEnd().length
-                        emit(firstTrailingSpaceOffset, "Trailing space(s)", true)
-                        violated = true
+
+            val modifiedLines =
+                lines
+                    .mapIndexed { index, line ->
+                        val modifiedLine = when {
+                            node.elementType != EOL_COMMENT && index == lines.size - 1 && node.nextLeaf() != null ->
+                                // Do not change the last line as it contains the indentation of the next element except
+                                // when it is an EOL comment which may also not contain trailing spaces
+                                line
+                            line.hasTrailingSpace() -> {
+                                val modifiedLine = line.trimEnd()
+                                val firstTrailingSpaceOffset = violationOffset + modifiedLine.length
+                                emit(firstTrailingSpaceOffset, "Trailing space(s)", true)
+                                violated = true
+                                modifiedLine
+                            }
+                            else -> line
+                        }
+                        violationOffset += line.length + 1
+                        modifiedLine
                     }
-                    violationOffset += line.length + 1
-                }
-            when {
-                node is PsiWhiteSpace && node.nextLeaf() != null ->
-                    // Ignore the last line as it contains the indentation of the next element
-                    Unit
-                lines.last().hasTrailingSpace() -> {
-                    val firstTrailingSpaceOffset = violationOffset + lines.last().trimEnd().length
-                    emit(firstTrailingSpaceOffset, "Trailing space(s)", true)
-                    violated = true
-                }
-            }
             if (violated && autoCorrect) {
-                val modifiedLines = lines.joinToString(separator = "\n") { it.trimEnd() }
-                (node as LeafPsiElement).rawReplaceWithText(modifiedLines)
+                (node as LeafPsiElement).rawReplaceWithText(modifiedLines.joinToString(separator = "\n"))
             }
         }
     }

ktlint-ruleset-standard/src/test/kotlin/com/pinterest/ktlint/ruleset/standard/NoTrailingSpacesRuleTest.kt

@@ -152,4 +152,45 @@ class NoTrailingSpacesRuleTest {
             )
         )
     }
+
+    @Test
+    fun `Issue 1334 - trailing spaces should not delete indent of the next line`() {
+        val code =
+            """
+            class Foo {
+                // something
+            ${"    "}
+                /**
+                 * Some KDoc
+                 */
+                val bar: String
+            ${"    "}
+                val foo = "foo"
+            }
+            """.trimIndent()
+        val codeExpected =
+            """
+            class Foo {
+                // something
+
+                /**
+                 * Some KDoc
+                 */
+                val bar: String
+
+                val foo = "foo"
+            }
+            """.trimIndent()
+        assertThat(
+            NoTrailingSpacesRule().format(code)
+        ).isEqualTo(codeExpected)
+        assertThat(
+            NoTrailingSpacesRule().lint(code)
+        ).isEqualTo(
+            listOf(
+                LintError(3, 1, "no-trailing-spaces", "Trailing space(s)"),
+                LintError(8, 1, "no-trailing-spaces", "Trailing space(s)")
+            )
+        )
+    }
 }