Do not delete blank lines in KDoc

Closes pinterest#1376

CHANGELOG.md

@@ -7,6 +7,7 @@ This project adheres to [Semantic Versioning](https://semver.org/).
 ### Added
 
 ### Fixed
+- Do not delete blank lines in KDoc (no-trailing-spaces) ([#1376](https://github.com/pinterest/ktlint/issues/1376))
 
 ### Changed
 

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

@@ -18,7 +18,14 @@ class NoTrailingSpacesRule : Rule("no-trailing-spaces") {
     ) {
         if (node.isPartOfKDoc()) {
             if (node.elementType == WHITE_SPACE && node.hasTrailingSpacesBeforeNewline()) {
-                emit(node.startOffset, "Trailing space(s)", true)
+                val offsetOfSpaceBeforeNewlineInText = node.text.indexOf(" \n")
+                val offsetOfFirstSpaceBeforeNewlineInText =
+                    node
+                        .text
+                        .take(offsetOfSpaceBeforeNewlineInText)
+                        .dropLastWhile { it == ' ' }
+                        .length
+                emit(node.startOffset + offsetOfFirstSpaceBeforeNewlineInText, "Trailing space(s)", true)
                 if (autoCorrect) {
                     node.removeTrailingSpacesBeforeNewline()
                 }
@@ -57,18 +64,20 @@ class NoTrailingSpacesRule : Rule("no-trailing-spaces") {
     private fun ASTNode.isPartOfKDoc() = parent({ it.psi is KDoc }, strict = false) != null
 
     private fun ASTNode.hasTrailingSpacesBeforeNewline() =
-        text.contains(
-            regex = Regex("\\s+\\n")
-        )
+        text.contains(SPACE_OR_TAB_BEFORE_NEWLINE_REGEX)
 
     private fun ASTNode.removeTrailingSpacesBeforeNewline() {
         val newText = text.replace(
-            regex = Regex("\\s+\\n"),
+            regex = SPACE_OR_TAB_BEFORE_NEWLINE_REGEX,
             replacement = "\n"
         )
         (this as LeafPsiElement).replaceWithText(newText)
     }
 
     private fun String.hasTrailingSpace() =
         takeLast(1) == " "
+
+    private companion object {
+        val SPACE_OR_TAB_BEFORE_NEWLINE_REGEX = Regex("[ ]+\\n")
+    }
 }

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

@@ -193,4 +193,52 @@ class NoTrailingSpacesRuleTest {
             )
         )
     }
+
+    @Test
+    fun `Issue 1376 - trailing spaces should not delete blank line inside kdoc`() {
+        val code =
+            """
+            /**
+             Paragraph 1 which should be followed by a blank line.
+
+
+             Paragraph 2 which should have a blank line before it.
+             */
+            class MyClass
+            """.trimIndent()
+        assertThat(NoTrailingSpacesRule().lint(code)).isEmpty()
+        assertThat(NoTrailingSpacesRule().format(code)).isEqualTo(code)
+    }
+
+    @Test
+    fun `Issue 1376 - trailing spaces should be removed from blank line inside kdoc`() {
+        val code =
+            """
+            /**
+             Paragraph 1 which should be followed by a blank line.
+             ${"    "}
+             ${"    "}
+             Paragraph 2 which should have a blank line before it.
+             */
+            class MyClass
+            """.trimIndent()
+        val formattedCode =
+            """
+            /**
+             Paragraph 1 which should be followed by a blank line.
+
+
+             Paragraph 2 which should have a blank line before it.
+             */
+            class MyClass
+            """.trimIndent()
+        assertThat(
+            NoTrailingSpacesRule().format(code)
+        ).isEqualTo(formattedCode)
+        assertThat(
+            NoTrailingSpacesRule().lint(code)
+        ).containsExactly(
+            LintError(3, 1, "no-trailing-spaces", "Trailing space(s)")
+        )
+    }
 }