NoConsecutiveBlankLinesRule: report blank line between class name and primary constructor

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

@@ -1,6 +1,9 @@
 package com.pinterest.ktlint.ruleset.standard
 
 import com.pinterest.ktlint.core.Rule
+import com.pinterest.ktlint.core.ast.ElementType.CLASS
+import com.pinterest.ktlint.core.ast.ElementType.IDENTIFIER
+import com.pinterest.ktlint.core.ast.ElementType.PRIMARY_CONSTRUCTOR
 import com.pinterest.ktlint.core.ast.nextLeaf
 import org.jetbrains.kotlin.com.intellij.lang.ASTNode
 import org.jetbrains.kotlin.com.intellij.psi.PsiWhiteSpace
@@ -20,12 +23,21 @@ class NoConsecutiveBlankLinesRule : Rule("no-consecutive-blank-lines") {
                 return
             }
             val eof = node.nextLeaf() == null
-            if (lfcount > 2 || eof) {
+            val prevNode = node.treePrev
+            val betweenClassAndPrimaryConstructor = prevNode.elementType == IDENTIFIER &&
+                prevNode.treeParent.elementType == CLASS &&
+                node.treeNext.elementType == PRIMARY_CONSTRUCTOR
+            if (lfcount > 2 || eof || betweenClassAndPrimaryConstructor) {
                 val split = text.split("\n")
                 emit(node.startOffset + split[0].length + split[1].length + 2, "Needless blank line(s)", true)
                 if (autoCorrect) {
-                    (node as LeafPsiElement)
-                        .rawReplaceWithText("${split.first()}\n${if (eof) "" else "\n"}${split.last()}")
+                    val newText = buildString {
+                        append(split.first())
+                        append("\n")
+                        if (!eof && !betweenClassAndPrimaryConstructor) append("\n")
+                        append(split.last())
+                    }
+                    (node as LeafPsiElement).rawReplaceWithText(newText)
                 }
             }
         }

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

@@ -71,7 +71,7 @@ class NoConsecutiveBlankLinesRuleTest {
             NoConsecutiveBlankLinesRule().lint(
                 """
                 package com.test
-                
+
                 fun main() {
                 }
                 """.trimIndent()
@@ -150,4 +150,61 @@ class NoConsecutiveBlankLinesRuleTest {
         assertThat(NoConsecutiveBlankLinesRule().format("class A\n\n")).isEqualTo("class A\n")
         assertThat(NoConsecutiveBlankLinesRule().format("class A\n")).isEqualTo("class A\n")
     }
+
+    @Test
+    fun `test two line breaks between class name and primary constructor`() {
+        assertThat(
+            NoConsecutiveBlankLinesRule().format(
+                """
+                class A
+
+                constructor(a: Int)
+
+                class B
+
+                private constructor(b: Int)
+                """.trimIndent()
+            )
+        ).isEqualTo(
+            """
+            class A
+            constructor(a: Int)
+
+            class B
+            private constructor(b: Int)
+            """.trimIndent()
+        )
+    }
+
+    @Test
+    fun `test three line breaks between class name and primary constructor`() {
+        assertThat(
+            NoConsecutiveBlankLinesRule().format(
+                """
+                class A
+
+
+                constructor(a: Int)
+                """.trimIndent()
+            )
+        ).isEqualTo(
+            """
+            class A
+            constructor(a: Int)
+            """.trimIndent()
+        )
+    }
+
+    @Test
+    fun `test two line breaks between comment and primary constructor`() {
+        assertThat(
+            NoConsecutiveBlankLinesRule().lint(
+                """
+                class A // comment
+
+                constructor(a: Int)
+                """.trimIndent()
+            )
+        ).isEmpty()
+    }
 }