Add file annotations rule

Author: t-kameyama

ktlint-core/src/main/kotlin/com/pinterest/ktlint/core/ast/package.kt

@@ -184,6 +184,8 @@ fun ASTNode.isPartOf(klass: KClass<out PsiElement>): Boolean {
 fun ASTNode.isPartOfString() =
     parent(STRING_TEMPLATE, strict = false) != null
 
+fun ASTNode?.isWhiteSpace() =
+    this != null && elementType == WHITE_SPACE
 fun ASTNode?.isWhiteSpaceWithNewline() =
     this != null && elementType == WHITE_SPACE && textContains('\n')
 fun ASTNode?.isWhiteSpaceWithoutNewline() =
@@ -228,3 +230,6 @@ fun ASTNode.visit(enter: (node: ASTNode) -> Unit, exit: (node: ASTNode) -> Unit)
     this.getChildren(null).forEach { it.visit(enter, exit) }
     exit(this)
 }
+
+fun ASTNode.lineNumber(): Int? =
+    this.psi.containingFile?.viewProvider?.document?.getLineNumber(this.startOffset)?.let { it + 1 }

ktlint-ruleset-experimental/src/main/kotlin/com/pinterest/ktlint/ruleset/experimental/AnnotationRule.kt

@@ -8,13 +8,20 @@ import com.pinterest.ktlint.core.ast.ElementType.VALUE_ARGUMENT
 import com.pinterest.ktlint.core.ast.ElementType.VALUE_PARAMETER
 import com.pinterest.ktlint.core.ast.children
 import com.pinterest.ktlint.core.ast.isPartOf
+import com.pinterest.ktlint.core.ast.isPartOfComment
+import com.pinterest.ktlint.core.ast.isWhiteSpace
+import com.pinterest.ktlint.core.ast.lineNumber
+import com.pinterest.ktlint.core.ast.nextSibling
+import com.pinterest.ktlint.core.ast.prevSibling
 import com.pinterest.ktlint.core.ast.upsertWhitespaceBeforeMe
 import org.jetbrains.kotlin.com.intellij.lang.ASTNode
 import org.jetbrains.kotlin.com.intellij.psi.PsiComment
 import org.jetbrains.kotlin.com.intellij.psi.PsiWhiteSpace
 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.KtAnnotationEntry
 import org.jetbrains.kotlin.psi.psiUtil.endOffset
+import org.jetbrains.kotlin.psi.psiUtil.getNextSiblingIgnoringWhitespaceAndComments
 import org.jetbrains.kotlin.psi.psiUtil.nextLeaf
 
 /**
@@ -30,6 +37,7 @@ class AnnotationRule : Rule("annotation") {
             "Multiple annotations should not be placed on the same line as the annotated construct"
         const val annotationsWithParametersAreNotOnSeparateLinesErrorMessage =
             "Annotations with parameters should all be placed on separate lines prior to the annotated construct"
+        const val fileAnnotationsShouldBeSeparated = "File annotations should be separated from packages with a blank line"
     }
 
     override fun visit(
@@ -62,7 +70,8 @@ class AnnotationRule : Rule("annotation") {
             .take(annotations.size)
             .toList()
 
-        val noWhiteSpaceAfterAnnotation = whiteSpaces.isEmpty() || whiteSpaces.last().nextSibling is KtAnnotationEntry
+        val noWhiteSpaceAfterAnnotation = node.elementType != FILE_ANNOTATION_LIST &&
+            (whiteSpaces.isEmpty() || whiteSpaces.last().nextSibling is KtAnnotationEntry)
         if (noWhiteSpaceAfterAnnotation) {
             emit(
                 annotations.last().endOffset - 1,
@@ -106,6 +115,29 @@ class AnnotationRule : Rule("annotation") {
                 }
             }
         }
+
+        if (node.elementType == FILE_ANNOTATION_LIST) {
+            val lineNumber = node.lineNumber()
+            val next = node.nextSibling {
+                !it.isWhiteSpace() && it.textLength > 0 && !(it.isPartOfComment() && it.lineNumber() == lineNumber)
+            }
+            val nextLineNumber = next?.lineNumber()
+            if (lineNumber != null && nextLineNumber != null) {
+                val diff = nextLineNumber - lineNumber
+                if (diff < 2) {
+                    emit(0, fileAnnotationsShouldBeSeparated, true)
+                    if (autoCorrect) {
+                        if (diff == 0) {
+                            node.psi.getNextSiblingIgnoringWhitespaceAndComments(withItself = false)?.node
+                                ?.prevSibling { it.isWhiteSpace() }
+                                ?.let { (it as? LeafPsiElement)?.delete() }
+                            next.treeParent.addChild(PsiWhiteSpaceImpl("\n"), next)
+                        }
+                        next.treeParent.addChild(PsiWhiteSpaceImpl("\n"), next)
+                    }
+                }
+            }
+        }
     }
 
     private fun getNewlineWithIndent(modifierListRoot: ASTNode): String {