Add rule to check that a single top level class name matches the file name

ktlint-ruleset-standard/src/main/kotlin/com/github/shyiko/ktlint/ruleset/standard/ClassNameMatchesFileNameRule.kt

@@ -0,0 +1,44 @@
+package com.github.shyiko.ktlint.ruleset.standard
+
+import com.github.shyiko.ktlint.core.KtLint
+import com.github.shyiko.ktlint.core.Rule
+import org.jetbrains.kotlin.com.intellij.lang.ASTNode
+import org.jetbrains.kotlin.lexer.KtTokens
+import org.jetbrains.kotlin.psi.stubs.elements.KtStubElementTypes
+import java.nio.file.Paths
+
+/**
+ * If there is only one top level class in a given file, then its name should match the file's name
+ */
+class ClassNameMatchesFileNameRule : Rule("class-name-matches-file-name"), Rule.Modifier.RestrictToRoot {
+
+    override fun visit(
+        node: ASTNode,
+        autoCorrect: Boolean,
+        emit: (offset: Int, errorMessage: String, canBeAutoCorrected: Boolean) -> Unit
+    ) {
+        // Ignore all non ".kt" files (including ".kts")
+        if (node.getUserData(KtLint.FILE_PATH_USER_DATA_KEY)?.endsWith(".kt") != true) {
+            return
+        }
+
+        val topLevelClassNames = mutableListOf<String>()
+
+        node.visit {
+            if (it.elementType == KtStubElementTypes.CLASS && it.treeParent.elementType == KtStubElementTypes.FILE) {
+                val classIdentifier = it.findChildByType(KtTokens.IDENTIFIER)
+                classIdentifier?.let {
+                    val className = it.text
+                    topLevelClassNames.add(className)
+                }
+            }
+        }
+
+        val name = Paths.get(node.getUserData(KtLint.FILE_PATH_USER_DATA_KEY)).fileName.toString().substringBefore(".")
+        if (topLevelClassNames.size == 1 && name != topLevelClassNames.first()) {
+            emit(0,
+                "Single top level class name [${topLevelClassNames.first()}] does not match file name",
+                false)
+        }
+    }
+}

ktlint-ruleset-standard/src/main/kotlin/com/github/shyiko/ktlint/ruleset/standard/NoMultipleSpacesRule.kt

@@ -78,9 +78,4 @@ class NoMultipleSpacesRule : Rule("no-multi-spaces") {
             }
         }
     }
-
-    private fun ASTNode.visit(cb: (node: ASTNode) -> Unit) {
-        cb(this)
-        this.getChildren(null).forEach { it.visit(cb) }
-    }
 }

ktlint-ruleset-standard/src/main/kotlin/com/github/shyiko/ktlint/ruleset/standard/NoUnusedImportsRule.kt

@@ -84,9 +84,4 @@ class NoUnusedImportsRule : Rule("no-unused-imports") {
     }
 
     private fun String.isComponentN() = componentNRegex.matches(this)
-
-    private fun ASTNode.visit(cb: (node: ASTNode) -> Unit) {
-        cb(this)
-        this.getChildren(null).forEach { it.visit(cb) }
-    }
 }

ktlint-ruleset-standard/src/main/kotlin/com/github/shyiko/ktlint/ruleset/standard/ParameterListWrappingRule.kt

@@ -115,11 +115,6 @@ class ParameterListWrappingRule : Rule("parameter-list-wrapping") {
             return offsetToTheLeft + 1
         }
 
-    private fun ASTNode.visit(cb: (node: ASTNode) -> Unit) {
-        cb(this)
-        this.getChildren(null).forEach { it.visit(cb) }
-    }
-
     private fun errorMessage(node: ASTNode) =
         when (node.elementType) {
             KtStubElementTypes.VALUE_PARAMETER ->

ktlint-ruleset-standard/src/main/kotlin/com/github/shyiko/ktlint/ruleset/standard/StandardRuleSetProvider.kt

@@ -7,6 +7,7 @@ class StandardRuleSetProvider : RuleSetProvider {
 
     override fun get(): RuleSet = RuleSet("standard",
         ChainWrappingRule(),
+        ClassNameMatchesFileNameRule(),
         FinalNewlineRule(),
         // disabled until it's clear how to reconcile difference in Intellij & Android Studio import layout
         // ImportOrderingRule(),

ktlint-ruleset-standard/src/main/kotlin/com/github/shyiko/ktlint/ruleset/standard/package.kt

@@ -1,5 +1,6 @@
 package com.github.shyiko.ktlint.ruleset.standard
 
+import org.jetbrains.kotlin.com.intellij.lang.ASTNode
 import org.jetbrains.kotlin.com.intellij.psi.PsiElement
 import org.jetbrains.kotlin.com.intellij.psi.impl.source.tree.LeafPsiElement
 import org.jetbrains.kotlin.com.intellij.psi.util.PsiTreeUtil
@@ -11,6 +12,10 @@ internal fun PsiElement.isPartOf(clazz: KClass<out PsiElement>) = getNonStrictPa
 internal fun PsiElement.isPartOfString() = isPartOf(KtStringTemplateEntry::class)
 internal fun PsiElement.prevLeaf(): LeafPsiElement? = PsiTreeUtil.prevLeaf(this) as LeafPsiElement?
 internal fun PsiElement.nextLeaf(): LeafPsiElement? = PsiTreeUtil.nextLeaf(this) as LeafPsiElement?
+internal fun ASTNode.visit(cb: (node: ASTNode) -> Unit) {
+    cb(this)
+    this.getChildren(null).forEach { it.visit(cb) }
+}
 
 internal fun <T> List<T>.head() = this.subList(0, this.size - 1)
 internal fun <T> List<T>.tail() = this.subList(1, this.size)

ktlint-ruleset-standard/src/test/kotlin/com/github/shyiko/ktlint/ruleset/standard/ClassNameMatchesFileNameRuleTest.kt

@@ -0,0 +1,81 @@
+package com.github.shyiko.ktlint.ruleset.standard
+
+import com.github.shyiko.ktlint.core.LintError
+import com.github.shyiko.ktlint.test.lint
+import org.assertj.core.api.Assertions.assertThat
+import org.testng.annotations.Test
+
+class ClassNameMatchesFileNameRuleTest {
+
+    @Test
+    fun testMatchingSingleClassName() {
+        assertThat(ClassNameMatchesFileNameRule().lint(
+            """
+                class A
+            """.trimIndent(),
+            fileName("/some/path/A.kt")
+        )).isEmpty()
+    }
+
+    @Test
+    fun testNonMatchingSingleClassName() {
+        assertThat(ClassNameMatchesFileNameRule().lint(
+            """
+                class B
+            """.trimIndent(),
+            fileName("A.kt")
+        )).isEqualTo(listOf(
+            LintError(1, 1, "class-name-matches-file-name", "Single top level class name [B] does not match file name")
+        ))
+    }
+
+    @Test
+    fun testMultipleTopLevelClasses() {
+        assertThat(ClassNameMatchesFileNameRule().lint(
+            """
+                class B
+                class C
+            """.trimIndent(),
+            fileName("A.kt")
+        )).isEmpty()
+    }
+
+    @Test
+    fun testMultipleNonTopLevelClasses() {
+        assertThat(ClassNameMatchesFileNameRule().lint(
+            """
+                class B {
+                    class C
+                    class D
+                }
+            """.trimIndent(),
+            fileName("A.kt")
+        )).isEqualTo(listOf(
+            LintError(1, 1, "class-name-matches-file-name", "Single top level class name [B] does not match file name")
+        ))
+    }
+
+    @Test
+    fun testCaseSensitiveMatching() {
+        assertThat(ClassNameMatchesFileNameRule().lint(
+            """
+                interface Woohoo
+            """.trimIndent(),
+            fileName("woohoo.kt")
+        )).isEqualTo(listOf(
+            LintError(1, 1, "class-name-matches-file-name", "Single top level class name [Woohoo] does not match file name")
+        ))
+    }
+
+    @Test
+    fun testIgnoreKotlinScriptFiles() {
+        assertThat(ClassNameMatchesFileNameRule().lint(
+            """
+                class B
+            """.trimIndent(),
+            fileName("A.kts")
+        )).isEmpty()
+    }
+
+    private fun fileName(fileName: String) = mapOf("file_path" to fileName)
+}