add scalafmt (#1601)

* add scalafmt
* add flint ci workflow

Signed-off-by: Peng Huo <[email protected]>

Author: penghuo

.scalafmt.conf

@@ -0,0 +1,3 @@
+version = 3.7.3
+
+runner.dialect = scala212

DEVELOPER_GUIDE.md

@@ -0,0 +1,17 @@
+# Developer Guide
+
+## Scala Formatting Guidelines
+
+For Scala code, We use [scalafmt](https://scalameta.org/scalafmt/) to format the code and check the code style. 
+
+To use the plugin, user could check the style
+```
+sbt scalafmtCheck
+```
+The code can be formatted with
+```
+sbt scalafmtAll
+```
+For more sbt tasks, read more in [scalafmt sbt](https://scalameta.org/scalafmt/docs/installation.html#sbt)
+
+For Intellij user, read more in [scalafmt IntelliJ](https://scalameta.org/scalafmt/docs/installation.html#intellij)

build.sbt

@@ -27,6 +27,9 @@ lazy val flintSparkIntegration = (project in file("flint-spark-integration"))
   .settings(
     name := "flint-spark-integration",
     scalaVersion := scala212,
+    Compile / compile := (Compile / compile)
+      .dependsOn(Compile / scalafmtCheck)
+      .value,
     libraryDependencies ++= Seq(
       "org.apache.spark" %% "spark-core" % sparkVersion,
       "org.apache.spark" %% "spark-sql" % sparkVersion

flint-core/src/main/scala/org/opensearch/flint/core/FlintIndex.scala

@@ -5,6 +5,4 @@
 
 package org.opensearch.flint.core
 
-class FlintIndex {
-
-}
+class FlintIndex {}

flint-spark-integration/src/main/scala/org/opensearch/flint/spark/FlintSparkExtensions.scala

@@ -9,6 +9,5 @@ import org.apache.spark.sql.SparkSessionExtensions
 
 class FlintSparkExtensions extends (SparkSessionExtensions => Unit) {
 
-  override def apply(v1: SparkSessionExtensions): Unit = {
-  }
+  override def apply(v1: SparkSessionExtensions): Unit = {}
 }

project/plugins.sbt

@@ -0,0 +1,6 @@
+/*
+ * Copyright OpenSearch Contributors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+addSbtPlugin("org.scalameta" % "sbt-scalafmt" % "2.4.6")