Pass scalafmt configuration from command line.

modules/cli-options/src/main/scala/scala/cli/commands/FmtOptions.scala

@@ -50,6 +50,11 @@ final case class FmtOptions(
   @Name("scalafmtConfig")
     scalafmtConf: Option[String] = None,
   @Group("Format")
+  @HelpMessage("Pass configuration as a string.")
+  @Name("scalafmtConfigStr")
+  @Name("scalafmtConfSnippet")
+    scalafmtConfStr: Option[String] = None,
+  @Group("Format")
   @HelpMessage("Pass a global dialect for scalafmt. This overrides whatever value is configured in the .scalafmt.conf file.")
   @Name("dialect")
     scalafmtDialect: Option[String] = None,

modules/cli/src/main/scala/scala/cli/commands/Fmt.scala

@@ -37,10 +37,9 @@ object Fmt extends ScalaCommand[FmtOptions] {
         (s, i.workspace, Some(i))
       }
     CurrentParams.workspaceOpt = Some(workspace)
-    val (versionMaybe, dialectMaybe, pathMaybe) =
-      readVersionAndDialectFromFile(workspace, options.scalafmtConf, logger)
-    val cache        = options.shared.buildOptions().archiveCache
-    val buildOptions = options.buildOptions
+    val (versionMaybe, dialectMaybe, pathMaybe) = readVersionAndDialect(workspace, options, logger)
+    val cache                                   = options.shared.buildOptions().archiveCache
+    val buildOptions                            = options.buildOptions
 
     if (sourceFiles.isEmpty)
       logger.debug("No source files, not formatting anything")

modules/cli/src/main/scala/scala/cli/commands/util/FmtUtil.scala

@@ -5,7 +5,9 @@ import com.typesafe.config.ConfigSyntax
 import com.typesafe.config.parser.ConfigDocument
 import com.typesafe.config.parser.ConfigDocumentFactory
 import scala.build.Logger
+import scala.build.internal.Constants
 import scala.util.control.NonFatal
+import scala.cli.commands.FmtOptions
 
 object FmtUtil {
   private def getGitRoot(workspace: os.Path, logger: Logger): Option[String] =
@@ -33,9 +35,9 @@ object FmtUtil {
     * @return
     *   path to found `.scalafmt.conf` file and `version` with `dialect` read from it
     */
-  def readVersionAndDialectFromFile(
+  def readVersionAndDialect(
     workspace: os.Path,
-    customConfPath: Option[String],
+    options: FmtOptions,
     logger: Logger
   ): (Option[String], Option[String], Option[os.Path]) = {
     case class RunnerMetaconfig(dialect: String = "")
@@ -57,25 +59,30 @@ object FmtUtil {
       implicit lazy val decoder: metaconfig.ConfDecoder[ScalafmtMetaconfig] =
         metaconfig.generic.deriveDecoder[ScalafmtMetaconfig](default)
     }
-
     val confName = ".scalafmt.conf"
     val pathMaybe =
-      customConfPath.flatMap { p =>
-        val confPath = os.Path(p, os.pwd)
-        logger.debug(s"Checking for $confPath.")
-        if (os.exists(confPath)) Some(confPath)
-        else
-          logger.message(s"WARNING: provided file doesn't exist $confPath")
-          None
+      options.scalafmtConfStr.flatMap { s =>
+        val tmpConfPath = workspace / Constants.workspaceDirName / ".scalafmt.conf"
+        os.write.over(tmpConfPath, s, createFolders = true)
+        Some(tmpConfPath)
       }.orElse {
-        logger.debug(s"Checking for $confName in cwd.")
-        val confInCwd = workspace / confName
-        if (os.exists(confInCwd)) Some(confInCwd)
-        else {
-          logger.debug(s"Checking for $confName in git root.")
-          val gitRootMaybe       = getGitRoot(workspace, logger)
-          val confInGitRootMaybe = gitRootMaybe.map(os.Path(_) / confName)
-          confInGitRootMaybe.find(os.exists(_))
+        options.scalafmtConf.flatMap { p =>
+          val confPath = os.Path(p, os.pwd)
+          logger.debug(s"Checking for $confPath.")
+          if (os.exists(confPath)) Some(confPath)
+          else
+            logger.message(s"WARNING: provided file doesn't exist $confPath")
+            None
+        }.orElse {
+          logger.debug(s"Checking for $confName in cwd.")
+          val confInCwd = workspace / confName
+          if (os.exists(confInCwd)) Some(confInCwd)
+          else {
+            logger.debug(s"Checking for $confName in git root.")
+            val gitRootMaybe       = getGitRoot(workspace, logger)
+            val confInGitRootMaybe = gitRootMaybe.map(os.Path(_) / confName)
+            confInGitRootMaybe.find(os.exists(_))
+          }
         }
       }
 

modules/cli/src/test/scala/cli/tests/ScalafmtTest.scala

@@ -3,6 +3,7 @@ import com.eed3si9n.expecty.Expecty.expect
 
 import scala.build.tests.{TestInputs, TestLogger}
 import scala.cli.commands.util.FmtUtil
+import scala.cli.commands.FmtOptions
 
 class ScalafmtTests extends munit.FunSuite {
 
@@ -16,15 +17,15 @@ class ScalafmtTests extends munit.FunSuite {
       os.write(confFilePath, confFile)
 
       val readVersionAndDialect =
-        FmtUtil.readVersionAndDialectFromFile(workspace = dirPath, None, TestLogger())
+        FmtUtil.readVersionAndDialect(workspace = dirPath, FmtOptions(), TestLogger())
       expect(readVersionAndDialect == (Some("3.1.2"), Some("scala213"), Some(confFilePath)))
     }
   }
 
   test("readVersionFromFile with missing .scalafmt.conf file") {
     TestInputs.withTmpDir("temp-dir") { dirPath =>
       val readVersionAndDialect =
-        FmtUtil.readVersionAndDialectFromFile(workspace = dirPath, None, TestLogger())
+        FmtUtil.readVersionAndDialect(workspace = dirPath, FmtOptions(), TestLogger())
       expect(readVersionAndDialect == (None, None, None))
     }
   }

modules/integration/src/test/scala/scala/cli/integration/FmtTests.scala

@@ -55,13 +55,11 @@ class FmtTests extends ScalaCliSuite {
   )
 
   val simpleInputsWithCustomConfLocation: TestInputs = TestInputs(
-    Seq(
-      os.rel / "custom.conf" ->
-        s"""|version = "3.5.5"
-            |runner.dialect = scala213
-            |""".stripMargin,
-      os.rel / "Foo.scala" -> simpleInputsUnformattedContent
-    )
+    os.rel / "custom.conf" ->
+      s"""|version = "3.5.5"
+          |runner.dialect = scala213
+          |""".stripMargin,
+    os.rel / "Foo.scala" -> simpleInputsUnformattedContent
   )
 
   private def noCrLf(input: String): String =
@@ -162,6 +160,21 @@ class FmtTests extends ScalaCliSuite {
     }
   }
 
+  test("--scalafmt-conf-str") {
+    simpleInputsWithVersionOnly.fromRoot { root =>
+      val confStr =
+        s"""version = 3.5.7${System.lineSeparator}runner.dialect = scala213${System.lineSeparator}"""
+      os.proc(TestUtil.cli, "fmt", ".", "--scalafmt-conf-str", s"$confStr").call(cwd = root)
+      val confLines      = os.read.lines(root / Constants.workspaceDirName / confFileName)
+      val versionInConf  = confLines(0).stripPrefix("version = ")
+      val dialectInConf  = confLines(1).stripPrefix("runner.dialect = ")
+      val updatedContent = noCrLf(os.read(root / "Foo.scala"))
+      expect(versionInConf == "\"3.5.7\"")
+      expect(dialectInConf == "scala213")
+      expect(updatedContent == expectedSimpleInputsFormattedContent)
+    }
+  }
+
   test("creating workspace conf file") {
     simpleInputsWithDialectOnly.fromRoot { root =>
       val workspaceConfPath = root / Constants.workspaceDirName / confFileName

website/docs/commands/fmt.md

@@ -30,6 +30,8 @@ You can skip passing either of those, which will make Scala CLI to infer a defau
 - If a `.scalafmt.conf` file is present in the workspace and it has the field defined, the value will be read from there, unless explicitly specified with Scala CLI options.
 - Otherwise, the default `scalafmt` **version** will be the latest one used by your Scala CLI version (so it is subject to change when updating Scala CLI). The default **dialect** will be inferred based on Scala version (defined explicitly by `-S` option, or default version if option would not be passed).
 
+It is possible to pass the configuration as a string directly from the command line, using `--scalafmt-conf-str` option. If the configuration is passed this way, Scala CLI will behave exactly the same as if it would find the specified configuration in a `.scalafmt.conf` file in the workspace.
+
 #### Example 1
 
 ``` text title=.scalafmt.conf
@@ -167,3 +169,7 @@ If the `--save-scalafmt-conf` option is passed, then `fmt` command behaves as fo
 - In the **first** case `fmt` uses the found `.scalafmt.conf` file to run `scalafmt`.
 - In the **second** case `fmt` [infers](/docs/commands/fmt#scalafmt-version-and-dialect) missing parameters, writes them directly into the previously found file and then uses this file to run `scalafmt`.
 - In the **third** case `fmt` creates a `.scalafmt.conf` file in the current workspace directory, writes [inferred](/docs/commands/fmt#scalafmt-version-and-dialect) version and dialect into it and uses it to run `scalafmt`.
+
+:::note
+If the configuration is passed in the `--scalafmt-conf-str` option, Scala CLI will behave exactly the same as if it would find the specified configuration in a `.scalafmt.conf` file in the workspace.
+:::

website/docs/reference/cli-options.md

@@ -528,6 +528,12 @@ Aliases: `--scalafmt-config`
 
 Custom path to the scalafmt configuration file.
 
+#### `--scalafmt-conf-str`
+
+Aliases: `--scalafmt-config-str`, `--scalafmt-conf-snippet`
+
+Pass configuration as a string.
+
 #### `--scalafmt-dialect`
 
 Aliases: `--dialect`