ScalafmtDynamic: throw if can't resolve config

Intellij invokes the createSession method directly and doesn't expect
the null value we return there, so throw ConfigError instead.

Similarly, in the Runner, change the implementation of MyInstanceSession
to verify the config first, so that the config parsing exception is not
thrown for every file we are trying to format.

scalafmt-cli/src/main/scala/org/scalafmt/cli/ScalafmtDynamicRunner.scala

@@ -8,6 +8,7 @@ import java.util.function.UnaryOperator
 
 import org.scalafmt.CompatCollections.ParConverters._
 import org.scalafmt.Error.{MisformattedFile, NoMatchingFiles}
+import org.scalafmt.dynamic.ScalafmtDynamicError
 import org.scalafmt.interfaces.Scalafmt
 import org.scalafmt.interfaces.ScalafmtSession
 import org.scalafmt.interfaces.ScalafmtSessionFactory
@@ -27,13 +28,17 @@ object ScalafmtDynamicRunner extends ScalafmtRunner {
       .withReporter(reporter)
       .withRespectProjectFilters(false)
 
-    val session = scalafmtInstance match {
-      case t: ScalafmtSessionFactory =>
-        val session = t.createSession(options.configPath)
-        if (session == null) return reporter.getExitCode // XXX: returning
-        session
-      case _ => new MyInstanceSession(options, scalafmtInstance)
-    }
+    val session =
+      try {
+        scalafmtInstance match {
+          case t: ScalafmtSessionFactory =>
+            t.createSession(options.configPath)
+          case _ => new MyInstanceSession(options, scalafmtInstance)
+        }
+      } catch {
+        case _: ScalafmtDynamicError.ConfigError =>
+          return reporter.getExitCode // XXX: returning
+      }
 
     def sessionMatcher(x: AbsoluteFile): Boolean =
       session.matchesProjectFilters(x.jfile.toPath)
@@ -79,6 +84,8 @@ object ScalafmtDynamicRunner extends ScalafmtRunner {
 
   private final class MyInstanceSession(opts: CliOptions, instance: Scalafmt)
       extends ScalafmtSession {
+    // check config first
+    instance.format(opts.configPath, opts.configPath, "")
     private val customFiles =
       if (opts.respectProjectFilters) Seq.empty
       else opts.customFiles.filter(_.jfile.isFile).map(_.jfile.toPath)

scalafmt-dynamic/src/main/scala/org/scalafmt/dynamic/ScalafmtDynamic.scala

@@ -75,6 +75,7 @@ final case class ScalafmtDynamic(
         codeFormatted
       case Left(error) =>
         reportError(file, error)
+        if (error.isInstanceOf[ConfigError]) throw error
         code
     }
   }
@@ -235,7 +236,7 @@ final case class ScalafmtDynamic(
 
   override def createSession(config: Path): ScalafmtSession =
     resolveConfig(config).fold(
-      error => { reportError(config, error); null },
+      error => { reportError(config, error); throw error },
       config => new MySession(config)
     )
 

scalafmt-tests/src/test/scala/org/scalafmt/dynamic/DynamicSuite.scala

@@ -11,9 +11,10 @@ import PositionSyntax._
 
 import scala.collection.mutable
 import scala.collection.mutable.ListBuffer
+import scala.reflect.ClassTag
 import scala.{meta => m}
-import org.scalatest.funsuite.AnyFunSuite
 
+import org.scalatest.funsuite.AnyFunSuite
 import org.scalafmt.util.DiffAssertions
 
 class DynamicSuite extends AnyFunSuite with DiffAssertions {
@@ -136,11 +137,19 @@ class DynamicSuite extends AnyFunSuite with DiffAssertions {
     def assertMissingVersion()(implicit pos: Position): Unit = {
       out.reset()
       missingVersions.clear()
-      val original = "object  A"
-      val obtained = dynamic.format(config, filename, original)
+      intercept[ScalafmtDynamicError.ConfigMissingVersion] {
+        dynamic.format(config, filename, "object  A")
+      }
       assert(out.toString().isEmpty)
       assert(missingVersions.nonEmpty)
-      assertNoDiff(obtained, original, "Formatter did not error")
+    }
+    def assertThrows[A <: AnyRef: ClassTag](
+        code: String = "object A  {  }"
+    )(implicit pos: Position): A = {
+      out.reset()
+      intercept[A] {
+        dynamic.format(config, filename, code)
+      }
     }
     def assertError(expected: String)(implicit pos: Position): Unit = {
       assertError("object A  {  }", expected)
@@ -278,7 +287,7 @@ class DynamicSuite extends AnyFunSuite with DiffAssertions {
         |version=$latest
         |""".stripMargin
     )
-    f.assertError(
+    f.assertThrows[ScalafmtDynamicError.ConfigParseError](
       """|error: path/.scalafmt.conf: Invalid config: Invalid field: max. Expected one of version, maxColumn, docstrings, optIn, binPack, continuationIndent, align, spaces, literals, lineEndings, rewriteTokens, rewrite, indentOperator, newlines, runner, indentYieldKeyword, importSelectors, unindentTopLevelOperators, includeCurlyBraceInSelectChains, includeNoParensInSelectChains, assumeStandardLibraryStripMargin, danglingParentheses, poorMansTrailingCommasInConfigStyle, trailingCommas, verticalMultilineAtDefinitionSite, verticalMultilineAtDefinitionSiteArityThreshold, verticalMultiline, onTestFailure, encoding, project
         |""".stripMargin
     )
@@ -318,7 +327,7 @@ class DynamicSuite extends AnyFunSuite with DiffAssertions {
 
   check("wrong-version") { f =>
     f.setVersion("1.0")
-    f.assertError(
+    f.assertThrows[ScalafmtDynamicError.CannotDownload](
       """|error: path/.scalafmt.conf: org.scalafmt.dynamic.exceptions.ScalafmtException: failed to download v=1.0
         |Caused by: org.scalafmt.dynamic.ScalafmtVersion$InvalidVersionException: Invalid scalafmt version 1.0
         |""".stripMargin
@@ -354,8 +363,10 @@ class DynamicSuite extends AnyFunSuite with DiffAssertions {
 
   check("no-config") { f =>
     Files.delete(f.config)
-    f.assertError("""|error: path/.scalafmt.conf: Missing config
-      |""".stripMargin)
+    f.assertThrows[ScalafmtDynamicError.ConfigDoesNotExist](
+      """|error: path/.scalafmt.conf: Missing config
+        |""".stripMargin
+    )
   }
 
   check("intellij-default-config") { f: Format =>