Gracefully handle parse errors

This commit changes error handling for parsing source files so that
users get nicely formatted error messages instead of a large stack trace.

src/main/scala/com/github/tkawachi/doctest/ScaladocExtractor.scala

@@ -1,5 +1,8 @@
 package com.github.tkawachi.doctest
 
+import java.io.File
+import java.nio.file.Files
+import java.nio.file.Path
 import scala.meta._
 import scala.meta.contrib._
 
@@ -12,8 +15,25 @@ object ScaladocExtractor {
     Set(DocToken.CodeBlock, DocToken.Description, DocToken.Example)
 
   def extract(scalaSource: String): List[ScaladocComment] = {
-
-    val code = scalaSource.parse[Source].get
+    extractFromInput(Input.String(scalaSource))
+  }
+  def extractFromFile(file: Path, encoding: String): List[ScaladocComment] = {
+    val text = new String(Files.readAllBytes(file), encoding)
+    // Workaround from https://github.com/scalameta/scalameta/issues/443#issuecomment-314797969
+    val trimmedText = text.replace("\r\n", "\n")
+    val input = Input.VirtualFile(file.toString, trimmedText)
+    extractFromInput(input)
+  }
+  def extractFromInput(scalaSource: Input): List[ScaladocComment] = {
+    scalaSource.parse[Source] match {
+      case Parsed.Success(tree) =>
+        extractFromTree(tree)
+      case error @ Parsed.Error(_, _, _) =>
+        println(error.toString())
+        Nil
+    }
+  }
+  def extractFromTree(code: Tree): List[ScaladocComment] = {
     val comments = AssociatedComments(code)
 
     object NamedMember {

src/main/scala/com/github/tkawachi/doctest/ScaladocTestGenerator.scala

@@ -1,10 +1,10 @@
 package com.github.tkawachi.doctest
 
 import java.io.File
-
-import scala.io.Source
+import java.nio.file.Files
 import org.apache.commons.io.FilenameUtils
 import org.apache.commons.lang3.StringEscapeUtils.unescapeHtml4
+import scala.meta.Input
 
 object ScaladocTestGenerator {
 
@@ -17,9 +17,8 @@ object ScaladocTestGenerator {
    * Generates test source code from scala source file.
    */
   def apply(srcFile: File, srcEncoding: String, testGen: TestGen, decodeHtmlEnabled: Boolean, onlyCodeBlocksMode: Boolean): Seq[TestSource] = {
-    val src = Source.fromFile(srcFile, srcEncoding).mkString
     val basename = FilenameUtils.getBaseName(srcFile.getName)
-    ScaladocExtractor.extract(src)
+    ScaladocExtractor.extractFromFile(srcFile.toPath, srcEncoding)
       .map(comment => if (decodeHtmlEnabled) decodeHtml(comment) else comment)
       .flatMap { comment =>
         val docTest = if (onlyCodeBlocksMode)

src/test/scala/com/github/tkawachi/doctest/ScaladocExtractorSpec.scala

@@ -1,17 +1,18 @@
 package com.github.tkawachi.doctest
 
+import java.io.ByteArrayOutputStream
+import java.io.PrintStream
+import java.nio.charset.StandardCharsets
+import java.nio.file.Paths
+import scala.meta.Input
 import utest._
 
-import scala.io.Source
-
 object ScaladocExtractorSpec extends TestSuite {
 
   val tests = this{
 
-    import ScaladocExtractor.extract
-
     def extractFromFile(path: String) =
-      extract(Source.fromFile(path).mkString)
+      ScaladocExtractor.extractFromFile(Paths.get(path), StandardCharsets.UTF_8.name())
 
     "extracts from Test.scala" - {
       val actual = extractFromFile("src/test/resources/Test.scala")
@@ -132,11 +133,28 @@ object ScaladocExtractorSpec extends TestSuite {
           |}
         """.stripMargin
 
-      val actual = extract(source)
+      val actual = ScaladocExtractor.extract(source)
       val expected = Nil
       assert(expected == actual)
     }
 
+    "parse errors are printed to stdout" - {
+      val input = Input.VirtualFile("filename.scala", "object Main {")
+      val out = new ByteArrayOutputStream()
+      val obtained = Console.withOut(new PrintStream(out)) {
+        ScaladocExtractor.extractFromInput(input)
+      }
+      assert(obtained == Nil)
+      val obtainedOut = out.toString(StandardCharsets.UTF_8.name).trim
+      val expectedOut =
+        """
+          |filename.scala:1: error: } expected but end of file found
+          |object Main {
+          |             ^
+        """.stripMargin.trim
+      assert(obtainedOut == expectedOut)
+    }
+
     "extracts from CodeExamples.scala" - {
       val actual = extractFromFile("src/test/resources/CodeExamples.scala")
       val expected =