SI-5717 error when bytecode cannot be written

If there's an existing file foo when emitting a class file for foo.Bar,
then emit an error at foo.Bar, similar to what javac does.

The error message looks something like:

foo.scala:4: error: error writing object Foo: ./mypkg/Foo.class: ./mypkg is not a directory

3 files changed, 54 insertions, 28 deletions

diff --git a/src/compiler/scala/tools/nsc/backend/jvm/BytecodeWriters.scala b/src/compiler/scala/tools/nsc/backend/jvm/BytecodeWriters.scala
index c1cd3204e0..66aed14d1c 100644
--- a/src/compiler/scala/tools/nsc/backend/jvm/BytecodeWriters.scala
+++ b/src/compiler/scala/tools/nsc/backend/jvm/BytecodeWriters.scala
@@ -6,12 +6,15 @@
 package scala.tools.nsc
 package backend.jvm
 
-import java.io.{ DataOutputStream, FileOutputStream, OutputStream, File => JFile }
+import java.io.{ DataOutputStream, FileOutputStream, IOException, OutputStream, File => JFile }
 import scala.tools.nsc.io._
 import scala.tools.nsc.util.ScalaClassLoader
 import java.util.jar.Attributes.Name
 import scala.language.postfixOps
 
+/** Can't output a file due to the state of the file system. */
+class FileConflictException(msg: String, val file: AbstractFile) extends IOException(msg)
+
 /** For the last mile: turning generated bytecode in memory into
  *  something you can use.  Has implementations for writing to class
  *  files, jars, and disassembled/javap output.
@@ -20,16 +23,20 @@ trait BytecodeWriters {
   val global: Global
   import global._
 
-  private def outputDirectory(sym: Symbol): AbstractFile = (
-    settings.outputDirs.outputDirFor(enteringFlatten(sym.sourceFile))
-  )
-  private def getFile(base: AbstractFile, /*cls.getName()*/ clsName: String, suffix: String): AbstractFile = {
+  private def outputDirectory(sym: Symbol): AbstractFile =
+    settings.outputDirs outputDirFor enteringFlatten(sym.sourceFile)
+
+  /**
+   * @param clsName cls.getName
+   */
+  private def getFile(base: AbstractFile, clsName: String, suffix: String): AbstractFile = {
+    def ensureDirectory(dir: AbstractFile): AbstractFile =
+      if (dir.isDirectory) dir
+      else throw new FileConflictException(s"${base.path}/$clsName$suffix: ${dir.path} is not a directory", dir)
     var dir = base
     val pathParts = clsName.split("[./]").toList
-    for (part <- pathParts.init) {
-      dir = dir.subdirectoryNamed(part)
-    }
-    dir.fileNamed(pathParts.last + suffix)
+    for (part <- pathParts.init) dir = ensureDirectory(dir) subdirectoryNamed part
+    ensureDirectory(dir) fileNamed pathParts.last + suffix
   }
   private def getFile(sym: Symbol, clsName: String, suffix: String): AbstractFile =
     getFile(outputDirectory(sym), clsName, suffix)
diff --git a/src/compiler/scala/tools/nsc/backend/jvm/GenASM.scala b/src/compiler/scala/tools/nsc/backend/jvm/GenASM.scala
index 4a3d1805d9..2e29633169 100644
--- a/src/compiler/scala/tools/nsc/backend/jvm/GenASM.scala
+++ b/src/compiler/scala/tools/nsc/backend/jvm/GenASM.scala
@@ -105,29 +105,30 @@ abstract class GenASM extends SubComponent with BytecodeWriters with GenJVMASM {
           "Such classes will overwrite one another on case-insensitive filesystems.")
       }
 
-      debuglog("Created new bytecode generator for " + classes.size + " classes.")
+      debuglog(s"Created new bytecode generator for ${classes.size} classes.")
       val bytecodeWriter  = initBytecodeWriter(sortedClasses filter isJavaEntryPoint)
       val plainCodeGen    = new JPlainBuilder(bytecodeWriter)
       val mirrorCodeGen   = new JMirrorBuilder(bytecodeWriter)
       val beanInfoCodeGen = new JBeanInfoBuilder(bytecodeWriter)
 
-      while(!sortedClasses.isEmpty) {
-        val c = sortedClasses.head
-
+      def emitFor(c: IClass) {
         if (isStaticModule(c.symbol) && isTopLevelModule(c.symbol)) {
-          if (c.symbol.companionClass == NoSymbol) {
-            mirrorCodeGen.genMirrorClass(c.symbol, c.cunit)
-          } else {
-            log("No mirror class for module with linked class: " + c.symbol.fullName)
-          }
+          if (c.symbol.companionClass == NoSymbol)
+            mirrorCodeGen genMirrorClass (c.symbol, c.cunit)
+          else
+            log(s"No mirror class for module with linked class: ${c.symbol.fullName}")
         }
+        plainCodeGen genClass c
+        if (c.symbol hasAnnotation BeanInfoAttr) beanInfoCodeGen genBeanInfoClass c
+      }
 
-        plainCodeGen.genClass(c)
-
-        if (c.symbol hasAnnotation BeanInfoAttr) {
-          beanInfoCodeGen.genBeanInfoClass(c)
+      while (!sortedClasses.isEmpty) {
+        val c = sortedClasses.head
+        try emitFor(c)
+        catch {
+          case e: FileConflictException =>
+            c.cunit.error(c.symbol.pos, s"error writing ${c.symbol}: ${e.getMessage}")
         }
-
         sortedClasses = sortedClasses.tail
         classes -= c.symbol // GC opportunity
       }
@@ -454,7 +455,7 @@ abstract class GenASM extends SubComponent with BytecodeWriters with GenJVMASM {
     }
 
     // -----------------------------------------------------------------------------------------
-    // utitilies useful when emitting plain, mirror, and beaninfo classes.
+    // utilities useful when emitting plain, mirror, and beaninfo classes.
     // -----------------------------------------------------------------------------------------
 
     def writeIfNotTooBig(label: String, jclassName: String, jclass: asm.ClassWriter, sym: Symbol) {
@@ -1397,7 +1398,6 @@ abstract class GenASM extends SubComponent with BytecodeWriters with GenJVMASM {
       addInnerClasses(clasz.symbol, jclass)
       jclass.visitEnd()
       writeIfNotTooBig("" + c.symbol.name, thisName, jclass, c.symbol)
-
     }
 
     /**
@@ -2903,7 +2903,7 @@ abstract class GenASM extends SubComponent with BytecodeWriters with GenJVMASM {
                                      JAVA_LANG_OBJECT.getInternalName,
                                      EMPTY_STRING_ARRAY)
 
-      log("Dumping mirror class for '%s'".format(mirrorName))
+      log(s"Dumping mirror class for '$mirrorName'")
 
       // typestate: entering mode with valid call sequences:
       //   [ visitSource ] [ visitOuterClass ] ( visitAnnotation | visitAttribute )*
@@ -2926,8 +2926,6 @@ abstract class GenASM extends SubComponent with BytecodeWriters with GenJVMASM {
       mirrorClass.visitEnd()
       writeIfNotTooBig("" + modsym.name, mirrorName, mirrorClass, modsym)
     }
-
-
   } // end of class JMirrorBuilder
 
 
diff --git a/test/files/run/t5717.scala b/test/files/run/t5717.scala
new file mode 100755
index 0000000000..a0997f5a49
--- /dev/null
+++ b/test/files/run/t5717.scala
@@ -0,0 +1,21 @@
+import scala.tools.partest._
+import java.io.File
+
+object Test extends StoreReporterDirectTest {
+  def code = ???
+
+  def compileCode(code: String) = {
+    val classpath = List(sys.props("partest.lib"), testOutput.path) mkString sys.props("path.separator")
+    compileString(newCompiler("-cp", classpath, "-d", testOutput.path))(code)
+  }
+  // TODO
+  // Don't assume output is on physical disk
+  // Let the compiler tell us output dir
+  // val sc = newCompiler("-cp", classpath, "-d", testOutput.path)
+  // val out = sc.settings.outputDirs.getSingleOutput.get
+  def show(): Unit = {
+    // Don't crash when we find a file 'a' where package 'a' should go.
+    scala.reflect.io.File(testOutput.path + "/a").writeAll("a")
+    compileCode("package a { class B }")
+  }
+}