SI-6440 Address regressions around MissingRequirementError

 Go back to using globalError to report when a stub's info is referenced,
 and only throw the MissingRequirementError when compilation really
 must abort due to having a StubTermSymbol in a place where a
 StubClassSymbol would have been a better choice.

 This situation arises when an entire package is missing from the
 classpath, as was the case in the reported bug.

 Adds `StoreReporterDirectTest`, which buffers messages issued
 during compilation for more structured interrogation. Use this
 in two test for manifests -- these tests were using a crude means
 of grepping compiler console output to focus on the relevant output,
 but this approach was insufficient with the new multi-line error
 message emitted as part of this change.

 Also used that base test class to add two new tests: one for
 the reported error (package missing), and another for a simpler
 error (class missing). The latter test shows how stub symbols
 allow code to compile if it doesn't the subset of signatures
 in some type that refer to a missing class.

 Gave the INFO/WARNING/ERROR members of Reporter sensible
 toString implementations; they inherit from Enumeration#Value
 in an unusual manner (why?) that means the built in toString of
 Enumeration printed `Severity@0`.

1 files changed, 44 insertions, 3 deletions

diff --git a/test/files/run/t6440.scala b/test/files/run/t6440.scala
index 2b690f31e1..5a3a4150d9 100644
--- a/test/files/run/t6440.scala
+++ b/test/files/run/t6440.scala
@@ -1,7 +1,48 @@
-object Test {
+import scala.tools.partest._
+import java.io.File
 
-  def main(args: Array[String]): Unit = {
-    println(Stream.continually(()).filterNot(_ => false).take(2))
+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)
   }
 
+  def library1 = """
+    package pack1
+    trait T
+  """
+
+  def library2 = """
+    package pack2
+    trait U extends pack1.T
+  """
+
+  def app = """
+    package pack3
+    object X {
+      trait U
+    }
+    import X._
+    import pack2._
+
+    trait V extends U
+  """
+
+  def show(): Unit = {
+    Seq(library1, library2) foreach compileCode
+    assert(filteredInfos.isEmpty, filteredInfos)
+
+    // blow away the entire package
+    val pack1 = new File(testOutput.path, "pack1")
+    val tClass = new File(pack1, "T.class")
+    assert(tClass.exists)
+    assert(tClass.delete())
+    assert(pack1.delete())
+
+    // bad symbolic reference error expected (but no stack trace!)
+    compileCode(app)
+    println(filteredInfos.mkString("\n"))
+  }
 }