Fix #1965: add proper testing infrastructure for reporting tests

compiler/test/dotty/tools/dotc/parsing/DocstringTest.scala

@@ -27,7 +27,7 @@ trait DocstringTest extends DottyTest {
 
   def checkFrontend(source: String)(docAssert: PartialFunction[Tree[Untyped], Unit]) = {
     checkCompile("frontend", source) { (_, ctx) =>
-      implicit val c = ctx
+      implicit val c: Context = ctx
       (docAssert orElse defaultAssertion)(ctx.compilationUnit.untpdTree)
     }
   }

compiler/test/dotty/tools/dotc/reporting/ErrorMessagesTest.scala

@@ -0,0 +1,70 @@
+package dotty.tools
+package dotc
+package reporting
+
+import diagnostic._
+import core.Contexts.Context
+
+import scala.collection.mutable
+
+import org.junit.Assert._
+
+trait ErrorMessagesTest extends DottyTest {
+
+  class Report(messages: List[Message], ictx: Context) {
+    def expect(f: (Context, List[Message]) => Unit): Unit = {
+      f(ictx, messages)
+    }
+
+    def expectNoErrors: Unit = this.isInstanceOf[FailedReport]
+  }
+
+  class FailedReport extends Report(Nil, null) {
+    override def expect(f: (Context, List[Message]) => Unit) =
+      fail("""|
+              |Couldn't capture errors from compiled sources, this can happen if
+              |there are no errors or the compiler crashes.""".stripMargin)
+  }
+
+  class CapturingReporter extends Reporter
+  with UniqueMessagePositions with HideNonSensicalMessages {
+    private[this] val buffer = new mutable.ListBuffer[Message]
+    private[this] var capturedContext: Context = _
+
+    def doReport(m: MessageContainer)(implicit ctx: Context) = {
+      capturedContext = ctx
+      buffer append m.contained
+    }
+
+    def toReport: Report =
+      if (capturedContext eq null)
+        new FailedReport
+      else {
+        val xs = buffer.reverse.toList
+        buffer.clear()
+
+        val ctx = capturedContext
+        capturedContext = null
+
+        new Report(xs, ctx)
+      }
+  }
+
+  ctx = freshReporter(ctx)
+
+  private def freshReporter(ctx: Context) =
+    ctx.fresh.setReporter(new CapturingReporter)
+
+  def checkMessages(source: String): Report = {
+    checkCompile("frontend", source) { (_,ictx) => () }
+    val rep = ctx.reporter.asInstanceOf[CapturingReporter].toReport
+    ctx = freshReporter(ctx)
+    rep
+  }
+
+  def messageCount(expected: Int, messages: List[Message]): Unit =
+    assertEquals(
+      expected,
+      messages.length
+    )
+}

compiler/test/dotty/tools/dotc/reporting/ErrorMessagesTests.scala

@@ -0,0 +1,45 @@
+package dotty.tools
+package dotc
+package reporting
+
+import core.Contexts.Context
+import diagnostic.messages._
+
+import org.junit.Assert._
+import org.junit.Test
+
+class ErrorMessagesTests extends ErrorMessagesTest {
+  // In the case where there are no errors, we can do "expectNoErrors" in the
+  // `Report`
+  @Test def noErrors =
+    checkMessages("""class Foo""")
+    .expectNoErrors
+
+  @Test def typeMismatch =
+    checkMessages {
+      """
+      |object Foo {
+      |  def bar: String = 1
+      |}
+      """.stripMargin
+    }
+    .expect { (ictx, messages) =>
+      implicit val ctx: Context = ictx
+      val defn = ictx.definitions
+
+      // Assert that we only got one error message
+      messageCount(1, messages)
+
+      // Pattern match out the expected error
+      val TypeMismatch(found, expected, _, _) :: Nil = messages
+
+      // The type of the right hand side will actually be the constant 1,
+      // therefore we check if it "derivesFrom"  `IntClass`
+      assert(found.derivesFrom(defn.IntClass), s"found was: $found")
+
+      // The expected type is `scala.String` which we dealias to
+      // `java.lang.String` and compare with `=:=` to `defn.StringType` which
+      // is a type reference to `java.lang.String`
+      assert(expected.dealias =:= defn.StringType, s"expected was: $expected")
+    }
+}