Fix messages leaking via suspended messages

It isn't clear what StoreReporter's purpose is.  Is it simply a store of
all messages, or is it a store of "real" messages, i.e. messages that
aren't suppressed with `@nowarn` or -Wconf (i.e. configurable warnings)?
I believe StoreReporter is often used as a way to get programmatic
access to the real messages.

Typer, with its TyperState, uses StoreReporter as a more general buffer
while making typing attempts, such as when trying to apply an implicit
conversion.  But with configurable warnings, we don't know if a warning
is real or not until we've typed all the `@nowarn` annotation in the
code, which is why we suspend the messages, on Run.

So we add an override for TyperState, so that StoreReporter is used as
simply a buffer.  When it then unbuffers its messages in flush to the
parent context's reporter, it will run through the regular
"issueIfNotSuppressed" code (assuming it's not another store reporter).

compiler/src/dotty/tools/dotc/core/TyperState.scala

@@ -103,7 +103,7 @@ class TyperState() {
     this
 
   /** A fresh typer state with the same constraint as this one. */
-  def fresh(reporter: Reporter = StoreReporter(this.reporter),
+  def fresh(reporter: Reporter = StoreReporter(this.reporter, fromTyperState = true),
       committable: Boolean = this.isCommittable): TyperState =
     util.Stats.record("TyperState.fresh")
     TyperState().init(this, this.constraint)

compiler/src/dotty/tools/dotc/reporting/ExploringReporter.scala

@@ -7,7 +7,7 @@ import core.Contexts.Context
 import Diagnostic._
 
 /** A re-usable Reporter used in Contexts#test */
-class ExploringReporter extends StoreReporter(null):
+class ExploringReporter extends StoreReporter(null, fromTyperState = false):
   infos = new mutable.ListBuffer[Diagnostic]
 
   override def hasUnreportedErrors: Boolean =

compiler/src/dotty/tools/dotc/reporting/StoreReporter.scala

@@ -17,7 +17,7 @@ import Diagnostic._
   * - The reporter is not flushed and the message containers capture a
   *   `Context` (about 4MB)
   */
-class StoreReporter(outer: Reporter = Reporter.NoReporter) extends Reporter {
+class StoreReporter(outer: Reporter = Reporter.NoReporter, fromTyperState: Boolean = false) extends Reporter {
 
   protected var infos: mutable.ListBuffer[Diagnostic] = null
 
@@ -40,4 +40,11 @@ class StoreReporter(outer: Reporter = Reporter.NoReporter) extends Reporter {
   override def pendingMessages(using Context): List[Diagnostic] = if (infos != null) infos.toList else Nil
 
   override def errorsReported: Boolean = hasErrors || (outer != null && outer.errorsReported)
+
+  // If this is a TyperState buffering reporter then buffer the messages,
+  // so that then only when the messages are unbuffered (when the reporter if flushed)
+  // do they go through -Wconf, and possibly then buffered on the Run as a suspended message
+  override def report(dia: Diagnostic)(using Context): Unit =
+    if fromTyperState then doReport(dia)
+    else super.report(dia)
 }

compiler/src/dotty/tools/dotc/reporting/TestReporter.scala

@@ -6,7 +6,7 @@ import collection.mutable
 import Diagnostic._
 
 /** A re-usable Reporter used in Contexts#test */
-class TestingReporter extends StoreReporter(null):
+class TestingReporter extends StoreReporter(null, fromTyperState = false):
   infos = new mutable.ListBuffer[Diagnostic]
   override def hasUnreportedErrors: Boolean = infos.exists(_.isInstanceOf[Error])
   def reset(): Unit = infos.clear()