Fixing a problem with swallowed errors

The problem was that in FunProto#typedArg we cache typed arguments, to retrieve them later, possibly in a different context (Example: typedArg might be computed during overloading resolution, and then cached copy
might be inserted in resolved call. The problem is that any errors, warnings or other diagnostics might be swallowed, if typedArg is computed in a context that is not committed but then re-used in a committed context.

The fix is to cache typed arguments only if no diagnostics were issued during their computation.

2 files changed, 15 insertions, 3 deletions

diff --git a/src/dotty/tools/dotc/reporting/Reporter.scala b/src/dotty/tools/dotc/reporting/Reporter.scala
index 72b9247c5..6e7a79306 100644
--- a/src/dotty/tools/dotc/reporting/Reporter.scala
+++ b/src/dotty/tools/dotc/reporting/Reporter.scala
@@ -219,6 +219,17 @@ abstract class Reporter {
   def hasErrors   = count(ERROR.level) > 0
   def hasWarnings = count(WARNING.level) > 0
 
+  def isSilent[T](op: => Unit): Boolean = {
+    val prevCount = count.clone
+    op
+    var i = 0
+    while (i < count.length) {
+      if (prevCount(i) != count(i)) return false
+      i += 1
+    }
+    true
+  }
+
   /** Returns a string meaning "n elements". */
   private def countElementsAsString(n: Int, elements: String): String =
     n match {
diff --git a/src/dotty/tools/dotc/typer/Inferencing.scala b/src/dotty/tools/dotc/typer/Inferencing.scala
index 3dac39854..ddd95fde1 100644
--- a/src/dotty/tools/dotc/typer/Inferencing.scala
+++ b/src/dotty/tools/dotc/typer/Inferencing.scala
@@ -110,13 +110,14 @@ object Inferencing {
     }
 
     /** Type single argument and remember the unadapted result in `myTypedArg`.
-     *  used to avoid repreated typings of trees when backtracking.
+     *  used to avoid repeated typings of trees when backtracking.
      */
     def typedArg(arg: untpd.Tree, formal: Type)(implicit ctx: Context): Tree = {
       var targ = myTypedArg(arg)
       if (targ == null) {
-        targ = typer.typedUnadapted(arg, formal)
-        myTypedArg = myTypedArg.updated(arg, targ)
+        if (ctx.typerState.reporter.isSilent {
+          targ = typer.typedUnadapted(arg, formal)
+        }) myTypedArg = myTypedArg.updated(arg, targ)
       }
       typer.adapt(targ, formal)
     }