Less implicit searches in overload resolution

If a directly applicable alternative exists, there is no need to try
every alternative (which would require searching for implicit
conversions for every argument that doesn't directly match). This should
not affect semantics since applicable overloads that require some
implicit conversions are dismissed in `narrowMostSpecific`

Author: smarter

src/dotty/tools/dotc/typer/Applications.scala

@@ -1146,11 +1146,17 @@ trait Applications extends Compatibility { self: Typer =>
             alts
         }
 
-        def narrowByTrees(alts: List[TermRef], args: List[Tree], resultType: Type): List[TermRef] =
-          alts filter ( alt =>
-            if (!ctx.isAfterTyper) isApplicable(alt, targs, args, resultType)
-            else isDirectlyApplicable(alt, targs, args, resultType)
+        def narrowByTrees(alts: List[TermRef], args: List[Tree], resultType: Type): List[TermRef] = {
+          val alts2 = alts.filter(alt =>
+            isDirectlyApplicable(alt, targs, args, resultType)
           )
+          if (alts2.isEmpty && !ctx.isAfterTyper)
+            alts.filter(alt =>
+              isApplicable(alt, targs, args, resultType)
+            )
+          else
+            alts2
+        }
 
         val alts1 = narrowBySize(alts)
         //ctx.log(i"narrowed by size: ${alts1.map(_.symbol.showDcl)}%, %")