more checks of overloaded specs

Summary: - if we cannot select a single sub-spec, - "unionize" types of parameters and check obvious cases when arguments are of wrong types

Reviewed By: VLanvin

Differential Revision: D63639932

fbshipit-source-id: c01c5f0ab0e61e0d8171739ed92e4207cd76665f

eqwalizer/src/main/resources/application.conf

@@ -16,4 +16,6 @@ eqwalizer {
     custom_maps_merge = ${?EQWALIZER_CUSTOM_MAPS_MERGE}
     ignored_overloaded_spec = false
     ignored_overloaded_spec = ${?EQWALIZER_IGNORED_OVERLOADED_SPEC}
+    overloaded_spec_domain_check = false
+    overloaded_spec_domain_check = ${?EQWALIZER_OVERLOADED_SPEC_DOMAIN_CHECK}
 }

eqwalizer/src/main/scala/com/whatsapp/eqwalizer/package.scala

@@ -38,6 +38,7 @@ package object eqwalizer {
       mode: Mode.Mode,
       errorDepth: Int,
       ignoredOverloadedSpec: Boolean,
+      overloadedSpecDomainCheck: Boolean,
   )
 
   lazy val config: Config = {
@@ -54,6 +55,7 @@ package object eqwalizer {
       mode,
       errorDepth = config.getInt("error_depth"),
       ignoredOverloadedSpec = config.getBoolean("ignored_overloaded_spec"),
+      overloadedSpecDomainCheck = config.getBoolean("overloaded_spec_domain_check"),
     )
   }
 }

eqwalizer/src/main/scala/com/whatsapp/eqwalizer/tc/ElabApplyOverloaded.scala

@@ -33,13 +33,28 @@ class ElabApplyOverloaded(pipelineContext: PipelineContext) {
       case _ =>
         if (pipelineCtx.overloadedSpecDynamicResult && typeInfo.isCollect)
           diagnosticsInfo.add(NoSpecialType(expr.pos, expr, argTys))
+        if (pipelineContext.overloadedSpecDomainCheck)
+          toFunType(depFunSpec).foreach(ft => elabApply.elabApply(check.freshen(ft), args, argTys, env1))
         (DynamicType, env1)
     }
   }
 
   def isOverloadedFun(remoteId: RemoteId): Boolean =
     util.getOverloadedSpec(remoteId).isDefined
 
+  private def toFunType(depFunSpec: OverloadedFunSpec): Option[FunType] = {
+    // If a sub-spec has generic vars, - transforming it to a FunType is tricky in general case.
+    // Skipping overloaded specs with generic vars for now (for simplicity).
+    if (depFunSpec.tys.forall(_.forall.isEmpty)) {
+      val result = depFunSpec.tys.reduce { (acc, elem) =>
+        val argTys = acc.argTys.zip(elem.argTys).map { case (t1, t2) => subtype.join(t1, t2) }
+        FunType(Nil, argTys, DynamicType)
+      }
+      Some(result)
+    } else
+      None
+  }
+
   private def mightOverlap(t1: Type, t2: Type): Boolean = {
     val approxMeet = narrow.meet(t1, t2)
     !subtype.subType(approxMeet, NoneType)

eqwalizer/src/main/scala/com/whatsapp/eqwalizer/tc/package.scala

@@ -70,5 +70,6 @@ package object tc {
     val overloadedSpecDynamicResult: Boolean = config.overloadedSpecDynamicResult
     val customMapsMerge: Boolean = config.customMapsMerge
     val ignoredOverloadedSpec: Boolean = config.ignoredOverloadedSpec
+    val overloadedSpecDomainCheck: Boolean = config.overloadedSpecDomainCheck
   }
 }