Merge pull request scala#7107 from retronym/topic/implicit-imports

Avoid expensive call to `imports` in implicit search
ronanM · Aug 20, 2018 · e7d934c · e7d934c
2 parents b339d6f + 2fae7d8
commit e7d934c
Showing 1 changed file with 7 additions and 4 deletions.
diff --git a/src/compiler/scala/tools/nsc/typechecker/Contexts.scala b/src/compiler/scala/tools/nsc/typechecker/Contexts.scala
@@ -1069,7 +1069,7 @@ trait Contexts { self: Analyzer =>
 
     /** @return None if a cycle is detected, or Some(infos) containing the in-scope implicits at this context */
     private def implicits(nextOuter: Context): Option[List[ImplicitInfo]] = {
-      val imports = this.imports
+      val firstImport = this.firstImport
       if (owner != nextOuter.owner && owner.isClass && !owner.isPackageClass && !inSelfSuperCall) {
         if (!owner.isInitialized) None
         else savingEnclClass(this) {
@@ -1082,13 +1082,14 @@ trait Contexts { self: Analyzer =>
         debuglog("collect local implicits " + scope.toList)//DEBUG
         Some(collectImplicits(scope, NoPrefix))
       } else if (firstImport != nextOuter.firstImport) {
-        assert(imports.tail.headOption == nextOuter.firstImport, (imports, nextOuter.imports))
-        Some(collectImplicitImports(imports.head))
+        if (isDeveloper)
+          assert(imports.tail.headOption == nextOuter.firstImport, (imports, nextOuter.imports))
+        Some(collectImplicitImports(firstImport.get))
       } else if (owner.isPackageClass) {
         // the corresponding package object may contain implicit members.
         val pre = owner.packageObject.typeOfThis
         Some(collectImplicits(pre.implicitMembers, pre))
-      } else Some(Nil)
+      } else SomeNil
     }
 
     //
@@ -1728,6 +1729,8 @@ trait Contexts { self: Analyzer =>
     private def imp1Explicit = imp1 isExplicitImport name
     private def imp2Explicit = imp2 isExplicitImport name
   }
+
+  private final val SomeNil = Some(Nil)
 }
 
 object ContextMode {