Refactor implementation of lookupCompanion

  - Check for module class up front to use sourceModule
  - Consolidate most of the logic in Contexts

Author: retronym

src/compiler/scala/tools/nsc/typechecker/Contexts.scala

@@ -1193,27 +1193,33 @@ trait Contexts { self: Analyzer =>
       res
     }
 
-    final def lookupCompanionOf(original: Symbol): Symbol = {
-      if (original.isModuleClass) original.sourceModule
-      else lookupScopeEntry(original) match {
-        case null => NoSymbol
-        case entry => entry.owner.lookupCompanion(original)
+    final def lookupCompanionInIncompleteOwner(original: Symbol): Symbol = {
+      /* Search scopes in current and enclosing contexts for the definition of `symbol` */
+      def lookupScopeEntry(symbol: Symbol): ScopeEntry = {
+        var res: ScopeEntry = null
+        var ctx = this
+        while (res == null && ctx.outer != ctx) {
+          val s = ctx.scope lookupSymbolEntry symbol
+          if (s != null)
+            res = s
+          else
+            ctx = ctx.outer
+        }
+        res
       }
-    }
 
-    /** Search scopes in current and enclosing contexts for the definition of `symbol` */
-    private def lookupScopeEntry(symbol: Symbol): ScopeEntry = {
-      var res: ScopeEntry = null
-      var ctx = this
-      while (res == null && ctx.outer != ctx) {
-        val s = ctx.scope lookupSymbolEntry symbol
-        if (s != null)
-          res = s
-        else
-          ctx = ctx.outer
+      // 1) Must be owned by the same Scope, to ensure that in
+      //   `{ class C; { ...; object C } }`, the class is not seen as a companion of the object.
+      // 2) Must be a class and module symbol, so that `{ class C; def C }` or `{ type T; object T }` are not companions.
+      lookupScopeEntry(original) match {
+        case null => NoSymbol
+        case entry =>
+          def isCompanion(sym: Symbol): Boolean =
+            (original.isModule && sym.isClass || sym.isModule && original.isClass) && sym.isCoDefinedWith(original)
+          entry.owner.lookupNameInSameScopeAs(original, original.name.companionName).filter(isCompanion)
       }
-      res
     }
+
   } //class Context
 
   /** A `Context` focussed on an `Import` tree */

src/compiler/scala/tools/nsc/typechecker/Namers.scala

@@ -1955,9 +1955,12 @@ trait Namers extends MethodSynthesis {
     //         Doing this generally would trigger cycles; that's what we also
     //         use the lower-level scan through the current Context as a fall back.
     if (!currentRun.compiles(owner)) owner.initialize
-    original.companionSymbol orElse {
-      ctx.lookupCompanionOf(original)
-    }
+
+    if (original.isModuleClass) original.sourceModule
+    else if (!owner.isTerm && owner.hasCompleteInfo)
+      original.companionSymbol
+    else
+      ctx.lookupCompanionInIncompleteOwner(original)
   }
 
   /** A version of `Symbol#linkedClassOfClass` that works with local companions, ala `companionSymbolOf`. */

src/reflect/scala/reflect/internal/Scopes.scala

@@ -291,25 +291,6 @@ trait Scopes extends api.Scopes { self: SymbolTable =>
       null
     }
 
-    final def lookupCompanion(original: Symbol): Symbol = {
-      lookupSymbolEntry(original) match {
-        case null =>
-        case entry =>
-          var e = lookupEntry(original.name.companionName)
-          while (e != null) {
-            // 1) Must be owned by the same Scope, to ensure that in
-            //   `{ class C; { ...; object C } }`, the class is not seen as a companion of the object.
-            // 2) Must be a class and module symbol, so that `{ class C; def C }` or `{ type T; object T }` are not companions.
-            def isClassAndModule(sym1: Symbol, sym2: Symbol) = sym1.isClass && sym2.isModule
-            if ((e.owner eq entry.owner) && (isClassAndModule(original, e.sym) || isClassAndModule(e.sym, original))) {
-              return if (e.sym.isCoDefinedWith(original)) e.sym else NoSymbol
-            }
-            e = lookupNextEntry(e)
-          }
-      }
-      NoSymbol
-    }
-
     /** lookup a symbol entry matching given name.
      *  @note from Martin: I believe this is a hotspot or will be one
      *  in future versions of the type system. I have reverted the previous
@@ -345,6 +326,20 @@ trait Scopes extends api.Scopes { self: SymbolTable =>
       e
     }
 
+    final def lookupNameInSameScopeAs(original: Symbol, companionName: Name): Symbol = {
+      lookupSymbolEntry(original) match {
+        case null =>
+        case entry =>
+          var e = lookupEntry(companionName)
+          while (e != null) {
+            if (e.owner eq entry.owner) return e.sym
+            e = lookupNextEntry(e)
+          }
+      }
+      NoSymbol
+    }
+
+
     /** TODO - we can test this more efficiently than checking isSubScope
      *  in both directions. However the size test might be enough to quickly
      *  rule out most failures.