Include mixins when checking for cyclic exports

Author: bracevac

compiler/src/dotty/tools/dotc/typer/Namer.scala

@@ -1179,11 +1179,11 @@ class Namer { typer: Typer =>
          * The export selects a member of the current class (issue #22147).
          * Assumes that cls.classInfo.selfType.derivesFrom(sym.owner) is true.
          */
-        def isCurrentMember: Boolean = expr match
+        def isCurrentClassMember: Boolean = expr match
           case id: (Ident | This) => // Access through self type or this
             /* Given the usage context below, where cls's self type is a subtype of sym.owner,
-               it suffices to check if the denotation is a ClassInfo */
-            id.denot.info.isInstanceOf[ClassInfo]
+               it suffices to check if symbol is the same class. */
+            cls == id.symbol
           case _ => false
         if !sym.isAccessibleFrom(pathType) then
           No("is not accessible")
@@ -1194,7 +1194,7 @@ class Namer { typer: Typer =>
         // * the symbols owner is the cls itself
         // * the symbol is not a deferred symbol
         // * the symbol is a member of the current class (#22147)
-        else if cls.classInfo.selfType.derivesFrom(sym.owner) && (sym.owner == cls || !sym.is(Deferred) || isCurrentMember) then
+        else if cls.classInfo.selfType.derivesFrom(sym.owner) && (sym.owner == cls || !sym.is(Deferred) || isCurrentClassMember) then
           No(i"is already a member of $cls")
         else if pathMethod.exists && mbr.isType then
           No("is a type, so it cannot be exported as extension method")

tests/neg/exports3.scala

@@ -12,7 +12,7 @@ trait R extends P:
   val a1: A
   val a2: A
 
-class B extends R:
+abstract class B extends R:
   self =>
     export this.baz     // error
     export self.bar     // error
@@ -34,4 +34,8 @@ abstract class F:
 
 class G(p: P):
   self: P =>
-    export p.foo
+    export p.foo
+
+class H(p: P):
+  self: P =>
+    export this.p.foo

tests/neg/i20245.check

@@ -15,3 +15,17 @@
    |               Run with both -explain-cyclic and -Ydebug-cyclic to see full stack trace.
    |
    | longer explanation available when compiling with `-explain`
+-- [E046] Cyclic Error: tests/neg/i20245/Typer_2.scala:10:7 ------------------------------------------------------------
+10 |import effekt.source.{ resolve } // error
+   |       ^
+   |       Cyclic reference involving class Context
+   |
+   |       The error occurred while trying to compute the base classes of class Context
+   |         which required to compute the base classes of trait TyperOps
+   |         which required to compute the signature of trait TyperOps
+   |         which required to elaborate the export clause export unification.requireSubtype
+   |         which required to compute the base classes of class Context
+   |
+   |        Run with both -explain-cyclic and -Ydebug-cyclic to see full stack trace.
+   |
+   | longer explanation available when compiling with `-explain`

tests/neg/i20245/Typer_2.scala

@@ -7,7 +7,7 @@ import effekt.util.messages.ErrorReporter
 import effekt.context.{ Context }
 
 // This import is also NECESSARY for the cyclic error
-import effekt.source.{ resolve }
+import effekt.source.{ resolve } // error
 
 
 trait TyperOps extends ErrorReporter { self: Context =>