Merge pull request #31 from mbovel/mb/object-anyref

Use CannotExtendAnyVal errors when an object extends AnyRef

Author: nicolasstucki

compiler/src/dotty/tools/dotc/reporting/messages.scala

@@ -876,7 +876,7 @@ extends Message(PatternMatchExhaustivityID) {
 
     val pathes = List(
       ActionPatch(
-        srcPos = endPos, 
+        srcPos = endPos,
         replacement = uncoveredCases.map(c => indent(s"case $c => ???", startColumn))
           .mkString("\n", "\n", "")
       ),
@@ -1678,10 +1678,15 @@ class CannotExtendAnyVal(sym: Symbol)(using Context)
   extends SyntaxMsg(CannotExtendAnyValID) {
   def msg(using Context) = i"""$sym cannot extend ${hl("AnyVal")}"""
   def explain(using Context) =
-    i"""Only classes (not traits) are allowed to extend ${hl("AnyVal")}, but traits may extend
-        |${hl("Any")} to become ${Green("\"universal traits\"")} which may only have ${hl("def")} members.
-        |Universal traits can be mixed into classes that extend ${hl("AnyVal")}.
-        |"""
+    if sym.is(Trait) then
+      i"""Only classes (not traits) are allowed to extend ${hl("AnyVal")}, but traits may extend
+          |${hl("Any")} to become ${Green("\"universal traits\"")} which may only have ${hl("def")} members.
+          |Universal traits can be mixed into classes that extend ${hl("AnyVal")}.
+          |"""
+    else if sym.is(Module) then
+      i"""Only classes (not objects) are allowed to extend ${hl("AnyVal")}.
+          |"""
+    else ""
 }
 
 class CannotExtendJavaEnum(sym: Symbol)(using Context)

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

@@ -716,6 +716,8 @@ object Checking {
     if (isDerivedValueClass(clazz)) {
       if (clazz.is(Trait))
         report.error(CannotExtendAnyVal(clazz), clazz.srcPos)
+      if clazz.is(Module) then
+        report.error(CannotExtendAnyVal(clazz), clazz.srcPos)
       if (clazz.is(Abstract))
         report.error(ValueClassesMayNotBeAbstract(clazz), clazz.srcPos)
       if (!clazz.isStatic)
@@ -738,10 +740,7 @@ object Checking {
               for (p <- params if !p.is(Erased))
                 report.error("value class can only have one non `erased` parameter", p.srcPos)
           case Nil =>
-            if clazz.is(Module) then
-              report.error("A module cannot extends AnyVal",clazz.srcPos)
-            else
-              report.error(ValueClassNeedsOneValParam(clazz), clazz.srcPos)
+            report.error(ValueClassNeedsOneValParam(clazz), clazz.srcPos)
         }
       }
       stats.foreach(checkValueClassMember)

tests/neg/i18274.check

@@ -1,4 +1,9 @@
--- Error: tests/neg/i18274.scala:1:7 -----------------------------------------------------------------------------------
-1 |object Foo extends AnyVal // error
+-- [E068] Syntax Error: tests/neg/i18274.scala:3:7 ---------------------------------------------------------------------
+3 |object Foo extends AnyVal // error
   |       ^
-  |       A module cannot extends AnyVal
+  |       object Foo cannot extend AnyVal
+  |---------------------------------------------------------------------------------------------------------------------
+  | Explanation (enabled by `-explain`)
+  |- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+  | Only classes (not objects) are allowed to extend AnyVal.
+   ---------------------------------------------------------------------------------------------------------------------

tests/neg/i18274.scala

@@ -1 +1,3 @@
+//> using options -explain
+
 object Foo extends AnyVal // error