From e7ad723937e62be432419a48b0df136458652e65 Mon Sep 17 00:00:00 2001
From: Nicolas Stucki <nicolas.stucki@gmail.com>
Date: Thu, 26 Aug 2021 15:39:33 +0200
Subject: [PATCH] Allow experimental erased in experimental scopes

Closes #13392
---
 .../src/dotty/tools/dotc/parsing/Parsers.scala  |  2 +-
 .../tools/dotc/transform/PruneErasedDefs.scala  | 11 +++++++++++
 .../no-experimental/experimentalErased.scala    | 17 +++++++++++++++++
 tests/pos/experimentalErased.scala              | 17 +++++++++++++++++
 tests/pos/i13392.scala                          | 11 +++++++++++
 5 files changed, 57 insertions(+), 1 deletion(-)
 create mode 100644 tests/neg-custom-args/no-experimental/experimentalErased.scala
 create mode 100644 tests/pos/experimentalErased.scala
 create mode 100644 tests/pos/i13392.scala

diff --git a/compiler/src/dotty/tools/dotc/parsing/Parsers.scala b/compiler/src/dotty/tools/dotc/parsing/Parsers.scala
index effbfe22f0e4..da2ed12214df 100644
--- a/compiler/src/dotty/tools/dotc/parsing/Parsers.scala
+++ b/compiler/src/dotty/tools/dotc/parsing/Parsers.scala
@@ -3115,7 +3115,7 @@ object Parsers {
         case Some(prefix) =>
           in.languageImportContext = in.languageImportContext.importContext(imp, NoSymbol)
           if prefix == nme.experimental
-             && selectors.exists(sel => Feature.experimental(sel.name) != Feature.scala2macros)
+             && selectors.exists(sel => Feature.experimental(sel.name) != Feature.scala2macros && Feature.experimental(sel.name) != Feature.erasedDefinitions)
           then
             Feature.checkExperimentalFeature("features", imp.srcPos)
           for
diff --git a/compiler/src/dotty/tools/dotc/transform/PruneErasedDefs.scala b/compiler/src/dotty/tools/dotc/transform/PruneErasedDefs.scala
index b8e7a7924a79..ea3dbe0fa652 100644
--- a/compiler/src/dotty/tools/dotc/transform/PruneErasedDefs.scala
+++ b/compiler/src/dotty/tools/dotc/transform/PruneErasedDefs.scala
@@ -12,6 +12,8 @@ import typer.RefChecks
 import MegaPhase.MiniPhase
 import StdNames.nme
 import ast.tpd
+import SymUtils._
+import config.Feature
 
 /** This phase makes all erased term members of classes private so that they cannot
  *  conflict with non-erased members. This is needed so that subsequent phases like
@@ -39,13 +41,22 @@ class PruneErasedDefs extends MiniPhase with SymTransformer { thisTransform =>
     else cpy.Apply(tree)(tree.fun, tree.args.map(trivialErasedTree))
 
   override def transformValDef(tree: ValDef)(using Context): Tree =
+    checkErasedInExperimental(tree.symbol)
     if !tree.symbol.isEffectivelyErased || tree.rhs.isEmpty then tree
     else cpy.ValDef(tree)(rhs = trivialErasedTree(tree.rhs))
 
   override def transformDefDef(tree: DefDef)(using Context): Tree =
+    checkErasedInExperimental(tree.symbol)
     if !tree.symbol.isEffectivelyErased || tree.rhs.isEmpty then tree
     else cpy.DefDef(tree)(rhs = trivialErasedTree(tree.rhs))
 
+  override def transformTypeDef(tree: TypeDef)(using Context): Tree =
+    checkErasedInExperimental(tree.symbol)
+    tree
+
+  def checkErasedInExperimental(sym: Symbol)(using Context): Unit =
+    if sym.is(Erased) && !sym.isInExperimentalScope then
+      Feature.checkExperimentalFeature("erased", sym.sourcePos)
 }
 
 object PruneErasedDefs {
diff --git a/tests/neg-custom-args/no-experimental/experimentalErased.scala b/tests/neg-custom-args/no-experimental/experimentalErased.scala
new file mode 100644
index 000000000000..171318e7eb97
--- /dev/null
+++ b/tests/neg-custom-args/no-experimental/experimentalErased.scala
@@ -0,0 +1,17 @@
+import language.experimental.erasedDefinitions
+import annotation.experimental
+
+@experimental
+erased class Foo
+
+erased class Bar // error
+
+@experimental
+erased def foo = 2
+
+erased def bar = 2 // error
+
+@experimental
+erased val foo2 = 2
+
+erased val bar2 = 2 // error
\ No newline at end of file
diff --git a/tests/pos/experimentalErased.scala b/tests/pos/experimentalErased.scala
new file mode 100644
index 000000000000..e46a305ae302
--- /dev/null
+++ b/tests/pos/experimentalErased.scala
@@ -0,0 +1,17 @@
+import language.experimental.erasedDefinitions
+import annotation.experimental
+
+@experimental
+erased class Foo
+
+erased class Bar
+
+@experimental
+erased def foo = 2
+
+erased def bar = 2
+
+@experimental
+erased val foo2 = 2
+
+erased val bar2 = 2
\ No newline at end of file
diff --git a/tests/pos/i13392.scala b/tests/pos/i13392.scala
new file mode 100644
index 000000000000..de489b9aa75a
--- /dev/null
+++ b/tests/pos/i13392.scala
@@ -0,0 +1,11 @@
+package scala
+import language.experimental.erasedDefinitions
+import annotation.{implicitNotFound, experimental}
+
+@experimental
+@implicitNotFound("The capability to throw exception ${E} is missing.\nThe capability can be provided by one of the following:\n - A using clause `(using CanThrow[${E}])`\n - A `throws` clause in a result type such as `X throws ${E}`\n - an enclosing `try` that catches ${E}")
+erased class CanThrow[-E <: Exception]
+
+@experimental
+object unsafeExceptions:
+  given canThrowAny: CanThrow[Exception] = ???