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Co-authored-by: Eugene Flesselle <[email protected]>

Author: odersky

compiler/src/dotty/tools/dotc/inlines/InlineReducer.scala

@@ -176,7 +176,7 @@ class InlineReducer(inliner: Inliner)(using Context):
 
     /** Adjust internaly generated value definitions;
      *   - If the RHS refers to an erased symbol, mark the val as erased
-     *   - If the RHS refers to an erased symbol, mark the val as unsuable
+     *   - If the RHS refers to an unusable symbol, mark the val as unusable
      */
     def adjustErased(sym: TermSymbol, rhs: Tree): Unit =
       rhs.foreachSubTree:

docs/_docs/reference/experimental/erased-defs-spec.md

@@ -8,9 +8,10 @@ nightlyOf: https://docs.scala-lang.org/scala3/reference/experimental/erased-defs
 
 1. `erased` is a soft modifier. It can appear in a `val` definition or in a parameter.
 
-2. A reference to an `erased` value can only be used
-   * Inside the expression of argument to an `erased` parameter
-   * Inside the body of an `erased` `val` or `def`
+2. A reference to an `erased` value can only be used in an *erased context*:
+   * Inside the expression of an argument to an `erased` parameter
+   * Inside the body of an `erased` `val`
+   * Inside the path of a dependent type expression
 
 3. `erased` can also be used in a function type, e.g.
 
@@ -25,7 +26,7 @@ nightlyOf: https://docs.scala-lang.org/scala3/reference/experimental/erased-defs
 
 5. Erasure semantics
    * All `erased` parameters are removed from the function
-   * All argument to `erased` parameters are not passed to the function
+   * All arguments to `erased` parameters are not passed to the function
    * All `erased` value definitions are removed
    * All `erased` argument types are removed from a function type
 

tests/neg/i23406.scala

@@ -13,8 +13,12 @@ inline def problem[T]: String =
 inline def ok[T]: String =
   inline compiletime.erasedValue[T] match
     case x: String => "hi"
+inline def alsoOk[T](erased x: T): String =
+  inline x match
+    case x: String => "hi again"
 
 def Test =
   funny[String]  // error
   problem[String] // error
-  ok[String]
+ok[String]
+alsoOk[String](compiletime.erasedValue)

tests/neg/magic-canthrow.scala

@@ -5,7 +5,7 @@ class CanThrow[-E <: Exception]
 
 def foo[E <: Exception](e: E)(using erased CanThrow[E]): Nothing = throw e
 
-erased def magic[E]: E = magic  // error
+inline def magic[E]: E = magic
 
-def Test = foo(new IOException)(using magic)
+def Test = foo(new IOException)(using magic) // error
 

tests/pos/erased-conforms.scala

@@ -5,7 +5,7 @@ class <::<[-From, +To] extends ErasedTerm
 
 class =::=[From, To] extends (From <::< To)
 
-inline given [X] => (X =::= X) = scala.caps.unsafe.unsafeErasedValue
+inline given [X] => (X =::= X) = new =::=
 
 extension [From](x: From)
   inline def cast[To](using From <::< To): To = x.asInstanceOf[To] // Safe cast because we know `From <:< To`

tests/pos/phantom-Evidence.scala

@@ -27,5 +27,5 @@ object WithNormalState {
 
 object Utils {
   type =::=[From, To]
-  inline given tpEquals: [A] => (A =::= A) = caps.unsafe.unsafeErasedValue
+inline given tpEquals: [A] => (A =::= A) = compiletime.erasedValue
 }