Merge pull request #14250 from dotty-staging/disallow-erased-inline

Disallow erased inline definitions

Author: nicolasstucki

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

@@ -541,6 +541,9 @@ object Checking {
     checkCombination(Abstract, Override)
     checkCombination(Private, Override)
     checkCombination(Lazy, Inline)
+    // The issue with `erased inline` is that the erased semantics get lost
+    // as the code is inlined and the reference is removed before the erased usage check.
+    checkCombination(Erased, Inline)
     checkNoConflict(Lazy, ParamAccessor, s"parameter may not be `lazy`")
   }
 

tests/pos-custom-args/erased/i7878.scala

@@ -2,7 +2,7 @@ object Boom {
   import scala.compiletime.*
   trait Fail[A <: Int, B <: Int]
 
-  erased transparent inline given fail[X <: Int, Y <: Int]: Fail[X, Y] = {
+  transparent inline given fail[X <: Int, Y <: Int]: Fail[X, Y] = {
      scala.compiletime.summonFrom {
        case t: Fail[X, y] if constValue[y] < constValue[Y] => ???
     }
@@ -12,4 +12,4 @@ object Boom {
   given ev1: Fail[a.type, 2] = null
 
   summon[Fail[a.type, 3]]
-}
+}

tests/pos-custom-args/erasedInline.scala

@@ -0,0 +1,4 @@
+import language.experimental.erasedDefinitions
+
+erased inline def f: Unit = () // error: illegal combination of modifiers: `erased` and `inline` for: method f
+inline def g: Unit = ()