Fix #2421: Add errors for inline on non supported trees

Author: nicolasstucki

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

@@ -550,6 +550,28 @@ trait Checking {
       tp
   }
 
+  /** Check that inline is only used on valid trees */
+  def checkInlineKeyword(tree: tpd.Tree)(implicit ctx: Context) = {
+    def errorOn(what: String) =
+      ctx.error("inlined keyword cannot be used on " + what, tree.pos)
+    val sym = tree.symbol
+    if (sym is Inline) {
+      tree match {
+        case _: TypeDef =>
+          if (!sym.isClass) errorOn("type")
+          else if (sym.is(Trait)) errorOn("trait")
+          else if (sym.is(Abstract)) errorOn("abstract class")
+          else errorOn("class") // Remove this to allow inline classes
+        case _: ValDef =>
+          if (sym.is(Module)) errorOn("object")
+          else if (sym.is(Mutable)) errorOn("var")
+          else if (sym.is(Lazy)) errorOn("lazy val")
+        case _ =>
+
+      }
+    }
+  }
+
   /** Check that `tree` is a pure expression of constant type */
   def checkInlineConformant(tree: Tree, what: => String)(implicit ctx: Context): Unit =
     tree.tpe match {

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

@@ -1228,6 +1228,7 @@ class Typer extends Namer with TypeAssigner with Applications with Implicits wit
       case rhs => typedExpr(rhs, tpt1.tpe)
     }
     val vdef1 = assignType(cpy.ValDef(vdef)(name, tpt1, rhs1), sym)
+    checkInlineKeyword(vdef1)
     if (sym.is(Inline, butNot = DeferredOrParamAccessor))
       checkInlineConformant(rhs1, em"right-hand side of inline $sym")
     patchIfLazy(vdef1)
@@ -1310,7 +1311,9 @@ class Typer extends Namer with TypeAssigner with Applications with Implicits wit
       case rhs =>
         typedType(rhs)
     }
-    assignType(cpy.TypeDef(tdef)(name, rhs1), sym)
+    val tdef1 = assignType(cpy.TypeDef(tdef)(name, rhs1), sym)
+    checkInlineKeyword(tdef1)
+    tdef1
   }
 
   def typedClassDef(cdef: untpd.TypeDef, cls: ClassSymbol)(implicit ctx: Context) = track("typedClassDef") {
@@ -1412,11 +1415,15 @@ class Typer extends Namer with TypeAssigner with Applications with Implicits wit
       // check value class constraints
       checkDerivedValueClass(cls, body1)
 
+      checkInlineKeyword(cdef1)
+
       if (ctx.settings.YretainTrees.value) {
         cls.myTree = cdef1
       }
       cdef1
 
+    cdef1
+
       // todo later: check that
       //  1. If class is non-abstract, it is instantiatable:
       //  - self type is s supertype of own type

tests/neg/i2421.scala

@@ -0,0 +1,10 @@
+inline object Foo // error: inlined keyword cannot be used on object
+inline class Bar // error: inlined keyword cannot be used on class
+inline abstract class Baz // error: inlined keyword cannot be used on abstract class
+inline trait Qux // error: inlined keyword cannot be used on trait
+
+object Quux {
+  inline type T // error: inlined keyword cannot be used on type
+  inline var x: Int = 42 // error: inlined keyword cannot be used on var
+  inline lazy val y: Int = 42 // error: inlined keyword cannot be used on lazy val
+}