Fix level checking for this.type in macros

compiler/src/dotty/tools/dotc/transform/ReifyQuotes.scala

@@ -237,7 +237,14 @@ class ReifyQuotes extends MacroTransformWithImplicits {
     def levelOK(sym: Symbol)(implicit ctx: Context): Boolean = levelOf.get(sym) match {
       case Some(l) =>
         l == level ||
-        level == -1 && sym == defn.TastyTasty_macroContext
+        level == -1 && (
+          sym == defn.TastyTasty_macroContext ||
+          // here we assume that Splicer.canBeSpliced was true before going to level -1,
+          // this implies that all non-inline arguments are quoted and that the following two cases are checked
+          // on inline parameters or type parameters.
+          sym.is(Param) ||
+          sym.isClass // reference to this in inline methods
+        )
       case None =>
         !sym.is(Param) || levelOK(sym.owner)
     }
@@ -584,9 +591,10 @@ class ReifyQuotes extends MacroTransformWithImplicits {
                   """Malformed macro.
                     |
                     |Expected the ~ to be at the top of the RHS:
-                    |  inline def foo(x: X, ..., y: Y): Int = ~impl(x, ... '(y))
+                    |  inline def foo(inline x: X, ..., y: Y): Int = ~impl(x, ... '(y))
                     |
-                    |The contents of the splice must call a static method. Arguments must be quoted or inlined.
+                    | * The contents of the splice must call a static method
+                    | * All arguments must be quoted or inline
                   """.stripMargin, tree.rhs.pos)
                 EmptyTree
             }

tests/neg/quote-this.scala

@@ -0,0 +1,29 @@
+import scala.quoted._
+
+class Foo {
+
+  def f: Unit = '{
+    def bar[T](x: T): T = x
+    bar[
+      this.type  // error
+      ] {
+      this  // error
+    }
+  }
+
+  inline def i(): Unit = ~Foo.impl[Any]('{
+    '(this) // error
+  })
+
+  inline def j(that: Foo): Unit = ~Foo.impl[Any]('{
+    '(that) // error
+  })
+
+  inline def k(): Unit = ~Foo.impl[Any](this) // error
+  inline def l(that: Foo): Unit = ~Foo.impl[Any](that) // error
+
+}
+
+object Foo {
+  def impl[T](x: Any): Expr[Unit] = '()
+}

tests/pos/quote-this.scala

@@ -0,0 +1,28 @@
+import scala.quoted._
+
+class Foo {
+  def a: Expr[Int] = '(1)
+  def b: Expr[Int] = '{
+    ~this.a
+  }
+
+  def d: Expr[Expr[Int]] = '{ '(1) }
+  def e: Expr[Expr[Int]] = '{
+    '( ~(~this.d) )
+  }
+
+  def foo[T](x: T): T = x
+
+  def f = '{
+    ~foo[this.type](this).a
+  }
+
+  inline def g(): Unit = ~Foo.impl[this.type](1)
+  inline def h(): Unit = ~Foo.impl[Any]('(this))
+  inline def i(that: Foo): Unit = ~Foo.impl[that.type](1)
+
+}
+
+object Foo {
+  def impl[T](x: Any): Expr[Unit] = '()
+}