Disallow old uses of quoted and spliced types

These have have been emitting migration warning in 3.0 and 3.1 even if the
syntax was already deprecated in 3.0. These where allowed syntax found
in older papers.

The case `'[T]` was actually buggy but no one reported this bug so far.
A good indication that this older syntax has not been used in a while.

First step towards fixing #15009.

Author: nicolasstucki

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

@@ -52,11 +52,12 @@ trait QuotesAndSplices {
     if ctx.mode.is(Mode.Pattern) then
       typedQuotePattern(tree, pt, qctx).withSpan(tree.span)
     else if tree.quoted.isType then
-      val msg = em"Consider using canonical type constructor scala.quoted.Type.of[${tree.quoted}] instead"
-      if sourceVersion.isAtLeast(`future-migration`) then report.error(msg, tree.srcPos)
-      else report.warning(msg, tree.srcPos)
-      val typeOfTree = untpd.TypeApply(untpd.ref(defn.QuotedTypeModule_of.termRef), tree.quoted :: Nil).withSpan(tree.span)
-      makeInlineable(typedTypeApply(typeOfTree, pt)(using quoteContext).select(nme.apply).appliedTo(qctx).withSpan(tree.span))
+      val msg = em"""Quoted types `'[..]` can only be used in patterns.
+                    |
+                    |Hint: To get a scala.quoted.Type[T] use scala.quoted.Type.of[T] instead.
+                    |""".stripMargin
+      report.error(msg, tree.srcPos)
+      EmptyTree
     else
       val exprQuoteTree = untpd.Apply(untpd.ref(defn.QuotedRuntime_exprQuote.termRef), tree.quoted)
       makeInlineable(typedApply(exprQuoteTree, pt)(using pushQuotes(qctx)).select(nme.apply).appliedTo(qctx).withSpan(tree.span))
@@ -135,7 +136,7 @@ trait QuotesAndSplices {
         case arg: untpd.Ident =>
           typedExpr(arg)
         case arg =>
-          report.error("Open patttern exprected an identifier", arg.srcPos)
+          report.error("Open pattern expected an identifier", arg.srcPos)
           EmptyTree
       }
       if args.isEmpty then
@@ -145,28 +146,16 @@ trait QuotesAndSplices {
       ref(defn.QuotedRuntimePatterns_patternHigherOrderHole).appliedToType(pt).appliedTo(typedPat, SeqLiteral(typedArgs, TypeTree(defn.AnyType)))
   }
 
-  /** Translate ${ t: Type[T] }` into type `t.splice` while tracking the quotation level in the context */
+  /** Emit error with migration hint */
   def typedTypSplice(tree: untpd.TypSplice, pt: Type)(using Context): Tree = {
-    record("typedTypSplice")
-    checkSpliceOutsideQuote(tree)
-    tree.expr match {
-      case untpd.Quote(innerType) if innerType.isType =>
-        report.warning("Canceled quote directly inside a splice. ${ '[ XYZ ] } is equivalent to XYZ.", tree.srcPos)
-      case _ =>
-    }
-
-    if ctx.mode.is(Mode.QuotedPattern) && level == 1 then
-      report.error(
-            """`$` for quote pattern variable is not supported anymore.
-               |Use lower cased variable name without the `$` instead.""".stripMargin,
-            tree.srcPos)
-      ref(defn.NothingType)
-    else
-      val tree1 = typedSelect(untpd.Select(tree.expr, tpnme.Underlying), pt)(using spliceContext).withSpan(tree.span)
-      val msg = em"Consider using canonical type reference ${tree1.tpe} instead"
-      if sourceVersion.isAtLeast(`future-migration`) then report.error(msg, tree.srcPos)
-      else report.warning(msg, tree.srcPos)
-      tree1
+    val msg = "Type splicing with `$` in quotes not supported anymore"
+    val hint =
+      if ctx.mode.is(Mode.QuotedPattern) && level == 1 then
+        "Use lower cased variable name without the `$` instead"
+      else
+        "Use a given Type[T] in a quote just write T directly"
+    report.error(s"$msg\n\nHint: $hint", tree.srcPos)
+    ref(defn.NothingType)
   }
 
   /** Type a pattern variable name `t` in quote pattern as `${given t$giveni: Type[t @ _]}`.

tests/neg/i15009a.check

@@ -0,0 +1,36 @@
+-- Error: tests/neg/i15009a.scala:3:2 ----------------------------------------------------------------------------------
+3 |  '[Int] // error
+  |  ^^^^^^
+  |  Quoted types `'[..]` can only be used in patterns.
+  |
+  |  Hint: To get a scala.quoted.Type[T] use scala.quoted.Type.of[T] instead.
+-- Error: tests/neg/i15009a.scala:4:2 ----------------------------------------------------------------------------------
+4 |  '[List[${Type.of[Int]}]] // error
+  |  ^^^^^^^^^^^^^^^^^^^^^^^^
+  |  Quoted types `'[..]` can only be used in patterns.
+  |
+  |  Hint: To get a scala.quoted.Type[T] use scala.quoted.Type.of[T] instead.
+-- Error: tests/neg/i15009a.scala:7:16 ---------------------------------------------------------------------------------
+7 |    case '[List[$a]] => // error
+  |                ^^
+  |                Type splicing with `$` in quotes not supported anymore
+  |
+  |                Hint: Use lower cased variable name without the `$` instead
+-- Error: tests/neg/i15009a.scala:10:16 --------------------------------------------------------------------------------
+10 |  '{ List.empty[$int] } // error
+   |                ^^^^
+   |                Type splicing with `$` in quotes not supported anymore
+   |
+   |                Hint: Use a given Type[T] in a quote just write T directly
+-- Error: tests/neg/i15009a.scala:11:9 ---------------------------------------------------------------------------------
+11 |  val t: ${int} = ??? // error
+   |         ^^^^^^
+   |         Type splicing with `$` in quotes not supported anymore
+   |
+   |         Hint: Use a given Type[T] in a quote just write T directly
+-- [E006] Not Found Error: tests/neg/i15009a.scala:12:2 ----------------------------------------------------------------
+12 |  $int // error: Not found: $int
+   |  ^^^^
+   |  Not found: $int
+   |
+   | longer explanation available when compiling with `-explain`

tests/neg/i15009a.scala

@@ -0,0 +1,13 @@
+import scala.quoted.*
+def test(using Quotes): Unit = {
+  '[Int] // error
+  '[List[${Type.of[Int]}]] // error
+
+  Type.of[Int] match
+    case '[List[$a]] => // error
+
+  val int = Type.of[Int]
+  '{ List.empty[$int] } // error
+  val t: ${int} = ??? // error
+  $int // error: Not found: $int
+}