Only allow access to inline args at level 0

If it is needed at level 1 it can be explicitly lifted.
This simplifies the rules that users need to know and
the implementation of the phase.

Author: nicolasstucki

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

@@ -236,7 +236,7 @@ class ReifyQuotes extends MacroTransformWithImplicits with InfoTransformer {
       case tree: DefTree =>
         val sym = tree.symbol
         if ((sym.isClass || !sym.maybeOwner.isType) && !levelOf.contains(sym)) {
-          levelOf(sym) = level
+          levelOf(sym) = if (sym.is(Inline)) level - 1 else level
           enteredSyms = sym :: enteredSyms
         }
       case _ =>
@@ -250,7 +250,7 @@ class ReifyQuotes extends MacroTransformWithImplicits with InfoTransformer {
     def levelOK(sym: Symbol)(implicit ctx: Context): Boolean = levelOf.get(sym) match {
       case Some(l) =>
         l == level ||
-        l == 1 && level == 0 && isStage0Value(sym)
+        (0 == level && isStage0Value(sym))
       case None =>
         !sym.is(Param) || levelOK(sym.owner)
     }
@@ -384,15 +384,9 @@ class ReifyQuotes extends MacroTransformWithImplicits with InfoTransformer {
       }
       else body match {
         case body: RefTree if isCaptured(body.symbol, level + 1) =>
-          if (isStage0Value(body.symbol)) {
-            // Optimization: avoid the full conversion when capturing inlined `x`
-            // in '{ x } to '{ x$1.toExpr.unary_~ } and go directly to `x$1.toExpr`
-            liftValue(capturers(body.symbol)(body))
-          } else {
-            // Optimization: avoid the full conversion when capturing `x`
-            // in '{ x } to '{ x$1.unary_~ } and go directly to `x$1`
-            capturers(body.symbol)(body)
-          }
+          // Optimization: avoid the full conversion when capturing `x`
+          // in '{ x } to '{ x$1.unary_~ } and go directly to `x$1`
+          capturers(body.symbol)(body)
         case _=>
           val (body1, splices) = nested(isQuote = true).split(body)
           pickledQuote(body1, splices, body.tpe, isType).withPos(quote.pos)
@@ -575,9 +569,8 @@ class ReifyQuotes extends MacroTransformWithImplicits with InfoTransformer {
             val capturer = capturers(tree.symbol)
             def captureAndSplice(t: Tree) =
               splice(t.select(if (tree.isTerm) nme.UNARY_~ else tpnme.UNARY_~))
-            if (!isStage0Value(tree.symbol)) captureAndSplice(capturer(tree))
-            else if (level == 0) capturer(tree)
-            else captureAndSplice(liftValue(capturer(tree)))
+            if (level == 0 && isStage0Value(tree.symbol)) capturer(tree)
+            else captureAndSplice(capturer(tree))
           case Block(stats, _) =>
             val last = enteredSyms
             stats.foreach(markDef)
@@ -632,21 +625,6 @@ class ReifyQuotes extends MacroTransformWithImplicits with InfoTransformer {
         }
       }
 
-    private def liftValue(tree: Tree)(implicit ctx: Context): Tree = {
-      val reqType = defn.QuotedLiftableType.appliedTo(tree.tpe.widen)
-      val liftable = ctx.typer.inferImplicitArg(reqType, tree.pos)
-      liftable.tpe match {
-        case fail: SearchFailureType =>
-          ctx.error(i"""
-                  |
-                  | The access would be accepted with the right Liftable, but
-                  | ${ctx.typer.missingArgMsg(liftable, reqType, "")}""")
-          EmptyTree
-        case _ =>
-          liftable.select("toExpr".toTermName).appliedTo(tree)
-      }
-    }
-
     private def isStage0Value(sym: Symbol)(implicit ctx: Context): Boolean =
       (sym.is(Inline) && sym.owner.is(Macro) && !defn.isFunctionType(sym.info)) ||
       sym == defn.TastyTopLevelSplice_compilationTopLevelSplice // intrinsic value at stage 0

docs/docs/reference/principled-meta-programming.md

@@ -400,7 +400,7 @@ as follows:
    function) of type Boolean, Byte, Short, Int, Long, Float, Double,
    Char or String, it can be accessed in all contexts where the number
    of splices minus the number of quotes between use and definition
-   is either 0 or 1.
+   is 0.
 
 ### Relationship with Staging
 

tests/neg/quote-macro-inline-args.scala

@@ -0,0 +1,9 @@
+object Test {
+
+  inline def foo(inline x: Int): Int = ~{
+    if (x == 1) '(3)
+    else '(x) // error
+  }
+
+}
+