From 8ef9cde33fc7eb98214b538bd0e9a3ff6226d6bd Mon Sep 17 00:00:00 2001
From: Nicolas Stucki <nicolas.stucki@gmail.com>
Date: Tue, 14 Nov 2023 15:25:07 +0100
Subject: [PATCH] Patch `underlyingArgument` to avoid mapping into modules

Fixes #18911

[Cherry-picked 9bfeb1c43e7f54ea36b53183726d6b83489d355a]
---
 compiler/src/dotty/tools/dotc/ast/tpd.scala |  2 +-
 tests/pos-macros/i18911/Macros_1.scala      | 91 +++++++++++++++++++++
 tests/pos-macros/i18911/Test_2.scala        |  5 ++
 3 files changed, 97 insertions(+), 1 deletion(-)
 create mode 100644 tests/pos-macros/i18911/Macros_1.scala
 create mode 100644 tests/pos-macros/i18911/Test_2.scala

diff --git a/compiler/src/dotty/tools/dotc/ast/tpd.scala b/compiler/src/dotty/tools/dotc/ast/tpd.scala
index d207e133f958..a1066a6131fc 100644
--- a/compiler/src/dotty/tools/dotc/ast/tpd.scala
+++ b/compiler/src/dotty/tools/dotc/ast/tpd.scala
@@ -1253,7 +1253,7 @@ object tpd extends Trees.Instance[Type] with TypedTreeInfo {
    */
   private class MapToUnderlying extends TreeMap {
     override def transform(tree: Tree)(using Context): Tree = tree match {
-      case tree: Ident if isBinding(tree.symbol) && skipLocal(tree.symbol) =>
+      case tree: Ident if isBinding(tree.symbol) && skipLocal(tree.symbol) && !tree.symbol.is(Module) =>
         tree.symbol.defTree match {
           case defTree: ValOrDefDef =>
             val rhs = defTree.rhs
diff --git a/tests/pos-macros/i18911/Macros_1.scala b/tests/pos-macros/i18911/Macros_1.scala
new file mode 100644
index 000000000000..677610fd9536
--- /dev/null
+++ b/tests/pos-macros/i18911/Macros_1.scala
@@ -0,0 +1,91 @@
+import scala.quoted._
+import scala.compiletime.testing.{typeChecks, typeCheckErrors}
+
+trait Assertion
+trait Bool {
+  def value: Boolean
+}
+class SimpleMacroBool(expression: Boolean) extends Bool {
+  override def value: Boolean = expression
+}
+class BinaryMacroBool(left: Any, operator: String, right: Any, expression: Boolean) extends Bool {
+  override def value: Boolean = expression
+}
+object Bool {
+  def simpleMacroBool(expression: Boolean): Bool = new SimpleMacroBool(expression)
+  def binaryMacroBool(left: Any, operator: String, right: Any, expression: Boolean): Bool =
+    new BinaryMacroBool(left, operator, right, expression)
+  def binaryMacroBool(left: Any, operator: String, right: Any, bool: Bool): Bool =
+    new BinaryMacroBool(left, operator, right, bool.value)
+}
+
+object Assertions {
+  inline def assert(inline condition: Boolean): Assertion =
+    ${ AssertionsMacro.assert('{ condition }) }
+}
+
+object AssertionsMacro {
+  def assert(condition: Expr[Boolean])(using Quotes): Expr[Assertion] =
+    transform(condition)
+
+  def transform(
+      condition: Expr[Boolean]
+  )(using Quotes): Expr[Assertion] = {
+    val bool = BooleanMacro.parse(condition)
+    '{
+      new Assertion {
+        val condition = $bool
+      }
+  }
+  }
+}
+
+object BooleanMacro {
+  private val supportedBinaryOperations =
+    Set("!=", "==")
+
+  def parse(condition: Expr[Boolean])(using Quotes): Expr[Bool] = {
+    import quotes.reflect._
+    import quotes.reflect.ValDef.let
+    import util._
+
+    def exprStr: String = condition.show
+    def defaultCase = '{ Bool.simpleMacroBool($condition) }
+
+    def isByNameMethodType(tp: TypeRepr): Boolean = tp.widen match {
+      case MethodType(_, ByNameType(_) :: Nil, _) => true
+      case _                                      => false
+    }
+
+    condition.asTerm.underlyingArgument match { // WARNING: unsound use of `underlyingArgument`
+      case Apply(sel @ Select(lhs, op), rhs :: Nil) =>
+        def binaryDefault =
+          if (isByNameMethodType(sel.tpe)) defaultCase
+          else if (supportedBinaryOperations.contains(op)) {
+            let(Symbol.spliceOwner, lhs) { left =>
+              let(Symbol.spliceOwner, rhs) { right =>
+                val app = left.select(sel.symbol).appliedTo(right)
+                let(Symbol.spliceOwner, app) { result =>
+                  val l = left.asExpr
+                  val r = right.asExpr
+                  val b = result.asExprOf[Boolean]
+                  val code = '{ Bool.binaryMacroBool($l, ${ Expr(op) }, $r, $b) }
+                  code.asTerm
+                }
+              }
+            }.asExprOf[Bool]
+          } else defaultCase
+
+        op match {
+          case "==" => binaryDefault
+          case _    => binaryDefault
+        }
+
+      case Literal(_) =>
+        '{ Bool.simpleMacroBool($condition) }
+
+      case _ =>
+        defaultCase
+    }
+  }
+}
diff --git a/tests/pos-macros/i18911/Test_2.scala b/tests/pos-macros/i18911/Test_2.scala
new file mode 100644
index 000000000000..5c253d5e8e1b
--- /dev/null
+++ b/tests/pos-macros/i18911/Test_2.scala
@@ -0,0 +1,5 @@
+@main def Test = {
+  case class Document()
+  val expected: Document = ???
+  Assertions.assert( expected == Document()) // error
+}