From b0b6ec52768699c1394558ef57f50114c91c113c Mon Sep 17 00:00:00 2001
From: Nicolas Stucki <nicolas.stucki@gmail.com>
Date: Fri, 16 Feb 2024 09:02:24 +0100
Subject: [PATCH] Add patch for undefined behavior with `object $`

Add an ad-hoc patch to make it possible to use the broken `object $`
definitions in https://github.com/com-lihaoyi/Ammonite/blob/main/amm/interp/api/src/main/scala/ammonite/Stubs.scala.

This is a temporary patch while these definitions get deprecated. There
is not guarantee that the semantics of these objects are correct. There
is also no way to adapt the spec to allow there definition without breaking
the language. For example consider `object $` and `object $$`, how would
we know if the `$$.class` is the class of `$$` or the module class of `$`.
We need to know this before we read the file.
---
 compiler/src/dotty/tools/dotc/classpath/FileUtils.scala | 4 ++++
 tests/pos/i19702/Macro_1.scala                          | 9 +++++++++
 tests/pos/i19702/Test_2.scala                           | 4 ++++
 3 files changed, 17 insertions(+)
 create mode 100644 tests/pos/i19702/Macro_1.scala
 create mode 100644 tests/pos/i19702/Test_2.scala

diff --git a/compiler/src/dotty/tools/dotc/classpath/FileUtils.scala b/compiler/src/dotty/tools/dotc/classpath/FileUtils.scala
index 8c31faa43186..b8cb9a2155dc 100644
--- a/compiler/src/dotty/tools/dotc/classpath/FileUtils.scala
+++ b/compiler/src/dotty/tools/dotc/classpath/FileUtils.scala
@@ -114,6 +114,10 @@ object FileUtils {
       if classOrModuleName.endsWith("$")
         && classOrModuleName != "Null$" // scala.runtime.Null$
         && classOrModuleName != "Nothing$" // scala.runtime.Nothing$
+        // Special case for `object $` in Amonite.
+        // This is an ad-hoc workaround for Amonite `object $`. See issue #19702
+        // This definition is not valid Scala.
+        && classOrModuleName != "$"
       then classOrModuleName.stripSuffix("$")
       else classOrModuleName
     className + SUFFIX_TASTY
diff --git a/tests/pos/i19702/Macro_1.scala b/tests/pos/i19702/Macro_1.scala
new file mode 100644
index 000000000000..79aab856dfda
--- /dev/null
+++ b/tests/pos/i19702/Macro_1.scala
@@ -0,0 +1,9 @@
+package test
+
+// IMPORTANT: this object has undefined behavior due to its illegal use of a $ in an identifier
+//            This test is only to check that the ad-hoc workaround for Amonite `object $` is working.
+//            If at some point it becomes impossible to support this test, we can drop it.
+//            Ideally Amonite will have deprecated the `object $` by then.
+object $ {
+  def test(): Int = 1
+}
diff --git a/tests/pos/i19702/Test_2.scala b/tests/pos/i19702/Test_2.scala
new file mode 100644
index 000000000000..c8bcd4287e0d
--- /dev/null
+++ b/tests/pos/i19702/Test_2.scala
@@ -0,0 +1,4 @@
+@main def hello =
+  test.$.test()
+
+  println("?")