From df18652deb260df9c057709c9bd3a8921fbe9e4e Mon Sep 17 00:00:00 2001
From: Olivier Blanvillain <olivier.blanvillain@gmail.com>
Date: Wed, 12 Jan 2022 22:57:10 +0100
Subject: [PATCH] Fix #7512: Normalize match type arguments

The newly added test is blacklisted for pickling tests because the after
pickler code path doesn't go thought TypeApplications and keeps types
un-normalized, albeit equivalant to their before pickling counterparts.
---
 .../src/dotty/tools/dotc/core/Types.scala     |  2 +-
 .../test/dotc/pos-test-pickling.blacklist     |  1 +
 tests/pos/7512.scala                          | 24 +++++++++++++++++++
 3 files changed, 26 insertions(+), 1 deletion(-)
 create mode 100644 tests/pos/7512.scala

diff --git a/compiler/src/dotty/tools/dotc/core/Types.scala b/compiler/src/dotty/tools/dotc/core/Types.scala
index 2d02546a6d5e..b090682a4cd1 100644
--- a/compiler/src/dotty/tools/dotc/core/Types.scala
+++ b/compiler/src/dotty/tools/dotc/core/Types.scala
@@ -4171,7 +4171,7 @@ object Types {
           case MatchAlias(alias) =>
             trace(i"normalize $this", typr, show = true) {
               MatchTypeTrace.recurseWith(this) {
-                alias.applyIfParameterized(args).tryNormalize
+                alias.applyIfParameterized(args.map(_.normalized)).tryNormalize
               }
             }
           case _ =>
diff --git a/compiler/test/dotc/pos-test-pickling.blacklist b/compiler/test/dotc/pos-test-pickling.blacklist
index c913933c6537..b42d41f0df85 100644
--- a/compiler/test/dotc/pos-test-pickling.blacklist
+++ b/compiler/test/dotc/pos-test-pickling.blacklist
@@ -39,6 +39,7 @@ i9999.scala
 9757.scala
 9890.scala
 13491.scala
+7512.scala
 
 # Opaque type
 i5720.scala
diff --git a/tests/pos/7512.scala b/tests/pos/7512.scala
new file mode 100644
index 000000000000..fbc8ae6a72e3
--- /dev/null
+++ b/tests/pos/7512.scala
@@ -0,0 +1,24 @@
+import scala.compiletime.ops.int.S
+
+object InfiniteLoopMatchType {
+    def main(args: Array[String]): Unit = {
+        testProd(2, 10)
+    }
+
+    def testProd(a: Int, b: Int)(using ev: (a.type * b.type) =:= (b.type * a.type)) = true
+
+    type *[A <: Int, B <: Int] <: Int = A match {
+        case 0 => 0
+        case _ => MultiplyLoop[A, B, 0]
+    }
+
+    type MultiplyLoop[A <: Int, B <: Int, Acc <: Int] <: Int = A match {
+        case 0 => Acc
+        case S[aMinusOne] => MultiplyLoop[aMinusOne, B, B + Acc]
+    }
+
+    type +[A <: Int, B <: Int] <: Int = A match {
+        case 0 => B
+        case S[aMinusOne] => aMinusOne + S[B]
+    }
+}