From debfc2e4e1e859bde3f679850767acd545a0d0f4 Mon Sep 17 00:00:00 2001
From: Justin Garcia <purefunctor@gmail.com>
Date: Tue, 27 Feb 2024 03:16:09 +0800
Subject: [PATCH] Fix compiler crash when a type operator is used in a type
 argument (#4536)

Add missing traversal branch for VisibleTypeApp in updateTypes
---
 CHANGELOG.d/fix_issue-4535.md              |  1 +
 src/Language/PureScript/Sugar/Operators.hs |  3 ++
 tests/purs/passing/4535.purs               | 43 ++++++++++++++++++++++
 3 files changed, 47 insertions(+)
 create mode 100644 CHANGELOG.d/fix_issue-4535.md
 create mode 100644 tests/purs/passing/4535.purs

diff --git a/CHANGELOG.d/fix_issue-4535.md b/CHANGELOG.d/fix_issue-4535.md
new file mode 100644
index 0000000000..77341885a9
--- /dev/null
+++ b/CHANGELOG.d/fix_issue-4535.md
@@ -0,0 +1 @@
+* Fix compiler crash when a type operator is used in a type argument
diff --git a/src/Language/PureScript/Sugar/Operators.hs b/src/Language/PureScript/Sugar/Operators.hs
index bb06486e82..93028d7e22 100644
--- a/src/Language/PureScript/Sugar/Operators.hs
+++ b/src/Language/PureScript/Sugar/Operators.hs
@@ -409,6 +409,9 @@ updateTypes goType = (goDecl, goExpr, goBinder)
   goExpr pos (TypedValue check v ty) = do
     ty' <- goType' pos ty
     return (pos, TypedValue check v ty')
+  goExpr pos (VisibleTypeApp v ty) = do
+    ty' <- goType' pos ty
+    return (pos, VisibleTypeApp v ty')
   goExpr pos other = return (pos, other)
 
   goBinder :: SourceSpan -> Binder -> m (SourceSpan, Binder)
diff --git a/tests/purs/passing/4535.purs b/tests/purs/passing/4535.purs
new file mode 100644
index 0000000000..424ba6e7e5
--- /dev/null
+++ b/tests/purs/passing/4535.purs
@@ -0,0 +1,43 @@
+module Main where
+
+import Prelude
+
+import Data.Maybe (Maybe(..))
+import Data.Tuple.Nested ((/\), type (/\))
+import Effect (Effect)
+import Effect.Console (log)
+import Type.Proxy (Proxy(..))
+
+singleArgument :: forall @a. a -> Unit
+singleArgument _ = unit
+
+multiArgument :: forall @a @b. a -> b -> Unit
+multiArgument _ _ = unit
+
+singleApplication :: Int /\ Number -> Unit
+singleApplication = singleArgument @(Int /\ Number)
+
+-- Like expression applications, visible type applications are left-associative.
+-- This test accounts for subsequent type applications nested in this manner.
+appNestingWorks :: Int /\ Number -> Number /\ Int -> Unit
+appNestingWorks = multiArgument @(Int /\ Number) @(Number /\ Int)
+
+-- This test accounts for type applications nested within other AST nodes.
+otherNestingWorks :: Array (Maybe (Int /\ Number))
+otherNestingWorks = [Just @(Int /\ Number) (0 /\ 0.0), Just @(Int /\ Number) (1 /\ 1.0)]
+
+type InSynonym = Int /\ Number
+
+-- This test accounts for type synonyms used as type arguments.
+-- Since expansion happens during checking, InSynonym would expand
+-- to an already-desugared type operator. This test exists for the
+-- sake of redundancy.
+inSynonym :: InSynonym -> Unit
+inSynonym = singleArgument @InSynonym
+
+-- This test accounts for type operators used as type arguments directly.
+operatorAsArgument :: Proxy (/\)
+operatorAsArgument = Proxy @(/\)
+
+main :: Effect Unit
+main = log "Done"