From 4bb7b84db0a0c2404d22eb0ed7f9e8ae3e9477a0 Mon Sep 17 00:00:00 2001
From: Kiryl Dziamura <kiryl.dziamura@gmail.com>
Date: Fri, 23 Jun 2023 00:56:19 +0200
Subject: [PATCH] Fix desugar step for pizza operator

---
 .../ast/src/lang/core/expr/expr_to_expr2.rs   |  8 +---
 crates/compiler/can/src/expr.rs               | 11 +++---
 crates/compiler/can/src/operator.rs           | 18 ++++++++-
 crates/reporting/tests/test_reporting.rs      | 38 +++++++++++++++++++
 4 files changed, 61 insertions(+), 14 deletions(-)

diff --git a/crates/ast/src/lang/core/expr/expr_to_expr2.rs b/crates/ast/src/lang/core/expr/expr_to_expr2.rs
index cdbc12a054f..c76375d478c 100644
--- a/crates/ast/src/lang/core/expr/expr_to_expr2.rs
+++ b/crates/ast/src/lang/core/expr/expr_to_expr2.rs
@@ -665,14 +665,10 @@ pub fn expr_to_expr2<'a>(
             ident,
         } => canonicalize_lookup(env, scope, module_name, ident, region),
 
+        ParensAround(sub_expr) => expr_to_expr2(env, scope, sub_expr, region),
+
         // Below this point, we shouln't see any of these nodes anymore because
         // operator desugaring should have removed them!
-        bad_expr @ ParensAround(_) => {
-            panic!(
-                "A ParensAround did not get removed during operator desugaring somehow: {:#?}",
-                bad_expr
-            );
-        }
         bad_expr @ SpaceBefore(_, _) => {
             panic!(
                 "A SpaceBefore did not get removed during operator desugaring somehow: {:#?}",
diff --git a/crates/compiler/can/src/expr.rs b/crates/compiler/can/src/expr.rs
index 62ee13504ba..0beecfd7004 100644
--- a/crates/compiler/can/src/expr.rs
+++ b/crates/compiler/can/src/expr.rs
@@ -1403,14 +1403,13 @@ pub fn canonicalize_expr<'a>(
 
             (answer, Output::default())
         }
+        &ast::Expr::ParensAround(sub_expr) => {
+            let (loc_expr, output) = canonicalize_expr(env, var_store, scope, region, sub_expr);
+
+            (loc_expr.value, output)
+        }
         // Below this point, we shouln't see any of these nodes anymore because
         // operator desugaring should have removed them!
-        bad_expr @ ast::Expr::ParensAround(_) => {
-            internal_error!(
-                "A ParensAround did not get removed during operator desugaring somehow: {:#?}",
-                bad_expr
-            );
-        }
         bad_expr @ ast::Expr::SpaceBefore(_, _) => {
             internal_error!(
                 "A SpaceBefore did not get removed during operator desugaring somehow: {:#?}",
diff --git a/crates/compiler/can/src/operator.rs b/crates/compiler/can/src/operator.rs
index 8db8f8ff76c..0efd582a9d0 100644
--- a/crates/compiler/can/src/operator.rs
+++ b/crates/compiler/can/src/operator.rs
@@ -288,7 +288,7 @@ pub fn desugar_expr<'a>(arena: &'a Bump, loc_expr: &'a Loc<Expr<'a>>) -> &'a Loc
 
                             break builder_arg.closure;
                         }
-                        SpaceBefore(expr, _) | SpaceAfter(expr, _) | ParensAround(expr) => {
+                        SpaceBefore(expr, _) | SpaceAfter(expr, _) => {
                             current = *expr;
                         }
                         _ => break loc_arg,
@@ -382,7 +382,7 @@ pub fn desugar_expr<'a>(arena: &'a Bump, loc_expr: &'a Loc<Expr<'a>>) -> &'a Loc
                 region: loc_expr.region,
             })
         }
-        SpaceBefore(expr, _) | SpaceAfter(expr, _) | ParensAround(expr) => {
+        SpaceBefore(expr, _) | SpaceAfter(expr, _) => {
             // Since we've already begun canonicalization, spaces and parens
             // are no longer needed and should be dropped.
             desugar_expr(
@@ -393,6 +393,20 @@ pub fn desugar_expr<'a>(arena: &'a Bump, loc_expr: &'a Loc<Expr<'a>>) -> &'a Loc
                 }),
             )
         }
+        ParensAround(expr) => {
+            let desugared = desugar_expr(
+                arena,
+                arena.alloc(Loc {
+                    value: **expr,
+                    region: loc_expr.region,
+                }),
+            );
+
+            arena.alloc(Loc {
+                value: ParensAround(&desugared.value),
+                region: loc_expr.region,
+            })
+        }
         If(if_thens, final_else_branch) => {
             // If does not get desugared into `when` so we can give more targeted error messages during type checking.
             let desugared_final_else = &*arena.alloc(desugar_expr(arena, final_else_branch));
diff --git a/crates/reporting/tests/test_reporting.rs b/crates/reporting/tests/test_reporting.rs
index 4d51d7c1907..574dba08661 100644
--- a/crates/reporting/tests/test_reporting.rs
+++ b/crates/reporting/tests/test_reporting.rs
@@ -13841,4 +13841,42 @@ In roc, functions are always written as a lambda, like{}
     Tip: It looks like it takes too many arguments. I'm seeing 1 extra.
     "###
     );
+
+    test_report!(
+        pizza_parens_right,
+        indoc!(
+            r#"
+            2 |> (Num.sub 3)
+            "#
+        ),
+        @r###"
+        ── TOO FEW ARGS ────────────────────────────────────────── /code/proj/Main.roc ─
+        The `sub` function expects 2 arguments, but it got only 1:
+        
+        4│      2 |> (Num.sub 3)
+                      ^^^^^^^
+        
+        Roc does not allow functions to be partially applied. Use a closure to
+        make partial application explicit.
+        "###
+    );
+
+    test_report!(
+        pizza_parens_middle,
+        indoc!(
+            r#"
+            2 |> (Num.sub 3) |> Num.sub 3
+            "#
+        ),
+        @r###"
+        ── TOO FEW ARGS ────────────────────────────────────────── /code/proj/Main.roc ─
+        The `sub` function expects 2 arguments, but it got only 1:
+        
+        4│      2 |> (Num.sub 3) |> Num.sub 3
+                      ^^^^^^^
+        
+        Roc does not allow functions to be partially applied. Use a closure to
+        make partial application explicit.
+        "###
+    );
 }