From f1c577aab64ef0cd083363869d2746b4374484ad Mon Sep 17 00:00:00 2001
From: Dan Lynch <pyramation@gmail.com>
Date: Sun, 15 Mar 2026 03:42:28 +0000
Subject: [PATCH] fix(deparser): preserve parentheses around binary expressions
 in unary operators

Fixes #285. The unary operator handler in A_Expr did not wrap a binary
A_Expr rexpr in parentheses, causing -(a - b) to deparse as - a - b,
which changes operator precedence and produces incorrect math.

Also affects TypeCast conversions: (-(a - b))::numeric became
CAST(- a - b AS numeric) instead of CAST(- (a - b) AS numeric).
---
 __fixtures__/generated/generated.json             |  4 +++-
 __fixtures__/kitchen-sink/misc/issues.sql         |  6 ++++++
 .../__tests__/kitchen-sink/misc-issues.test.ts    |  4 +++-
 packages/deparser/src/deparser.ts                 | 15 +++++++++++----
 4 files changed, 23 insertions(+), 6 deletions(-)

diff --git a/__fixtures__/generated/generated.json b/__fixtures__/generated/generated.json
index 4f0f5b75..4082f320 100644
--- a/__fixtures__/generated/generated.json
+++ b/__fixtures__/generated/generated.json
@@ -21330,7 +21330,9 @@
   "misc/issues-15.sql": "select \"A\" from \"table_name\"",
   "misc/issues-16.sql": "select \"AA\" from \"table_name\"",
   "misc/issues-17.sql": "SELECT CAST(t.date AT TIME ZONE $$America/New_York$$ AS text)::date FROM tbl t",
-  "misc/issues-18.sql": "CREATE TABLE test_exclude_where (\n  id uuid PRIMARY KEY,\n  database_id uuid NOT NULL,\n  status text NOT NULL DEFAULT 'pending',\n  EXCLUDE USING btree (database_id WITH =)\n    WHERE (status = 'pending')\n)",
+  "misc/issues-18.sql": "SELECT (- (-10 - -12))::numeric AS delta",
+  "misc/issues-19.sql": "SELECT (- (a.actual_eur - a.budget_eur))::numeric AS delta_eur FROM accounts a",
+  "misc/issues-20.sql": "CREATE TABLE test_exclude_where (\n  id uuid PRIMARY KEY,\n  database_id uuid NOT NULL,\n  status text NOT NULL DEFAULT 'pending',\n  EXCLUDE USING btree (database_id WITH =)\n    WHERE (status = 'pending')\n)",
   "misc/inflection-1.sql": "CREATE SCHEMA inflection",
   "misc/inflection-2.sql": "GRANT USAGE ON SCHEMA inflection TO PUBLIC",
   "misc/inflection-3.sql": "ALTER DEFAULT PRIVILEGES IN SCHEMA inflection \n GRANT EXECUTE ON FUNCTIONS  TO PUBLIC",
diff --git a/__fixtures__/kitchen-sink/misc/issues.sql b/__fixtures__/kitchen-sink/misc/issues.sql
index e069822a..88c2c106 100644
--- a/__fixtures__/kitchen-sink/misc/issues.sql
+++ b/__fixtures__/kitchen-sink/misc/issues.sql
@@ -76,6 +76,12 @@ select "AA" from "table_name";
 -- https://github.com/constructive-io/pgsql-parser/issues/217
 SELECT CAST(t.date AT TIME ZONE $$America/New_York$$ AS text)::date FROM tbl t;
 
+-- https://github.com/constructive-io/pgsql-parser/issues/285
+-- TypeCast with unary minus loses parentheses around inner expression
+-- (- (a - b))::numeric becomes CAST(- a - b AS numeric) which changes the math
+SELECT (- (-10 - -12))::numeric AS delta;
+SELECT (- (a.actual_eur - a.budget_eur))::numeric AS delta_eur FROM accounts a;
+
 -- https://github.com/constructive-io/pgsql-parser/issues/287
 -- EXCLUDE constraint with WHERE clause (partial exclusion constraint)
 -- The deparser drops the WHERE clause from EXCLUDE USING ... WHERE (...)
diff --git a/packages/deparser/__tests__/kitchen-sink/misc-issues.test.ts b/packages/deparser/__tests__/kitchen-sink/misc-issues.test.ts
index 53ab1b5d..02bc60ff 100644
--- a/packages/deparser/__tests__/kitchen-sink/misc-issues.test.ts
+++ b/packages/deparser/__tests__/kitchen-sink/misc-issues.test.ts
@@ -21,6 +21,8 @@ it('misc-issues', async () => {
   "misc/issues-15.sql",
   "misc/issues-16.sql",
   "misc/issues-17.sql",
-  "misc/issues-18.sql"
+  "misc/issues-18.sql",
+  "misc/issues-19.sql",
+  "misc/issues-20.sql"
 ]);
 });
diff --git a/packages/deparser/src/deparser.ts b/packages/deparser/src/deparser.ts
index a3713d94..ecdbb409 100644
--- a/packages/deparser/src/deparser.ts
+++ b/packages/deparser/src/deparser.ts
@@ -720,10 +720,17 @@ export class Deparser implements DeparserVisitor {
 
           return context.format([leftExpr, operator, rightExpr]);
         }else if (rexpr) {
-          return context.format([
-            this.deparseOperatorName(name, context),
-            this.visit(rexpr, context)
-          ]);
+          // Unary operator (e.g., unary minus: - expr)
+          const operator = this.deparseOperatorName(name, context);
+          let rightExpr = this.visit(rexpr, context);
+
+          // Wrap in parentheses if rexpr is a binary A_Expr to preserve semantics
+          // e.g., -(a - b) must stay -(a - b), not become -a - b
+          if (rexpr && 'A_Expr' in rexpr && rexpr.A_Expr?.kind === 'AEXPR_OP' && rexpr.A_Expr?.lexpr) {
+            rightExpr = context.parens(rightExpr);
+          }
+
+          return context.format([operator, rightExpr]);
         }
         break;
       case 'AEXPR_OP_ANY':