Fix unary minus rendering into -- line comments

src/ast/mod.rs

@@ -1965,8 +1965,14 @@ impl fmt::Display for Expr {
                 | UnaryOperator::PGAbs
                 | UnaryOperator::QuestionDash
                 | UnaryOperator::QuestionPipe => write!(f, "{op} {expr}"),
+                UnaryOperator::Minus => {
+                    if starts_with_operator_char(expr) {
+                        write!(f, "{op} {expr}")
+                    } else {
+                        write!(f, "{op}{expr}")
+                    }
+                }
                 UnaryOperator::Plus
-                | UnaryOperator::Minus
                 | UnaryOperator::BangNot
                 | UnaryOperator::PGPrefixFactorial
                 | UnaryOperator::PGSquareRoot
@@ -8083,6 +8089,26 @@ impl fmt::Display for FunctionArg {
     }
 }
 
+/// Whether `expr` renders with an operator character first. A prefix `-`
+/// must not abut one, since `--` starts a line comment and operator-run
+/// dialects fuse `-@`, `-~`, `-#`, `-!!` and `-||/` into single tokens.
+fn starts_with_operator_char(expr: &Expr) -> bool {
+    use fmt::Write;
+    struct FirstChar(Option<char>);
+    impl fmt::Write for FirstChar {
+        fn write_str(&mut self, s: &str) -> fmt::Result {
+            if self.0.is_none() {
+                self.0 = s.chars().next();
+            }
+            Ok(())
+        }
+    }
+    let mut first = FirstChar(None);
+    let _ = write!(first, "{expr}");
+    const OPERATOR_CHARS: &str = "+-*/<>=~!@%#^&|";
+    first.0.is_some_and(|c| OPERATOR_CHARS.contains(c))
+}
+
 /// `FunctionArgOperator::Space` has no token of its own, so the name and the
 /// value are separated by a single space instead.
 fn fmt_named_function_arg(

tests/sqlparser_common.rs

@@ -20072,3 +20072,11 @@ fn parse_bitwise_not_renders_apart_from_operand() {
     all_dialects().verified_stmt("SELECT ~ -1");
     all_dialects().verified_stmt("SELECT ~ ~ 1");
 }
+
+#[test]
+fn parse_unary_minus_never_renders_line_comment() {
+    all_dialects().verified_stmt("SELECT - -1");
+    all_dialects().verified_stmt("SELECT - - -1");
+    all_dialects().verified_stmt("SELECT -1");
+    all_dialects().verified_stmt("SELECT -x");
+}

tests/sqlparser_postgres.rs

@@ -9975,3 +9975,12 @@ fn parse_bitwise_not_before_pg_prefix_operators() {
     pg().verified_stmt("SELECT ~ @ 2");
     pg().one_statement_parses_to("SELECT ~ #x", "SELECT ~ # x");
 }
+
+#[test]
+fn parse_unary_minus_before_pg_prefix_operators() {
+    pg().one_statement_parses_to("SELECT - ~1", "SELECT - ~ 1");
+    pg().verified_stmt("SELECT - ~ 1");
+    pg().one_statement_parses_to("SELECT - @2", "SELECT - @ 2");
+    pg().verified_stmt("SELECT - @ 2");
+    pg().one_statement_parses_to("SELECT - #x", "SELECT - # x");
+}