fix issue #325: defaults with negative values

`default!(i32, -1)` now works correctly.  The `-` causes syn to emit a `UnaryExpr` with a `Neg` op value.

Author: eeeebbbbrrrr

pgx-tests/src/tests/default_arg_value_tests.rs

@@ -3,6 +3,11 @@
 
 use pgx::*;
 
+#[pg_extern]
+fn negative_default_argument(i: default!(i32, -1)) -> i32 {
+    i
+}
+
 #[pg_extern]
 fn default_argument(a: default!(i32, 99)) -> i32 {
     a
@@ -27,6 +32,13 @@ mod tests {
     #[test]
     fn make_idea_happy() {}
 
+    #[pg_test]
+    fn test_negative_default_argument() {
+        let result = Spi::get_one::<i32>("SELECT negative_default_argument();")
+            .expect("didn't get SPI result");
+        assert_eq!(result, -1);
+    }
+
     #[pg_test]
     fn test_default_argument() {
         let result =

pgx-utils/src/sql_entity_graph/pg_extern/argument.rs

@@ -192,6 +192,28 @@ fn handle_default(
                     let value = def.value();
                     Ok((true_ty, Some(value.to_string())))
                 }
+                syn::Expr::Unary(syn::ExprUnary {
+                    op: syn::UnOp::Neg(_),
+                    ref expr,
+                    ..
+                }) => match &**expr {
+                    syn::Expr::Lit(syn::ExprLit {
+                        lit: syn::Lit::Int(def),
+                        ..
+                    }) => {
+                        let value = def.base10_digits();
+                        Ok((true_ty, Some("-".to_owned() + value)))
+                    }
+                    _ => {
+                        return Err(syn::Error::new(
+                            Span::call_site(),
+                            format!(
+                                "Unrecognized UnaryExpr in `default!()` macro, got: {:?}",
+                                out.expr
+                            ),
+                        ))
+                    }
+                },
                 syn::Expr::Type(syn::ExprType { ref ty, .. }) => match ty.deref() {
                     syn::Type::Path(syn::TypePath {
                         path: syn::Path { segments, .. },