chore: Attach Diagnostic to "incompatible type in unary expression" error

datafusion/sql/src/expr/unary_op.rs

@@ -16,7 +16,7 @@
 // under the License.
 
 use crate::planner::{ContextProvider, PlannerContext, SqlToRel};
-use datafusion_common::{not_impl_err, plan_err, DFSchema, Result};
+use datafusion_common::{not_impl_err, plan_err, DFSchema, Diagnostic, Result};
 use datafusion_expr::{
     type_coercion::{is_interval, is_timestamp},
     Expr, ExprSchemable,
@@ -45,7 +45,16 @@ impl<S: ContextProvider> SqlToRel<'_, S> {
                 {
                     Ok(operand)
                 } else {
-                    plan_err!("Unary operator '+' only supports numeric, interval and timestamp types")
+                    plan_err!("Unary operator '+' only supports numeric, interval and timestamp types").map_err(|e| {
+                        let span = operand.spans().and_then(|s| s.first());
+                        let mut diagnostic = Diagnostic::new_error(
+                            format!("+ cannot be used with {data_type}"), 
+                            span
+                        );
+                        diagnostic.add_note("+ can only be used with numbers, intervals, and timestamps", None);
+                        diagnostic.add_help(format!("perhaps you need to cast {operand}"), None);
+                        e.with_diagnostic(diagnostic)
+                    })
                 }
             }
             UnaryOperator::Minus => {

datafusion/sql/tests/cases/diagnostic.rs

@@ -351,6 +351,44 @@ fn test_in_subquery_multiple_columns() -> Result<(), Box<dyn std::error::Error>>
             .collect::<Vec<_>>(),
         vec!["Select only one column in the subquery"]
     );
+    Ok(())
+}
 
+#[test]
+fn test_unary_op_plus_with_column() -> Result<()> {
+    // Test with a direct query that references a column with an incompatible type
+    let query = "SELECT +/*whole*/first_name/*whole*/ FROM person";
+    let spans = get_spans(query);
+    let diag = do_query(query);
+    assert_eq!(diag.message, "+ cannot be used with Utf8");
+    assert_eq!(diag.span, Some(spans["whole"]));
+    assert_eq!(
+        diag.notes[0].message,
+        "+ can only be used with numbers, intervals, and timestamps"
+    );
+    assert_eq!(
+        diag.helps[0].message,
+        "perhaps you need to cast person.first_name"
+    );
+    Ok(())
+}
+
+#[test]
+fn test_unary_op_plus_with_non_column() -> Result<()> {
+    // create a table with a column of type varchar
+    let query = "SELECT +'a'";
+    let diag = do_query(query);
+    assert_eq!(diag.message, "+ cannot be used with Utf8");
+    assert_eq!(
+        diag.notes[0].message,
+        "+ can only be used with numbers, intervals, and timestamps"
+    );
+    assert_eq!(diag.notes[0].span, None);
+    assert_eq!(
+        diag.helps[0].message,
+        "perhaps you need to cast Utf8(\"a\")"
+    );
+    assert_eq!(diag.helps[0].span, None);
+    assert_eq!(diag.span, None);
     Ok(())
 }