refactor error message and add note and help in diagnostic

Author: onlyjackfrost

datafusion/sql/src/expr/unary_op.rs

@@ -46,10 +46,15 @@ impl<S: ContextProvider> SqlToRel<'_, S> {
                     Ok(operand)
                 } else {
                     plan_err!("Unary operator '+' only supports numeric, interval and timestamp types").map_err(|e| {
-                        let spans = operand.spans();
-                        let span = if let Some(s) = spans.as_ref() { s.first() } else { None };
-                        let diagnostic =
-                        Diagnostic::new_error("Unary operator '+' only supports numeric, interval and timestamp types".to_string(), span);
+                        let span = operand.spans().and_then(|s| s.first());
+                        let mut diagnostic = Diagnostic::new_error(
+                            format!("+ cannot be used with {data_type}"), 
+                            span
+                        );
+                        if span.is_none() {
+                            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)
                     })
                 }

datafusion/sql/tests/cases/diagnostic.rs

@@ -292,10 +292,17 @@ fn test_unary_op_plus_with_non_column() -> Result<()> {
     // create a table with a column of type varchar
     let query = "SELECT /*whole*/+'a'/*whole*/ ";
     let diag = do_query(query);
+    assert_eq!(diag.message, "+ cannot be used with Utf8");
     assert_eq!(
-        diag.message,
-        "Unary operator '+' only supports numeric, interval and timestamp types"
+        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(())
 }
@@ -306,10 +313,7 @@ fn test_unary_op_plus_with_column() -> Result<()> {
     let query = "SELECT +/*whole*/first_name/*whole*/ FROM person";
     let spans = get_spans(query);
     let diag = do_query(query);
-    assert_eq!(
-        diag.message,
-        "Unary operator '+' only supports numeric, interval and timestamp types"
-    );
+    assert_eq!(diag.message, "+ cannot be used with Utf8");
     assert_eq!(diag.span, Some(spans["whole"]));
     Ok(())
 }