Add parent node information when providing error about printing empty…

… selections

Reviewed By: josephsavona

Differential Revision: D44369237

fbshipit-source-id: 81e5732c765043b71b080ef65e40f765df14c632

compiler/crates/graphql-text-printer/src/print_to_text.rs

@@ -143,7 +143,7 @@ pub fn write_selections(
     mut result: &mut impl Write,
 ) -> FmtResult {
     let mut printer = Printer::new(schema, &mut result, PrinterOptions::default());
-    printer.print_selections(selections)
+    printer.print_selections(selections, "unknown".intern())
 }
 
 pub fn write_selection(
@@ -222,7 +222,7 @@ impl<'schema, 'writer, W: Write> Printer<'schema, 'writer, W> {
         write!(self.writer, "{} {}", operation.kind, operation.name.item)?;
         self.print_variable_definitions(&operation.variable_definitions)?;
         self.print_directives(&operation.directives, None, None)?;
-        self.print_selections(&operation.selections)
+        self.print_selections(&operation.selections, operation.name.item.0)
     }
 
     fn print_fragment(mut self, fragment: &FragmentDefinition) -> FmtResult {
@@ -243,10 +243,10 @@ impl<'schema, 'writer, W: Write> Printer<'schema, 'writer, W> {
             None,
             Some(&fragment.variable_definitions),
         )?;
-        self.print_selections(&fragment.selections)
+        self.print_selections(&fragment.selections, fragment_name.0)
     }
 
-    fn print_selections(&mut self, selections: &[Selection]) -> FmtResult {
+    fn print_selections(&mut self, selections: &[Selection], name: StringKey) -> FmtResult {
         let len = selections.len();
         if len > 0 {
             self.print_optional_space()?;
@@ -266,7 +266,8 @@ impl<'schema, 'writer, W: Write> Printer<'schema, 'writer, W> {
             write!(self.writer, "}}")?;
         } else {
             panic!(
-                "Cannot print empty selections. Please, check transforms that may produce invalid selections."
+                "Cannot print empty selections for {}. Please, check transforms that may produce invalid selections.",
+                name
             );
         }
         Ok(())
@@ -306,7 +307,7 @@ impl<'schema, 'writer, W: Write> Printer<'schema, 'writer, W> {
         self.print_alias_and_name(&field.alias, schema_field.name.item)?;
         self.print_arguments(&field.arguments)?;
         self.print_directives(&field.directives, conditions, None)?;
-        self.print_selections(&field.selections)?;
+        self.print_selections(&field.selections, schema_field.name.item)?;
         Ok(())
     }
 
@@ -342,7 +343,17 @@ impl<'schema, 'writer, W: Write> Printer<'schema, 'writer, W> {
             )?;
         };
         self.print_directives(&field.directives, conditions, None)?;
-        self.print_selections(&field.selections)
+
+        let name = if let Some(type_condition) = field.type_condition {
+            format!(
+                "... on {}",
+                self.schema.get_type_name(type_condition).lookup()
+            )
+            .intern()
+        } else {
+            "...".intern()
+        };
+        self.print_selections(&field.selections, name)
     }
 
     fn print_condition(