Ensure sorting is stable (#16)

Author: gaborbernat

rust/src/helpers/table.rs

@@ -61,19 +61,23 @@ impl Tables {
         }
         next.push(String::new());
         for (name, next_name) in zip(order.iter(), next.iter()) {
-            let mut entries = self.get(name).unwrap().borrow().clone();
-            if entries.is_empty() {
-                continue;
-            }
-            entry_count += entries.len();
-            let last = entries.last().unwrap();
-            if name.is_empty() && last.kind() == SyntaxKind::NEWLINE && entries.len() == 1 {
-                continue;
-            }
-            if last.kind() == SyntaxKind::NEWLINE && get_key(name) != get_key(next_name) {
-                entries.splice(entries.len() - 1..entries.len(), [make_empty_newline()]);
+            let entries = self.get(name).unwrap().borrow();
+            if !entries.is_empty() {
+                entry_count += entries.len();
+                let last = entries.last().unwrap();
+                if name.is_empty() && last.kind() == SyntaxKind::NEWLINE && entries.len() == 1 {
+                    continue;
+                }
+                let mut add = entries.clone();
+                if get_key(name) != get_key(next_name) {
+                    if last.kind() == SyntaxKind::NEWLINE {
+                        // replace existing newline to ensure single newline
+                        add.pop();
+                    }
+                    add.push(make_empty_newline());
+                }
+                to_insert.extend(add);
             }
-            to_insert.extend(entries);
         }
         root_ast.splice_children(0..entry_count, to_insert);
     }

rust/src/main.rs

@@ -195,6 +195,7 @@ mod tests {
       "Programming Language :: Python :: 3 :: Only",
       "Programming Language :: Python :: 3.8",
     ]
+
     [tool.coverage]
     a = 0
     [tool.coverage.report]
@@ -215,16 +216,16 @@ mod tests {
         #[case] keep_full_version: bool,
         #[case] max_supported_python: (u8, u8),
     ) {
-        let got = format_toml(
-            start,
-            &Settings {
-                column_width: 1,
-                indent,
-                keep_full_version,
-                max_supported_python,
-                min_supported_python: (3, 8),
-            },
-        );
+        let settings = Settings {
+            column_width: 1,
+            indent,
+            keep_full_version,
+            max_supported_python,
+            min_supported_python: (3, 8),
+        };
+        let got = format_toml(start, &settings);
         assert_eq!(got, expected);
+        let second = format_toml(got.as_str(), &settings);
+        assert_eq!(got, second);
     }
 }