Fix the behavior of list removals in the Rust option code. (#20793)

In the Python code, removals trump adds at any precedence. 

Previously, the Rust code applied removals and adds in
source precedence order. This PR makes the Rust implementation
align with the existing Python behavior. 

It adds tests to verify this behavior, copied directly from the Python
tests.

src/rust/engine/options/src/lib.rs

@@ -489,19 +489,30 @@ impl OptionParser {
             }
             derivation = Some(derivations);
         }
+
+        // Removals from any source apply after adds from any source (but are themselves
+        // overridden by later replacements), so we collect them here and apply them later.
+        let mut removal_lists: Vec<Vec<T>> = vec![];
+
         let mut highest_priority_source = Source::Default;
         for (source_type, source) in self.sources.iter() {
             if let Some(list_edits) = getter(source, id)? {
                 highest_priority_source = source_type.clone();
                 for list_edit in list_edits {
                     match list_edit.action {
-                        ListEditAction::Replace => list = list_edit.items,
+                        ListEditAction::Replace => {
+                            list = list_edit.items;
+                            removal_lists.clear();
+                        }
                         ListEditAction::Add => list.extend(list_edit.items),
-                        ListEditAction::Remove => remover(&mut list, &list_edit.items),
+                        ListEditAction::Remove => removal_lists.push(list_edit.items),
                     }
                 }
             }
         }
+        for removals in removal_lists {
+            remover(&mut list, &removals);
+        }
         Ok(ListOptionValue {
             derivation,
             source: highest_priority_source,

src/rust/engine/options/src/tests.rs

@@ -280,7 +280,7 @@ fn test_parse_list_options() {
     );
 
     check(
-        vec![1, 3, 4],
+        vec![1, 3],
         vec![
             (Source::Default, vec![replace(vec![0])]),
             (config_source(), vec![replace(vec![1, 2])]),
@@ -290,7 +290,7 @@ fn test_parse_list_options() {
         vec![],
         vec![("PANTS_SCOPE_FOO", "+[3, 4]")],
         "[scope]\nfoo = [1, 2]",
-        "[scope]\nfoo = '-[2, 4]'", // 2 should be removed, but not 4, since env has precedence.
+        "[scope]\nfoo = '-[2, 4]'",
     );
 
     check(
@@ -330,6 +330,63 @@ fn test_parse_list_options() {
         "",
         "",
     );
+
+    // Filtering all instances of repeated values.
+    check(
+        vec![1, 2, 2, 4],
+        vec![
+            (Source::Default, vec![replace(vec![0])]),
+            (config_source(), vec![add(vec![1, 2, 3, 2, 0, 3, 3, 4])]),
+            (Source::Env, vec![remove(vec![0, 3])]),
+        ],
+        vec![],
+        vec![("PANTS_SCOPE_FOO", "-[0, 3]")],
+        "[scope]\nfoo.add = [1, 2, 3, 2, 0, 3, 3, 4]",
+        "",
+    );
+
+    // Filtering a value even though it was appended again at a higher rank.
+    check(
+        vec![0, 2],
+        vec![
+            (Source::Default, vec![replace(vec![0])]),
+            (config_source(), vec![add(vec![1, 2])]),
+            (Source::Env, vec![remove(vec![1])]),
+            (Source::Flag, vec![add(vec![1])]),
+        ],
+        vec!["--scope-foo=+[1]"],
+        vec![("PANTS_SCOPE_FOO", "-[1]")],
+        "[scope]\nfoo.add = [1, 2]",
+        "",
+    );
+
+    // Filtering a value even though it was appended again at the same rank.
+    check(
+        vec![0, 2],
+        vec![
+            (Source::Default, vec![replace(vec![0])]),
+            (config_source(), vec![add(vec![1, 2])]),
+            (Source::Env, vec![remove(vec![1]), add(vec![1])]),
+        ],
+        vec![],
+        vec![("PANTS_SCOPE_FOO", "-[1],+[1]")],
+        "[scope]\nfoo.add = [1, 2]",
+        "",
+    );
+
+    // Overwriting cancels filters.
+    check(
+        vec![0],
+        vec![
+            (Source::Default, vec![replace(vec![0])]),
+            (config_source(), vec![remove(vec![0])]),
+            (Source::Env, vec![replace(vec![0])]),
+        ],
+        vec![],
+        vec![("PANTS_SCOPE_FOO", "[0]")],
+        "[scope]\nfoo.remove = [0]",
+        "",
+    );
 }
 
 #[test]