fix: assure that sections can be deleted properly with `File::remove_…

…section_filter()` (#1826)

The underlying issue isn't fixed, as ids in the lookup table remain even after deletion.
However, for now it was easiest to defensively access this data, while assuring that
the API (still) does what it claims.

gix-config/src/file/access/mutate.rs

@@ -86,10 +86,8 @@ impl<'event> File<'event> {
             .section_ids_by_name_and_subname(name.as_ref(), subsection_name)
             .ok()
             .and_then(|it| {
-                it.rev().find(|id| {
-                    let s = &self.sections[id];
-                    filter(s.meta())
-                })
+                it.rev()
+                    .find(|id| self.sections.get(id).is_some_and(|s| filter(s.meta())))
             }) {
             Some(id) => {
                 let nl = self.detect_newline_style_smallvec();
@@ -305,7 +303,7 @@ impl<'event> File<'event> {
             .section_ids_by_name_and_subname(name, subsection_name)
             .ok()?
             .rev()
-            .find(|id| filter(self.sections.get(id).expect("each id has a section").meta()))?;
+            .find(|id| self.sections.get(id).is_some_and(|section| filter(section.meta())))?;
         self.section_order.remove(
             self.section_order
                 .iter()

gix-config/tests/config/file/access/mutate.rs

@@ -25,25 +25,59 @@ mod remove_section {
     }
 
     #[test]
-    fn removal_is_complete_and_sections_can_be_readded() {
+    fn removal_is_complete_and_sections_can_be_read() {
         let mut file = gix_config::File::try_from("[core] \na = b\nb=c\n\n[core \"name\"]\nd = 1\ne = 2").unwrap();
         assert_eq!(file.sections().count(), 2);
 
         let removed = file.remove_section("core", None).expect("removed correct section");
         assert_eq!(removed.header().name(), "core");
         assert_eq!(removed.header().subsection_name(), None);
         assert_eq!(file.sections().count(), 1);
+        assert_eq!(file.remove_section("core", None), None, "it's OK to try again");
 
         let removed = file.remove_section("core", Some("name".into())).expect("found");
         assert_eq!(removed.header().name(), "core");
         assert_eq!(removed.header().subsection_name().expect("present"), "name");
         assert_eq!(file.sections().count(), 0);
+        assert_eq!(file.remove_section("core", Some("name".into())), None);
 
         file.section_mut_or_create_new("core", None).expect("creation succeeds");
         file.section_mut_or_create_new("core", Some("name".into()))
             .expect("creation succeeds");
     }
 }
+mod remove_section_filter {
+    #[test]
+    fn removal_of_section_is_complete() {
+        let mut file = gix_config::File::try_from("[core] \na = b\nb=c\n\n[core \"name\"]\nd = 1\ne = 2").unwrap();
+        assert_eq!(file.sections().count(), 2);
+
+        let removed = file
+            .remove_section_filter("core", None, |_| true)
+            .expect("removed correct section");
+        assert_eq!(removed.header().name(), "core");
+        assert_eq!(removed.header().subsection_name(), None);
+        assert_eq!(file.sections().count(), 1);
+        let removed = file
+            .remove_section_filter("core", Some("name".into()), |_| true)
+            .expect("found");
+        assert_eq!(removed.header().name(), "core");
+        assert_eq!(removed.header().subsection_name().expect("present"), "name");
+        assert_eq!(file.sections().count(), 0);
+
+        assert_eq!(
+            file.remove_section_filter("core", None, |_| true),
+            None,
+            "it's OK to try again"
+        );
+        assert_eq!(file.remove_section_filter("core", Some("name".into()), |_| true), None);
+
+        file.section_mut_or_create_new("core", None).expect("creation succeeds");
+        file.section_mut_or_create_new("core", Some("name".into()))
+            .expect("creation succeeds");
+    }
+}
+
 mod rename_section {
     use std::borrow::Cow;