Indent statements under C/C++ case labels (#60758)

# Objective

Fixes #60261

Nothing under a `case` gets indented in C or C++, and the next `case`
doesn't come back out. It stays flat until you hit `editor: format`.

## Solution

The indent queries had no rule for case labels. Added the same pair
`cpp/indents.scm` uses for `access_specifier`: open an indent range at
the label, close it at the switch's `}`, outdent on the next label.

The part that got me: `@start` uses the *end* of the node you capture.
Fine for `access_specifier`, which is just `public:`. But a
`case_statement` swallows the statements under it, so capturing the node
starts the range after the last one. Capture the `:` instead. `default:`
is a `case_statement` too, so it comes along free.

Only affects what happens after a label, so existing `case` alignment
doesn't move.

## Testing

`test_c_autoindent_switch_case` and `test_cpp_autoindent_switch_case`
cover a plain case, fall-through labels and `default`. Both fail on
main. The `access_specifier` tests still pass.

Not mine, but worth knowing: `typescript::tests::test_outline` and
`test_generator_function_outline` are flaky on main, failing about half
my full `cargo test -p languages --lib` runs with or without this
change.

## Self-Review Checklist:

- [x] I've reviewed my own diff for quality, security, and reliability
- [x] Unsafe blocks (if any) have justifying comments
- [x] The content adheres to Zed's UI standards
([UX/UI](https://github.com/zed-industries/zed/blob/main/CONTRIBUTING.md#uiux-checklist)
and
[icon](https://github.com/zed-industries/zed/blob/main/crates/icons/README.md)
guidelines)
- [x] Tests cover the new/changed behavior
- [x] Performance impact has been considered and is acceptable

Release Notes:

- Fixed statements under a `case` label not being indented in C and C++
([#60261](https://github.com/zed-industries/zed/issues/60261)).

crates/grammars/src/c/indents.scm

@@ -17,6 +17,15 @@
   "{"
   "}" @end) @indent
 
+(compound_statement
+  (case_statement
+    ":" @start)
+  "}" @end) @indent
+
+(compound_statement
+  (case_statement)
+  (case_statement) @outdent)
+
 (_
   "("
   ")" @end) @indent

crates/grammars/src/cpp/indents.scm

@@ -25,6 +25,15 @@
   (access_specifier)
   (access_specifier) @outdent)
 
+(compound_statement
+  (case_statement
+    ":" @start)
+  "}" @end) @indent
+
+(compound_statement
+  (case_statement)
+  (case_statement) @outdent)
+
 (_
   "("
   ")" @end) @indent

crates/languages/src/c.rs

@@ -451,6 +451,70 @@ mod tests {
         });
     }
 
+    #[gpui::test]
+    async fn test_c_autoindent_switch_case(cx: &mut TestAppContext) {
+        cx.update(|cx| {
+            let test_settings = SettingsStore::test(cx);
+            cx.set_global(test_settings);
+            cx.update_global::<SettingsStore, _>(|store, cx| {
+                store.update_user_settings(cx, |s| {
+                    s.project.all_languages.defaults.tab_size = NonZeroU32::new(2);
+                });
+            });
+        });
+        let language = crate::language("c", tree_sitter_c::LANGUAGE.into());
+
+        cx.new(|cx| {
+            let mut buffer = Buffer::local("", cx).with_language(language, cx);
+
+            buffer.edit(
+                [(
+                    0..0,
+                    r#"
+                    int main() {
+                    switch (a) {
+                    case 1:
+                    b++;
+                    break;
+                    case 2:
+                    case 3:
+                    c++;
+                    break;
+                    default:
+                    d++;
+                    }
+                    }
+                    "#
+                    .unindent(),
+                )],
+                Some(AutoindentMode::EachLine),
+                cx,
+            );
+            assert_eq!(
+                buffer.text(),
+                r#"
+                int main() {
+                  switch (a) {
+                    case 1:
+                      b++;
+                      break;
+                    case 2:
+                    case 3:
+                      c++;
+                      break;
+                    default:
+                      d++;
+                  }
+                }
+                "#
+                .unindent(),
+                "statements under a case label should be indented, and the next label outdented"
+            );
+
+            buffer
+        });
+    }
+
     #[gpui::test]
     async fn test_c_autoindent_if_else(cx: &mut TestAppContext) {
         cx.update(|cx| {

crates/languages/src/cpp.rs

@@ -16,6 +16,70 @@ mod tests {
     use std::num::NonZeroU32;
     use unindent::Unindent;
 
+    #[gpui::test]
+    async fn test_cpp_autoindent_switch_case(cx: &mut TestAppContext) {
+        cx.update(|cx| {
+            let test_settings = SettingsStore::test(cx);
+            cx.set_global(test_settings);
+            cx.update_global::<SettingsStore, _>(|store, cx| {
+                store.update_user_settings(cx, |s| {
+                    s.project.all_languages.defaults.tab_size = NonZeroU32::new(2);
+                });
+            });
+        });
+        let language = crate::language("cpp", tree_sitter_cpp::LANGUAGE.into());
+
+        cx.new(|cx| {
+            let mut buffer = Buffer::local("", cx).with_language(language, cx);
+
+            buffer.edit(
+                [(
+                    0..0,
+                    r#"
+                    int main() {
+                    switch (a) {
+                    case 1:
+                    b++;
+                    break;
+                    case 2:
+                    case 3:
+                    c++;
+                    break;
+                    default:
+                    d++;
+                    }
+                    }
+                    "#
+                    .unindent(),
+                )],
+                Some(AutoindentMode::EachLine),
+                cx,
+            );
+            assert_eq!(
+                buffer.text(),
+                r#"
+                int main() {
+                  switch (a) {
+                    case 1:
+                      b++;
+                      break;
+                    case 2:
+                    case 3:
+                      c++;
+                      break;
+                    default:
+                      d++;
+                  }
+                }
+                "#
+                .unindent(),
+                "statements under a case label should be indented, and the next label outdented"
+            );
+
+            buffer
+        });
+    }
+
     #[gpui::test]
     async fn test_cpp_autoindent_access_specifier(cx: &mut TestAppContext) {
         cx.update(|cx| {