chore: add EntryFallback completion support

Add `#[completion(EntryFallback)]` syntax to enable custom
completion suggestions for unmatched entries, merging fallback
results with default completions via `Suggest::combine()`.

3 files changed, 38 insertions, 2 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index c954123..6062103 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -168,6 +168,29 @@ None
 
     Also reorganized the `[features]` section of `mingling/Cargo.toml` into logical subsections (Presets, Core, Special features, Features, LEGACY) for improved maintainability and documentation.
 
+8. **[`core`]** **[`macros`]** Added the `#[completion(EntryFallback)]` syntax to the `#[completion]` macro, mirroring the `#[help(EntryFallback)]` pattern. When the `EntryFallback` identifier is passed (either as a bare path in the attribute arguments), the macro generates a chain handler for the `EntryFallback` type (the program's fallback entry pack type generated by `gen_program!()`). This handler is invoked during the default-completion path when no explicit dispatcher match is found.
+
+    When the program's dispatcher fails to find a match in the completion pipeline, the `CompletionHelper::complete` method now:
+
+    - Checks for an explicit completion handler via the chain pipeline for the `EntryFallback` type (calling `P::do_comp(&P::build_entry_fallback(vec![]), ctx)`).
+    - If that produces suggestions, they are combined with the default completion suggestions via `Suggest::combine()` (which merges `BTreeSet`s for `Suggest::Suggest` values).
+    - Falls back to the standard `default_completion::<P>(ctx)` behavior when no explicit fallback handler yields results.
+
+    This enables users to provide custom completion suggestions for the fallback/unmatched case:
+
+    ```rust,ignore
+    #[completion(EntryFallback)]
+    fn complete_fallback(_ctx: &ShellContext) -> Suggest {
+        suggest! { "fallback" }
+    }
+    ```
+
+    The generated chain handler for `EntryFallback` is identical to how `#[chain]`-annotated functions targeting entry pack types work — the `EntryFallback` type name is resolved through the same `chain` code-generation path used for `Entry{Type}` types, allowing users to write a dedicated completion function for the fallback entry point without manually registering it in the program's dispatcher.
+
+    Internal changes:
+    - `mingling_macros/src/attr/completion.rs` updated to detect the `EntryFallback` identifier in attribute arguments.
+    - `CompletionHelper::complete` in `mingling_core/src/comp.rs` now invokes the fallback completion handler via `P::do_comp(&P::build_entry_fallback(vec![]), ctx)` and merges results with `Suggest::combine()`.
+
 #### **BREAKING CHANGES** (API CHANGES):
 
 1. **[`macros`]** **[BREAKING]** Renamed the `extra_macros` feature to `extras`. All feature-gated macro re-exports in `mingling/src/lib.rs` (and throughout the codebase) have been updated from `#[cfg(feature = "extra_macros")]` to `#[cfg(feature = "extras")]`.
diff --git a/docs/dev/pages/issues/the-shit-time.md b/docs/dev/pages/issues/the-shit-time.md
index 9d6c429..b23854e 100644
--- a/docs/dev/pages/issues/the-shit-time.md
+++ b/docs/dev/pages/issues/the-shit-time.md
@@ -9,7 +9,7 @@ Of course, you can also contribute to this document.
 
 ---
 
-## Why is there no fallback completion logic?
+## Why is there no fallback completion logic? (Solved)
 
 (completion) (fallback)
 
@@ -34,6 +34,17 @@ fn complete(ctx: &ShellContext) -> Suggest {
     // ...
 }
 ```
+
+Final implementation:
+
+By adding support for `EntryFallback` (formerly `ErrorDispatcherNotFound`) to the Completion system, `EntryFallback` can now be used as a completion entry point when no subcommand is matched:
+
+```rust
+#[completion(EntryFallback)]
+fn complete_fallback(_ctx: &ShellContext) -> Suggest {
+    suggest! { "fallback" }
+}
+```
  
 ---
 
diff --git a/mingling_core/src/comp.rs b/mingling_core/src/comp.rs
index a4e4f0b..021793b 100644
--- a/mingling_core/src/comp.rs
+++ b/mingling_core/src/comp.rs
@@ -163,7 +163,9 @@ impl CompletionHelper {
             }
             None => {
                 trace!("using default completion");
-                default_completion::<P>(ctx)
+                let fallback = P::do_comp(&P::build_entry_fallback(vec![]), ctx);
+                let default = default_completion::<P>(ctx);
+                fallback.combine(default)
             }
         }
     }