feat(complete): Allow de-duplicating of candidates

clap_complete/src/engine/candidate.rs

@@ -8,6 +8,7 @@ use clap::builder::StyledStr;
 pub struct CompletionCandidate {
     value: OsString,
     help: Option<StyledStr>,
+    id: Option<String>,
     hidden: bool,
 }
 
@@ -27,6 +28,14 @@ impl CompletionCandidate {
         self
     }
 
+    /// Only first for a given Id is shown
+    ///
+    /// To reduce the risk of conflicts, this should likely contain a namespace.
+    pub fn id(mut self, id: Option<String>) -> Self {
+        self.id = id;
+        self
+    }
+
     /// Set the visibility of the completion candidate
     ///
     /// Only shown when there is no visible candidate for completing the current argument.
@@ -60,6 +69,11 @@ impl CompletionCandidate {
         self.help.as_ref()
     }
 
+    /// Get the id used for de-duplicating
+    pub fn get_id(&self) -> Option<&String> {
+        self.id.as_ref()
+    }
+
     /// Get the visibility of the completion candidate
     pub fn is_hide_set(&self) -> bool {
         self.hidden

clap_complete/src/engine/complete.rs

@@ -257,6 +257,14 @@ fn complete_arg(
     if completions.iter().any(|a| !a.is_hide_set()) {
         completions.retain(|a| !a.is_hide_set());
     }
+    let mut seen_ids = std::collections::HashSet::new();
+    completions.retain(move |a| {
+        if let Some(id) = a.get_id().cloned() {
+            seen_ids.insert(id)
+        } else {
+            true
+        }
+    });
 
     Ok(completions)
 }