feat(clap_complete): Support delimiter values in native completions

clap_complete/src/dynamic/complete.rs

@@ -262,6 +262,9 @@ fn complete_arg_value(
     let mut values = Vec::new();
     debug!("complete_arg_value: arg={arg:?}, value={value:?}");
 
+    let (prefix, value) =
+        rsplit_delimiter(value, arg.get_value_delimiter()).unwrap_or((None, value));
+
     let value_os = match value {
         Ok(value) => OsStr::new(value),
         Err(value_os) => value_os,
@@ -316,9 +319,28 @@ fn complete_arg_value(
         values.sort();
     }
 
+    if let Some(prefix) = prefix {
+        values = values
+            .into_iter()
+            .map(|comp| comp.add_prefix(prefix))
+            .collect();
+    }
     values
 }
 
+fn rsplit_delimiter<'s, 'o>(
+    value: Result<&'s str, &'o OsStr>,
+    delimiter: Option<char>,
+) -> Option<(Option<&'s str>, Result<&'s str, &'o OsStr>)> {
+    let delimiter = delimiter?;
+    let value = value.ok()?;
+    let pos = value.rfind(delimiter)?;
+    let (prefix, value) = value
+        .split_at_checked(pos + delimiter.len_utf8())
+        .expect("since delimiter was found, it is within bounds");
+    Some((Some(prefix), Ok(value)))
+}
+
 fn complete_path(
     value_os: &OsStr,
     current_dir: Option<&std::path::Path>,

clap_complete/tests/testsuite/dynamic.rs

@@ -661,18 +661,35 @@ tab"
         snapbox::str!["--delimiter=comma"]
     );
 
-    assert_data_eq!(complete!(cmd, "--delimiter comma,[TAB]"), snapbox::str![""]);
+    assert_data_eq!(
+        complete!(cmd, "--delimiter comma,[TAB]"),
+        snapbox::str![
+            "comma,comma
+comma,space
+comma,tab"
+        ]
+    );
 
-    assert_data_eq!(complete!(cmd, "--delimiter=comma,[TAB]"), snapbox::str![""]);
+    assert_data_eq!(
+        complete!(cmd, "--delimiter=comma,[TAB]"),
+        snapbox::str![
+            "--delimiter=comma,comma
+--delimiter=comma,space
+--delimiter=comma,tab
+--delimiter=comma,a_pos
+--delimiter=comma,b_pos
+--delimiter=comma,c_pos"
+        ]
+    );
 
     assert_data_eq!(
         complete!(cmd, "--delimiter comma,s[TAB]"),
-        snapbox::str![""]
+        snapbox::str!["comma,space"]
     );
 
     assert_data_eq!(
         complete!(cmd, "--delimiter=comma,s[TAB]"),
-        snapbox::str![""]
+        snapbox::str!["--delimiter=comma,space"]
     );
 
     assert_data_eq!(
@@ -697,13 +714,36 @@ tab"
 
     assert_data_eq!(complete!(cmd, "-D=c[TAB]"), snapbox::str!["-D=comma"]);
 
-    assert_data_eq!(complete!(cmd, "-D comma,[TAB]"), snapbox::str![""]);
+    assert_data_eq!(
+        complete!(cmd, "-D comma,[TAB]"),
+        snapbox::str![
+            "comma,comma
+comma,space
+comma,tab"
+        ]
+    );
 
-    assert_data_eq!(complete!(cmd, "-D=comma,[TAB]"), snapbox::str![""]);
+    assert_data_eq!(
+        complete!(cmd, "-D=comma,[TAB]"),
+        snapbox::str![
+            "-D=comma,comma
+-D=comma,space
+-D=comma,tab
+-D=comma,a_pos
+-D=comma,b_pos
+-D=comma,c_pos"
+        ]
+    );
 
-    assert_data_eq!(complete!(cmd, "-D comma,s[TAB]"), snapbox::str![""]);
+    assert_data_eq!(
+        complete!(cmd, "-D comma,s[TAB]"),
+        snapbox::str!["comma,space"]
+    );
 
-    assert_data_eq!(complete!(cmd, "-D=comma,s[TAB]"), snapbox::str![""]);
+    assert_data_eq!(
+        complete!(cmd, "-D=comma,s[TAB]"),
+        snapbox::str!["-D=comma,space"]
+    );
 
     assert_data_eq!(
         complete!(cmd, "-- [TAB]"),
@@ -718,9 +758,19 @@ c_pos"
         ]
     );
 
-    assert_data_eq!(complete!(cmd, " -- a_pos,[TAB]"), snapbox::str![""]);
+    assert_data_eq!(
+        complete!(cmd, " -- a_pos,[TAB]"),
+        snapbox::str![
+            "a_pos,a_pos
+a_pos,b_pos
+a_pos,c_pos"
+        ]
+    );
 
-    assert_data_eq!(complete!(cmd, "-- a_pos,b[TAB]"), snapbox::str![""]);
+    assert_data_eq!(
+        complete!(cmd, "-- a_pos,b[TAB]"),
+        snapbox::str!["a_pos,b_pos"]
+    );
 }
 
 fn complete(cmd: &mut Command, args: impl AsRef<str>, current_dir: Option<&Path>) -> String {