Allow different names for ...rest (#3954)

* Allow different names for ...rest

* Resolves #3945

* This change requires an explicit name for the rest argument in `WholeStreamCommand`,
  which is why there are so many changed files.

* Remove redundant clone

* Add tests

crates/nu-parser/src/flag.rs

@@ -88,7 +88,7 @@ mod tests {
         Signature::build("bundle add")
             .switch("skip-install", "Adds the gem to the Gemfile but does not install it.", None)
             .named("group", SyntaxShape::String, "Specify the group(s) for the added gem. Multiple groups should be separated by commas.", Some('g'))
-            .rest(SyntaxShape::Any, "options")
+            .rest("rest", SyntaxShape::Any, "options")
     }
 
     #[test]

crates/nu-parser/src/parse.rs

@@ -1601,7 +1601,7 @@ fn parse_internal_command(
 
             positional.push(arg);
             current_positional += 1;
-        } else if let Some((rest_type, _)) = &signature.rest_positional {
+        } else if let Some((_, rest_type, _)) = &signature.rest_positional {
             let (arg, err) = parse_arg(*rest_type, scope, &lite_cmd.parts[idx]);
             if error.is_none() {
                 error = err;

crates/nu-parser/src/parse/def/primitives.rs

@@ -185,20 +185,20 @@ pub fn parse_type_token(type_: &Token) -> (SyntaxShape, Option<ParseError>) {
     }
 }
 
-pub(crate) fn parse_rest_name(name_token: &Token) -> Option<ParseError> {
+pub(crate) fn parse_rest_name(name_token: &Token) -> (Spanned<String>, Option<ParseError>) {
     return if let TokenContents::Baseline(name) = &name_token.contents {
-        if !name.starts_with("...") {
-            Some(parse_rest_name_err(name_token))
-        } else if !name.starts_with("...rest") {
-            Some(ParseError::mismatch(
-                "rest argument name to be 'rest'",
-                token_to_spanned_string(name_token),
-            ))
-        } else {
-            None
+        match name.strip_prefix("...") {
+            Some(var_name) => (var_name.to_string().spanned(name_token.span), None),
+            None => (
+                "InternalError".to_string().spanned(name_token.span),
+                Some(parse_rest_name_err(name_token)),
+            ),
         }
     } else {
-        Some(parse_rest_name_err(name_token))
+        (
+            "InternalError".to_string().spanned(name_token.span),
+            Some(parse_rest_name_err(name_token)),
+        )
     };
 
     fn parse_rest_name_err(token: &Token) -> ParseError {

crates/nu-parser/src/parse/def/signature.rs

@@ -231,7 +231,7 @@ fn parse_rest(
     tokens: &[Token],
     tokens_as_str: &Spanned<String>,
 ) -> (
-    Option<(SyntaxShape, Description)>,
+    Option<(String, SyntaxShape, Description)>,
     usize,
     Option<ParseError>,
 ) {
@@ -251,7 +251,7 @@ fn parse_rest(
     let mut type_ = SyntaxShape::Any;
     let mut comment = "".to_string();
 
-    let error = parse_rest_name(&tokens[i]);
+    let (name, error) = parse_rest_name(&tokens[i]);
     err = err.or(error);
     i += 1;
 
@@ -268,7 +268,7 @@ fn parse_rest(
         comment = parsed_comment.unwrap_or_else(|| "".to_string());
     }
 
-    (Some((type_, comment)), i, err)
+    (Some((name.item, type_, comment)), i, err)
 }
 
 fn parse_optional_type(tokens: &[Token]) -> (Option<SyntaxShape>, usize, Option<ParseError>) {
@@ -352,7 +352,7 @@ fn to_signature(
     name: &str,
     params: Vec<Parameter>,
     flags: Vec<Flag>,
-    rest: Option<(SyntaxShape, Description)>,
+    rest: Option<(String, SyntaxShape, Description)>,
 ) -> Signature {
     let mut sign = Signature::new(name);
 

crates/nu-parser/src/parse/def/tests.rs

@@ -332,7 +332,23 @@ fn simple_def_with_rest_arg() {
     assert!(err.is_none());
     assert_eq!(
         sign.rest_positional,
-        Some((SyntaxShape::Any, "".to_string()))
+        Some(("rest".to_string(), SyntaxShape::Any, "".to_string()))
+    );
+}
+
+#[test]
+fn simple_def_with_rest_arg_other_name() {
+    let name = "my_func";
+    let sign = "[ ...paths:path # A pathological test]";
+    let (sign, err) = parse_signature(name, &sign.to_string().spanned_unknown());
+    assert!(err.is_none());
+    assert_eq!(
+        sign.rest_positional,
+        Some((
+            "paths".to_string(),
+            SyntaxShape::FilePath,
+            "A pathological test".to_string()
+        ))
     );
 }
 
@@ -344,7 +360,11 @@ fn simple_def_with_rest_arg_with_type_and_comment() {
     assert!(err.is_none());
     assert_eq!(
         sign.rest_positional,
-        Some((SyntaxShape::FilePath, "My super cool rest arg".to_string()))
+        Some((
+            "rest".to_string(),
+            SyntaxShape::FilePath,
+            "My super cool rest arg".to_string()
+        ))
     );
 }
 
@@ -380,6 +400,10 @@ fn simple_def_with_param_flag_and_rest() {
     );
     assert_eq!(
         sign.rest_positional,
-        Some((SyntaxShape::Table, "Another rest".to_string()))
+        Some((
+            "rest".to_string(),
+            SyntaxShape::Table,
+            "Another rest".to_string()
+        ))
     );
 }