grammar: Make UseTree less ultra-janky

compiler/cl-ast/src/ast.rs

@@ -228,15 +228,17 @@ pub enum ImplKind {
 /// An import of nonlocal [Item]s
 #[derive(Clone, Debug, PartialEq, Eq, Hash)]
 pub struct Use {
+    pub absolute: bool,
     pub tree: UseTree,
 }
 
 /// A tree of [Item] imports
 #[derive(Clone, Debug, PartialEq, Eq, Hash)]
 pub enum UseTree {
-    Tree(Path, Vec<UseTree>),
+    Tree(Vec<UseTree>),
-    Alias(Path, Identifier),
+    Path(PathPart, Box<UseTree>),
-    Path(Path),
+    Alias(Identifier, Identifier),
+    Name(Identifier),
     Glob,
 }
 

compiler/cl-ast/src/ast_impl.rs

@@ -283,20 +283,22 @@ mod display {
 
     impl Display for Use {
         fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-            let Self { tree } = self;
+            let Self { absolute, tree } = self;
+            if *absolute {
+                write!(f, "use ::{tree}")
+            } else {
                 write!(f, "use {tree}")
             }
         }
+    }
 
     impl Display for UseTree {
         fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
             match self {
-                UseTree::Tree(path, tree) => {
+                UseTree::Tree(tree) => separate(tree, ", ")(f.delimit(INLINE_BRACES)),
-                    write!(f, "{path}")?;
+                UseTree::Path(path, rest) => write!(f, "{path}::{rest}"),
-                    separate(tree, ", ")(f.delimit(INLINE_BRACES))
-                }
                 UseTree::Alias(path, name) => write!(f, "{path} as {name}"),
-                UseTree::Path(path) => write!(f, "{path}"),
+                UseTree::Name(name) => write!(f, "{name}"),
                 UseTree::Glob => write!(f, "*"),
             }
         }

compiler/cl-ast/src/ast_visitor/fold.rs

@@ -159,8 +159,8 @@ pub trait Fold {
         or_fold_impl_kind(self, kind)
     }
     fn fold_use(&mut self, u: Use) -> Use {
-        let Use { tree } = u;
+        let Use { absolute, tree } = u;
-        Use { tree: self.fold_use_tree(tree) }
+        Use { absolute, tree: self.fold_use_tree(tree) }
     }
     fn fold_use_tree(&mut self, tree: UseTree) -> UseTree {
         or_fold_use_tree(self, tree)
@@ -468,16 +468,19 @@ pub fn or_fold_impl_kind<F: Fold + ?Sized>(folder: &mut F, kind: ImplKind) -> Im
 #[inline]
 pub fn or_fold_use_tree<F: Fold + ?Sized>(folder: &mut F, tree: UseTree) -> UseTree {
     match tree {
-        UseTree::Tree(path, tree) => UseTree::Tree(
+        UseTree::Tree(tree) => UseTree::Tree(
-            folder.fold_path(path),
             tree.into_iter()
                 .map(|tree| folder.fold_use_tree(tree))
                 .collect(),
         ),
+        UseTree::Path(path, rest) => UseTree::Path(
+            folder.fold_path_part(path),
+            Box::new(folder.fold_use_tree(*rest)),
+        ),
         UseTree::Alias(path, name) => {
-            UseTree::Alias(folder.fold_path(path), folder.fold_identifier(name))
+            UseTree::Alias(folder.fold_identifier(path), folder.fold_identifier(name))
         }
-        UseTree::Path(path) => UseTree::Path(folder.fold_path(path)),
+        UseTree::Name(name) => UseTree::Name(folder.fold_identifier(name)),
         UseTree::Glob => UseTree::Glob,
     }
 }

compiler/cl-ast/src/ast_visitor/visit.rs

@@ -131,7 +131,7 @@ pub trait Visit<'a>: Sized {
         or_visit_impl_kind(self, target)
     }
     fn visit_use(&mut self, u: &'a Use) {
-        let Use { tree } = u;
+        let Use { absolute: _, tree } = u;
         self.visit_use_tree(tree);
     }
     fn visit_use_tree(&mut self, tree: &'a UseTree) {
@@ -386,15 +386,20 @@ pub fn or_visit_impl_kind<'a, V: Visit<'a>>(visitor: &mut V, target: &'a ImplKin
 
 pub fn or_visit_use_tree<'a, V: Visit<'a>>(visitor: &mut V, tree: &'a UseTree) {
     match tree {
-        UseTree::Tree(path, tree) => {
+        UseTree::Tree(tree) => {
-            visitor.visit_path(path);
             tree.iter().for_each(|tree| visitor.visit_use_tree(tree));
         }
+        UseTree::Path(path, rest) => {
+            visitor.visit_path_part(path);
+            visitor.visit_use_tree(rest)
+        }
         UseTree::Alias(path, name) => {
-            visitor.visit_path(path);
+            visitor.visit_identifier(path);
+            visitor.visit_identifier(name);
+        }
+        UseTree::Name(name) => {
             visitor.visit_identifier(name);
         }
-        UseTree::Path(path) => visitor.visit_path(path),
         UseTree::Glob => {}
     }
 }

compiler/cl-parser/src/parser.rs

@@ -607,30 +607,40 @@ impl<'t> Parser<'t> {
 
     pub fn parse_use(&mut self) -> PResult<Use> {
         self.consume_peeked();
-        Ok(Use { tree: self.parse_use_tree()? })
+        let absolute = self.match_op(Punct::ColonColon, Parsing::Use).is_ok();
+        let tree = self.parse_use_tree()?;
+        self.match_op(Punct::Semi, Parsing::Use)?;
+        Ok(Use { tree, absolute })
     }
 
     pub fn parse_use_tree(&mut self) -> PResult<UseTree> {
         const PARSING: Parsing = Parsing::UseTree;
         // glob import
-        if self.match_op(Punct::Star, PARSING).is_ok() {
+        Ok(match self.peek_kind(PARSING)? {
-            return Ok(UseTree::Glob);
+            TokenKind::Punct(Punct::Star) => {
-        }
-        let path = self.path()?;
-        Ok(match self.peek_kind(PARSING) {
-            Ok(TokenKind::As) => {
                 self.consume_peeked();
-                UseTree::Alias(path, self.identifier()?)
+                UseTree::Glob
             }
-            Ok(TokenKind::Punct(Punct::LCurly)) => UseTree::Tree(
+            TokenKind::Punct(Punct::LCurly) => UseTree::Tree(delim(
-                path,
-                delim(
                 sep(Self::parse_use_tree, Punct::Comma, CURLIES.1, PARSING),
                 CURLIES,
                 PARSING,
-                )(self)?,
+            )(self)?),
-            ),
+            TokenKind::SelfKw | TokenKind::Super | TokenKind::Identifier => {
-            _ => UseTree::Path(path),
+                let name = self.path_part()?;
+                if self.match_op(Punct::ColonColon, PARSING).is_ok() {
+                    UseTree::Path(name, Box::new(self.parse_use_tree()?))
+                } else {
+                    let PathPart::Ident(name) = name else {
+                        Err(self.error(
+                            ErrorKind::ExpectedParsing { want: Parsing::Identifier },
+                            PARSING,
+                        ))?
+                    };
+                    UseTree::Name(name)
+                }
+            }
+            t => Err(self.error(Unexpected(t), Parsing::UseTree))?,
         })
     }
 

compiler/cl-repl/examples/yaml.rs

@@ -325,16 +325,17 @@ pub mod yamlify {
     }
     impl Yamlify for Use {
         fn yaml(&self, y: &mut Yamler) {
-            let Self { tree } = self;
+            let Self { absolute, tree } = self;
-            y.key("Use").yaml(tree);
+            y.key("Use").pair("absolute", absolute).yaml(tree);
         }
     }
     impl Yamlify for UseTree {
         fn yaml(&self, y: &mut Yamler) {
             match self {
-                UseTree::Tree(path, tree) => y.pair("path", path).pair("tree", tree),
+                UseTree::Tree(trees) => y.pair("trees", trees),
-                UseTree::Alias(path, name) => y.pair("path", path).pair("name", name),
+                UseTree::Path(path, tree) => y.pair("path", path).pair("tree", tree),
-                UseTree::Path(path) => y.pair("path", path),
+                UseTree::Alias(from, to) => y.pair("from", from).pair("to", to),
+                UseTree::Name(name) => y.pair("name", name),
                 UseTree::Glob => y.value("Glob"),
             };
         }

grammar.ebnf

@@ -45,10 +45,9 @@ Alias       = "type" Identifier ('=' Ty)? ';' ;
 Impl        = "impl" Path '{' Item* '}' ;
 (* TODO: Impl Trait for Target*)
 
-Use         = "use" UseTree ;
+Use         = "use" '::'? UseTree ';' ;
-UseTree     = Path '{' (UseTree ',')* UseTree? '}'
+UseTree     = '*' | '{' (UseTree ',')* UseTree? '}'
-            | Path "as" Identifier
+            | PathPart ('::' UseTree | "as" Identifier)? ;
-            | Path | '*' ;
 
 (* type *)
 Ty          = Never | Empty | Path | TyTuple | TyRef | TyFn ;