ast: Add metadata attributes on Items

TODO: decide what other places attributes belong

grammar.ebnf

@@ -8,7 +8,11 @@ Visibility  = "pub"? ;
 File        = Item* EOI ;
 
 
-Item        = Visibility ItemKind ;
+Attrs       = ('#' '[' (Meta ',') Meta? ']')* ;
+Meta        = Identifier ('=' Literal | '(' (Literal ',')* Literal? ')')? ;
+
+
+Item        = Attrs* Visibility ItemKind ;
 ItemKind    = Const    | Static | Module 
             | Function | Struct | Enum 
             | Alias    | Impl ;

libconlang/src/ast.rs

@@ -32,11 +32,31 @@ pub struct File {
     pub items: Vec<Item>,
 }
 
+// Metadata decorators
+#[derive(Clone, Debug, PartialEq, Eq)]
+pub struct Attrs {
+    pub meta: Vec<Meta>,
+}
+
+#[derive(Clone, Debug, PartialEq, Eq)]
+pub struct Meta {
+    pub name: Identifier,
+    pub kind: MetaKind,
+}
+
+#[derive(Clone, Debug, PartialEq, Eq)]
+pub enum MetaKind {
+    Plain,
+    Equals(Literal),
+    Func(Vec<Literal>),
+}
+
 // Items
 /// Stores an [ItemKind] and associated metadata
 #[derive(Clone, Debug, PartialEq, Eq)]
 pub struct Item {
     pub extents: Span,
+    pub attrs: Attrs,
     pub vis: Visibility,
     pub kind: ItemKind,
 }

libconlang/src/ast/ast_impl.rs

@@ -77,10 +77,39 @@ mod display {
         }
     }
 
+    impl Display for Attrs {
+        fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+            let Self { meta } = self;
+            if meta.is_empty() {
+                return Ok(());
+            }
+            "#".fmt(f)?;
+            delimit(separate(meta, ", "), INLINE_SQUARE)(f)?;
+            "\n".fmt(f)
+        }
+    }
+    impl Display for Meta {
+        fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+            let Self { name, kind } = self;
+            write!(f, "{name}{kind}")
+        }
+    }
+    impl Display for MetaKind {
+        fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+            match self {
+                MetaKind::Plain => Ok(()),
+                MetaKind::Equals(v) => write!(f, " = {v}"),
+                MetaKind::Func(args) => delimit(separate(args, ", "), INLINE_PARENS)(f),
+            }
+        }
+    }
+
     impl Display for Item {
         fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-            self.vis.fmt(f)?;
-            match &self.kind {
+            let Self { extents: _, attrs, vis, kind } = self;
+            attrs.fmt(f)?;
+            vis.fmt(f)?;
+            match kind {
                 ItemKind::Alias(v) => v.fmt(f),
                 ItemKind::Const(v) => v.fmt(f),
                 ItemKind::Static(v) => v.fmt(f),

libconlang/src/parser.rs

@@ -68,6 +68,9 @@ pub mod error {
     pub enum Parsing {
         File,
 
+        Attrs,
+        Meta,
+
         Item,
         Visibility,
         Mutability,
@@ -161,6 +164,10 @@ pub mod error {
         fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
             match self {
                 Parsing::File => "a file",
+
+                Parsing::Attrs => "an attribute-set",
+                Parsing::Meta => "an attribute",
+
                 Parsing::Item => "an item",
                 Parsing::Visibility => "a visibility qualifier",
                 Parsing::Mutability => "a mutability qualifier",
@@ -371,7 +378,8 @@ fn rep<'t, T>(
 
 /// Expands to a pattern which matches item-like [Token] [Type]s
 macro item_like() {
-    Type::Keyword(
+    Type::Hash
+        | Type::Keyword(
         Keyword::Pub
             | Keyword::Type
             | Keyword::Const
@@ -406,6 +414,7 @@ impl<'t> Parser<'t> {
         let start = self.loc();
         Ok(Item {
             vis: self.visibility()?,
+            attrs: self.attributes()?,
             kind: self.itemkind()?,
             extents: Span(start, self.loc()),
         })
@@ -464,6 +473,41 @@ impl<'t> Parser<'t> {
     }
 }
 
+/// Attribute parsing
+impl<'t> Parser<'t> {
+    /// Parses an [attribute set](Attrs)
+    pub fn attributes(&mut self) -> PResult<Attrs> {
+        if self.match_type(Type::Hash, Parsing::Attrs).is_err() {
+            return Ok(Attrs { meta: vec![] });
+        }
+        let meta = delim(
+            sep(Self::meta, Type::Comma, BRACKETS.1, Parsing::Attrs),
+            BRACKETS,
+            Parsing::Attrs,
+        );
+        Ok(Attrs { meta: meta(self)? })
+    }
+    pub fn meta(&mut self) -> PResult<Meta> {
+        Ok(Meta { name: self.identifier()?, kind: self.meta_kind()? })
+    }
+    pub fn meta_kind(&mut self) -> PResult<MetaKind> {
+        const PARSING: Parsing = Parsing::Meta;
+        let lit_tuple = delim(
+            sep(Self::literal, Type::Comma, PARENS.1, PARSING),
+            PARENS,
+            PARSING,
+        );
+        Ok(match self.peek_type(PARSING) {
+            Ok(Type::Eq) => {
+                self.consume_peeked();
+                MetaKind::Equals(self.literal()?)
+            }
+            Ok(Type::LParen) => MetaKind::Func(lit_tuple(self)?),
+            _ => MetaKind::Plain,
+        })
+    }
+}
+
 /// Item parsing
 impl<'t> Parser<'t> {
     /// Parses an [ItemKind]