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Attempt to try to resolve blocking concerns
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c410-f3r committed Dec 2, 2023
1 parent 64d7e0d commit 0278505
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144 changes: 144 additions & 0 deletions compiler/rustc_data_structures/src/tagged_ptr/impl_tag.rs
Original file line number Diff line number Diff line change
Expand Up @@ -81,6 +81,7 @@
/// E::A,
/// }
/// ```
#[cfg(bootstrap)]
#[macro_export]
macro_rules! impl_tag {
(
Expand Down Expand Up @@ -140,5 +141,148 @@ macro_rules! impl_tag {
};
}

/// Implements [`Tag`] for a given type.
///
/// You can use `impl_tag` on structs and enums.
/// You need to specify the type and all its possible values,
/// which can only be paths with optional fields.
///
/// [`Tag`]: crate::tagged_ptr::Tag
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// #![feature(macro_metavar_expr)]
/// use rustc_data_structures::{impl_tag, tagged_ptr::Tag};
///
/// #[derive(Copy, Clone, PartialEq, Debug)]
/// enum SomeTag {
/// A,
/// B,
/// X { v: bool },
/// Y(bool, bool),
/// }
///
/// impl_tag! {
/// // The type for which the `Tag` will be implemented
/// impl Tag for SomeTag;
/// // You need to specify all possible tag values:
/// SomeTag::A, // 0
/// SomeTag::B, // 1
/// // For variants with fields, you need to specify the fields:
/// SomeTag::X { v: true }, // 2
/// SomeTag::X { v: false }, // 3
/// // For tuple variants use named syntax:
/// SomeTag::Y { 0: true, 1: true }, // 4
/// SomeTag::Y { 0: false, 1: true }, // 5
/// SomeTag::Y { 0: true, 1: false }, // 6
/// SomeTag::Y { 0: false, 1: false }, // 7
/// }
///
/// // Tag values are assigned in order:
/// assert_eq!(SomeTag::A.into_usize(), 0);
/// assert_eq!(SomeTag::X { v: false }.into_usize(), 3);
/// assert_eq!(SomeTag::Y(false, true).into_usize(), 5);
///
/// assert_eq!(unsafe { SomeTag::from_usize(1) }, SomeTag::B);
/// assert_eq!(unsafe { SomeTag::from_usize(2) }, SomeTag::X { v: true });
/// assert_eq!(unsafe { SomeTag::from_usize(7) }, SomeTag::Y(false, false));
/// ```
///
/// Structs are supported:
///
/// ```
/// #![feature(macro_metavar_expr)]
/// # use rustc_data_structures::impl_tag;
/// #[derive(Copy, Clone)]
/// struct Flags { a: bool, b: bool }
///
/// impl_tag! {
/// impl Tag for Flags;
/// Flags { a: true, b: true },
/// Flags { a: false, b: true },
/// Flags { a: true, b: false },
/// Flags { a: false, b: false },
/// }
/// ```
///
/// Not specifying all values results in a compile error:
///
/// ```compile_fail,E0004
/// #![feature(macro_metavar_expr)]
/// # use rustc_data_structures::impl_tag;
/// #[derive(Copy, Clone)]
/// enum E {
/// A,
/// B,
/// }
///
/// impl_tag! {
/// impl Tag for E;
/// E::A,
/// }
/// ```
#[cfg(not(bootstrap))]
#[macro_export]
macro_rules! impl_tag {
(
impl Tag for $Self:ty;
$(
$($path:ident)::* $( { $( $fields:tt )* })?,
)*
) => {
// Safety:
// `bits_for_tags` is called on the same `${index()}`-es as
// `into_usize` returns, thus `BITS` constant is correct.
unsafe impl $crate::tagged_ptr::Tag for $Self {
const BITS: u32 = $crate::tagged_ptr::bits_for_tags(&[
$(
${index()},
$( ${ignore($path)} )*
)*
]);

#[inline]
fn into_usize(self) -> usize {
// This forbids use of repeating patterns (`Enum::V`&`Enum::V`, etc)
// (or at least it should, see <https://github.com/rust-lang/rust/issues/110613>)
#[forbid(unreachable_patterns)]
match self {
// `match` is doing heavy lifting here, by requiring exhaustiveness
$(
$($path)::* $( { $( $fields )* } )? => ${index()},
)*
}
}

#[inline]
unsafe fn from_usize(tag: usize) -> Self {
match tag {
$(
${index()} => $($path)::* $( { $( $fields )* } )?,
)*

// Safety:
// `into_usize` only returns `${index()}` of the same
// repetition as we are filtering above, thus if this is
// reached, the safety contract of this function was
// already breached.
_ => unsafe {
debug_assert!(
false,
"invalid tag: {tag}\
(this is a bug in the caller of `from_usize`)"
);
std::hint::unreachable_unchecked()
},
}
}

}
};
}

#[cfg(test)]
mod tests;
126 changes: 126 additions & 0 deletions compiler/rustc_expand/src/expand.rs
Original file line number Diff line number Diff line change
Expand Up @@ -41,6 +41,7 @@ use std::path::PathBuf;
use std::rc::Rc;
use std::{iter, mem};

#[cfg(bootstrap)]
macro_rules! ast_fragments {
(
$($Kind:ident($AstTy:ty) {
Expand Down Expand Up @@ -165,6 +166,131 @@ macro_rules! ast_fragments {
}
}

#[cfg(not(bootstrap))]
macro_rules! ast_fragments {
(
$($Kind:ident($AstTy:ty) {
$kind_name:expr;
$(one fn $mut_visit_ast:ident; fn $visit_ast:ident;)?
$(many fn $flat_map_ast_elt:ident; fn $visit_ast_elt:ident($($args:tt)*);)?
fn $make_ast:ident;
})*
) => {
/// A fragment of AST that can be produced by a single macro expansion.
/// Can also serve as an input and intermediate result for macro expansion operations.
pub enum AstFragment {
OptExpr(Option<P<ast::Expr>>),
MethodReceiverExpr(P<ast::Expr>),
$($Kind($AstTy),)*
}

/// "Discriminant" of an AST fragment.
#[derive(Copy, Clone, PartialEq, Eq)]
pub enum AstFragmentKind {
OptExpr,
MethodReceiverExpr,
$($Kind,)*
}

impl AstFragmentKind {
pub fn name(self) -> &'static str {
match self {
AstFragmentKind::OptExpr => "expression",
AstFragmentKind::MethodReceiverExpr => "expression",
$(AstFragmentKind::$Kind => $kind_name,)*
}
}

fn make_from<'a>(self, result: Box<dyn MacResult + 'a>) -> Option<AstFragment> {
match self {
AstFragmentKind::OptExpr =>
result.make_expr().map(Some).map(AstFragment::OptExpr),
AstFragmentKind::MethodReceiverExpr =>
result.make_expr().map(AstFragment::MethodReceiverExpr),
$(AstFragmentKind::$Kind => result.$make_ast().map(AstFragment::$Kind),)*
}
}
}

impl AstFragment {
pub fn add_placeholders(&mut self, placeholders: &[NodeId]) {
if placeholders.is_empty() {
return;
}
match self {
$($(AstFragment::$Kind(ast) => ast.extend(placeholders.iter().flat_map(|id| {
${ignore($flat_map_ast_elt)}
placeholder(AstFragmentKind::$Kind, *id, None).$make_ast()
})),)?)*
_ => panic!("unexpected AST fragment kind")
}
}

pub fn make_opt_expr(self) -> Option<P<ast::Expr>> {
match self {
AstFragment::OptExpr(expr) => expr,
_ => panic!("AstFragment::make_* called on the wrong kind of fragment"),
}
}

pub fn make_method_receiver_expr(self) -> P<ast::Expr> {
match self {
AstFragment::MethodReceiverExpr(expr) => expr,
_ => panic!("AstFragment::make_* called on the wrong kind of fragment"),
}
}

$(pub fn $make_ast(self) -> $AstTy {
match self {
AstFragment::$Kind(ast) => ast,
_ => panic!("AstFragment::make_* called on the wrong kind of fragment"),
}
})*

fn make_ast<T: InvocationCollectorNode>(self) -> T::OutputTy {
T::fragment_to_output(self)
}

pub fn mut_visit_with<F: MutVisitor>(&mut self, vis: &mut F) {
match self {
AstFragment::OptExpr(opt_expr) => {
visit_clobber(opt_expr, |opt_expr| {
if let Some(expr) = opt_expr {
vis.filter_map_expr(expr)
} else {
None
}
});
}
AstFragment::MethodReceiverExpr(expr) => vis.visit_method_receiver_expr(expr),
$($(AstFragment::$Kind(ast) => vis.$mut_visit_ast(ast),)?)*
$($(AstFragment::$Kind(ast) =>
ast.flat_map_in_place(|ast| vis.$flat_map_ast_elt(ast)),)?)*
}
}

pub fn visit_with<'a, V: Visitor<'a>>(&'a self, visitor: &mut V) {
match self {
AstFragment::OptExpr(Some(expr)) => visitor.visit_expr(expr),
AstFragment::OptExpr(None) => {}
AstFragment::MethodReceiverExpr(expr) => visitor.visit_method_receiver_expr(expr),
$($(AstFragment::$Kind(ast) => visitor.$visit_ast(ast),)?)*
$($(AstFragment::$Kind(ast) => for ast_elt in &ast[..] {
visitor.$visit_ast_elt(ast_elt, $($args)*);
})?)*
}
}
}

impl<'a> MacResult for crate::mbe::macro_rules::ParserAnyMacro<'a> {
$(fn $make_ast(self: Box<crate::mbe::macro_rules::ParserAnyMacro<'a>>)
-> Option<$AstTy> {
Some(self.make(AstFragmentKind::$Kind).$make_ast())
})*
}
}
}

ast_fragments! {
Expr(P<ast::Expr>) { "expression"; one fn visit_expr; fn visit_expr; fn make_expr; }
Pat(P<ast::Pat>) { "pattern"; one fn visit_pat; fn visit_pat; fn make_pat; }
Expand Down
32 changes: 26 additions & 6 deletions compiler/rustc_expand/src/mbe/metavar_expr.rs
Original file line number Diff line number Diff line change
Expand Up @@ -10,9 +10,8 @@ use rustc_span::Span;
/// A meta-variable expression, for expansions based on properties of meta-variables.
#[derive(Debug, Clone, PartialEq, Encodable, Decodable)]
pub(crate) enum MetaVarExpr {
/// The number of repetitions of an identifier, optionally limited to a number
/// of outer-most repetition depths. If the depth limit is `None` then the depth is unlimited.
Count(Ident, Option<usize>),
/// The number of repetitions of an identifier.
Count(Ident, usize),

/// Ignore a meta-variable for repetition without expansion.
Ignore(Ident),
Expand Down Expand Up @@ -43,7 +42,10 @@ impl MetaVarExpr {
let mut iter = args.trees();
let rslt = match ident.as_str() {
"count" => parse_count(&mut iter, sess, ident.span)?,
"ignore" => MetaVarExpr::Ignore(parse_ident(&mut iter, sess, ident.span)?),
"ignore" => {
eat_dollar(&mut iter, sess, ident.span)?;
MetaVarExpr::Ignore(parse_ident(&mut iter, sess, ident.span)?)
}
"index" => MetaVarExpr::Index(parse_depth(&mut iter, sess, ident.span)?),
"length" => MetaVarExpr::Length(parse_depth(&mut iter, sess, ident.span)?),
_ => {
Expand Down Expand Up @@ -92,6 +94,7 @@ fn parse_count<'sess>(
sess: &'sess ParseSess,
span: Span,
) -> PResult<'sess, MetaVarExpr> {
eat_dollar(iter, sess, span)?;
let ident = parse_ident(iter, sess, span)?;
let depth = if try_eat_comma(iter) {
if iter.look_ahead(0).is_none() {
Expand All @@ -100,9 +103,9 @@ fn parse_count<'sess>(
"`count` followed by a comma must have an associated index indicating its depth",
));
}
Some(parse_depth(iter, sess, span)?)
parse_depth(iter, sess, span)?
} else {
None
0
};
Ok(MetaVarExpr::Count(ident, depth))
}
Expand Down Expand Up @@ -166,3 +169,20 @@ fn try_eat_comma(iter: &mut RefTokenTreeCursor<'_>) -> bool {
}
false
}

/// Expects that the next item is a dollar sign.
fn eat_dollar<'sess>(
iter: &mut RefTokenTreeCursor<'_>,
sess: &'sess ParseSess,
span: Span,
) -> PResult<'sess, ()> {
if let Some(TokenTree::Token(token::Token { kind: token::Dollar, .. }, _)) = iter.look_ahead(0)
{
let _ = iter.next();
return Ok(());
}
Err(sess.span_diagnostic.struct_span_err(
span,
"meta-variables within meta-variable expressions must be referenced using a dollar sign",
))
}
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