reorganize compiler crates

ast/src/constant.rs

@@ -0,0 +1,223 @@
+use num_bigint::BigInt;
+pub use rustpython_bytecode::ConversionFlag;
+
+#[derive(Debug, PartialEq)]
+pub enum Constant {
+    None,
+    Bool(bool),
+    Str(String),
+    Bytes(Vec<u8>),
+    Int(BigInt),
+    Tuple(Vec<Constant>),
+    Float(f64),
+    Complex { real: f64, imag: f64 },
+    Ellipsis,
+}
+
+impl From<String> for Constant {
+    fn from(s: String) -> Constant {
+        Self::Str(s)
+    }
+}
+impl From<Vec<u8>> for Constant {
+    fn from(b: Vec<u8>) -> Constant {
+        Self::Bytes(b)
+    }
+}
+impl From<bool> for Constant {
+    fn from(b: bool) -> Constant {
+        Self::Bool(b)
+    }
+}
+impl From<BigInt> for Constant {
+    fn from(i: BigInt) -> Constant {
+        Self::Int(i)
+    }
+}
+
+#[cfg(feature = "rustpython-common")]
+impl std::fmt::Display for Constant {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            Constant::None => f.pad("None"),
+            Constant::Bool(b) => f.pad(if *b { "True" } else { "False" }),
+            Constant::Str(s) => rustpython_common::str::repr(s).fmt(f),
+            Constant::Bytes(b) => f.pad(&rustpython_common::bytes::repr(b)),
+            Constant::Int(i) => i.fmt(f),
+            Constant::Tuple(tup) => {
+                if let [elt] = &**tup {
+                    write!(f, "({},)", elt)
+                } else {
+                    f.write_str("(")?;
+                    for (i, elt) in tup.iter().enumerate() {
+                        if i != 0 {
+                            f.write_str(", ")?;
+                        }
+                        elt.fmt(f)?;
+                    }
+                    f.write_str(")")
+                }
+            }
+            Constant::Float(fp) => f.pad(&rustpython_common::float_ops::to_string(*fp)),
+            Constant::Complex { real, imag } => {
+                if *real == 0.0 {
+                    write!(f, "{}j", imag)
+                } else {
+                    write!(f, "({}{:+}j)", real, imag)
+                }
+            }
+            Constant::Ellipsis => f.pad("..."),
+        }
+    }
+}
+
+#[cfg(feature = "constant-optimization")]
+#[non_exhaustive]
+#[derive(Default)]
+pub struct ConstantOptimizer {}
+
+#[cfg(feature = "constant-optimization")]
+impl ConstantOptimizer {
+    #[inline]
+    pub fn new() -> Self {
+        Self {}
+    }
+}
+
+#[cfg(feature = "constant-optimization")]
+impl<U> crate::fold::Fold<U> for ConstantOptimizer {
+    type TargetU = U;
+    type Error = std::convert::Infallible;
+    #[inline]
+    fn map_user(&mut self, user: U) -> Result<Self::TargetU, Self::Error> {
+        Ok(user)
+    }
+    fn fold_expr(&mut self, node: crate::Expr<U>) -> Result<crate::Expr<U>, Self::Error> {
+        match node.node {
+            crate::ExprKind::Tuple { elts, ctx } => {
+                let elts = elts
+                    .into_iter()
+                    .map(|x| self.fold_expr(x))
+                    .collect::<Result<Vec<_>, _>>()?;
+                let expr = if elts
+                    .iter()
+                    .all(|e| matches!(e.node, crate::ExprKind::Constant { .. }))
+                {
+                    let tuple = elts
+                        .into_iter()
+                        .map(|e| match e.node {
+                            crate::ExprKind::Constant { value, .. } => value,
+                            _ => unreachable!(),
+                        })
+                        .collect();
+                    crate::ExprKind::Constant {
+                        value: Constant::Tuple(tuple),
+                        kind: None,
+                    }
+                } else {
+                    crate::ExprKind::Tuple { elts, ctx }
+                };
+                Ok(crate::Expr {
+                    node: expr,
+                    custom: node.custom,
+                    location: node.location,
+                })
+            }
+            _ => crate::fold::fold_expr(self, node),
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    #[cfg(feature = "constant-optimization")]
+    #[test]
+    fn test_constant_opt() {
+        use super::*;
+        use crate::fold::Fold;
+        use crate::*;
+
+        let location = Location::new(0, 0);
+        let custom = ();
+        let ast = Located {
+            location,
+            custom,
+            node: ExprKind::Tuple {
+                ctx: ExprContext::Load,
+                elts: vec![
+                    Located {
+                        location,
+                        custom,
+                        node: ExprKind::Constant {
+                            value: BigInt::from(1).into(),
+                            kind: None,
+                        },
+                    },
+                    Located {
+                        location,
+                        custom,
+                        node: ExprKind::Constant {
+                            value: BigInt::from(2).into(),
+                            kind: None,
+                        },
+                    },
+                    Located {
+                        location,
+                        custom,
+                        node: ExprKind::Tuple {
+                            ctx: ExprContext::Load,
+                            elts: vec![
+                                Located {
+                                    location,
+                                    custom,
+                                    node: ExprKind::Constant {
+                                        value: BigInt::from(3).into(),
+                                        kind: None,
+                                    },
+                                },
+                                Located {
+                                    location,
+                                    custom,
+                                    node: ExprKind::Constant {
+                                        value: BigInt::from(4).into(),
+                                        kind: None,
+                                    },
+                                },
+                                Located {
+                                    location,
+                                    custom,
+                                    node: ExprKind::Constant {
+                                        value: BigInt::from(5).into(),
+                                        kind: None,
+                                    },
+                                },
+                            ],
+                        },
+                    },
+                ],
+            },
+        };
+        let new_ast = ConstantOptimizer::new()
+            .fold_expr(ast)
+            .unwrap_or_else(|e| match e {});
+        assert_eq!(
+            new_ast,
+            Located {
+                location,
+                custom,
+                node: ExprKind::Constant {
+                    value: Constant::Tuple(vec![
+                        BigInt::from(1).into(),
+                        BigInt::from(2).into(),
+                        Constant::Tuple(vec![
+                            BigInt::from(3).into(),
+                            BigInt::from(4).into(),
+                            BigInt::from(5).into(),
+                        ])
+                    ]),
+                    kind: None
+                },
+            }
+        );
+    }
+}

ast/src/fold_helpers.rs

@@ -0,0 +1,66 @@
+use crate::constant;
+use crate::fold::Fold;
+
+pub(crate) trait Foldable<T, U> {
+    type Mapped;
+    fn fold<F: Fold<T, TargetU = U> + ?Sized>(
+        self,
+        folder: &mut F,
+    ) -> Result<Self::Mapped, F::Error>;
+}
+
+impl<T, U, X> Foldable<T, U> for Vec<X>
+where
+    X: Foldable<T, U>,
+{
+    type Mapped = Vec<X::Mapped>;
+    fn fold<F: Fold<T, TargetU = U> + ?Sized>(
+        self,
+        folder: &mut F,
+    ) -> Result<Self::Mapped, F::Error> {
+        self.into_iter().map(|x| x.fold(folder)).collect()
+    }
+}
+
+impl<T, U, X> Foldable<T, U> for Option<X>
+where
+    X: Foldable<T, U>,
+{
+    type Mapped = Option<X::Mapped>;
+    fn fold<F: Fold<T, TargetU = U> + ?Sized>(
+        self,
+        folder: &mut F,
+    ) -> Result<Self::Mapped, F::Error> {
+        self.map(|x| x.fold(folder)).transpose()
+    }
+}
+
+impl<T, U, X> Foldable<T, U> for Box<X>
+where
+    X: Foldable<T, U>,
+{
+    type Mapped = Box<X::Mapped>;
+    fn fold<F: Fold<T, TargetU = U> + ?Sized>(
+        self,
+        folder: &mut F,
+    ) -> Result<Self::Mapped, F::Error> {
+        (*self).fold(folder).map(Box::new)
+    }
+}
+
+macro_rules! simple_fold {
+    ($($t:ty),+$(,)?) => {
+        $(impl<T, U> $crate::fold_helpers::Foldable<T, U> for $t {
+            type Mapped = Self;
+            #[inline]
+            fn fold<F: Fold<T, TargetU = U> + ?Sized>(
+                self,
+                _folder: &mut F,
+            ) -> Result<Self::Mapped, F::Error> {
+                Ok(self)
+            }
+        })+
+    };
+}
+
+simple_fold!(usize, String, bool, constant::Constant);

ast/src/impls.rs

@@ -0,0 +1,60 @@
+use crate::{Constant, ExprKind};
+
+impl<U> ExprKind<U> {
+    /// Returns a short name for the node suitable for use in error messages.
+    pub fn name(&self) -> &'static str {
+        match self {
+            ExprKind::BoolOp { .. } | ExprKind::BinOp { .. } | ExprKind::UnaryOp { .. } => {
+                "operator"
+            }
+            ExprKind::Subscript { .. } => "subscript",
+            ExprKind::Await { .. } => "await expression",
+            ExprKind::Yield { .. } | ExprKind::YieldFrom { .. } => "yield expression",
+            ExprKind::Compare { .. } => "comparison",
+            ExprKind::Attribute { .. } => "attribute",
+            ExprKind::Call { .. } => "function call",
+            ExprKind::Constant { value, .. } => match value {
+                Constant::Str(_)
+                | Constant::Int(_)
+                | Constant::Float(_)
+                | Constant::Complex { .. }
+                | Constant::Bytes(_) => "literal",
+                Constant::Tuple(_) => "tuple",
+                Constant::Bool(b) => {
+                    if *b {
+                        "True"
+                    } else {
+                        "False"
+                    }
+                }
+                Constant::None => "None",
+                Constant::Ellipsis => "ellipsis",
+            },
+            ExprKind::List { .. } => "list",
+            ExprKind::Tuple { .. } => "tuple",
+            ExprKind::Dict { .. } => "dict display",
+            ExprKind::Set { .. } => "set display",
+            ExprKind::ListComp { .. } => "list comprehension",
+            ExprKind::DictComp { .. } => "dict comprehension",
+            ExprKind::SetComp { .. } => "set comprehension",
+            ExprKind::GeneratorExp { .. } => "generator expression",
+            ExprKind::Starred { .. } => "starred",
+            ExprKind::Slice { .. } => "slice",
+            ExprKind::JoinedStr { values } => {
+                if values
+                    .iter()
+                    .any(|e| matches!(e.node, ExprKind::JoinedStr { .. }))
+                {
+                    "f-string expression"
+                } else {
+                    "literal"
+                }
+            }
+            ExprKind::FormattedValue { .. } => "f-string expression",
+            ExprKind::Name { .. } => "name",
+            ExprKind::Lambda { .. } => "lambda",
+            ExprKind::IfExp { .. } => "conditional expression",
+            ExprKind::NamedExpr { .. } => "named expression",
+        }
+    }
+}

ast/src/lib.rs

@@ -0,0 +1,13 @@
+mod ast_gen;
+mod constant;
+#[cfg(feature = "fold")]
+mod fold_helpers;
+mod impls;
+mod location;
+#[cfg(feature = "unparse")]
+mod unparse;
+
+pub use ast_gen::*;
+pub use location::Location;
+
+pub type Suite<U = ()> = Vec<Stmt<U>>;

ast/src/location.rs

@@ -0,0 +1,79 @@
+//! Datatypes to support source location information.
+
+use std::fmt;
+
+/// A location somewhere in the sourcecode.
+#[derive(Clone, Copy, Debug, Default, PartialEq, Eq)]
+pub struct Location {
+    row: usize,
+    column: usize,
+}
+
+impl fmt::Display for Location {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "line {} column {}", self.row, self.column)
+    }
+}
+
+impl Location {
+    pub fn visualize<'a>(
+        &self,
+        line: &'a str,
+        desc: impl fmt::Display + 'a,
+    ) -> impl fmt::Display + 'a {
+        struct Visualize<'a, D: fmt::Display> {
+            loc: Location,
+            line: &'a str,
+            desc: D,
+        }
+        impl<D: fmt::Display> fmt::Display for Visualize<'_, D> {
+            fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+                write!(
+                    f,
+                    "{}\n{}{arrow:>pad$}",
+                    self.desc,
+                    self.line,
+                    pad = self.loc.column,
+                    arrow = "^",
+                )
+            }
+        }
+        Visualize {
+            loc: *self,
+            line,
+            desc,
+        }
+    }
+}
+
+impl Location {
+    pub fn new(row: usize, column: usize) -> Self {
+        Location { row, column }
+    }
+
+    pub fn row(&self) -> usize {
+        self.row
+    }
+
+    pub fn column(&self) -> usize {
+        self.column
+    }
+
+    pub fn reset(&mut self) {
+        self.row = 1;
+        self.column = 1;
+    }
+
+    pub fn go_right(&mut self) {
+        self.column += 1;
+    }
+
+    pub fn go_left(&mut self) {
+        self.column -= 1;
+    }
+
+    pub fn newline(&mut self) {
+        self.row += 1;
+        self.column = 1;
+    }
+}

ast/src/unparse.rs

@@ -0,0 +1,530 @@
+use crate::{
+    Arg, Arguments, Boolop, Cmpop, Comprehension, Constant, ConversionFlag, Expr, ExprKind,
+    Operator,
+};
+use std::fmt;
+
+mod precedence {
+    macro_rules! precedence {
+        ($($op:ident,)*) => {
+            precedence!(@0, $($op,)*);
+        };
+        (@$i:expr, $op1:ident, $($op:ident,)*) => {
+            pub const $op1: u8 = $i;
+            precedence!(@$i + 1, $($op,)*);
+        };
+        (@$i:expr,) => {};
+    }
+    precedence!(
+        TUPLE, TEST, OR, AND, NOT, CMP, // "EXPR" =
+        BOR, BXOR, BAND, SHIFT, ARITH, TERM, FACTOR, POWER, AWAIT, ATOM,
+    );
+    pub const EXPR: u8 = BOR;
+}
+
+#[repr(transparent)]
+struct Unparser<'a> {
+    f: fmt::Formatter<'a>,
+}
+impl<'a> Unparser<'a> {
+    fn new<'b>(f: &'b mut fmt::Formatter<'a>) -> &'b mut Unparser<'a> {
+        unsafe { &mut *(f as *mut fmt::Formatter<'a> as *mut Unparser<'a>) }
+    }
+
+    fn p(&mut self, s: &str) -> fmt::Result {
+        self.f.write_str(s)
+    }
+    fn p_if(&mut self, cond: bool, s: &str) -> fmt::Result {
+        if cond {
+            self.f.write_str(s)?;
+        }
+        Ok(())
+    }
+    fn p_delim(&mut self, first: &mut bool, s: &str) -> fmt::Result {
+        self.p_if(!std::mem::take(first), s)
+    }
+    fn write_fmt(&mut self, f: fmt::Arguments<'_>) -> fmt::Result {
+        self.f.write_fmt(f)
+    }
+
+    fn unparse_expr<U>(&mut self, ast: &Expr<U>, level: u8) -> fmt::Result {
+        macro_rules! opprec {
+            ($opty:ident, $x:expr, $enu:path, $($var:ident($op:literal, $prec:ident)),*$(,)?) => {
+                match $x {
+                    $(<$enu>::$var => (opprec!(@space $opty, $op), precedence::$prec),)*
+                }
+            };
+            (@space bin, $op:literal) => {
+                concat!(" ", $op, " ")
+            };
+            (@space un, $op:literal) => {
+                $op
+            };
+        }
+        macro_rules! group_if {
+            ($lvl:expr, $body:block) => {{
+                let group = level > $lvl;
+                self.p_if(group, "(")?;
+                let ret = $body;
+                self.p_if(group, ")")?;
+                ret
+            }};
+        }
+        match &ast.node {
+            ExprKind::BoolOp { op, values } => {
+                let (op, prec) = opprec!(bin, op, Boolop, And("and", AND), Or("or", OR));
+                group_if!(prec, {
+                    let mut first = true;
+                    for val in values {
+                        self.p_delim(&mut first, op)?;
+                        self.unparse_expr(val, prec + 1)?;
+                    }
+                })
+            }
+            ExprKind::NamedExpr { target, value } => {
+                group_if!(precedence::TUPLE, {
+                    self.unparse_expr(target, precedence::ATOM)?;
+                    self.p(" := ")?;
+                    self.unparse_expr(value, precedence::ATOM)?;
+                })
+            }
+            ExprKind::BinOp { left, op, right } => {
+                let rassoc = matches!(op, Operator::Pow);
+                let (op, prec) = opprec!(
+                    bin,
+                    op,
+                    Operator,
+                    Add("+", ARITH),
+                    Sub("-", ARITH),
+                    Mult("*", TERM),
+                    MatMult("@", TERM),
+                    Div("/", TERM),
+                    Mod("%", TERM),
+                    Pow("**", POWER),
+                    LShift("<<", SHIFT),
+                    RShift(">>", SHIFT),
+                    BitOr("|", BOR),
+                    BitXor("^", BXOR),
+                    BitAnd("&", BAND),
+                    FloorDiv("//", TERM),
+                );
+                group_if!(prec, {
+                    self.unparse_expr(left, prec + rassoc as u8)?;
+                    self.p(op)?;
+                    self.unparse_expr(right, prec + !rassoc as u8)?;
+                })
+            }
+            ExprKind::UnaryOp { op, operand } => {
+                let (op, prec) = opprec!(
+                    un,
+                    op,
+                    crate::Unaryop,
+                    Invert("~", FACTOR),
+                    Not("not ", NOT),
+                    UAdd("+", FACTOR),
+                    USub("-", FACTOR)
+                );
+                group_if!(prec, {
+                    self.p(op)?;
+                    self.unparse_expr(operand, prec)?;
+                })
+            }
+            ExprKind::Lambda { args, body } => {
+                group_if!(precedence::TEST, {
+                    let npos = args.args.len() + args.posonlyargs.len();
+                    self.p(if npos > 0 { "lambda " } else { "lambda" })?;
+                    self.unparse_args(args)?;
+                    write!(self, ": {}", **body)?;
+                })
+            }
+            ExprKind::IfExp { test, body, orelse } => {
+                group_if!(precedence::TEST, {
+                    self.unparse_expr(body, precedence::TEST + 1)?;
+                    self.p(" if ")?;
+                    self.unparse_expr(test, precedence::TEST + 1)?;
+                    self.p(" else ")?;
+                    self.unparse_expr(orelse, precedence::TEST)?;
+                })
+            }
+            ExprKind::Dict { keys, values } => {
+                self.p("{")?;
+                let mut first = true;
+                let (packed, unpacked) = values.split_at(keys.len());
+                for (k, v) in keys.iter().zip(packed) {
+                    self.p_delim(&mut first, ", ")?;
+                    write!(self, "{}: {}", *k, *v)?;
+                }
+                for d in unpacked {
+                    self.p_delim(&mut first, ", ")?;
+                    write!(self, "**{}", *d)?;
+                }
+                self.p("}")?;
+            }
+            ExprKind::Set { elts } => {
+                self.p("{")?;
+                let mut first = true;
+                for v in elts {
+                    self.p_delim(&mut first, ", ")?;
+                    self.unparse_expr(v, precedence::TEST)?;
+                }
+                self.p("}")?;
+            }
+            ExprKind::ListComp { elt, generators } => {
+                self.p("[")?;
+                self.unparse_expr(elt, precedence::TEST)?;
+                self.unparse_comp(generators)?;
+                self.p("]")?;
+            }
+            ExprKind::SetComp { elt, generators } => {
+                self.p("{")?;
+                self.unparse_expr(elt, precedence::TEST)?;
+                self.unparse_comp(generators)?;
+                self.p("}")?;
+            }
+            ExprKind::DictComp {
+                key,
+                value,
+                generators,
+            } => {
+                self.p("{")?;
+                self.unparse_expr(key, precedence::TEST)?;
+                self.p(": ")?;
+                self.unparse_expr(value, precedence::TEST)?;
+                self.unparse_comp(generators)?;
+                self.p("}")?;
+            }
+            ExprKind::GeneratorExp { elt, generators } => {
+                self.p("(")?;
+                self.unparse_expr(elt, precedence::TEST)?;
+                self.unparse_comp(generators)?;
+                self.p(")")?;
+            }
+            ExprKind::Await { value } => {
+                group_if!(precedence::AWAIT, {
+                    self.p("await ")?;
+                    self.unparse_expr(value, precedence::ATOM)?;
+                })
+            }
+            ExprKind::Yield { value } => {
+                if let Some(value) = value {
+                    write!(self, "(yield {})", **value)?;
+                } else {
+                    self.p("(yield)")?;
+                }
+            }
+            ExprKind::YieldFrom { value } => {
+                write!(self, "(yield from {})", **value)?;
+            }
+            ExprKind::Compare {
+                left,
+                ops,
+                comparators,
+            } => {
+                group_if!(precedence::CMP, {
+                    let new_lvl = precedence::CMP + 1;
+                    self.unparse_expr(left, new_lvl)?;
+                    for (op, cmp) in ops.iter().zip(comparators) {
+                        let op = match op {
+                            Cmpop::Eq => " == ",
+                            Cmpop::NotEq => " != ",
+                            Cmpop::Lt => " < ",
+                            Cmpop::LtE => " <= ",
+                            Cmpop::Gt => " > ",
+                            Cmpop::GtE => " >= ",
+                            Cmpop::Is => " is ",
+                            Cmpop::IsNot => " is not ",
+                            Cmpop::In => " in ",
+                            Cmpop::NotIn => " not in ",
+                        };
+                        self.p(op)?;
+                        self.unparse_expr(cmp, new_lvl)?;
+                    }
+                })
+            }
+            ExprKind::Call {
+                func,
+                args,
+                keywords,
+            } => {
+                self.unparse_expr(func, precedence::ATOM)?;
+                self.p("(")?;
+                if let (
+                    [Expr {
+                        node: ExprKind::GeneratorExp { elt, generators },
+                        ..
+                    }],
+                    [],
+                ) = (&**args, &**keywords)
+                {
+                    // make sure a single genexp doesn't get double parens
+                    self.unparse_expr(elt, precedence::TEST)?;
+                    self.unparse_comp(generators)?;
+                } else {
+                    let mut first = true;
+                    for arg in args {
+                        self.p_delim(&mut first, ", ")?;
+                        self.unparse_expr(arg, precedence::TEST)?;
+                    }
+                    for kw in keywords {
+                        self.p_delim(&mut first, ", ")?;
+                        if let Some(arg) = &kw.node.arg {
+                            self.p(arg)?;
+                            self.p("=")?;
+                        } else {
+                            self.p("**")?;
+                        }
+                        self.unparse_expr(&kw.node.value, precedence::TEST)?;
+                    }
+                }
+                self.p(")")?;
+            }
+            ExprKind::FormattedValue {
+                value,
+                conversion,
+                format_spec,
+            } => self.unparse_formatted(value, *conversion, format_spec.as_deref())?,
+            ExprKind::JoinedStr { values } => self.unparse_joinedstr(values, false)?,
+            ExprKind::Constant { value, kind } => {
+                if let Some(kind) = kind {
+                    self.p(kind)?;
+                }
+                assert_eq!(f64::MAX_10_EXP, 308);
+                let inf_str = "1e309";
+                match value {
+                    Constant::Float(f) if f.is_infinite() => self.p(inf_str)?,
+                    Constant::Complex { real, imag }
+                        if real.is_infinite() || imag.is_infinite() =>
+                    {
+                        self.p(&value.to_string().replace("inf", inf_str))?
+                    }
+                    _ => fmt::Display::fmt(value, &mut self.f)?,
+                }
+            }
+            ExprKind::Attribute { value, attr, .. } => {
+                self.unparse_expr(value, precedence::ATOM)?;
+                let period = if let ExprKind::Constant {
+                    value: Constant::Int(_),
+                    ..
+                } = &value.node
+                {
+                    " ."
+                } else {
+                    "."
+                };
+                self.p(period)?;
+                self.p(attr)?;
+            }
+            ExprKind::Subscript { value, slice, .. } => {
+                self.unparse_expr(value, precedence::ATOM)?;
+                let mut lvl = precedence::TUPLE;
+                if let ExprKind::Tuple { elts, .. } = &slice.node {
+                    if elts
+                        .iter()
+                        .any(|expr| matches!(expr.node, ExprKind::Starred { .. }))
+                    {
+                        lvl += 1
+                    }
+                }
+                self.p("[")?;
+                self.unparse_expr(slice, lvl)?;
+                self.p("]")?;
+            }
+            ExprKind::Starred { value, .. } => {
+                self.p("*")?;
+                self.unparse_expr(value, precedence::EXPR)?;
+            }
+            ExprKind::Name { id, .. } => self.p(id)?,
+            ExprKind::List { elts, .. } => {
+                self.p("[")?;
+                let mut first = true;
+                for elt in elts {
+                    self.p_delim(&mut first, ", ")?;
+                    self.unparse_expr(elt, precedence::TEST)?;
+                }
+                self.p("]")?;
+            }
+            ExprKind::Tuple { elts, .. } => {
+                if elts.is_empty() {
+                    self.p("()")?;
+                } else {
+                    group_if!(precedence::TUPLE, {
+                        let mut first = true;
+                        for elt in elts {
+                            self.p_delim(&mut first, ", ")?;
+                            self.unparse_expr(elt, precedence::TEST)?;
+                        }
+                        self.p_if(elts.len() == 1, ",")?;
+                    })
+                }
+            }
+            ExprKind::Slice { lower, upper, step } => {
+                if let Some(lower) = lower {
+                    self.unparse_expr(lower, precedence::TEST)?;
+                }
+                self.p(":")?;
+                if let Some(upper) = upper {
+                    self.unparse_expr(upper, precedence::TEST)?;
+                }
+                if let Some(step) = step {
+                    self.p(":")?;
+                    self.unparse_expr(step, precedence::TEST)?;
+                }
+            }
+        }
+        Ok(())
+    }
+
+    fn unparse_args<U>(&mut self, args: &Arguments<U>) -> fmt::Result {
+        let mut first = true;
+        let defaults_start = args.posonlyargs.len() + args.args.len() - args.defaults.len();
+        for (i, arg) in args.posonlyargs.iter().chain(&args.args).enumerate() {
+            self.p_delim(&mut first, ", ")?;
+            self.unparse_arg(arg)?;
+            if let Some(i) = i.checked_sub(defaults_start) {
+                write!(self, "={}", &args.defaults[i])?;
+            }
+            self.p_if(i + 1 == args.posonlyargs.len(), ", /")?;
+        }
+        if args.vararg.is_some() || !args.kwonlyargs.is_empty() {
+            self.p_delim(&mut first, ", ")?;
+            self.p("*")?;
+        }
+        if let Some(vararg) = &args.vararg {
+            self.unparse_arg(vararg)?;
+        }
+        let defaults_start = args.kwonlyargs.len() - args.kw_defaults.len();
+        for (i, kwarg) in args.kwonlyargs.iter().enumerate() {
+            self.p_delim(&mut first, ", ")?;
+            self.unparse_arg(kwarg)?;
+            if let Some(default) = i
+                .checked_sub(defaults_start)
+                .and_then(|i| args.kw_defaults.get(i))
+            {
+                write!(self, "={}", default)?;
+            }
+        }
+        if let Some(kwarg) = &args.kwarg {
+            self.p_delim(&mut first, ", ")?;
+            self.p("**")?;
+            self.unparse_arg(kwarg)?;
+        }
+        Ok(())
+    }
+    fn unparse_arg<U>(&mut self, arg: &Arg<U>) -> fmt::Result {
+        self.p(&arg.node.arg)?;
+        if let Some(ann) = &arg.node.annotation {
+            write!(self, ": {}", **ann)?;
+        }
+        Ok(())
+    }
+
+    fn unparse_comp<U>(&mut self, generators: &[Comprehension<U>]) -> fmt::Result {
+        for comp in generators {
+            self.p(if comp.is_async > 0 {
+                " async for "
+            } else {
+                " for "
+            })?;
+            self.unparse_expr(&comp.target, precedence::TUPLE)?;
+            self.p(" in ")?;
+            self.unparse_expr(&comp.iter, precedence::TEST + 1)?;
+            for cond in &comp.ifs {
+                self.p(" if ")?;
+                self.unparse_expr(cond, precedence::TEST + 1)?;
+            }
+        }
+        Ok(())
+    }
+
+    fn unparse_fstring_body<U>(&mut self, values: &[Expr<U>], is_spec: bool) -> fmt::Result {
+        for value in values {
+            self.unparse_fstring_elem(value, is_spec)?;
+        }
+        Ok(())
+    }
+
+    fn unparse_formatted<U>(
+        &mut self,
+        val: &Expr<U>,
+        conversion: usize,
+        spec: Option<&Expr<U>>,
+    ) -> fmt::Result {
+        let buffered = to_string_fmt(|f| Unparser::new(f).unparse_expr(val, precedence::TEST + 1));
+        let brace = if buffered.starts_with('{') {
+            // put a space to avoid escaping the bracket
+            "{ "
+        } else {
+            "{"
+        };
+        self.p(brace)?;
+        self.p(&buffered)?;
+        drop(buffered);
+
+        if conversion != ConversionFlag::None as usize {
+            self.p("!")?;
+            let buf = &[conversion as u8];
+            let c = std::str::from_utf8(buf).unwrap();
+            self.p(c)?;
+        }
+
+        if let Some(spec) = spec {
+            self.p(":")?;
+            self.unparse_fstring_elem(spec, true)?;
+        }
+
+        self.p("}")?;
+
+        Ok(())
+    }
+
+    fn unparse_fstring_elem<U>(&mut self, expr: &Expr<U>, is_spec: bool) -> fmt::Result {
+        match &expr.node {
+            ExprKind::Constant { value, .. } => {
+                if let Constant::Str(s) = value {
+                    self.unparse_fstring_str(s)
+                } else {
+                    unreachable!()
+                }
+            }
+            ExprKind::JoinedStr { values } => self.unparse_joinedstr(values, is_spec),
+            ExprKind::FormattedValue {
+                value,
+                conversion,
+                format_spec,
+            } => self.unparse_formatted(value, *conversion, format_spec.as_deref()),
+            _ => unreachable!(),
+        }
+    }
+
+    fn unparse_fstring_str(&mut self, s: &str) -> fmt::Result {
+        let s = s.replace('{', "{{").replace('}', "}}");
+        self.p(&s)
+    }
+
+    fn unparse_joinedstr<U>(&mut self, values: &[Expr<U>], is_spec: bool) -> fmt::Result {
+        if is_spec {
+            self.unparse_fstring_body(values, is_spec)
+        } else {
+            self.p("f")?;
+            let body = to_string_fmt(|f| Unparser::new(f).unparse_fstring_body(values, is_spec));
+            fmt::Display::fmt(&rustpython_common::str::repr(&body), &mut self.f)
+        }
+    }
+}
+
+impl<U> fmt::Display for Expr<U> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        Unparser::new(f).unparse_expr(self, precedence::TEST)
+    }
+}
+
+fn to_string_fmt(f: impl FnOnce(&mut fmt::Formatter) -> fmt::Result) -> String {
+    use std::cell::Cell;
+    struct Fmt<F>(Cell<Option<F>>);
+    impl<F: FnOnce(&mut fmt::Formatter) -> fmt::Result> fmt::Display for Fmt<F> {
+        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+            self.0.take().unwrap()(f)
+        }
+    }
+    Fmt(Cell::new(Some(f))).to_string()
+}