Expand format_args!() in rust_ast_lowering.

Cargo.lock

@@ -3699,6 +3699,7 @@ name = "rustc_ast_pretty"
 version = "0.0.0"
 dependencies = [
  "rustc_ast",
+ "rustc_parse_format",
  "rustc_span",
 ]
 

compiler/rustc_ast/src/ast.rs

@@ -18,6 +18,7 @@
 //! - [`Attribute`]: Metadata associated with item.
 //! - [`UnOp`], [`BinOp`], and [`BinOpKind`]: Unary and binary operators.
 
+pub use crate::format::*;
 pub use crate::util::parser::ExprPrecedence;
 pub use GenericArgs::*;
 pub use UnsafeSource::*;
@@ -1269,6 +1270,7 @@ impl Expr {
             ExprKind::Try(..) => ExprPrecedence::Try,
             ExprKind::Yield(..) => ExprPrecedence::Yield,
             ExprKind::Yeet(..) => ExprPrecedence::Yeet,
+            ExprKind::FormatArgs(..) => ExprPrecedence::FormatArgs,
             ExprKind::Err => ExprPrecedence::Err,
         }
     }
@@ -1498,6 +1500,9 @@ pub enum ExprKind {
     /// with a `ByteStr` literal.
     IncludedBytes(Lrc<[u8]>),
 
+    /// A `format_args!()` expression.
+    FormatArgs(P<FormatArgs>),
+
     /// Placeholder for an expression that wasn't syntactically well formed in some way.
     Err,
 }

compiler/rustc_ast/src/format.rs

@@ -1,5 +1,5 @@
-use rustc_ast::ptr::P;
+use crate::ptr::P;
-use rustc_ast::Expr;
+use crate::Expr;
 use rustc_data_structures::fx::FxHashMap;
 use rustc_span::symbol::{Ident, Symbol};
 use rustc_span::Span;
@@ -39,7 +39,7 @@ use rustc_span::Span;
 /// Basically the "AST" for a complete `format_args!()`.
 ///
 /// E.g., `format_args!("hello {name}");`.
-#[derive(Clone, Debug)]
+#[derive(Clone, Encodable, Decodable, Debug)]
 pub struct FormatArgs {
     pub span: Span,
     pub template: Vec<FormatArgsPiece>,
@@ -49,7 +49,7 @@ pub struct FormatArgs {
 /// A piece of a format template string.
 ///
 /// E.g. "hello" or "{name}".
-#[derive(Clone, Debug)]
+#[derive(Clone, Encodable, Decodable, Debug)]
 pub enum FormatArgsPiece {
     Literal(Symbol),
     Placeholder(FormatPlaceholder),
@@ -59,7 +59,7 @@ pub enum FormatArgsPiece {
 ///
 /// E.g. `1, 2, name="ferris", n=3`,
 /// but also implicit captured arguments like `x` in `format_args!("{x}")`.
-#[derive(Clone, Debug)]
+#[derive(Clone, Encodable, Decodable, Debug)]
 pub struct FormatArguments {
     arguments: Vec<FormatArgument>,
     num_unnamed_args: usize,
@@ -121,18 +121,22 @@ impl FormatArguments {
         &self.arguments[..self.num_explicit_args]
     }
 
-    pub fn into_vec(self) -> Vec<FormatArgument> {
+    pub fn all_args(&self) -> &[FormatArgument] {
-        self.arguments
+        &self.arguments[..]
+    }
+
+    pub fn all_args_mut(&mut self) -> &mut [FormatArgument] {
+        &mut self.arguments[..]
     }
 }
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Encodable, Decodable, Debug)]
 pub struct FormatArgument {
     pub kind: FormatArgumentKind,
     pub expr: P<Expr>,
 }
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Encodable, Decodable, Debug)]
 pub enum FormatArgumentKind {
     /// `format_args(…, arg)`
     Normal,
@@ -152,7 +156,7 @@ impl FormatArgumentKind {
     }
 }
 
-#[derive(Clone, Debug, PartialEq, Eq)]
+#[derive(Clone, Encodable, Decodable, Debug, PartialEq, Eq)]
 pub struct FormatPlaceholder {
     /// Index into [`FormatArgs::arguments`].
     pub argument: FormatArgPosition,
@@ -164,7 +168,7 @@ pub struct FormatPlaceholder {
     pub format_options: FormatOptions,
 }
 
-#[derive(Clone, Debug, PartialEq, Eq)]
+#[derive(Clone, Encodable, Decodable, Debug, PartialEq, Eq)]
 pub struct FormatArgPosition {
     /// Which argument this position refers to (Ok),
     /// or would've referred to if it existed (Err).
@@ -175,7 +179,7 @@ pub struct FormatArgPosition {
     pub span: Option<Span>,
 }
 
-#[derive(Copy, Clone, Debug, PartialEq, Eq)]
+#[derive(Copy, Clone, Encodable, Decodable, Debug, PartialEq, Eq)]
 pub enum FormatArgPositionKind {
     /// `{}` or `{:.*}`
     Implicit,
@@ -185,7 +189,7 @@ pub enum FormatArgPositionKind {
     Named,
 }
 
-#[derive(Copy, Clone, Debug, Hash, PartialEq, Eq)]
+#[derive(Copy, Clone, Encodable, Decodable, Debug, PartialEq, Eq, Hash)]
 pub enum FormatTrait {
     /// `{}`
     Display,
@@ -207,7 +211,7 @@ pub enum FormatTrait {
     UpperHex,
 }
 
-#[derive(Clone, Debug, Default, PartialEq, Eq)]
+#[derive(Clone, Encodable, Decodable, Default, Debug, PartialEq, Eq)]
 pub struct FormatOptions {
     /// The width. E.g. `{:5}` or `{:width$}`.
     pub width: Option<FormatCount>,
@@ -221,7 +225,7 @@ pub struct FormatOptions {
     pub flags: u32,
 }
 
-#[derive(Clone, Debug, PartialEq, Eq)]
+#[derive(Copy, Clone, Encodable, Decodable, Debug, PartialEq, Eq)]
 pub enum FormatAlignment {
     /// `{:<}`
     Left,
@@ -231,7 +235,7 @@ pub enum FormatAlignment {
     Center,
 }
 
-#[derive(Clone, Debug, PartialEq, Eq)]
+#[derive(Clone, Encodable, Decodable, Debug, PartialEq, Eq)]
 pub enum FormatCount {
     /// `{:5}` or `{:.5}`
     Literal(usize),

compiler/rustc_ast/src/lib.rs

@@ -42,6 +42,7 @@ pub mod ast_traits;
 pub mod attr;
 pub mod entry;
 pub mod expand;
+pub mod format;
 pub mod mut_visit;
 pub mod node_id;
 pub mod ptr;
@@ -51,6 +52,7 @@ pub mod visit;
 
 pub use self::ast::*;
 pub use self::ast_traits::{AstDeref, AstNodeWrapper, HasAttrs, HasNodeId, HasSpan, HasTokens};
+pub use self::format::*;
 
 use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
 

compiler/rustc_ast/src/mut_visit.rs

@@ -297,6 +297,10 @@ pub trait MutVisitor: Sized {
     fn visit_inline_asm_sym(&mut self, sym: &mut InlineAsmSym) {
         noop_visit_inline_asm_sym(sym, self)
     }
+
+    fn visit_format_args(&mut self, fmt: &mut FormatArgs) {
+        noop_visit_format_args(fmt, self)
+    }
 }
 
 /// Use a map-style function (`FnOnce(T) -> T`) to overwrite a `&mut T`. Useful
@@ -1284,6 +1288,15 @@ pub fn noop_visit_inline_asm_sym<T: MutVisitor>(
     vis.visit_path(path);
 }
 
+pub fn noop_visit_format_args<T: MutVisitor>(fmt: &mut FormatArgs, vis: &mut T) {
+    for arg in fmt.arguments.all_args_mut() {
+        if let FormatArgumentKind::Named(name) = &mut arg.kind {
+            vis.visit_ident(name);
+        }
+        vis.visit_expr(&mut arg.expr);
+    }
+}
+
 pub fn noop_visit_expr<T: MutVisitor>(
     Expr { kind, id, span, attrs, tokens }: &mut Expr,
     vis: &mut T,
@@ -1423,6 +1436,7 @@ pub fn noop_visit_expr<T: MutVisitor>(
             visit_opt(expr, |expr| vis.visit_expr(expr));
         }
         ExprKind::InlineAsm(asm) => vis.visit_inline_asm(asm),
+        ExprKind::FormatArgs(fmt) => vis.visit_format_args(fmt),
         ExprKind::MacCall(mac) => vis.visit_mac_call(mac),
         ExprKind::Struct(se) => {
             let StructExpr { qself, path, fields, rest } = se.deref_mut();

compiler/rustc_ast/src/util/parser.rs

@@ -271,6 +271,7 @@ pub enum ExprPrecedence {
     Try,
     InlineAsm,
     Mac,
+    FormatArgs,
 
     Array,
     Repeat,
@@ -335,7 +336,8 @@ impl ExprPrecedence {
             | ExprPrecedence::Index
             | ExprPrecedence::Try
             | ExprPrecedence::InlineAsm
-            | ExprPrecedence::Mac => PREC_POSTFIX,
+            | ExprPrecedence::Mac
+            | ExprPrecedence::FormatArgs => PREC_POSTFIX,
 
             // Never need parens
             ExprPrecedence::Array

compiler/rustc_ast/src/visit.rs

@@ -242,6 +242,9 @@ pub trait Visitor<'ast>: Sized {
     fn visit_inline_asm(&mut self, asm: &'ast InlineAsm) {
         walk_inline_asm(self, asm)
     }
+    fn visit_format_args(&mut self, fmt: &'ast FormatArgs) {
+        walk_format_args(self, fmt)
+    }
     fn visit_inline_asm_sym(&mut self, sym: &'ast InlineAsmSym) {
         walk_inline_asm_sym(self, sym)
     }
@@ -756,6 +759,15 @@ pub fn walk_inline_asm_sym<'a, V: Visitor<'a>>(visitor: &mut V, sym: &'a InlineA
     visitor.visit_path(&sym.path, sym.id);
 }
 
+pub fn walk_format_args<'a, V: Visitor<'a>>(visitor: &mut V, fmt: &'a FormatArgs) {
+    for arg in fmt.arguments.all_args() {
+        if let FormatArgumentKind::Named(name) = arg.kind {
+            visitor.visit_ident(name);
+        }
+        visitor.visit_expr(&arg.expr);
+    }
+}
+
 pub fn walk_expr<'a, V: Visitor<'a>>(visitor: &mut V, expression: &'a Expr) {
     walk_list!(visitor, visit_attribute, expression.attrs.iter());
 
@@ -895,6 +907,7 @@ pub fn walk_expr<'a, V: Visitor<'a>>(visitor: &mut V, expression: &'a Expr) {
         ExprKind::MacCall(mac) => visitor.visit_mac_call(mac),
         ExprKind::Paren(subexpression) => visitor.visit_expr(subexpression),
         ExprKind::InlineAsm(asm) => visitor.visit_inline_asm(asm),
+        ExprKind::FormatArgs(f) => visitor.visit_format_args(f),
         ExprKind::Yield(optional_expression) => {
             walk_list!(visitor, visit_expr, optional_expression);
         }

compiler/rustc_ast_lowering/src/expr.rs

@@ -292,6 +292,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
                 ExprKind::InlineAsm(asm) => {
                     hir::ExprKind::InlineAsm(self.lower_inline_asm(e.span, asm))
                 }
+                ExprKind::FormatArgs(fmt) => self.lower_format_args(e.span, fmt),
                 ExprKind::Struct(se) => {
                     let rest = match &se.rest {
                         StructRest::Base(e) => Some(self.lower_expr(e)),

compiler/rustc_ast_lowering/src/format.rs

@@ -0,0 +1,356 @@
+use super::LoweringContext;
+use rustc_ast as ast;
+use rustc_ast::visit::{self, Visitor};
+use rustc_ast::*;
+use rustc_data_structures::fx::FxIndexSet;
+use rustc_hir as hir;
+use rustc_span::{
+    sym,
+    symbol::{kw, Ident},
+    Span,
+};
+
+impl<'hir> LoweringContext<'_, 'hir> {
+    pub(crate) fn lower_format_args(&mut self, sp: Span, fmt: &FormatArgs) -> hir::ExprKind<'hir> {
+        expand_format_args(self, sp, fmt)
+    }
+}
+
+#[derive(Copy, Clone, Debug, Hash, PartialEq, Eq)]
+enum ArgumentType {
+    Format(FormatTrait),
+    Usize,
+}
+
+fn make_argument<'hir>(
+    ctx: &mut LoweringContext<'_, 'hir>,
+    sp: Span,
+    arg: &'hir hir::Expr<'hir>,
+    ty: ArgumentType,
+) -> hir::Expr<'hir> {
+    // Generate:
+    //     ::core::fmt::ArgumentV1::new_…(arg)
+    use ArgumentType::*;
+    use FormatTrait::*;
+    let new_fn = ctx.arena.alloc(ctx.expr_lang_item_type_relative(
+        sp,
+        hir::LangItem::FormatArgument,
+        match ty {
+            Format(Display) => sym::new_display,
+            Format(Debug) => sym::new_debug,
+            Format(LowerExp) => sym::new_lower_exp,
+            Format(UpperExp) => sym::new_upper_exp,
+            Format(Octal) => sym::new_octal,
+            Format(Pointer) => sym::new_pointer,
+            Format(Binary) => sym::new_binary,
+            Format(LowerHex) => sym::new_lower_hex,
+            Format(UpperHex) => sym::new_upper_hex,
+            Usize => sym::from_usize,
+        },
+    ));
+    ctx.expr_call_mut(sp, new_fn, std::slice::from_ref(arg))
+}
+
+fn make_count<'hir>(
+    ctx: &mut LoweringContext<'_, 'hir>,
+    sp: Span,
+    count: &Option<FormatCount>,
+    argmap: &mut FxIndexSet<(usize, ArgumentType)>,
+) -> hir::Expr<'hir> {
+    // Generate:
+    //     ::core::fmt::rt::v1::Count::…(…)
+    match count {
+        Some(FormatCount::Literal(n)) => {
+            let count_is = ctx.arena.alloc(ctx.expr_lang_item_type_relative(
+                sp,
+                hir::LangItem::FormatCount,
+                sym::Is,
+            ));
+            let value = ctx.arena.alloc_from_iter([ctx.expr_usize(sp, *n)]);
+            ctx.expr_call_mut(sp, count_is, value)
+        }
+        Some(FormatCount::Argument(arg)) => {
+            if let Ok(arg_index) = arg.index {
+                let (i, _) = argmap.insert_full((arg_index, ArgumentType::Usize));
+                let count_param = ctx.arena.alloc(ctx.expr_lang_item_type_relative(
+                    sp,
+                    hir::LangItem::FormatCount,
+                    sym::Param,
+                ));
+                let value = ctx.arena.alloc_from_iter([ctx.expr_usize(sp, i)]);
+                ctx.expr_call_mut(sp, count_param, value)
+            } else {
+                ctx.expr(sp, hir::ExprKind::Err)
+            }
+        }
+        None => ctx.expr_lang_item_type_relative(sp, hir::LangItem::FormatCount, sym::Implied),
+    }
+}
+
+fn make_format_spec<'hir>(
+    ctx: &mut LoweringContext<'_, 'hir>,
+    sp: Span,
+    placeholder: &FormatPlaceholder,
+    argmap: &mut FxIndexSet<(usize, ArgumentType)>,
+) -> hir::Expr<'hir> {
+    // Generate:
+    //     ::core::fmt::rt::v1::Argument {
+    //         position: 0usize,
+    //         format: ::core::fmt::rt::v1::FormatSpec {
+    //             fill: ' ',
+    //             align: ::core::fmt::rt::v1::Alignment::Unknown,
+    //             flags: 0u32,
+    //             precision: ::core::fmt::rt::v1::Count::Implied,
+    //             width: ::core::fmt::rt::v1::Count::Implied,
+    //         },
+    //     }
+    let position = match placeholder.argument.index {
+        Ok(arg_index) => {
+            let (i, _) =
+                argmap.insert_full((arg_index, ArgumentType::Format(placeholder.format_trait)));
+            ctx.expr_usize(sp, i)
+        }
+        Err(_) => ctx.expr(sp, hir::ExprKind::Err),
+    };
+    let fill = ctx.expr_char(sp, placeholder.format_options.fill.unwrap_or(' '));
+    let align = ctx.expr_lang_item_type_relative(
+        sp,
+        hir::LangItem::FormatAlignment,
+        match placeholder.format_options.alignment {
+            Some(FormatAlignment::Left) => sym::Left,
+            Some(FormatAlignment::Right) => sym::Right,
+            Some(FormatAlignment::Center) => sym::Center,
+            None => sym::Unknown,
+        },
+    );
+    let flags = ctx.expr_u32(sp, placeholder.format_options.flags);
+    let prec = make_count(ctx, sp, &placeholder.format_options.precision, argmap);
+    let width = make_count(ctx, sp, &placeholder.format_options.width, argmap);
+    let format_placeholder_new = ctx.arena.alloc(ctx.expr_lang_item_type_relative(
+        sp,
+        hir::LangItem::FormatPlaceholder,
+        sym::new,
+    ));
+    let args = ctx.arena.alloc_from_iter([position, fill, align, flags, prec, width]);
+    ctx.expr_call_mut(sp, format_placeholder_new, args)
+}
+
+fn expand_format_args<'hir>(
+    ctx: &mut LoweringContext<'_, 'hir>,
+    macsp: Span,
+    fmt: &FormatArgs,
+) -> hir::ExprKind<'hir> {
+    let lit_pieces =
+        ctx.arena.alloc_from_iter(fmt.template.iter().enumerate().filter_map(|(i, piece)| {
+            match piece {
+                &FormatArgsPiece::Literal(s) => Some(ctx.expr_str(fmt.span, s)),
+                &FormatArgsPiece::Placeholder(_) => {
+                    // Inject empty string before placeholders when not already preceded by a literal piece.
+                    if i == 0 || matches!(fmt.template[i - 1], FormatArgsPiece::Placeholder(_)) {
+                        Some(ctx.expr_str(fmt.span, kw::Empty))
+                    } else {
+                        None
+                    }
+                }
+            }
+        }));
+    let lit_pieces = ctx.expr_array_ref(fmt.span, lit_pieces);
+
+    // Whether we'll use the `Arguments::new_v1_formatted` form (true),
+    // or the `Arguments::new_v1` form (false).
+    let mut use_format_options = false;
+
+    // Create a list of all _unique_ (argument, format trait) combinations.
+    // E.g. "{0} {0:x} {0} {1}" -> [(0, Display), (0, LowerHex), (1, Display)]
+    let mut argmap = FxIndexSet::default();
+    for piece in &fmt.template {
+        let FormatArgsPiece::Placeholder(placeholder) = piece else { continue };
+        if placeholder.format_options != Default::default() {
+            // Can't use basic form if there's any formatting options.
+            use_format_options = true;
+        }
+        if let Ok(index) = placeholder.argument.index {
+            if !argmap.insert((index, ArgumentType::Format(placeholder.format_trait))) {
+                // Duplicate (argument, format trait) combination,
+                // which we'll only put once in the args array.
+                use_format_options = true;
+            }
+        }
+    }
+
+    let format_options = use_format_options.then(|| {
+        // Generate:
+        //     &[format_spec_0, format_spec_1, format_spec_2]
+        let elements: Vec<_> = fmt
+            .template
+            .iter()
+            .filter_map(|piece| {
+                let FormatArgsPiece::Placeholder(placeholder) = piece else { return None };
+                Some(make_format_spec(ctx, macsp, placeholder, &mut argmap))
+            })
+            .collect();
+        ctx.expr_array_ref(macsp, ctx.arena.alloc_from_iter(elements))
+    });
+
+    let arguments = fmt.arguments.all_args();
+
+    // If the args array contains exactly all the original arguments once,
+    // in order, we can use a simple array instead of a `match` construction.
+    // However, if there's a yield point in any argument except the first one,
+    // we don't do this, because an ArgumentV1 cannot be kept across yield points.
+    let use_simple_array = argmap.len() == arguments.len()
+        && argmap.iter().enumerate().all(|(i, &(j, _))| i == j)
+        && arguments.iter().skip(1).all(|arg| !may_contain_yield_point(&arg.expr));
+
+    let args = if use_simple_array {
+        // Generate:
+        //     &[
+        //         ::core::fmt::ArgumentV1::new_display(&arg0),
+        //         ::core::fmt::ArgumentV1::new_lower_hex(&arg1),
+        //         ::core::fmt::ArgumentV1::new_debug(&arg2),
+        //     ]
+        let elements: Vec<_> = arguments
+            .iter()
+            .zip(argmap)
+            .map(|(arg, (_, ty))| {
+                let sp = arg.expr.span.with_ctxt(macsp.ctxt());
+                let arg = ctx.lower_expr(&arg.expr);
+                let ref_arg = ctx.arena.alloc(ctx.expr(
+                    sp,
+                    hir::ExprKind::AddrOf(hir::BorrowKind::Ref, hir::Mutability::Not, arg),
+                ));
+                make_argument(ctx, sp, ref_arg, ty)
+            })
+            .collect();
+        ctx.expr_array_ref(macsp, ctx.arena.alloc_from_iter(elements))
+    } else {
+        // Generate:
+        //     &match (&arg0, &arg1, &arg2) {
+        //         args => [
+        //             ::core::fmt::ArgumentV1::new_display(args.0),
+        //             ::core::fmt::ArgumentV1::new_lower_hex(args.1),
+        //             ::core::fmt::ArgumentV1::new_debug(args.0),
+        //         ]
+        //     }
+        let args_ident = Ident::new(sym::args, macsp);
+        let (args_pat, args_hir_id) = ctx.pat_ident(macsp, args_ident);
+        let args = ctx.arena.alloc_from_iter(argmap.iter().map(|&(arg_index, ty)| {
+            if let Some(arg) = arguments.get(arg_index) {
+                let sp = arg.expr.span.with_ctxt(macsp.ctxt());
+                let args_ident_expr = ctx.expr_ident(macsp, args_ident, args_hir_id);
+                let arg = ctx.arena.alloc(ctx.expr(
+                    sp,
+                    hir::ExprKind::Field(
+                        args_ident_expr,
+                        Ident::new(sym::integer(arg_index), macsp),
+                    ),
+                ));
+                make_argument(ctx, sp, arg, ty)
+            } else {
+                ctx.expr(macsp, hir::ExprKind::Err)
+            }
+        }));
+        let elements: Vec<_> = arguments
+            .iter()
+            .map(|arg| {
+                let arg_expr = ctx.lower_expr(&arg.expr);
+                ctx.expr(
+                    arg.expr.span.with_ctxt(macsp.ctxt()),
+                    hir::ExprKind::AddrOf(hir::BorrowKind::Ref, hir::Mutability::Not, arg_expr),
+                )
+            })
+            .collect();
+        let args_tuple = ctx
+            .arena
+            .alloc(ctx.expr(macsp, hir::ExprKind::Tup(ctx.arena.alloc_from_iter(elements))));
+        let array = ctx.arena.alloc(ctx.expr(macsp, hir::ExprKind::Array(args)));
+        let match_arms = ctx.arena.alloc_from_iter([ctx.arm(args_pat, array)]);
+        let match_expr = ctx.arena.alloc(ctx.expr_match(
+            macsp,
+            args_tuple,
+            match_arms,
+            hir::MatchSource::FormatArgs,
+        ));
+        ctx.expr(
+            macsp,
+            hir::ExprKind::AddrOf(hir::BorrowKind::Ref, hir::Mutability::Not, match_expr),
+        )
+    };
+
+    if let Some(format_options) = format_options {
+        // Generate:
+        //     ::core::fmt::Arguments::new_v1_formatted(
+        //         lit_pieces,
+        //         args,
+        //         format_options,
+        //         unsafe { ::core::fmt::UnsafeArg::new() }
+        //     )
+        let new_v1_formatted = ctx.arena.alloc(ctx.expr_lang_item_type_relative(
+            macsp,
+            hir::LangItem::FormatArguments,
+            sym::new_v1_formatted,
+        ));
+        let unsafe_arg_new = ctx.arena.alloc(ctx.expr_lang_item_type_relative(
+            macsp,
+            hir::LangItem::FormatUnsafeArg,
+            sym::new,
+        ));
+        let unsafe_arg_new_call = ctx.expr_call(macsp, unsafe_arg_new, &[]);
+        let hir_id = ctx.next_id();
+        let unsafe_arg = ctx.expr_block(ctx.arena.alloc(hir::Block {
+            stmts: &[],
+            expr: Some(unsafe_arg_new_call),
+            hir_id,
+            rules: hir::BlockCheckMode::UnsafeBlock(hir::UnsafeSource::CompilerGenerated),
+            span: macsp,
+            targeted_by_break: false,
+        }));
+        let args = ctx.arena.alloc_from_iter([lit_pieces, args, format_options, unsafe_arg]);
+        hir::ExprKind::Call(new_v1_formatted, args)
+    } else {
+        // Generate:
+        //     ::core::fmt::Arguments::new_v1(
+        //         lit_pieces,
+        //         args,
+        //     )
+        let new_v1 = ctx.arena.alloc(ctx.expr_lang_item_type_relative(
+            macsp,
+            hir::LangItem::FormatArguments,
+            sym::new_v1,
+        ));
+        let new_args = ctx.arena.alloc_from_iter([lit_pieces, args]);
+        hir::ExprKind::Call(new_v1, new_args)
+    }
+}
+
+fn may_contain_yield_point(e: &ast::Expr) -> bool {
+    struct MayContainYieldPoint(bool);
+
+    impl Visitor<'_> for MayContainYieldPoint {
+        fn visit_expr(&mut self, e: &ast::Expr) {
+            if let ast::ExprKind::Await(_) | ast::ExprKind::Yield(_) = e.kind {
+                self.0 = true;
+            } else {
+                visit::walk_expr(self, e);
+            }
+        }
+
+        fn visit_mac_call(&mut self, _: &ast::MacCall) {
+            self.0 = true;
+        }
+
+        fn visit_attribute(&mut self, _: &ast::Attribute) {
+            // Conservatively assume this may be a proc macro attribute in
+            // expression position.
+            self.0 = true;
+        }
+
+        fn visit_item(&mut self, _: &ast::Item) {
+            // Do not recurse into nested items.
+        }
+    }
+
+    let mut visitor = MayContainYieldPoint(false);
+    visitor.visit_expr(e);
+    visitor.0
+}

compiler/rustc_ast_lowering/src/lib.rs

@@ -80,6 +80,7 @@ mod asm;
 mod block;
 mod errors;
 mod expr;
+mod format;
 mod index;
 mod item;
 mod lifetime_collector;

compiler/rustc_ast_pretty/Cargo.toml

@@ -6,5 +6,6 @@ edition = "2021"
 [lib]
 
 [dependencies]
-rustc_span = { path = "../rustc_span" }
 rustc_ast = { path = "../rustc_ast" }
+rustc_parse_format = { path = "../rustc_parse_format" }
+rustc_span = { path = "../rustc_span" }

compiler/rustc_ast_pretty/src/pprust/state/expr.rs

@@ -6,6 +6,8 @@ use rustc_ast::token;
 use rustc_ast::util::literal::escape_byte_str_symbol;
 use rustc_ast::util::parser::{self, AssocOp, Fixity};
 use rustc_ast::{self as ast, BlockCheckMode};
+use rustc_ast::{FormatAlignment, FormatArgPosition, FormatArgsPiece, FormatCount, FormatTrait};
+use std::fmt::Write;
 
 impl<'a> State<'a> {
     fn print_else(&mut self, els: Option<&ast::Expr>) {
@@ -528,6 +530,18 @@ impl<'a> State<'a> {
                 self.word("asm!");
                 self.print_inline_asm(a);
             }
+            ast::ExprKind::FormatArgs(fmt) => {
+                self.word("format_args!");
+                self.popen();
+                self.rbox(0, Inconsistent);
+                self.word(reconstruct_format_args_template_string(&fmt.template));
+                for arg in fmt.arguments.all_args() {
+                    self.word_space(",");
+                    self.print_expr(&arg.expr);
+                }
+                self.end();
+                self.pclose();
+            }
             ast::ExprKind::MacCall(m) => self.print_mac(m),
             ast::ExprKind::Paren(e) => {
                 self.popen();
@@ -627,3 +641,91 @@ impl<'a> State<'a> {
         }
     }
 }
+
+pub fn reconstruct_format_args_template_string(pieces: &[FormatArgsPiece]) -> String {
+    let mut template = "\"".to_string();
+    for piece in pieces {
+        match piece {
+            FormatArgsPiece::Literal(s) => {
+                for c in s.as_str().escape_debug() {
+                    template.push(c);
+                    if let '{' | '}' = c {
+                        template.push(c);
+                    }
+                }
+            }
+            FormatArgsPiece::Placeholder(p) => {
+                template.push('{');
+                let (Ok(n) | Err(n)) = p.argument.index;
+                write!(template, "{n}").unwrap();
+                if p.format_options != Default::default() || p.format_trait != FormatTrait::Display
+                {
+                    template.push_str(":");
+                }
+                if let Some(fill) = p.format_options.fill {
+                    template.push(fill);
+                }
+                match p.format_options.alignment {
+                    Some(FormatAlignment::Left) => template.push_str("<"),
+                    Some(FormatAlignment::Right) => template.push_str(">"),
+                    Some(FormatAlignment::Center) => template.push_str("^"),
+                    None => {}
+                }
+                let flags = p.format_options.flags;
+                if flags >> (rustc_parse_format::FlagSignPlus as usize) & 1 != 0 {
+                    template.push('+');
+                }
+                if flags >> (rustc_parse_format::FlagSignMinus as usize) & 1 != 0 {
+                    template.push('-');
+                }
+                if flags >> (rustc_parse_format::FlagAlternate as usize) & 1 != 0 {
+                    template.push('#');
+                }
+                if flags >> (rustc_parse_format::FlagSignAwareZeroPad as usize) & 1 != 0 {
+                    template.push('0');
+                }
+                if let Some(width) = &p.format_options.width {
+                    match width {
+                        FormatCount::Literal(n) => write!(template, "{n}").unwrap(),
+                        FormatCount::Argument(FormatArgPosition {
+                            index: Ok(n) | Err(n), ..
+                        }) => {
+                            write!(template, "{n}$").unwrap();
+                        }
+                    }
+                }
+                if let Some(precision) = &p.format_options.precision {
+                    template.push('.');
+                    match precision {
+                        FormatCount::Literal(n) => write!(template, "{n}").unwrap(),
+                        FormatCount::Argument(FormatArgPosition {
+                            index: Ok(n) | Err(n), ..
+                        }) => {
+                            write!(template, "{n}$").unwrap();
+                        }
+                    }
+                }
+                if flags >> (rustc_parse_format::FlagDebugLowerHex as usize) & 1 != 0 {
+                    template.push('X');
+                }
+                if flags >> (rustc_parse_format::FlagDebugUpperHex as usize) & 1 != 0 {
+                    template.push('x');
+                }
+                template.push_str(match p.format_trait {
+                    FormatTrait::Display => "",
+                    FormatTrait::Debug => "?",
+                    FormatTrait::LowerExp => "e",
+                    FormatTrait::UpperExp => "E",
+                    FormatTrait::Octal => "o",
+                    FormatTrait::Pointer => "p",
+                    FormatTrait::Binary => "b",
+                    FormatTrait::LowerHex => "x",
+                    FormatTrait::UpperHex => "X",
+                });
+                template.push('}');
+            }
+        }
+    }
+    template.push('"');
+    template
+}

compiler/rustc_builtin_macros/src/assert/context.rs

@@ -297,6 +297,7 @@ impl<'cx, 'a> Context<'cx, 'a> {
             | ExprKind::Continue(_)
             | ExprKind::Err
             | ExprKind::Field(_, _)
+            | ExprKind::FormatArgs(_)
             | ExprKind::ForLoop(_, _, _, _)
             | ExprKind::If(_, _, _)
             | ExprKind::IncludedBytes(..)

compiler/rustc_builtin_macros/src/format.rs

@@ -1,7 +1,11 @@
 use rustc_ast::ptr::P;
 use rustc_ast::token;
 use rustc_ast::tokenstream::TokenStream;
-use rustc_ast::Expr;
+use rustc_ast::{
+    Expr, ExprKind, FormatAlignment, FormatArgPosition, FormatArgPositionKind, FormatArgs,
+    FormatArgsPiece, FormatArgument, FormatArgumentKind, FormatArguments, FormatCount,
+    FormatOptions, FormatPlaceholder, FormatTrait,
+};
 use rustc_data_structures::fx::FxHashSet;
 use rustc_errors::{pluralize, Applicability, MultiSpan, PResult};
 use rustc_expand::base::{self, *};
@@ -12,12 +16,6 @@ use rustc_span::{BytePos, InnerSpan, Span};
 use rustc_lint_defs::builtin::NAMED_ARGUMENTS_USED_POSITIONALLY;
 use rustc_lint_defs::{BufferedEarlyLint, BuiltinLintDiagnostics, LintId};
 
-mod ast;
-use ast::*;
-
-mod expand;
-use expand::expand_parsed_format_args;
-
 // The format_args!() macro is expanded in three steps:
 //  1. First, `parse_args` will parse the `(literal, arg, arg, name=arg, name=arg)` syntax,
 //     but doesn't parse the template (the literal) itself.
@@ -850,7 +848,7 @@ fn expand_format_args_impl<'cx>(
     match parse_args(ecx, sp, tts) {
         Ok((efmt, args)) => {
             if let Ok(format_args) = make_format_args(ecx, efmt, args, nl) {
-                MacEager::expr(expand_parsed_format_args(ecx, format_args))
+                MacEager::expr(ecx.expr(sp, ExprKind::FormatArgs(P(format_args))))
             } else {
                 MacEager::expr(DummyResult::raw_expr(sp, true))
             }

compiler/rustc_builtin_macros/src/format/expand.rs

@@ -1,353 +0,0 @@
-use super::*;
-use rustc_ast as ast;
-use rustc_ast::visit::{self, Visitor};
-use rustc_ast::{BlockCheckMode, UnsafeSource};
-use rustc_data_structures::fx::FxIndexSet;
-use rustc_span::{sym, symbol::kw};
-
-#[derive(Copy, Clone, Debug, Hash, PartialEq, Eq)]
-enum ArgumentType {
-    Format(FormatTrait),
-    Usize,
-}
-
-fn make_argument(ecx: &ExtCtxt<'_>, sp: Span, arg: P<ast::Expr>, ty: ArgumentType) -> P<ast::Expr> {
-    // Generate:
-    //     ::core::fmt::ArgumentV1::new_…(arg)
-    use ArgumentType::*;
-    use FormatTrait::*;
-    ecx.expr_call_global(
-        sp,
-        ecx.std_path(&[
-            sym::fmt,
-            sym::ArgumentV1,
-            match ty {
-                Format(Display) => sym::new_display,
-                Format(Debug) => sym::new_debug,
-                Format(LowerExp) => sym::new_lower_exp,
-                Format(UpperExp) => sym::new_upper_exp,
-                Format(Octal) => sym::new_octal,
-                Format(Pointer) => sym::new_pointer,
-                Format(Binary) => sym::new_binary,
-                Format(LowerHex) => sym::new_lower_hex,
-                Format(UpperHex) => sym::new_upper_hex,
-                Usize => sym::from_usize,
-            },
-        ]),
-        vec![arg],
-    )
-}
-
-fn make_count(
-    ecx: &ExtCtxt<'_>,
-    sp: Span,
-    count: &Option<FormatCount>,
-    argmap: &mut FxIndexSet<(usize, ArgumentType)>,
-) -> P<ast::Expr> {
-    // Generate:
-    //     ::core::fmt::rt::v1::Count::…(…)
-    match count {
-        Some(FormatCount::Literal(n)) => ecx.expr_call_global(
-            sp,
-            ecx.std_path(&[sym::fmt, sym::rt, sym::v1, sym::Count, sym::Is]),
-            vec![ecx.expr_usize(sp, *n)],
-        ),
-        Some(FormatCount::Argument(arg)) => {
-            if let Ok(arg_index) = arg.index {
-                let (i, _) = argmap.insert_full((arg_index, ArgumentType::Usize));
-                ecx.expr_call_global(
-                    sp,
-                    ecx.std_path(&[sym::fmt, sym::rt, sym::v1, sym::Count, sym::Param]),
-                    vec![ecx.expr_usize(sp, i)],
-                )
-            } else {
-                DummyResult::raw_expr(sp, true)
-            }
-        }
-        None => ecx.expr_path(ecx.path_global(
-            sp,
-            ecx.std_path(&[sym::fmt, sym::rt, sym::v1, sym::Count, sym::Implied]),
-        )),
-    }
-}
-
-fn make_format_spec(
-    ecx: &ExtCtxt<'_>,
-    sp: Span,
-    placeholder: &FormatPlaceholder,
-    argmap: &mut FxIndexSet<(usize, ArgumentType)>,
-) -> P<ast::Expr> {
-    // Generate:
-    //     ::core::fmt::rt::v1::Argument {
-    //         position: 0usize,
-    //         format: ::core::fmt::rt::v1::FormatSpec {
-    //             fill: ' ',
-    //             align: ::core::fmt::rt::v1::Alignment::Unknown,
-    //             flags: 0u32,
-    //             precision: ::core::fmt::rt::v1::Count::Implied,
-    //             width: ::core::fmt::rt::v1::Count::Implied,
-    //         },
-    //     }
-    let position = match placeholder.argument.index {
-        Ok(arg_index) => {
-            let (i, _) =
-                argmap.insert_full((arg_index, ArgumentType::Format(placeholder.format_trait)));
-            ecx.expr_usize(sp, i)
-        }
-        Err(_) => DummyResult::raw_expr(sp, true),
-    };
-    let fill = ecx.expr_char(sp, placeholder.format_options.fill.unwrap_or(' '));
-    let align = ecx.expr_path(ecx.path_global(
-        sp,
-        ecx.std_path(&[
-            sym::fmt,
-            sym::rt,
-            sym::v1,
-            sym::Alignment,
-            match placeholder.format_options.alignment {
-                Some(FormatAlignment::Left) => sym::Left,
-                Some(FormatAlignment::Right) => sym::Right,
-                Some(FormatAlignment::Center) => sym::Center,
-                None => sym::Unknown,
-            },
-        ]),
-    ));
-    let flags = ecx.expr_u32(sp, placeholder.format_options.flags);
-    let prec = make_count(ecx, sp, &placeholder.format_options.precision, argmap);
-    let width = make_count(ecx, sp, &placeholder.format_options.width, argmap);
-    ecx.expr_struct(
-        sp,
-        ecx.path_global(sp, ecx.std_path(&[sym::fmt, sym::rt, sym::v1, sym::Argument])),
-        vec![
-            ecx.field_imm(sp, Ident::new(sym::position, sp), position),
-            ecx.field_imm(
-                sp,
-                Ident::new(sym::format, sp),
-                ecx.expr_struct(
-                    sp,
-                    ecx.path_global(
-                        sp,
-                        ecx.std_path(&[sym::fmt, sym::rt, sym::v1, sym::FormatSpec]),
-                    ),
-                    vec![
-                        ecx.field_imm(sp, Ident::new(sym::fill, sp), fill),
-                        ecx.field_imm(sp, Ident::new(sym::align, sp), align),
-                        ecx.field_imm(sp, Ident::new(sym::flags, sp), flags),
-                        ecx.field_imm(sp, Ident::new(sym::precision, sp), prec),
-                        ecx.field_imm(sp, Ident::new(sym::width, sp), width),
-                    ],
-                ),
-            ),
-        ],
-    )
-}
-
-pub fn expand_parsed_format_args(ecx: &mut ExtCtxt<'_>, fmt: FormatArgs) -> P<ast::Expr> {
-    let macsp = ecx.with_def_site_ctxt(ecx.call_site());
-
-    let lit_pieces = ecx.expr_array_ref(
-        fmt.span,
-        fmt.template
-            .iter()
-            .enumerate()
-            .filter_map(|(i, piece)| match piece {
-                &FormatArgsPiece::Literal(s) => Some(ecx.expr_str(fmt.span, s)),
-                &FormatArgsPiece::Placeholder(_) => {
-                    // Inject empty string before placeholders when not already preceded by a literal piece.
-                    if i == 0 || matches!(fmt.template[i - 1], FormatArgsPiece::Placeholder(_)) {
-                        Some(ecx.expr_str(fmt.span, kw::Empty))
-                    } else {
-                        None
-                    }
-                }
-            })
-            .collect(),
-    );
-
-    // Whether we'll use the `Arguments::new_v1_formatted` form (true),
-    // or the `Arguments::new_v1` form (false).
-    let mut use_format_options = false;
-
-    // Create a list of all _unique_ (argument, format trait) combinations.
-    // E.g. "{0} {0:x} {0} {1}" -> [(0, Display), (0, LowerHex), (1, Display)]
-    let mut argmap = FxIndexSet::default();
-    for piece in &fmt.template {
-        let FormatArgsPiece::Placeholder(placeholder) = piece else { continue };
-        if placeholder.format_options != Default::default() {
-            // Can't use basic form if there's any formatting options.
-            use_format_options = true;
-        }
-        if let Ok(index) = placeholder.argument.index {
-            if !argmap.insert((index, ArgumentType::Format(placeholder.format_trait))) {
-                // Duplicate (argument, format trait) combination,
-                // which we'll only put once in the args array.
-                use_format_options = true;
-            }
-        }
-    }
-
-    let format_options = use_format_options.then(|| {
-        // Generate:
-        //     &[format_spec_0, format_spec_1, format_spec_2]
-        ecx.expr_array_ref(
-            macsp,
-            fmt.template
-                .iter()
-                .filter_map(|piece| {
-                    let FormatArgsPiece::Placeholder(placeholder) = piece else { return None };
-                    Some(make_format_spec(ecx, macsp, placeholder, &mut argmap))
-                })
-                .collect(),
-        )
-    });
-
-    let arguments = fmt.arguments.into_vec();
-
-    // If the args array contains exactly all the original arguments once,
-    // in order, we can use a simple array instead of a `match` construction.
-    // However, if there's a yield point in any argument except the first one,
-    // we don't do this, because an ArgumentV1 cannot be kept across yield points.
-    let use_simple_array = argmap.len() == arguments.len()
-        && argmap.iter().enumerate().all(|(i, &(j, _))| i == j)
-        && arguments.iter().skip(1).all(|arg| !may_contain_yield_point(&arg.expr));
-
-    let args = if use_simple_array {
-        // Generate:
-        //     &[
-        //         ::core::fmt::ArgumentV1::new_display(&arg0),
-        //         ::core::fmt::ArgumentV1::new_lower_hex(&arg1),
-        //         ::core::fmt::ArgumentV1::new_debug(&arg2),
-        //     ]
-        ecx.expr_array_ref(
-            macsp,
-            arguments
-                .into_iter()
-                .zip(argmap)
-                .map(|(arg, (_, ty))| {
-                    let sp = arg.expr.span.with_ctxt(macsp.ctxt());
-                    make_argument(ecx, sp, ecx.expr_addr_of(sp, arg.expr), ty)
-                })
-                .collect(),
-        )
-    } else {
-        // Generate:
-        //     match (&arg0, &arg1, &arg2) {
-        //         args => &[
-        //             ::core::fmt::ArgumentV1::new_display(args.0),
-        //             ::core::fmt::ArgumentV1::new_lower_hex(args.1),
-        //             ::core::fmt::ArgumentV1::new_debug(args.0),
-        //         ]
-        //     }
-        let args_ident = Ident::new(sym::args, macsp);
-        let args = argmap
-            .iter()
-            .map(|&(arg_index, ty)| {
-                if let Some(arg) = arguments.get(arg_index) {
-                    let sp = arg.expr.span.with_ctxt(macsp.ctxt());
-                    make_argument(
-                        ecx,
-                        sp,
-                        ecx.expr_field(
-                            sp,
-                            ecx.expr_ident(macsp, args_ident),
-                            Ident::new(sym::integer(arg_index), macsp),
-                        ),
-                        ty,
-                    )
-                } else {
-                    DummyResult::raw_expr(macsp, true)
-                }
-            })
-            .collect();
-        ecx.expr_addr_of(
-            macsp,
-            ecx.expr_match(
-                macsp,
-                ecx.expr_tuple(
-                    macsp,
-                    arguments
-                        .into_iter()
-                        .map(|arg| {
-                            ecx.expr_addr_of(arg.expr.span.with_ctxt(macsp.ctxt()), arg.expr)
-                        })
-                        .collect(),
-                ),
-                vec![ecx.arm(macsp, ecx.pat_ident(macsp, args_ident), ecx.expr_array(macsp, args))],
-            ),
-        )
-    };
-
-    if let Some(format_options) = format_options {
-        // Generate:
-        //     ::core::fmt::Arguments::new_v1_formatted(
-        //         lit_pieces,
-        //         args,
-        //         format_options,
-        //         unsafe { ::core::fmt::UnsafeArg::new() }
-        //     )
-        ecx.expr_call_global(
-            macsp,
-            ecx.std_path(&[sym::fmt, sym::Arguments, sym::new_v1_formatted]),
-            vec![
-                lit_pieces,
-                args,
-                format_options,
-                ecx.expr_block(P(ast::Block {
-                    stmts: vec![ecx.stmt_expr(ecx.expr_call_global(
-                        macsp,
-                        ecx.std_path(&[sym::fmt, sym::UnsafeArg, sym::new]),
-                        Vec::new(),
-                    ))],
-                    id: ast::DUMMY_NODE_ID,
-                    rules: BlockCheckMode::Unsafe(UnsafeSource::CompilerGenerated),
-                    span: macsp,
-                    tokens: None,
-                    could_be_bare_literal: false,
-                })),
-            ],
-        )
-    } else {
-        // Generate:
-        //     ::core::fmt::Arguments::new_v1(
-        //         lit_pieces,
-        //         args,
-        //     )
-        ecx.expr_call_global(
-            macsp,
-            ecx.std_path(&[sym::fmt, sym::Arguments, sym::new_v1]),
-            vec![lit_pieces, args],
-        )
-    }
-}
-
-fn may_contain_yield_point(e: &ast::Expr) -> bool {
-    struct MayContainYieldPoint(bool);
-
-    impl Visitor<'_> for MayContainYieldPoint {
-        fn visit_expr(&mut self, e: &ast::Expr) {
-            if let ast::ExprKind::Await(_) | ast::ExprKind::Yield(_) = e.kind {
-                self.0 = true;
-            } else {
-                visit::walk_expr(self, e);
-            }
-        }
-
-        fn visit_mac_call(&mut self, _: &ast::MacCall) {
-            self.0 = true;
-        }
-
-        fn visit_attribute(&mut self, _: &ast::Attribute) {
-            // Conservatively assume this may be a proc macro attribute in
-            // expression position.
-            self.0 = true;
-        }
-
-        fn visit_item(&mut self, _: &ast::Item) {
-            // Do not recurse into nested items.
-        }
-    }
-
-    let mut visitor = MayContainYieldPoint(false);
-    visitor.visit_expr(e);
-    visitor.0
-}

compiler/rustc_hir/src/hir.rs

@@ -2108,6 +2108,8 @@ pub enum MatchSource {
     TryDesugar,
     /// A desugared `<expr>.await`.
     AwaitDesugar,
+    /// A desugared `format_args!()`.
+    FormatArgs,
 }
 
 impl MatchSource {
@@ -2119,6 +2121,7 @@ impl MatchSource {
             ForLoopDesugar => "for",
             TryDesugar => "?",
             AwaitDesugar => ".await",
+            FormatArgs => "format_args!()",
         }
     }
 }

compiler/rustc_mir_build/src/thir/pattern/check_match.rs

@@ -208,9 +208,9 @@ impl<'p, 'tcx> MatchVisitor<'_, 'p, 'tcx> {
             // Don't report arm reachability of desugared `match $iter.into_iter() { iter => .. }`
             // when the iterator is an uninhabited type. unreachable_code will trigger instead.
             hir::MatchSource::ForLoopDesugar if arms.len() == 1 => {}
-            hir::MatchSource::ForLoopDesugar | hir::MatchSource::Normal => {
+            hir::MatchSource::ForLoopDesugar
-                report_arm_reachability(&cx, &report)
+            | hir::MatchSource::Normal
-            }
+            | hir::MatchSource::FormatArgs => report_arm_reachability(&cx, &report),
             // Unreachable patterns in try and await expressions occur when one of
             // the arms are an uninhabited type. Which is OK.
             hir::MatchSource::AwaitDesugar | hir::MatchSource::TryDesugar => {}

compiler/rustc_passes/src/check_const.rs

@@ -48,7 +48,7 @@ impl NonConstExpr {
             Self::Match(TryDesugar) => &[sym::const_try],
 
             // All other expressions are allowed.
-            Self::Loop(Loop | While) | Self::Match(Normal) => &[],
+            Self::Loop(Loop | While) | Self::Match(Normal | FormatArgs) => &[],
         };
 
         Some(gates)

compiler/rustc_passes/src/hir_stats.rs

@@ -567,7 +567,7 @@ impl<'v> ast_visit::Visitor<'v> for StatCollector<'v> {
                 Box, Array, ConstBlock, Call, MethodCall, Tup, Binary, Unary, Lit, Cast, Type, Let,
                 If, While, ForLoop, Loop, Match, Closure, Block, Async, Await, TryBlock, Assign,
                 AssignOp, Field, Index, Range, Underscore, Path, AddrOf, Break, Continue, Ret,
-                InlineAsm, MacCall, Struct, Repeat, Paren, Try, Yield, Yeet, IncludedBytes, Err
+                InlineAsm, FormatArgs, MacCall, Struct, Repeat, Paren, Try, Yield, Yeet, IncludedBytes, Err
             ]
         );
         ast_visit::walk_expr(self, e)