Rollup merge of #100738 - nidnogg:diagnostics_migr_const_eval, r=davidtwco

[rust.git] / compiler / rustc_builtin_macros / src / format.rs

use ArgumentType::*;
use Position::*;

use rustc_ast as ast;
use rustc_ast::ptr::P;
use rustc_ast::tokenstream::TokenStream;
use rustc_ast::visit::{self, Visitor};
use rustc_ast::{token, BlockCheckMode, UnsafeSource};
use rustc_data_structures::fx::{FxHashMap, FxHashSet};
use rustc_errors::{pluralize, Applicability, MultiSpan, PResult};
use rustc_expand::base::{self, *};
use rustc_parse_format as parse;
use rustc_span::symbol::{sym, Ident, Symbol};
use rustc_span::{BytePos, InnerSpan, Span};
use smallvec::SmallVec;

use rustc_lint_defs::builtin::NAMED_ARGUMENTS_USED_POSITIONALLY;
use rustc_lint_defs::{BufferedEarlyLint, BuiltinLintDiagnostics, LintId};
use rustc_parse_format::Count;
use std::borrow::Cow;
use std::collections::hash_map::Entry;

#[derive(PartialEq)]
enum ArgumentType {
    Placeholder(&'static str),
    Count,
}

enum Position {
    Exact(usize),
    Capture(usize),
    Named(Symbol, InnerSpan),
}

/// Indicates how positional named argument (i.e. an named argument which is used by position
/// instead of by name) is used in format string
/// * `Arg` is the actual argument to print
/// * `Width` is width format argument
/// * `Precision` is precion format argument
/// Example: `{Arg:Width$.Precision$}
#[derive(Debug, Eq, PartialEq)]
enum PositionalNamedArgType {
    Arg,
    Width,
    Precision,
}

/// Contains information necessary to create a lint for a positional named argument
#[derive(Debug)]
struct PositionalNamedArg {
    ty: PositionalNamedArgType,
    /// The piece of the using this argument (multiple pieces can use the same argument)
    cur_piece: usize,
    /// The InnerSpan for in the string to be replaced with the named argument
    /// This will be None when the position is implicit
    inner_span_to_replace: Option<rustc_parse_format::InnerSpan>,
    /// The name to use instead of the position
    replacement: Symbol,
    /// The span for the positional named argument (so the lint can point a message to it)
    positional_named_arg_span: Span,
    has_formatting: bool,
}

impl PositionalNamedArg {
    /// Determines:
    /// 1) span to be replaced with the name of the named argument and
    /// 2) span to be underlined for error messages
    fn get_positional_arg_spans(&self, cx: &Context<'_, '_>) -> (Option<Span>, Option<Span>) {
        if let Some(inner_span) = &self.inner_span_to_replace {
            let span =
                cx.fmtsp.from_inner(InnerSpan { start: inner_span.start, end: inner_span.end });
            (Some(span), Some(span))
        } else if self.ty == PositionalNamedArgType::Arg {
            // In the case of a named argument whose position is implicit, if the argument *has*
            // formatting, there will not be a span to replace. Instead, we insert the name after
            // the `{`, which will be the first character of arg_span. If the argument does *not*
            // have formatting, there may or may not be a span to replace. This is because
            // whitespace is allowed in arguments without formatting (such as `format!("{  }", 1);`)
            // but is not allowed in arguments with formatting (an error will be generated in cases
            // like `format!("{ :1.1}", 1.0f32);`.
            // For the message span, if there is formatting, we want to use the opening `{` and the
            // next character, which will the `:` indicating the start of formatting. If there is
            // not any formatting, we want to underline the entire span.
            cx.arg_spans.get(self.cur_piece).map_or((None, None), |arg_span| {
                if self.has_formatting {
                    (
                        Some(arg_span.with_lo(arg_span.lo() + BytePos(1)).shrink_to_lo()),
                        Some(arg_span.with_hi(arg_span.lo() + BytePos(2))),
                    )
                } else {
                    let replace_start = arg_span.lo() + BytePos(1);
                    let replace_end = arg_span.hi() - BytePos(1);
                    let to_replace = arg_span.with_lo(replace_start).with_hi(replace_end);
                    (Some(to_replace), Some(*arg_span))
                }
            })
        } else {
            (None, None)
        }
    }
}

/// Encapsulates all the named arguments that have been used positionally
#[derive(Debug)]
struct PositionalNamedArgsLint {
    positional_named_args: Vec<PositionalNamedArg>,
}

impl PositionalNamedArgsLint {
    /// For a given positional argument, check if the index is for a named argument.
    ///
    /// Since positional arguments are required to come before named arguments, if the positional
    /// index is greater than or equal to the start of named arguments, we know it's a named
    /// argument used positionally.
    ///
    /// Example:
    /// println!("{} {} {2}", 0, a=1, b=2);
    ///
    /// In this case, the first piece (`{}`) would be ArgumentImplicitlyIs with an index of 0. The
    /// total number of arguments is 3 and the number of named arguments is 2, so the start of named
    /// arguments is index 1. Therefore, the index of 0 is okay.
    ///
    /// The second piece (`{}`) would be ArgumentImplicitlyIs with an index of 1, which is the start
    /// of named arguments, and so we should add a lint to use the named argument `a`.
    ///
    /// The third piece (`{2}`) would be ArgumentIs with an index of 2, which is greater than the
    /// start of named arguments, and so we should add a lint to use the named argument `b`.
    ///
    /// This same check also works for width and precision formatting when either or both are
    /// CountIsParam, which contains an index into the arguments.
    fn maybe_add_positional_named_arg(
        &mut self,
        arg: Option<&FormatArg>,
        ty: PositionalNamedArgType,
        cur_piece: usize,
        inner_span_to_replace: Option<rustc_parse_format::InnerSpan>,
        has_formatting: bool,
    ) {
        if let Some(arg) = arg {
            if let Some(name) = arg.name {
                self.push(name, ty, cur_piece, inner_span_to_replace, has_formatting)
            }
        }
    }

    /// Construct a PositionalNamedArg struct and push it into the vec of positional
    /// named arguments.
    fn push(
        &mut self,
        arg_name: Ident,
        ty: PositionalNamedArgType,
        cur_piece: usize,
        inner_span_to_replace: Option<rustc_parse_format::InnerSpan>,
        has_formatting: bool,
    ) {
        // In FormatSpec, `precision_span` starts at the leading `.`, which we want to keep in
        // the lint suggestion, so increment `start` by 1 when `PositionalArgumentType` is
        // `Precision`.
        let inner_span_to_replace = if ty == PositionalNamedArgType::Precision {
            inner_span_to_replace
                .map(|is| rustc_parse_format::InnerSpan { start: is.start + 1, end: is.end })
        } else {
            inner_span_to_replace
        };
        self.positional_named_args.push(PositionalNamedArg {
            ty,
            cur_piece,
            inner_span_to_replace,
            replacement: arg_name.name,
            positional_named_arg_span: arg_name.span,
            has_formatting,
        });
    }
}

struct Context<'a, 'b> {
    ecx: &'a mut ExtCtxt<'b>,
    /// The macro's call site. References to unstable formatting internals must
    /// use this span to pass the stability checker.
    macsp: Span,
    /// The span of the format string literal.
    fmtsp: Span,

    /// List of parsed argument expressions.
    /// Named expressions are resolved early, and are appended to the end of
    /// argument expressions.
    ///
    /// Example showing the various data structures in motion:
    ///
    /// * Original: `"{foo:o} {:o} {foo:x} {0:x} {1:o} {:x} {1:x} {0:o}"`
    /// * Implicit argument resolution: `"{foo:o} {0:o} {foo:x} {0:x} {1:o} {1:x} {1:x} {0:o}"`
    /// * Name resolution: `"{2:o} {0:o} {2:x} {0:x} {1:o} {1:x} {1:x} {0:o}"`
    /// * `arg_types` (in JSON): `[[0, 1, 0], [0, 1, 1], [0, 1]]`
    /// * `arg_unique_types` (in simplified JSON): `[["o", "x"], ["o", "x"], ["o", "x"]]`
    /// * `names` (in JSON): `{"foo": 2}`
    args: Vec<FormatArg>,
    /// The number of arguments that were added by implicit capturing.
    num_captured_args: usize,
    /// Placeholder slot numbers indexed by argument.
    arg_types: Vec<Vec<usize>>,
    /// Unique format specs seen for each argument.
    arg_unique_types: Vec<Vec<ArgumentType>>,
    /// Map from named arguments to their resolved indices.
    names: FxHashMap<Symbol, usize>,

    /// The latest consecutive literal strings, or empty if there weren't any.
    literal: String,

    /// Collection of the compiled `rt::Argument` structures
    pieces: Vec<P<ast::Expr>>,
    /// Collection of string literals
    str_pieces: Vec<P<ast::Expr>>,
    /// Stays `true` if all formatting parameters are default (as in "{}{}").
    all_pieces_simple: bool,

    /// Mapping between positional argument references and indices into the
    /// final generated static argument array. We record the starting indices
    /// corresponding to each positional argument, and number of references
    /// consumed so far for each argument, to facilitate correct `Position`
    /// mapping in `build_piece`. In effect this can be seen as a "flattened"
    /// version of `arg_unique_types`.
    ///
    /// Again with the example described above in docstring for `args`:
    ///
    /// * `arg_index_map` (in JSON): `[[0, 1, 0], [2, 3, 3], [4, 5]]`
    arg_index_map: Vec<Vec<usize>>,

    /// Starting offset of count argument slots.
    count_args_index_offset: usize,

    /// Count argument slots and tracking data structures.
    /// Count arguments are separately tracked for de-duplication in case
    /// multiple references are made to one argument. For example, in this
    /// format string:
    ///
    /// * Original: `"{:.*} {:.foo$} {1:.*} {:.0$}"`
    /// * Implicit argument resolution: `"{1:.0$} {2:.foo$} {1:.3$} {4:.0$}"`
    /// * Name resolution: `"{1:.0$} {2:.5$} {1:.3$} {4:.0$}"`
    /// * `count_positions` (in JSON): `{0: 0, 5: 1, 3: 2}`
    /// * `count_args`: `vec![0, 5, 3]`
    count_args: Vec<usize>,
    /// Relative slot numbers for count arguments.
    count_positions: FxHashMap<usize, usize>,
    /// Number of count slots assigned.
    count_positions_count: usize,

    /// Current position of the implicit positional arg pointer, as if it
    /// still existed in this phase of processing.
    /// Used only for `all_pieces_simple` tracking in `build_piece`.
    curarg: usize,
    /// Current piece being evaluated, used for error reporting.
    curpiece: usize,
    /// Keep track of invalid references to positional arguments.
    invalid_refs: Vec<(usize, usize)>,
    /// Spans of all the formatting arguments, in order.
    arg_spans: Vec<Span>,
    /// All the formatting arguments that have formatting flags set, in order for diagnostics.
    arg_with_formatting: Vec<parse::FormatSpec<'a>>,

    /// Whether this format string came from a string literal, as opposed to a macro.
    is_literal: bool,
    unused_names_lint: PositionalNamedArgsLint,
}

pub struct FormatArg {
    expr: P<ast::Expr>,
    name: Option<Ident>,
}

/// Parses the arguments from the given list of tokens, returning the diagnostic
/// if there's a parse error so we can continue parsing other format!
/// expressions.
///
/// If parsing succeeds, the return value is:
///
/// ```text
/// Some((fmtstr, parsed arguments, index map for named arguments))
/// ```
fn parse_args<'a>(
    ecx: &mut ExtCtxt<'a>,
    sp: Span,
    tts: TokenStream,
) -> PResult<'a, (P<ast::Expr>, Vec<FormatArg>, FxHashMap<Symbol, usize>)> {
    let mut args = Vec::<FormatArg>::new();
    let mut names = FxHashMap::<Symbol, usize>::default();

    let mut p = ecx.new_parser_from_tts(tts);

    if p.token == token::Eof {
        return Err(ecx.struct_span_err(sp, "requires at least a format string argument"));
    }

    let first_token = &p.token;
    let fmtstr = match first_token.kind {
        token::TokenKind::Literal(token::Lit {
            kind: token::LitKind::Str | token::LitKind::StrRaw(_),
            ..
        }) => {
            // If the first token is a string literal, then a format expression
            // is constructed from it.
            //
            // This allows us to properly handle cases when the first comma
            // after the format string is mistakenly replaced with any operator,
            // which cause the expression parser to eat too much tokens.
            p.parse_literal_maybe_minus()?
        }
        _ => {
            // Otherwise, we fall back to the expression parser.
            p.parse_expr()?
        }
    };

    let mut first = true;
    let mut named = false;

    while p.token != token::Eof {
        if !p.eat(&token::Comma) {
            if first {
                p.clear_expected_tokens();
            }

            match p.expect(&token::Comma) {
                Err(mut err) => {
                    match token::TokenKind::Comma.similar_tokens() {
                        Some(tks) if tks.contains(&p.token.kind) => {
                            // If a similar token is found, then it may be a typo. We
                            // consider it as a comma, and continue parsing.
                            err.emit();
                            p.bump();
                        }
                        // Otherwise stop the parsing and return the error.
                        _ => return Err(err),
                    }
                }
                Ok(recovered) => {
                    assert!(recovered);
                }
            }
        }
        first = false;
        if p.token == token::Eof {
            break;
        } // accept trailing commas
        match p.token.ident() {
            Some((ident, _)) if p.look_ahead(1, |t| *t == token::Eq) => {
                named = true;
                p.bump();
                p.expect(&token::Eq)?;
                let e = p.parse_expr()?;
                if let Some(&prev) = names.get(&ident.name) {
                    ecx.struct_span_err(e.span, &format!("duplicate argument named `{}`", ident))
                        .span_label(args[prev].expr.span, "previously here")
                        .span_label(e.span, "duplicate argument")
                        .emit();
                    continue;
                }

                // Resolve names into slots early.
                // Since all the positional args are already seen at this point
                // if the input is valid, we can simply append to the positional
                // args. And remember the names.
                let slot = args.len();
                names.insert(ident.name, slot);
                args.push(FormatArg { expr: e, name: Some(ident) });
            }
            _ => {
                let e = p.parse_expr()?;
                if named {
                    let mut err = ecx.struct_span_err(
                        e.span,
                        "positional arguments cannot follow named arguments",
                    );
                    err.span_label(e.span, "positional arguments must be before named arguments");
                    for &pos in names.values() {
                        err.span_label(args[pos].expr.span, "named argument");
                    }
                    err.emit();
                }
                args.push(FormatArg { expr: e, name: None });
            }
        }
    }
    Ok((fmtstr, args, names))
}

impl<'a, 'b> Context<'a, 'b> {
    /// The number of arguments that were explicitly given.
    fn num_args(&self) -> usize {
        self.args.len() - self.num_captured_args
    }

    fn resolve_name_inplace(&mut self, p: &mut parse::Piece<'_>) {
        // NOTE: the `unwrap_or` branch is needed in case of invalid format
        // arguments, e.g., `format_args!("{foo}")`.
        let lookup = |s: &str| self.names.get(&Symbol::intern(s)).copied().unwrap_or(0);

        match *p {
            parse::String(_) => {}
            parse::NextArgument(ref mut arg) => {
                if let parse::ArgumentNamed(s) = arg.position {
                    arg.position = parse::ArgumentIs(lookup(s));
                }
                if let parse::CountIsName(s, _) = arg.format.width {
                    arg.format.width = parse::CountIsParam(lookup(s));
                }
                if let parse::CountIsName(s, _) = arg.format.precision {
                    arg.format.precision = parse::CountIsParam(lookup(s));
                }
            }
        }
    }

    /// Verifies one piece of a parse string, and remembers it if valid.
    /// All errors are not emitted as fatal so we can continue giving errors
    /// about this and possibly other format strings.
    fn verify_piece(&mut self, p: &parse::Piece<'a>) {
        match *p {
            parse::String(..) => {}
            parse::NextArgument(ref arg) => {
                // width/precision first, if they have implicit positional
                // parameters it makes more sense to consume them first.
                self.verify_count(
                    arg.format.width,
                    &arg.format.width_span,
                    PositionalNamedArgType::Width,
                );
                self.verify_count(
                    arg.format.precision,
                    &arg.format.precision_span,
                    PositionalNamedArgType::Precision,
                );

                let has_precision = arg.format.precision != Count::CountImplied;
                let has_width = arg.format.width != Count::CountImplied;

                if has_precision || has_width {
                    // push before named params are resolved to aid diagnostics
                    self.arg_with_formatting.push(arg.format);
                }

                // argument second, if it's an implicit positional parameter
                // it's written second, so it should come after width/precision.
                let pos = match arg.position {
                    parse::ArgumentIs(i) => {
                        self.unused_names_lint.maybe_add_positional_named_arg(
                            self.args.get(i),
                            PositionalNamedArgType::Arg,
                            self.curpiece,
                            Some(arg.position_span),
                            has_precision || has_width,
                        );

                        Exact(i)
                    }
                    parse::ArgumentImplicitlyIs(i) => {
                        self.unused_names_lint.maybe_add_positional_named_arg(
                            self.args.get(i),
                            PositionalNamedArgType::Arg,
                            self.curpiece,
                            None,
                            has_precision || has_width,
                        );
                        Exact(i)
                    }
                    parse::ArgumentNamed(s) => {
                        let symbol = Symbol::intern(s);
                        let span = arg.position_span;
                        Named(symbol, InnerSpan::new(span.start, span.end))
                    }
                };

                let ty = Placeholder(match arg.format.ty {
                    "" => "Display",
                    "?" => "Debug",
                    "e" => "LowerExp",
                    "E" => "UpperExp",
                    "o" => "Octal",
                    "p" => "Pointer",
                    "b" => "Binary",
                    "x" => "LowerHex",
                    "X" => "UpperHex",
                    _ => {
                        let fmtsp = self.fmtsp;
                        let sp = arg
                            .format
                            .ty_span
                            .map(|sp| fmtsp.from_inner(InnerSpan::new(sp.start, sp.end)));
                        let mut err = self.ecx.struct_span_err(
                            sp.unwrap_or(fmtsp),
                            &format!("unknown format trait `{}`", arg.format.ty),
                        );
                        err.note(
                            "the only appropriate formatting traits are:\n\
                                - ``, which uses the `Display` trait\n\
                                - `?`, which uses the `Debug` trait\n\
                                - `e`, which uses the `LowerExp` trait\n\
                                - `E`, which uses the `UpperExp` trait\n\
                                - `o`, which uses the `Octal` trait\n\
                                - `p`, which uses the `Pointer` trait\n\
                                - `b`, which uses the `Binary` trait\n\
                                - `x`, which uses the `LowerHex` trait\n\
                                - `X`, which uses the `UpperHex` trait",
                        );
                        if let Some(sp) = sp {
                            for (fmt, name) in &[
                                ("", "Display"),
                                ("?", "Debug"),
                                ("e", "LowerExp"),
                                ("E", "UpperExp"),
                                ("o", "Octal"),
                                ("p", "Pointer"),
                                ("b", "Binary"),
                                ("x", "LowerHex"),
                                ("X", "UpperHex"),
                            ] {
                                // FIXME: rustfix (`run-rustfix`) fails to apply suggestions.
                                // > "Cannot replace slice of data that was already replaced"
                                err.tool_only_span_suggestion(
                                    sp,
                                    &format!("use the `{}` trait", name),
                                    *fmt,
                                    Applicability::MaybeIncorrect,
                                );
                            }
                        }
                        err.emit();
                        "<invalid>"
                    }
                });
                self.verify_arg_type(pos, ty);
                self.curpiece += 1;
            }
        }
    }

    fn verify_count(
        &mut self,
        c: parse::Count<'_>,
        inner_span: &Option<rustc_parse_format::InnerSpan>,
        named_arg_type: PositionalNamedArgType,
    ) {
        match c {
            parse::CountImplied | parse::CountIs(..) => {}
            parse::CountIsParam(i) => {
                self.unused_names_lint.maybe_add_positional_named_arg(
                    self.args.get(i),
                    named_arg_type,
                    self.curpiece,
                    *inner_span,
                    true,
                );
                self.verify_arg_type(Exact(i), Count);
            }
            parse::CountIsName(s, span) => {
                self.verify_arg_type(
                    Named(Symbol::intern(s), InnerSpan::new(span.start, span.end)),
                    Count,
                );
            }
        }
    }

    fn describe_num_args(&self) -> Cow<'_, str> {
        match self.num_args() {
            0 => "no arguments were given".into(),
            1 => "there is 1 argument".into(),
            x => format!("there are {} arguments", x).into(),
        }
    }

    /// Handle invalid references to positional arguments. Output different
    /// errors for the case where all arguments are positional and for when
    /// there are named arguments or numbered positional arguments in the
    /// format string.
    fn report_invalid_references(&self, numbered_position_args: bool) {
        let mut e;
        let sp = if !self.arg_spans.is_empty() {
            // Point at the formatting arguments.
            MultiSpan::from_spans(self.arg_spans.clone())
        } else {
            MultiSpan::from_span(self.fmtsp)
        };
        let refs =
            self.invalid_refs.iter().map(|(r, pos)| (r.to_string(), self.arg_spans.get(*pos)));

        let mut zero_based_note = false;

        let count = self.pieces.len()
            + self
                .arg_with_formatting
                .iter()
                .filter(|fmt| matches!(fmt.precision, parse::CountIsParam(_)))
                .count();
        if self.names.is_empty() && !numbered_position_args && count != self.num_args() {
            e = self.ecx.struct_span_err(
                sp,
                &format!(
                    "{} positional argument{} in format string, but {}",
                    count,
                    pluralize!(count),
                    self.describe_num_args(),
                ),
            );
            for arg in &self.args {
                // Point at the arguments that will be formatted.
                e.span_label(arg.expr.span, "");
            }
        } else {
            let (mut refs, spans): (Vec<_>, Vec<_>) = refs.unzip();
            // Avoid `invalid reference to positional arguments 7 and 7 (there is 1 argument)`
            // for `println!("{7:7$}", 1);`
            refs.sort();
            refs.dedup();
            let spans: Vec<_> = spans.into_iter().filter_map(|sp| sp.copied()).collect();
            let sp = if self.arg_spans.is_empty() || spans.is_empty() {
                MultiSpan::from_span(self.fmtsp)
            } else {
                MultiSpan::from_spans(spans)
            };
            let arg_list = if refs.len() == 1 {
                format!("argument {}", refs[0])
            } else {
                let reg = refs.pop().unwrap();
                format!("arguments {head} and {tail}", head = refs.join(", "), tail = reg)
            };

            e = self.ecx.struct_span_err(
                sp,
                &format!(
                    "invalid reference to positional {} ({})",
                    arg_list,
                    self.describe_num_args()
                ),
            );
            zero_based_note = true;
        };

        for fmt in &self.arg_with_formatting {
            if let Some(span) = fmt.precision_span {
                let span = self.fmtsp.from_inner(InnerSpan::new(span.start, span.end));
                match fmt.precision {
                    parse::CountIsParam(pos) if pos > self.num_args() => {
                        e.span_label(
                            span,
                            &format!(
                                "this precision flag expects an `usize` argument at position {}, \
                             but {}",
                                pos,
                                self.describe_num_args(),
                            ),
                        );
                        zero_based_note = true;
                    }
                    parse::CountIsParam(pos) => {
                        let count = self.pieces.len()
                            + self
                                .arg_with_formatting
                                .iter()
                                .filter(|fmt| matches!(fmt.precision, parse::CountIsParam(_)))
                                .count();
                        e.span_label(
                            span,
                            &format!(
                            "this precision flag adds an extra required argument at position {}, \
                             which is why there {} expected",
                            pos,
                            if count == 1 {
                                "is 1 argument".to_string()
                            } else {
                                format!("are {} arguments", count)
                            },
                        ),
                        );
                        if let Some(arg) = self.args.get(pos) {
                            e.span_label(
                                arg.expr.span,
                                "this parameter corresponds to the precision flag",
                            );
                        }
                        zero_based_note = true;
                    }
                    _ => {}
                }
            }
            if let Some(span) = fmt.width_span {
                let span = self.fmtsp.from_inner(InnerSpan::new(span.start, span.end));
                match fmt.width {
                    parse::CountIsParam(pos) if pos >= self.num_args() => {
                        e.span_label(
                            span,
                            &format!(
                                "this width flag expects an `usize` argument at position {}, \
                             but {}",
                                pos,
                                self.describe_num_args(),
                            ),
                        );
                        zero_based_note = true;
                    }
                    _ => {}
                }
            }
        }
        if zero_based_note {
            e.note("positional arguments are zero-based");
        }
        if !self.arg_with_formatting.is_empty() {
            e.note(
                "for information about formatting flags, visit \
                    https://doc.rust-lang.org/std/fmt/index.html",
            );
        }

        e.emit();
    }

    /// Actually verifies and tracks a given format placeholder
    /// (a.k.a. argument).
    fn verify_arg_type(&mut self, arg: Position, ty: ArgumentType) {
        if let Exact(arg) = arg {
            if arg >= self.num_args() {
                self.invalid_refs.push((arg, self.curpiece));
                return;
            }
        }

        match arg {
            Exact(arg) | Capture(arg) => {
                match ty {
                    Placeholder(_) => {
                        // record every (position, type) combination only once
                        let seen_ty = &mut self.arg_unique_types[arg];
                        let i = seen_ty.iter().position(|x| *x == ty).unwrap_or_else(|| {
                            let i = seen_ty.len();
                            seen_ty.push(ty);
                            i
                        });
                        self.arg_types[arg].push(i);
                    }
                    Count => {
                        if let Entry::Vacant(e) = self.count_positions.entry(arg) {
                            let i = self.count_positions_count;
                            e.insert(i);
                            self.count_args.push(arg);
                            self.count_positions_count += 1;
                        }
                    }
                }
            }

            Named(name, span) => {
                match self.names.get(&name) {
                    Some(&idx) => {
                        // Treat as positional arg.
                        self.verify_arg_type(Capture(idx), ty)
                    }
                    None => {
                        // For the moment capturing variables from format strings expanded from macros is
                        // disabled (see RFC #2795)
                        if self.is_literal {
                            // Treat this name as a variable to capture from the surrounding scope
                            let idx = self.args.len();
                            self.arg_types.push(Vec::new());
                            self.arg_unique_types.push(Vec::new());
                            let span = if self.is_literal {
                                self.fmtsp.from_inner(span)
                            } else {
                                self.fmtsp
                            };
                            self.num_captured_args += 1;
                            self.args.push(FormatArg {
                                expr: self.ecx.expr_ident(span, Ident::new(name, span)),
                                name: Some(Ident::new(name, span)),
                            });
                            self.names.insert(name, idx);
                            self.verify_arg_type(Capture(idx), ty)
                        } else {
                            let msg = format!("there is no argument named `{}`", name);
                            let sp = if self.is_literal {
                                self.fmtsp.from_inner(span)
                            } else {
                                self.fmtsp
                            };
                            let mut err = self.ecx.struct_span_err(sp, &msg);

                            err.note(&format!(
                                "did you intend to capture a variable `{}` from \
                                 the surrounding scope?",
                                name
                            ));
                            err.note(
                                "to avoid ambiguity, `format_args!` cannot capture variables \
                                 when the format string is expanded from a macro",
                            );

                            err.emit();
                        }
                    }
                }
            }
        }
    }

    /// Builds the mapping between format placeholders and argument objects.
    fn build_index_map(&mut self) {
        // NOTE: Keep the ordering the same as `into_expr`'s expansion would do!
        let args_len = self.args.len();
        self.arg_index_map.reserve(args_len);

        let mut sofar = 0usize;

        // Map the arguments
        for i in 0..args_len {
            let arg_types = &self.arg_types[i];
            let arg_offsets = arg_types.iter().map(|offset| sofar + *offset).collect::<Vec<_>>();
            self.arg_index_map.push(arg_offsets);
            sofar += self.arg_unique_types[i].len();
        }

        // Record starting index for counts, which appear just after arguments
        self.count_args_index_offset = sofar;
    }

    fn rtpath(ecx: &ExtCtxt<'_>, s: Symbol) -> Vec<Ident> {
        ecx.std_path(&[sym::fmt, sym::rt, sym::v1, s])
    }

    fn build_count(&self, c: parse::Count<'_>) -> P<ast::Expr> {
        let sp = self.macsp;
        let count = |c, arg| {
            let mut path = Context::rtpath(self.ecx, sym::Count);
            path.push(Ident::new(c, sp));
            match arg {
                Some(arg) => self.ecx.expr_call_global(sp, path, vec![arg]),
                None => self.ecx.expr_path(self.ecx.path_global(sp, path)),
            }
        };
        match c {
            parse::CountIs(i) => count(sym::Is, Some(self.ecx.expr_usize(sp, i))),
            parse::CountIsParam(i) => {
                // This needs mapping too, as `i` is referring to a macro
                // argument. If `i` is not found in `count_positions` then
                // the error had already been emitted elsewhere.
                let i = self.count_positions.get(&i).cloned().unwrap_or(0)
                    + self.count_args_index_offset;
                count(sym::Param, Some(self.ecx.expr_usize(sp, i)))
            }
            parse::CountImplied => count(sym::Implied, None),
            // should never be the case, names are already resolved
            parse::CountIsName(..) => panic!("should never happen"),
        }
    }

    /// Build a literal expression from the accumulated string literals
    fn build_literal_string(&mut self) -> P<ast::Expr> {
        let sp = self.fmtsp;
        let s = Symbol::intern(&self.literal);
        self.literal.clear();
        self.ecx.expr_str(sp, s)
    }

    /// Builds a static `rt::Argument` from a `parse::Piece` or append
    /// to the `literal` string.
    fn build_piece(
        &mut self,
        piece: &parse::Piece<'a>,
        arg_index_consumed: &mut Vec<usize>,
    ) -> Option<P<ast::Expr>> {
        let sp = self.macsp;
        match *piece {
            parse::String(s) => {
                self.literal.push_str(s);
                None
            }
            parse::NextArgument(ref arg) => {
                // Build the position
                let pos = {
                    match arg.position {
                        parse::ArgumentIs(i, ..) | parse::ArgumentImplicitlyIs(i) => {
                            // Map to index in final generated argument array
                            // in case of multiple types specified
                            let arg_idx = match arg_index_consumed.get_mut(i) {
                                None => 0, // error already emitted elsewhere
                                Some(offset) => {
                                    let idx_map = &self.arg_index_map[i];
                                    // unwrap_or branch: error already emitted elsewhere
                                    let arg_idx = *idx_map.get(*offset).unwrap_or(&0);
                                    *offset += 1;
                                    arg_idx
                                }
                            };
                            self.ecx.expr_usize(sp, arg_idx)
                        }

                        // should never be the case, because names are already
                        // resolved.
                        parse::ArgumentNamed(..) => panic!("should never happen"),
                    }
                };

                let simple_arg = parse::Argument {
                    position: {
                        // We don't have ArgumentNext any more, so we have to
                        // track the current argument ourselves.
                        let i = self.curarg;
                        self.curarg += 1;
                        parse::ArgumentIs(i)
                    },
                    position_span: arg.position_span,
                    format: parse::FormatSpec {
                        fill: None,
                        align: parse::AlignUnknown,
                        flags: 0,
                        precision: parse::CountImplied,
                        precision_span: arg.format.precision_span,
                        width: parse::CountImplied,
                        width_span: arg.format.width_span,
                        ty: arg.format.ty,
                        ty_span: arg.format.ty_span,
                    },
                };

                let fill = arg.format.fill.unwrap_or(' ');
                let pos_simple = arg.position.index() == simple_arg.position.index();

                if !pos_simple || arg.format != simple_arg.format {
                    self.all_pieces_simple = false;
                }

                // Build the format
                let fill = self.ecx.expr_char(sp, fill);
                let align = |name| {
                    let mut p = Context::rtpath(self.ecx, sym::Alignment);
                    p.push(Ident::new(name, sp));
                    self.ecx.path_global(sp, p)
                };
                let align = match arg.format.align {
                    parse::AlignLeft => align(sym::Left),
                    parse::AlignRight => align(sym::Right),
                    parse::AlignCenter => align(sym::Center),
                    parse::AlignUnknown => align(sym::Unknown),
                };
                let align = self.ecx.expr_path(align);
                let flags = self.ecx.expr_u32(sp, arg.format.flags);
                let prec = self.build_count(arg.format.precision);
                let width = self.build_count(arg.format.width);
                let path = self.ecx.path_global(sp, Context::rtpath(self.ecx, sym::FormatSpec));
                let fmt = self.ecx.expr_struct(
                    sp,
                    path,
                    vec![
                        self.ecx.field_imm(sp, Ident::new(sym::fill, sp), fill),
                        self.ecx.field_imm(sp, Ident::new(sym::align, sp), align),
                        self.ecx.field_imm(sp, Ident::new(sym::flags, sp), flags),
                        self.ecx.field_imm(sp, Ident::new(sym::precision, sp), prec),
                        self.ecx.field_imm(sp, Ident::new(sym::width, sp), width),
                    ],
                );

                let path = self.ecx.path_global(sp, Context::rtpath(self.ecx, sym::Argument));
                Some(self.ecx.expr_struct(
                    sp,
                    path,
                    vec![
                        self.ecx.field_imm(sp, Ident::new(sym::position, sp), pos),
                        self.ecx.field_imm(sp, Ident::new(sym::format, sp), fmt),
                    ],
                ))
            }
        }
    }

    /// Actually builds the expression which the format_args! block will be
    /// expanded to.
    fn into_expr(self) -> P<ast::Expr> {
        let mut original_args = self.args;
        let mut fmt_args = Vec::with_capacity(
            self.arg_unique_types.iter().map(|v| v.len()).sum::<usize>() + self.count_args.len(),
        );

        // First, build up the static array which will become our precompiled
        // format "string"
        let pieces = self.ecx.expr_array_ref(self.fmtsp, self.str_pieces);

        // We need to construct a &[ArgumentV1] to pass into the fmt::Arguments
        // constructor. In general the expressions in this slice might be
        // permuted from their order in original_args (such as in the case of
        // "{1} {0}"), or may have multiple entries referring to the same
        // element of original_args ("{0} {0}").
        //
        // The following vector has one item per element of our output slice,
        // identifying the index of which element of original_args it's passing,
        // and that argument's type.
        let mut fmt_arg_index_and_ty = SmallVec::<[(usize, &ArgumentType); 8]>::new();
        for (i, unique_types) in self.arg_unique_types.iter().enumerate() {
            fmt_arg_index_and_ty.extend(unique_types.iter().map(|ty| (i, ty)));
        }
        fmt_arg_index_and_ty.extend(self.count_args.iter().map(|&i| (i, &Count)));

        // Figure out whether there are permuted or repeated elements. If not,
        // we can generate simpler code.
        //
        // The sequence has no indices out of order or repeated if: for every
        // adjacent pair of elements, the first one's index is less than the
        // second one's index.
        let nicely_ordered =
            fmt_arg_index_and_ty.array_windows().all(|[(i, _i_ty), (j, _j_ty)]| i < j);

        // We want to emit:
        //
        //     [ArgumentV1::new(&$arg0, …), ArgumentV1::new(&$arg1, …), …]
        //
        // However, it's only legal to do so if $arg0, $arg1, … were written in
        // exactly that order by the programmer. When arguments are permuted, we
        // want them evaluated in the order written by the programmer, not in
        // the order provided to fmt::Arguments. When arguments are repeated, we
        // want the expression evaluated only once.
        //
        // Further, if any arg _after the first one_ contains a yield point such
        // as `await` or `yield`, the above short form is inconvenient for the
        // caller because it would keep a temporary of type ArgumentV1 alive
        // across the yield point. ArgumentV1 can't implement Send since it
        // holds a type-erased arbitrary type.
        //
        // Thus in the not nicely ordered case, and in the yielding case, we
        // emit the following instead:
        //
        //     match (&$arg0, &$arg1, …) {
        //         args => [ArgumentV1::new(args.$i, …), ArgumentV1::new(args.$j, …), …]
        //     }
        //
        // for the sequence of indices $i, $j, … governed by fmt_arg_index_and_ty.
        // This more verbose representation ensures that all arguments are
        // evaluated a single time each, in the order written by the programmer,
        // and that the surrounding future/generator (if any) is Send whenever
        // possible.
        let no_need_for_match = nicely_ordered
            && !original_args.iter().skip(1).any(|arg| may_contain_yield_point(&arg.expr));

        for (arg_index, arg_ty) in fmt_arg_index_and_ty {
            let e = &mut original_args[arg_index].expr;
            let span = e.span;
            let arg = if no_need_for_match {
                let expansion_span = e.span.with_ctxt(self.macsp.ctxt());
                // The indices are strictly ordered so e has not been taken yet.
                self.ecx.expr_addr_of(expansion_span, P(e.take()))
            } else {
                let def_site = self.ecx.with_def_site_ctxt(span);
                let args_tuple = self.ecx.expr_ident(def_site, Ident::new(sym::args, def_site));
                let member = Ident::new(sym::integer(arg_index), def_site);
                self.ecx.expr(def_site, ast::ExprKind::Field(args_tuple, member))
            };
            fmt_args.push(Context::format_arg(self.ecx, self.macsp, span, arg_ty, arg));
        }

        let args_array = self.ecx.expr_array(self.macsp, fmt_args);
        let args_slice = self.ecx.expr_addr_of(
            self.macsp,
            if no_need_for_match {
                args_array
            } else {
                // In the !no_need_for_match case, none of the exprs were moved
                // away in the previous loop.
                //
                // This uses the arg span for `&arg` so that borrowck errors
                // point to the specific expression passed to the macro (the
                // span is otherwise unavailable in the MIR used by borrowck).
                let heads = original_args
                    .into_iter()
                    .map(|arg| {
                        self.ecx.expr_addr_of(arg.expr.span.with_ctxt(self.macsp.ctxt()), arg.expr)
                    })
                    .collect();

                let pat = self.ecx.pat_ident(self.macsp, Ident::new(sym::args, self.macsp));
                let arm = self.ecx.arm(self.macsp, pat, args_array);
                let head = self.ecx.expr(self.macsp, ast::ExprKind::Tup(heads));
                self.ecx.expr_match(self.macsp, head, vec![arm])
            },
        );

        // Now create the fmt::Arguments struct with all our locals we created.
        let (fn_name, fn_args) = if self.all_pieces_simple {
            ("new_v1", vec![pieces, args_slice])
        } else {
            // Build up the static array which will store our precompiled
            // nonstandard placeholders, if there are any.
            let fmt = self.ecx.expr_array_ref(self.macsp, self.pieces);

            let path = self.ecx.std_path(&[sym::fmt, sym::UnsafeArg, sym::new]);
            let unsafe_arg = self.ecx.expr_call_global(self.macsp, path, Vec::new());
            let unsafe_expr = self.ecx.expr_block(P(ast::Block {
                stmts: vec![self.ecx.stmt_expr(unsafe_arg)],
                id: ast::DUMMY_NODE_ID,
                rules: BlockCheckMode::Unsafe(UnsafeSource::CompilerGenerated),
                span: self.macsp,
                tokens: None,
                could_be_bare_literal: false,
            }));

            ("new_v1_formatted", vec![pieces, args_slice, fmt, unsafe_expr])
        };

        let path = self.ecx.std_path(&[sym::fmt, sym::Arguments, Symbol::intern(fn_name)]);
        self.ecx.expr_call_global(self.macsp, path, fn_args)
    }

    fn format_arg(
        ecx: &ExtCtxt<'_>,
        macsp: Span,
        mut sp: Span,
        ty: &ArgumentType,
        arg: P<ast::Expr>,
    ) -> P<ast::Expr> {
        sp = ecx.with_def_site_ctxt(sp);
        let trait_ = match *ty {
            Placeholder(trait_) if trait_ == "<invalid>" => return DummyResult::raw_expr(sp, true),
            Placeholder(trait_) => trait_,
            Count => {
                let path = ecx.std_path(&[sym::fmt, sym::ArgumentV1, sym::from_usize]);
                return ecx.expr_call_global(macsp, path, vec![arg]);
            }
        };
        let new_fn_name = match trait_ {
            "Display" => "new_display",
            "Debug" => "new_debug",
            "LowerExp" => "new_lower_exp",
            "UpperExp" => "new_upper_exp",
            "Octal" => "new_octal",
            "Pointer" => "new_pointer",
            "Binary" => "new_binary",
            "LowerHex" => "new_lower_hex",
            "UpperHex" => "new_upper_hex",
            _ => unreachable!(),
        };

        let path = ecx.std_path(&[sym::fmt, sym::ArgumentV1, Symbol::intern(new_fn_name)]);
        ecx.expr_call_global(sp, path, vec![arg])
    }
}

fn expand_format_args_impl<'cx>(
    ecx: &'cx mut ExtCtxt<'_>,
    mut sp: Span,
    tts: TokenStream,
    nl: bool,
) -> Box<dyn base::MacResult + 'cx> {
    sp = ecx.with_def_site_ctxt(sp);
    match parse_args(ecx, sp, tts) {
        Ok((efmt, args, names)) => {
            MacEager::expr(expand_preparsed_format_args(ecx, sp, efmt, args, names, nl))
        }
        Err(mut err) => {
            err.emit();
            DummyResult::any(sp)
        }
    }
}

pub fn expand_format_args<'cx>(
    ecx: &'cx mut ExtCtxt<'_>,
    sp: Span,
    tts: TokenStream,
) -> Box<dyn base::MacResult + 'cx> {
    expand_format_args_impl(ecx, sp, tts, false)
}

pub fn expand_format_args_nl<'cx>(
    ecx: &'cx mut ExtCtxt<'_>,
    sp: Span,
    tts: TokenStream,
) -> Box<dyn base::MacResult + 'cx> {
    expand_format_args_impl(ecx, sp, tts, true)
}

fn create_lints_for_named_arguments_used_positionally(cx: &mut Context<'_, '_>) {
    for named_arg in &cx.unused_names_lint.positional_named_args {
        let (position_sp_to_replace, position_sp_for_msg) = named_arg.get_positional_arg_spans(cx);

        let msg = format!("named argument `{}` is not used by name", named_arg.replacement);

        cx.ecx.buffered_early_lint.push(BufferedEarlyLint {
            span: MultiSpan::from_span(named_arg.positional_named_arg_span),
            msg: msg.into(),
            node_id: ast::CRATE_NODE_ID,
            lint_id: LintId::of(&NAMED_ARGUMENTS_USED_POSITIONALLY),
            diagnostic: BuiltinLintDiagnostics::NamedArgumentUsedPositionally {
                position_sp_to_replace,
                position_sp_for_msg,
                named_arg_sp: named_arg.positional_named_arg_span,
                named_arg_name: named_arg.replacement.to_string(),
                is_formatting_arg: named_arg.ty != PositionalNamedArgType::Arg,
            },
        });
    }
}

/// Take the various parts of `format_args!(efmt, args..., name=names...)`
/// and construct the appropriate formatting expression.
pub fn expand_preparsed_format_args(
    ecx: &mut ExtCtxt<'_>,
    sp: Span,
    efmt: P<ast::Expr>,
    args: Vec<FormatArg>,
    names: FxHashMap<Symbol, usize>,
    append_newline: bool,
) -> P<ast::Expr> {
    // NOTE: this verbose way of initializing `Vec<Vec<ArgumentType>>` is because
    // `ArgumentType` does not derive `Clone`.
    let arg_types: Vec<_> = (0..args.len()).map(|_| Vec::new()).collect();
    let arg_unique_types: Vec<_> = (0..args.len()).map(|_| Vec::new()).collect();

    let mut macsp = ecx.call_site();
    macsp = ecx.with_def_site_ctxt(macsp);

    let msg = "format argument must be a string literal";
    let fmt_sp = efmt.span;
    let efmt_kind_is_lit: bool = matches!(efmt.kind, ast::ExprKind::Lit(_));
    let (fmt_str, fmt_style, fmt_span) = match expr_to_spanned_string(ecx, efmt, msg) {
        Ok(mut fmt) if append_newline => {
            fmt.0 = Symbol::intern(&format!("{}\n", fmt.0));
            fmt
        }
        Ok(fmt) => fmt,
        Err(err) => {
            if let Some((mut err, suggested)) = err {
                let sugg_fmt = match args.len() {
                    0 => "{}".to_string(),
                    _ => format!("{}{{}}", "{} ".repeat(args.len())),
                };
                if !suggested {
                    err.span_suggestion(
                        fmt_sp.shrink_to_lo(),
                        "you might be missing a string literal to format with",
                        format!("\"{}\", ", sugg_fmt),
                        Applicability::MaybeIncorrect,
                    );
                }
                err.emit();
            }
            return DummyResult::raw_expr(sp, true);
        }
    };

    let str_style = match fmt_style {
        ast::StrStyle::Cooked => None,
        ast::StrStyle::Raw(raw) => Some(raw as usize),
    };

    let fmt_str = fmt_str.as_str(); // for the suggestions below
    let fmt_snippet = ecx.source_map().span_to_snippet(fmt_sp).ok();
    let mut parser = parse::Parser::new(
        fmt_str,
        str_style,
        fmt_snippet,
        append_newline,
        parse::ParseMode::Format,
    );

    let mut unverified_pieces = Vec::new();
    while let Some(piece) = parser.next() {
        if !parser.errors.is_empty() {
            break;
        } else {
            unverified_pieces.push(piece);
        }
    }

    if !parser.errors.is_empty() {
        let err = parser.errors.remove(0);
        let sp = if efmt_kind_is_lit {
            fmt_span.from_inner(InnerSpan::new(err.span.start, err.span.end))
        } else {
            // The format string could be another macro invocation, e.g.:
            //     format!(concat!("abc", "{}"), 4);
            // However, `err.span` is an inner span relative to the *result* of
            // the macro invocation, which is why we would get a nonsensical
            // result calling `fmt_span.from_inner(err.span)` as above, and
            // might even end up inside a multibyte character (issue #86085).
            // Therefore, we conservatively report the error for the entire
            // argument span here.
            fmt_span
        };
        let mut e = ecx.struct_span_err(sp, &format!("invalid format string: {}", err.description));
        e.span_label(sp, err.label + " in format string");
        if let Some(note) = err.note {
            e.note(&note);
        }
        if let Some((label, span)) = err.secondary_label {
            if efmt_kind_is_lit {
                e.span_label(fmt_span.from_inner(InnerSpan::new(span.start, span.end)), label);
            }
        }
        if err.should_be_replaced_with_positional_argument {
            let captured_arg_span =
                fmt_span.from_inner(InnerSpan::new(err.span.start, err.span.end));
            let n_positional_args =
                args.iter().rposition(|arg| arg.name.is_none()).map_or(0, |i| i + 1);
            if let Ok(arg) = ecx.source_map().span_to_snippet(captured_arg_span) {
                let span = match args[..n_positional_args].last() {
                    Some(arg) => arg.expr.span,
                    None => fmt_sp,
                };
                e.multipart_suggestion_verbose(
                    "consider using a positional formatting argument instead",
                    vec![
                        (captured_arg_span, n_positional_args.to_string()),
                        (span.shrink_to_hi(), format!(", {}", arg)),
                    ],
                    Applicability::MachineApplicable,
                );
            }
        }
        e.emit();
        return DummyResult::raw_expr(sp, true);
    }

    let arg_spans = parser
        .arg_places
        .iter()
        .map(|span| fmt_span.from_inner(InnerSpan::new(span.start, span.end)))
        .collect();

    let mut cx = Context {
        ecx,
        args,
        num_captured_args: 0,
        arg_types,
        arg_unique_types,
        names,
        curarg: 0,
        curpiece: 0,
        arg_index_map: Vec::new(),
        count_args: Vec::new(),
        count_positions: FxHashMap::default(),
        count_positions_count: 0,
        count_args_index_offset: 0,
        literal: String::new(),
        pieces: Vec::with_capacity(unverified_pieces.len()),
        str_pieces: Vec::with_capacity(unverified_pieces.len()),
        all_pieces_simple: true,
        macsp,
        fmtsp: fmt_span,
        invalid_refs: Vec::new(),
        arg_spans,
        arg_with_formatting: Vec::new(),
        is_literal: parser.is_literal,
        unused_names_lint: PositionalNamedArgsLint { positional_named_args: vec![] },
    };

    // This needs to happen *after* the Parser has consumed all pieces to create all the spans
    let pieces = unverified_pieces
        .into_iter()
        .map(|mut piece| {
            cx.verify_piece(&piece);
            cx.resolve_name_inplace(&mut piece);
            piece
        })
        .collect::<Vec<_>>();

    let numbered_position_args = pieces.iter().any(|arg: &parse::Piece<'_>| match *arg {
        parse::String(_) => false,
        parse::NextArgument(arg) => matches!(arg.position, parse::Position::ArgumentIs(..)),
    });

    cx.build_index_map();

    let mut arg_index_consumed = vec![0usize; cx.arg_index_map.len()];

    for piece in pieces {
        if let Some(piece) = cx.build_piece(&piece, &mut arg_index_consumed) {
            let s = cx.build_literal_string();
            cx.str_pieces.push(s);
            cx.pieces.push(piece);
        }
    }

    if !cx.literal.is_empty() {
        let s = cx.build_literal_string();
        cx.str_pieces.push(s);
    }

    if !cx.invalid_refs.is_empty() {
        cx.report_invalid_references(numbered_position_args);
    }

    // Make sure that all arguments were used and all arguments have types.
    let errs = cx
        .arg_types
        .iter()
        .enumerate()
        .filter(|(i, ty)| ty.is_empty() && !cx.count_positions.contains_key(&i))
        .map(|(i, _)| {
            let msg = if cx.args[i].name.is_some() {
                "named argument never used"
            } else {
                "argument never used"
            };
            (cx.args[i].expr.span, msg)
        })
        .collect::<Vec<_>>();

    let errs_len = errs.len();
    if !errs.is_empty() {
        let args_used = cx.arg_types.len() - errs_len;
        let args_unused = errs_len;

        let mut diag = {
            if let [(sp, msg)] = &errs[..] {
                let mut diag = cx.ecx.struct_span_err(*sp, *msg);
                diag.span_label(*sp, *msg);
                diag
            } else {
                let mut diag = cx.ecx.struct_span_err(
                    errs.iter().map(|&(sp, _)| sp).collect::<Vec<Span>>(),
                    "multiple unused formatting arguments",
                );
                diag.span_label(cx.fmtsp, "multiple missing formatting specifiers");
                for (sp, msg) in errs {
                    diag.span_label(sp, msg);
                }
                diag
            }
        };

        // Used to ensure we only report translations for *one* kind of foreign format.
        let mut found_foreign = false;
        // Decide if we want to look for foreign formatting directives.
        if args_used < args_unused {
            use super::format_foreign as foreign;

            // The set of foreign substitutions we've explained.  This prevents spamming the user
            // with `%d should be written as {}` over and over again.
            let mut explained = FxHashSet::default();

            macro_rules! check_foreign {
                ($kind:ident) => {{
                    let mut show_doc_note = false;

                    let mut suggestions = vec![];
                    // account for `"` and account for raw strings `r#`
                    let padding = str_style.map(|i| i + 2).unwrap_or(1);
                    for sub in foreign::$kind::iter_subs(fmt_str, padding) {
                        let (trn, success) = match sub.translate() {
                            Ok(trn) => (trn, true),
                            Err(Some(msg)) => (msg, false),

                            // If it has no translation, don't call it out specifically.
                            _ => continue,
                        };

                        let pos = sub.position();
                        let sub = String::from(sub.as_str());
                        if explained.contains(&sub) {
                            continue;
                        }
                        explained.insert(sub.clone());

                        if !found_foreign {
                            found_foreign = true;
                            show_doc_note = true;
                        }

                        if let Some(inner_sp) = pos {
                            let sp = fmt_sp.from_inner(inner_sp);

                            if success {
                                suggestions.push((sp, trn));
                            } else {
                                diag.span_note(
                                    sp,
                                    &format!("format specifiers use curly braces, and {}", trn),
                                );
                            }
                        } else {
                            if success {
                                diag.help(&format!("`{}` should be written as `{}`", sub, trn));
                            } else {
                                diag.note(&format!(
                                    "`{}` should use curly braces, and {}",
                                    sub, trn
                                ));
                            }
                        }
                    }

                    if show_doc_note {
                        diag.note(concat!(
                            stringify!($kind),
                            " formatting not supported; see the documentation for `std::fmt`",
                        ));
                    }
                    if suggestions.len() > 0 {
                        diag.multipart_suggestion(
                            "format specifiers use curly braces",
                            suggestions,
                            Applicability::MachineApplicable,
                        );
                    }
                }};
            }

            check_foreign!(printf);
            if !found_foreign {
                check_foreign!(shell);
            }
        }
        if !found_foreign && errs_len == 1 {
            diag.span_label(cx.fmtsp, "formatting specifier missing");
        }

        diag.emit();
    } else if cx.invalid_refs.is_empty() && cx.ecx.sess.err_count() == 0 {
        // Only check for unused named argument names if there are no other errors to avoid causing
        // too much noise in output errors, such as when a named argument is entirely unused.
        create_lints_for_named_arguments_used_positionally(&mut cx);
    }

    cx.into_expr()
}

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
}