format_args.rs

use std::collections::hash_map::Entry;

use arrayvec::ArrayVec;
use clippy_config::Conf;
use clippy_utils::diagnostics::{span_lint, span_lint_and_help, span_lint_and_sugg, span_lint_and_then};
use clippy_utils::macros::{
    FormatArgsStorage, FormatParamUsage, MacroCall, find_format_arg_expr, format_arg_removal_span,
    format_placeholder_format_span, is_assert_macro, is_format_macro, is_panic, matching_root_macro_call,
    root_macro_call_first_node,
};
use clippy_utils::msrvs::{self, Msrv};
use clippy_utils::res::MaybeDef;
use clippy_utils::source::{SpanRangeExt, snippet, snippet_opt};
use clippy_utils::ty::implements_trait;
use clippy_utils::{is_from_proc_macro, is_in_test, peel_hir_expr_while, sym, trait_ref_of_method};
use itertools::Itertools;
use rustc_ast::FormatTrait::{Binary, Debug, Display, LowerExp, LowerHex, Octal, Pointer, UpperExp, UpperHex};
use rustc_ast::{
    BorrowKind, FormatArgPosition, FormatArgPositionKind, FormatArgsPiece, FormatArgumentKind, FormatCount,
    FormatOptions, FormatPlaceholder,
};
use rustc_data_structures::fx::FxHashMap;
use rustc_errors::Applicability;
use rustc_errors::SuggestionStyle::{CompletelyHidden, ShowCode};
use rustc_hir::{Expr, ExprKind, LangItem, RustcVersion, find_attr};
use rustc_lint::{LateContext, LateLintPass, LintContext};
use rustc_middle::ty::adjustment::{Adjust, Adjustment, DerefAdjustKind};
use rustc_middle::ty::{self, GenericArg, List, TraitRef, Ty, TyCtxt, Unnormalized, Upcast};
use rustc_session::impl_lint_pass;
use rustc_span::edition::Edition::Edition2021;
use rustc_span::{BytePos, Pos, Span, Symbol};
use rustc_trait_selection::infer::TyCtxtInferExt;
use rustc_trait_selection::traits::{Obligation, ObligationCause, Selection, SelectionContext};

declare_clippy_lint! {
    /// ### What it does
    /// Detects `format!` within the arguments of another macro that does
    /// formatting such as `format!` itself, `write!` or `println!`. Suggests
    /// inlining the `format!` call.
    ///
    /// ### Why is this bad?
    /// The recommended code is both shorter and avoids a temporary allocation.
    ///
    /// ### Example
    /// ```no_run
    /// # use std::panic::Location;
    /// println!("error: {}", format!("something failed at {}", Location::caller()));
    /// ```
    /// Use instead:
    /// ```no_run
    /// # use std::panic::Location;
    /// println!("error: something failed at {}", Location::caller());
    /// ```
    #[clippy::version = "1.58.0"]
    pub FORMAT_IN_FORMAT_ARGS,
    perf,
    "`format!` used in a macro that does formatting"
}

declare_clippy_lint! {
    /// ### What it does
    /// Detects [pointer format] as well as `Debug` formatting of raw pointers or function pointers
    /// or any types that have a derived `Debug` impl that recursively contains them.
    ///
    /// ### Why restrict this?
    /// The addresses are only useful in very specific contexts, and certain projects may want to keep addresses of
    /// certain data structures or functions from prying hacker eyes as an additional line of security.
    ///
    /// ### Known problems
    /// The lint currently only looks through derived `Debug` implementations. Checking whether a manual
    /// implementation prints an address is left as an exercise to the next lint implementer.
    ///
    /// ### Example
    /// ```no_run
    /// let foo = &0_u32;
    /// fn bar() {}
    /// println!("{:p}", foo);
    /// let _ = format!("{:?}", &(bar as fn()));
    /// ```
    ///
    /// [pointer format]: https://doc.rust-lang.org/std/fmt/index.html#formatting-traits
    #[clippy::version = "1.89.0"]
    pub POINTER_FORMAT,
    restriction,
    "formatting a pointer"
}

declare_clippy_lint! {
    /// ### What it does
    /// Checks for [`ToString::to_string`](https://doc.rust-lang.org/std/string/trait.ToString.html#tymethod.to_string)
    /// applied to a type that implements [`Display`](https://doc.rust-lang.org/std/fmt/trait.Display.html)
    /// in a macro that does formatting.
    ///
    /// ### Why is this bad?
    /// Since the type implements `Display`, the use of `to_string` is
    /// unnecessary.
    ///
    /// ### Example
    /// ```no_run
    /// # use std::panic::Location;
    /// println!("error: something failed at {}", Location::caller().to_string());
    /// ```
    /// Use instead:
    /// ```no_run
    /// # use std::panic::Location;
    /// println!("error: something failed at {}", Location::caller());
    /// ```
    #[clippy::version = "1.58.0"]
    pub TO_STRING_IN_FORMAT_ARGS,
    perf,
    "`to_string` applied to a type that implements `Display` in format args"
}

declare_clippy_lint! {
    /// ### What it does
    /// Detect when a variable is not inlined in a format string,
    /// and suggests to inline it.
    ///
    /// ### Why is this bad?
    /// Non-inlined code is slightly more difficult to read and understand,
    /// as it requires arguments to be matched against the format string.
    /// The inlined syntax, where allowed, is simpler.
    ///
    /// ### Example
    /// ```no_run
    /// # let var = 42;
    /// # let width = 1;
    /// # let prec = 2;
    /// format!("{}", var);
    /// format!("{:?}", var);
    /// format!("{v:?}", v = var);
    /// format!("{0} {0}", var);
    /// format!("{0:1$}", var, width);
    /// format!("{:.*}", prec, var);
    /// ```
    /// Use instead:
    /// ```no_run
    /// # let var = 42;
    /// # let width = 1;
    /// # let prec = 2;
    /// format!("{var}");
    /// format!("{var:?}");
    /// format!("{var:?}");
    /// format!("{var} {var}");
    /// format!("{var:width$}");
    /// format!("{var:.prec$}");
    /// ```
    ///
    /// If `allow-mixed-uninlined-format-args` is set to `false` in clippy.toml,
    /// the following code will also trigger the lint:
    /// ```no_run
    /// # let var = 42;
    /// format!("{} {}", var, 1+2);
    /// ```
    /// Use instead:
    /// ```no_run
    /// # let var = 42;
    /// format!("{var} {}", 1+2);
    /// ```
    ///
    /// ### Known Problems
    ///
    /// If a format string contains a numbered argument that cannot be inlined
    /// nothing will be suggested, e.g. `println!("{0}={1}", var, 1+2)`.
    #[clippy::version = "1.66.0"]
    pub UNINLINED_FORMAT_ARGS,
    pedantic,
    "using non-inlined variables in `format!` calls"
}

declare_clippy_lint! {
    /// ### What it does
    /// Checks for `Debug` formatting (`{:?}`) applied to an `OsStr` or `Path`.
    ///
    /// This includes:
    /// - Format specifiers on `format_args!()` (width, precision have no effect)
    /// - Format width too small for the format trait (e.g. `{:#02x}` outputs "0x1"
    ///   so width 2 has no effect; minimum is 4 for alternate hex/octal/binary)
    ///
    /// ### Why is this bad?
    /// Rust doesn't guarantee what `Debug` formatting looks like, and it could
    /// change in the future. `OsStr`s and `Path`s can be `Display` formatted
    /// using their `display` methods.
    ///
    /// Furthermore, with `Debug` formatting, certain characters are escaped.
    /// Thus, a `Debug` formatted `Path` is less likely to be clickable.
    ///
    /// ### Example
    /// ```no_run
    /// # use std::path::Path;
    /// let path = Path::new("...");
    /// println!("The path is {:?}", path);
    /// ```
    /// Use instead:
    /// ```no_run
    /// # use std::path::Path;
    /// let path = Path::new("…");
    /// println!("The path is {}", path.display());
    /// ```
    #[clippy::version = "1.87.0"]
    pub UNNECESSARY_DEBUG_FORMATTING,
    pedantic,
    "`Debug` formatting applied to an `OsStr` or `Path` when `.display()` is available"
}

declare_clippy_lint! {
    /// ### What it does
    /// Suggests removing an unnecessary trailing comma before the closing parenthesis in
    /// single-line macro invocations.
    ///
    /// ### Why is this bad?
    /// The trailing comma is redundant and removing it is more consistent with how
    /// `rustfmt` formats regular function calls.
    ///
    /// ### Known limitations
    /// This lint currently only runs on format-like macros (e.g. `format!`, `println!`,
    /// `write!`) because it relies on format-argument parsing; applying it to arbitrary
    /// user macros could cause incorrect suggestions. It may be extended to other
    /// macros in the future. Only single-line macro invocations are linted.
    ///
    /// ### Example
    /// ```no_run
    /// println!("Foo={}", 1,);
    /// ```
    /// Use instead:
    /// ```no_run
    /// println!("Foo={}", 1);
    /// ```
    #[clippy::version = "1.95.0"]
    pub UNNECESSARY_TRAILING_COMMA,
    pedantic,
    "unnecessary trailing comma before closing parenthesis"
}

declare_clippy_lint! {
    /// ### What it does
    /// Detects [formatting parameters] that have no effect on the output of
    /// `format!()`, `println!()` or similar macros.
    ///
    /// This includes:
    /// - Format specifiers on `format_args!()` (width, precision have no effect)
    /// - Format width too small for the format trait (e.g. `{:#02x}` outputs "0x1"
    ///   so width 2 has no effect; minimum is 4 for alternate hex/octal/binary)
    ///
    /// ### Why is this bad?
    /// Shorter format specifiers are easier to read, it may also indicate that
    /// an expected formatting operation such as adding padding isn't happening.
    ///
    /// ### Example
    /// ```no_run
    /// println!("{:.}", 1.0);
    ///
    /// println!("not padded: {:5}", format_args!("..."));
    ///
    /// // width 2 has no effect for alternate hex (outputs "0x1")
    /// format!("{:#02x}", 1_u8);
    /// ```
    /// Use instead:
    /// ```no_run
    /// println!("{}", 1.0);
    ///
    /// println!("not padded: {}", format_args!("..."));
    /// // OR
    /// println!("padded: {:5}", format!("..."));
    ///
    /// format!("{:#04x}", 1_u8);  // width 4 for two-digit zero-padded hex
    /// ```
    ///
    /// [formatting parameters]: https://doc.rust-lang.org/std/fmt/index.html#formatting-parameters
    #[clippy::version = "1.66.0"]
    pub UNUSED_FORMAT_SPECS,
    complexity,
    "use of a format specifier that has no effect"
}

declare_clippy_lint! {
    /// ### What it does
    /// Detects format!-style macros (e.g. `format!`, `println!`, `write!`) where an argument
    /// is passed with an explicit `&` but the value is already a reference, resulting in a
    /// double reference (e.g. `&&T`).
    ///
    /// ### Why is this bad?
    /// The extra `&` is redundant and can make the code less clear. Format macros take
    /// references to the arguments internally, so passing `&x` when `x` is already a
    /// reference produces a double reference. The compiler is currently unable to
    /// optimize double references, which results in about 6% degradation per call.
    ///
    /// ### Example
    /// ```no_run
    /// let s: &str = "hello";
    /// println!("{}", &s);
    /// ```
    /// Use instead:
    /// ```no_run
    /// let s: &str = "hello";
    /// println!("{}", s);
    /// ```
    #[clippy::version = "1.97.0"]
    pub USELESS_BORROWS_IN_FORMATTING,
    perf,
    "redundant reference in format args causes double reference"
}

impl_lint_pass!(FormatArgs<'_> => [
    FORMAT_IN_FORMAT_ARGS,
    POINTER_FORMAT,
    TO_STRING_IN_FORMAT_ARGS,
    UNINLINED_FORMAT_ARGS,
    UNNECESSARY_DEBUG_FORMATTING,
    UNNECESSARY_TRAILING_COMMA,
    UNUSED_FORMAT_SPECS,
    USELESS_BORROWS_IN_FORMATTING,
]);

#[expect(clippy::struct_field_names)]
pub struct FormatArgs<'tcx> {
    format_args: FormatArgsStorage,
    msrv: Msrv,
    ignore_mixed: bool,
    ty_msrv_map: FxHashMap<Ty<'tcx>, Option<RustcVersion>>,
    has_derived_debug: FxHashMap<Ty<'tcx>, bool>,
    has_pointer_format: FxHashMap<Ty<'tcx>, bool>,
}

impl<'tcx> FormatArgs<'tcx> {
    pub fn new(tcx: TyCtxt<'tcx>, conf: &'static Conf, format_args: FormatArgsStorage) -> Self {
        let ty_msrv_map = make_ty_msrv_map(tcx);
        Self {
            format_args,
            msrv: conf.msrv,
            ignore_mixed: conf.allow_mixed_uninlined_format_args,
            ty_msrv_map,
            has_derived_debug: FxHashMap::default(),
            has_pointer_format: FxHashMap::default(),
        }
    }
}

impl<'tcx> LateLintPass<'tcx> for FormatArgs<'tcx> {
    fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) {
        if let Some(macro_call) = root_macro_call_first_node(cx, expr)
            && is_format_macro(cx, macro_call.def_id)
            && let Some(format_args) = self.format_args.get(cx, expr, macro_call.expn)
        {
            let mut linter = FormatArgsExpr {
                cx,
                expr,
                macro_call: &macro_call,
                format_args,
                ignore_mixed: self.ignore_mixed,
                msrv: &self.msrv,
                ty_msrv_map: &self.ty_msrv_map,
                has_derived_debug: &mut self.has_derived_debug,
                has_pointer_format: &mut self.has_pointer_format,
            };

            linter.check_trailing_comma();
            linter.check_templates();

            if self.msrv.meets(cx, msrvs::FORMAT_ARGS_CAPTURE) {
                linter.check_uninlined_args();
            }
        }
    }
}

struct FormatArgsExpr<'a, 'tcx> {
    cx: &'a LateContext<'tcx>,
    expr: &'tcx Expr<'tcx>,
    macro_call: &'a MacroCall,
    format_args: &'a rustc_ast::FormatArgs,
    ignore_mixed: bool,
    msrv: &'a Msrv,
    ty_msrv_map: &'a FxHashMap<Ty<'tcx>, Option<RustcVersion>>,
    has_derived_debug: &'a mut FxHashMap<Ty<'tcx>, bool>,
    has_pointer_format: &'a mut FxHashMap<Ty<'tcx>, bool>,
}

impl<'tcx> FormatArgsExpr<'_, 'tcx> {
    /// Check if there is a comma after the last format macro arg.
    fn check_trailing_comma(&self) {
        let span = self.macro_call.span;
        if let Some(src) = span.get_source_text(self.cx)
            && let Some(src) = src.strip_suffix([')', ']', '}'])
            && let src = src.trim_end_matches(|c: char| c.is_whitespace() && c != '\n')
            && let Some(src) = src.strip_suffix(',')
            && let src = src.trim_end_matches(|c: char| c.is_whitespace() && c != '\n')
            && !src.ends_with('\n')
        {
            span_lint_and_sugg(
                self.cx,
                UNNECESSARY_TRAILING_COMMA,
                span.with_lo(span.lo() + BytePos::from_usize(src.len()))
                    .with_hi(span.hi() - BytePos(1)),
                "unnecessary trailing comma",
                "remove the trailing comma",
                String::new(),
                Applicability::MachineApplicable,
            );
        }
    }

    fn check_templates(&mut self) {
        for piece in &self.format_args.template {
            if let FormatArgsPiece::Placeholder(placeholder) = piece
                && let Ok(index) = placeholder.argument.index
                && let Some(arg) = self.format_args.arguments.all_args().get(index)
                && let Some(arg_expr) = find_format_arg_expr(self.expr, arg)
            {
                self.check_unused_format_specifier(placeholder, arg_expr);
                self.check_useless_format_width(placeholder);
                self.check_useless_borrows_in_formatting(placeholder, arg_expr);

                // Check width and precision arguments the same way as the value
                for opt in [&placeholder.format_options.width, &placeholder.format_options.precision] {
                    if let Some(FormatCount::Argument(position)) = opt.as_ref()
                        && let Ok(pos_index) = position.index
                        && let Some(pos_arg) = self.format_args.arguments.all_args().get(pos_index)
                        && let Some(pos_arg_expr) = find_format_arg_expr(self.expr, pos_arg)
                    {
                        self.check_useless_borrows_in_formatting(placeholder, pos_arg_expr);
                    }
                }

                if placeholder.format_trait == Display
                    && placeholder.format_options == FormatOptions::default()
                    && !self.is_aliased(index)
                {
                    let name = self.cx.tcx.item_name(self.macro_call.def_id);
                    self.check_format_in_format_args(name, arg_expr);
                    self.check_to_string_in_format_args(name, arg_expr);
                }

                if placeholder.format_trait == Debug {
                    let name = self.cx.tcx.item_name(self.macro_call.def_id);
                    self.check_unnecessary_debug_formatting(name, arg_expr);
                    if let Some(span) = placeholder.span
                        && self.has_pointer_debug(self.cx.typeck_results().expr_ty(arg_expr), 0)
                    {
                        span_lint(self.cx, POINTER_FORMAT, span, "pointer formatting detected");
                    }
                }

                if placeholder.format_trait == Pointer
                    && let Some(span) = placeholder.span
                {
                    span_lint(self.cx, POINTER_FORMAT, span, "pointer formatting detected");
                }
            }
        }
    }

    fn check_useless_borrows_in_formatting(&self, placeholder: &FormatPlaceholder, arg_expr: &Expr<'tcx>) {
        if !arg_expr.span.from_expansion()
            && !is_from_proc_macro(self.cx, arg_expr)
            && let Some(fmt_trait) = match placeholder.format_trait {
                Display => self.cx.tcx.get_diagnostic_item(sym::Display),
                Debug => self.cx.tcx.get_diagnostic_item(sym::Debug),
                _ => None,
            }
            && let Some(sized_trait) = self.cx.tcx.lang_items().sized_trait()
            && let peeled_expr = peel_hir_expr_while(arg_expr, |e| {
                // Need to handle `&&&T` to `&T` when a single ref is still required
                if let ExprKind::AddrOf(BorrowKind::Ref, _, e) = e.kind
                    && let ty = self.cx.typeck_results().expr_ty(e)
                    && implements_trait(self.cx, ty, sized_trait, &[])
                    && implements_trait(self.cx, ty, fmt_trait, &[])
                {
                    Some(e)
                } else {
                    None
                }
            })
            && !std::ptr::eq(arg_expr, peeled_expr)
            && let Some(peeled_snippet) = snippet_opt(self.cx, peeled_expr.span)
        {
            let name = self.cx.tcx.item_name(self.macro_call.def_id);
            span_lint_and_sugg(
                self.cx,
                USELESS_BORROWS_IN_FORMATTING,
                arg_expr.span,
                format!("redundant reference in `{name}!` argument"),
                "remove the redundant `&`",
                peeled_snippet,
                Applicability::MachineApplicable,
            );
        }
    }

    fn check_unused_format_specifier(&self, placeholder: &FormatPlaceholder, arg: &Expr<'_>) {
        let options = &placeholder.format_options;

        if let Some(placeholder_span) = placeholder.span
            && *options != FormatOptions::default()
            && let ty = self.cx.typeck_results().expr_ty(arg).peel_refs()
            && ty.is_lang_item(self.cx, LangItem::FormatArguments)
        {
            span_lint_and_then(
                self.cx,
                UNUSED_FORMAT_SPECS,
                placeholder_span,
                "format specifiers have no effect on `format_args!()`",
                |diag| {
                    let mut suggest_format = |spec| {
                        let message = format!("for the {spec} to apply consider using `format!()`");

                        if let Some(mac_call) = matching_root_macro_call(self.cx, arg.span, sym::format_args_macro) {
                            diag.span_suggestion(
                                self.cx.sess().source_map().span_until_char(mac_call.span, '!'),
                                message,
                                "format",
                                Applicability::MaybeIncorrect,
                            );
                        } else {
                            diag.help(message);
                        }
                    };

                    if options.width.is_some() {
                        suggest_format("width");
                    }

                    if options.precision.is_some() {
                        suggest_format("precision");
                    }

                    if let Some(format_span) = format_placeholder_format_span(placeholder) {
                        diag.span_suggestion_verbose(
                            format_span,
                            "if the current behavior is intentional, remove the format specifiers",
                            "",
                            Applicability::MaybeIncorrect,
                        );
                    }
                },
            );
        }
    }

    /// Lint when format width has no effect on the output because the format trait's
    /// minimum output is larger (e.g. `{:#02X}` outputs "0x1" so width 2 has no effect).
    fn check_useless_format_width(&self, placeholder: &FormatPlaceholder) {
        let min_width = match placeholder.format_trait {
            // 0x prefix, e.g. 0x1, 0o1, 0b1
            LowerHex | UpperHex | Octal | Binary if placeholder.format_options.alternate => 4,
            LowerExp | UpperExp | Pointer => 4, // e.g. 1e0 with exponent, 0x1 for pointer
            _ => return,
        };
        if let Some(FormatCount::Literal(width_value)) = placeholder.format_options.width
            && width_value < min_width
            && let Some(placeholder_span) = placeholder.span
        {
            span_lint_and_help(
                self.cx,
                UNUSED_FORMAT_SPECS,
                placeholder_span,
                "format width has no effect on the output for this format trait",
                None,
                format!("consider removing the width or increasing it to at least {min_width}"),
            );
        }
    }

    fn check_uninlined_args(&self) {
        if self.format_args.span.from_expansion() {
            return;
        }
        if self.macro_call.span.edition() < Edition2021
            && (is_panic(self.cx, self.macro_call.def_id) || is_assert_macro(self.cx, self.macro_call.def_id))
        {
            // panic!, assert!, and debug_assert! before 2021 edition considers a single string argument as
            // non-format
            return;
        }

        let mut fixes = Vec::new();
        // If any of the arguments are referenced by an index number,
        // and that argument is not a simple variable and cannot be inlined,
        // we cannot remove any other arguments in the format string,
        // because the index numbers might be wrong after inlining.
        // Example of an un-inlinable format:  print!("{}{1}", foo, 2)
        for (pos, usage) in self.format_arg_positions() {
            if !self.check_one_arg(pos, usage, &mut fixes) {
                return;
            }
        }

        if fixes.is_empty() {
            return;
        }

        // multiline span display suggestion is sometimes broken: https://github.com/rust-lang/rust/pull/102729#discussion_r988704308
        // in those cases, make the code suggestion hidden
        let multiline_fix = fixes
            .iter()
            .any(|(span, _)| self.cx.sess().source_map().is_multiline(*span));

        // Suggest removing each argument only once, for example in `format!("{0} {0}", arg)`.
        fixes.sort_unstable_by_key(|(span, _)| *span);
        fixes.dedup_by_key(|(span, _)| *span);

        span_lint_and_then(
            self.cx,
            UNINLINED_FORMAT_ARGS,
            self.macro_call.span,
            "variables can be used directly in the `format!` string",
            |diag| {
                diag.multipart_suggestion_with_style(
                    "change this to",
                    fixes,
                    Applicability::MachineApplicable,
                    if multiline_fix { CompletelyHidden } else { ShowCode },
                );
            },
        );
    }

    fn check_one_arg(&self, pos: &FormatArgPosition, usage: FormatParamUsage, fixes: &mut Vec<(Span, String)>) -> bool {
        let index = pos.index.unwrap();
        let arg = &self.format_args.arguments.all_args()[index];

        if !matches!(arg.kind, FormatArgumentKind::Captured(_))
            && let rustc_ast::ExprKind::Path(None, path) = &arg.expr.kind
            && let [segment] = path.segments.as_slice()
            && segment.args.is_none()
            && let Some(arg_span) = format_arg_removal_span(self.format_args, index)
            && let Some(pos_span) = pos.span
        {
            let replacement = match usage {
                FormatParamUsage::Argument => segment.ident.name.to_string(),
                FormatParamUsage::Width => format!("{}$", segment.ident.name),
                FormatParamUsage::Precision => format!(".{}$", segment.ident.name),
            };
            fixes.push((pos_span, replacement));
            fixes.push((arg_span, String::new()));
            true // successful inlining, continue checking
        } else {
            // Do not continue inlining (return false) in case
            // * if we can't inline a numbered argument, e.g. `print!("{0} ...", foo.bar, ...)`
            // * if allow_mixed_uninlined_format_args is false and this arg hasn't been inlined already
            pos.kind != FormatArgPositionKind::Number
                && (!self.ignore_mixed || matches!(arg.kind, FormatArgumentKind::Captured(_)))
        }
    }

    fn check_format_in_format_args(&self, name: Symbol, arg: &Expr<'_>) {
        let expn_data = arg.span.ctxt().outer_expn_data();
        if expn_data.call_site.from_expansion() {
            return;
        }
        let Some(mac_id) = expn_data.macro_def_id else { return };
        if !self.cx.tcx.is_diagnostic_item(sym::format_macro, mac_id) {
            return;
        }
        span_lint_and_then(
            self.cx,
            FORMAT_IN_FORMAT_ARGS,
            self.macro_call.span,
            format!("`format!` in `{name}!` args"),
            |diag| {
                diag.help(format!(
                    "combine the `format!(..)` arguments with the outer `{name}!(..)` call"
                ));
                diag.help("or consider changing `format!` to `format_args!`");
            },
        );
    }

    fn check_to_string_in_format_args(&self, name: Symbol, value: &Expr<'_>) {
        let cx = self.cx;
        if !value.span.from_expansion()
            && let ExprKind::MethodCall(_, receiver, [], to_string_span) = value.kind
            && cx
                .typeck_results()
                .type_dependent_def_id(value.hir_id)
                .opt_parent(cx)
                .is_diag_item(cx, sym::ToString)
            && let receiver_ty = cx.typeck_results().expr_ty(receiver)
            && let Some(display_trait_id) = cx.tcx.get_diagnostic_item(sym::Display)
            && let (n_needed_derefs, target) =
                count_needed_derefs(receiver_ty, cx.typeck_results().expr_adjustments(receiver).iter())
            && implements_trait(cx, target, display_trait_id, &[])
            && let Some(sized_trait_id) = cx.tcx.lang_items().sized_trait()
            && let Some(receiver_snippet) = receiver.span.source_callsite().get_source_text(cx)
        {
            let needs_ref = !implements_trait(cx, receiver_ty, sized_trait_id, &[]);
            if n_needed_derefs == 0 && !needs_ref {
                span_lint_and_sugg(
                    cx,
                    TO_STRING_IN_FORMAT_ARGS,
                    to_string_span.with_lo(receiver.span.source_callsite().hi()),
                    format!("`to_string` applied to a type that implements `Display` in `{name}!` args"),
                    "remove this",
                    String::new(),
                    Applicability::MachineApplicable,
                );
            } else {
                span_lint_and_sugg(
                    cx,
                    TO_STRING_IN_FORMAT_ARGS,
                    value.span,
                    format!("`to_string` applied to a type that implements `Display` in `{name}!` args"),
                    "use this",
                    format!(
                        "{}{:*>n_needed_derefs$}{receiver_snippet}",
                        if needs_ref { "&" } else { "" },
                        ""
                    ),
                    Applicability::MachineApplicable,
                );
            }
        }
    }

    fn check_unnecessary_debug_formatting(&self, name: Symbol, value: &Expr<'tcx>) {
        let cx = self.cx;
        if !is_in_test(cx.tcx, value.hir_id)
            && !value.span.from_expansion()
            && !is_from_proc_macro(cx, value)
            && let ty = cx.typeck_results().expr_ty(value)
            && self.can_display_format(ty)
        {
            // If the parent function is a method of `Debug`, we don't want to lint
            // because it is likely that the user wants to use `Debug` formatting.
            let parent_fn = cx.tcx.hir_get_parent_item(value.hir_id);
            if let Some(trait_ref) = trait_ref_of_method(cx, parent_fn)
                && let Some(trait_def_id) = trait_ref.trait_def_id()
                && cx.tcx.is_diagnostic_item(sym::Debug, trait_def_id)
            {
                return;
            }

            let snippet = snippet(cx.sess(), value.span, "..");
            span_lint_and_then(
                cx,
                UNNECESSARY_DEBUG_FORMATTING,
                value.span,
                format!("unnecessary `Debug` formatting in `{name}!` args"),
                |diag| {
                    diag.help(format!(
                        "use `Display` formatting and change this to `{snippet}.display()`"
                    ));
                    diag.note(
                        "switching to `Display` formatting will change how the value is shown; \
                         escaped characters will no longer be escaped and surrounding quotes will \
                         be removed",
                    );
                },
            );
        }
    }

    fn format_arg_positions(&self) -> impl Iterator<Item = (&FormatArgPosition, FormatParamUsage)> {
        self.format_args.template.iter().flat_map(|piece| match piece {
            FormatArgsPiece::Placeholder(placeholder) => {
                let mut positions = ArrayVec::<_, 3>::new();

                positions.push((&placeholder.argument, FormatParamUsage::Argument));
                if let Some(FormatCount::Argument(position)) = &placeholder.format_options.width {
                    positions.push((position, FormatParamUsage::Width));
                }
                if let Some(FormatCount::Argument(position)) = &placeholder.format_options.precision {
                    positions.push((position, FormatParamUsage::Precision));
                }

                positions
            },
            FormatArgsPiece::Literal(_) => ArrayVec::new(),
        })
    }

    /// Returns true if the format argument at `index` is referred to by multiple format params
    fn is_aliased(&self, index: usize) -> bool {
        self.format_arg_positions()
            .filter(|(position, _)| position.index == Ok(index))
            .at_most_one()
            .is_err()
    }

    fn can_display_format(&self, ty: Ty<'tcx>) -> bool {
        let ty = ty.peel_refs();

        if let Some(msrv) = self.ty_msrv_map.get(&ty)
            && msrv.is_none_or(|msrv| self.msrv.meets(self.cx, msrv))
        {
            return true;
        }

        // Even if `ty` is not in `self.ty_msrv_map`, check whether `ty` implements `Deref` with
        // a `Target` that is in `self.ty_msrv_map`.
        if let Some(deref_trait_id) = self.cx.tcx.lang_items().deref_trait()
            && implements_trait(self.cx, ty, deref_trait_id, &[])
            && let Some(target_ty) = self.cx.get_associated_type(ty, deref_trait_id, sym::Target)
            && let Some(msrv) = self.ty_msrv_map.get(&target_ty)
            && msrv.is_none_or(|msrv| self.msrv.meets(self.cx, msrv))
        {
            return true;
        }

        false
    }

    fn has_pointer_debug(&mut self, ty: Ty<'tcx>, depth: usize) -> bool {
        let cx = self.cx;
        let tcx = cx.tcx;
        if !tcx.recursion_limit().value_within_limit(depth) {
            return false;
        }
        let depth = depth + 1;
        let typing_env = cx.typing_env();
        let ty = tcx.normalize_erasing_regions(typing_env, Unnormalized::new_wip(ty));
        match ty.kind() {
            ty::RawPtr(..) | ty::FnPtr(..) | ty::FnDef(..) => true,
            ty::Ref(_, t, _) | ty::Slice(t) | ty::Array(t, _) => self.has_pointer_debug(*t, depth),
            ty::Tuple(ts) => ts.iter().any(|t| self.has_pointer_debug(t, depth)),
            ty::Adt(adt, args) => {
                match self.has_pointer_format.entry(ty) {
                    Entry::Occupied(o) => return *o.get(),
                    Entry::Vacant(v) => v.insert(false),
                };
                let derived_debug = if let Some(&known) = self.has_derived_debug.get(&ty) {
                    known
                } else {
                    let Some(trait_id) = tcx.get_diagnostic_item(sym::Debug) else {
                        return false;
                    };
                    let (infcx, param_env) = tcx.infer_ctxt().build_with_typing_env(typing_env);
                    let trait_ref = TraitRef::new(tcx, trait_id, [GenericArg::from(ty)]);
                    let obligation = Obligation {
                        cause: ObligationCause::dummy(),
                        param_env,
                        recursion_depth: 0,
                        predicate: trait_ref.upcast(tcx),
                    };
                    let selection = SelectionContext::new(&infcx).select(&obligation);
                    let derived = if let Ok(Some(Selection::UserDefined(data))) = selection {
                        find_attr!(tcx, data.impl_def_id, AutomaticallyDerived(..))
                    } else {
                        false
                    };
                    self.has_derived_debug.insert(ty, derived);
                    derived
                };
                let pointer_debug = derived_debug
                    && adt.all_fields().any(|f| {
                        self.has_pointer_debug(
                            tcx.normalize_erasing_regions(typing_env, Unnormalized::new_wip(f.ty(tcx, args))),
                            depth,
                        )
                    });
                self.has_pointer_format.insert(ty, pointer_debug);
                pointer_debug
            },
            _ => false,
        }
    }
}

fn make_ty_msrv_map(tcx: TyCtxt<'_>) -> FxHashMap<Ty<'_>, Option<RustcVersion>> {
    [(sym::OsStr, Some(msrvs::OS_STR_DISPLAY)), (sym::Path, None)]
        .into_iter()
        .filter_map(|(name, feature)| {
            tcx.get_diagnostic_item(name).map(|def_id| {
                let ty = Ty::new_adt(tcx, tcx.adt_def(def_id), List::empty());
                (ty, feature)
            })
        })
        .collect()
}

fn count_needed_derefs<'tcx, I>(mut ty: Ty<'tcx>, mut iter: I) -> (usize, Ty<'tcx>)
where
    I: Iterator<Item = &'tcx Adjustment<'tcx>>,
{
    let mut n_total = 0;
    let mut n_needed = 0;
    loop {
        if let Some(Adjustment {
            kind: Adjust::Deref(deref),
            target,
        }) = iter.next()
        {
            n_total += 1;
            if let DerefAdjustKind::Overloaded(..) = deref {
                n_needed = n_total;
            }
            ty = *target;
        } else {
            return (n_needed, ty);
        }
    }
}