src/tools/clippy/clippy_lints/src/format_args.rs

   1 use clippy_utils::diagnostics::{span_lint_and_sugg, span_lint_and_then};
   2 use clippy_utils::is_diag_trait_item;
   3 use clippy_utils::macros::{is_format_macro, FormatArgsExpn};
   4 use clippy_utils::source::snippet_opt;
   5 use clippy_utils::ty::implements_trait;
   6 use if_chain::if_chain;
   7 use itertools::Itertools;
   8 use rustc_errors::Applicability;
   9 use rustc_hir::{Expr, ExprKind, HirId};
  10 use rustc_lint::{LateContext, LateLintPass};
  11 use rustc_middle::ty::adjustment::{Adjust, Adjustment};
  12 use rustc_middle::ty::Ty;
  13 use rustc_session::{declare_lint_pass, declare_tool_lint};
  14 use rustc_span::{sym, ExpnData, ExpnKind, Span, Symbol};
  15
  16 declare_clippy_lint! {
  17     /// ### What it does
  18     /// Detects `format!` within the arguments of another macro that does
  19     /// formatting such as `format!` itself, `write!` or `println!`. Suggests
  20     /// inlining the `format!` call.
  21     ///
  22     /// ### Why is this bad?
  23     /// The recommended code is both shorter and avoids a temporary allocation.
  24     ///
  25     /// ### Example
  26     /// ```rust
  27     /// # use std::panic::Location;
  28     /// println!("error: {}", format!("something failed at {}", Location::caller()));
  29     /// ```
  30     /// Use instead:
  31     /// ```rust
  32     /// # use std::panic::Location;
  33     /// println!("error: something failed at {}", Location::caller());
  34     /// ```
  35     #[clippy::version = "1.58.0"]
  36     pub FORMAT_IN_FORMAT_ARGS,
  37     perf,
  38     "`format!` used in a macro that does formatting"
  39 }
  40
  41 declare_clippy_lint! {
  42     /// ### What it does
  43     /// Checks for [`ToString::to_string`](https://doc.rust-lang.org/std/string/trait.ToString.html#tymethod.to_string)
  44     /// applied to a type that implements [`Display`](https://doc.rust-lang.org/std/fmt/trait.Display.html)
  45     /// in a macro that does formatting.
  46     ///
  47     /// ### Why is this bad?
  48     /// Since the type implements `Display`, the use of `to_string` is
  49     /// unnecessary.
  50     ///
  51     /// ### Example
  52     /// ```rust
  53     /// # use std::panic::Location;
  54     /// println!("error: something failed at {}", Location::caller().to_string());
  55     /// ```
  56     /// Use instead:
  57     /// ```rust
  58     /// # use std::panic::Location;
  59     /// println!("error: something failed at {}", Location::caller());
  60     /// ```
  61     #[clippy::version = "1.58.0"]
  62     pub TO_STRING_IN_FORMAT_ARGS,
  63     perf,
  64     "`to_string` applied to a type that implements `Display` in format args"
  65 }
  66
  67 declare_lint_pass!(FormatArgs => [FORMAT_IN_FORMAT_ARGS, TO_STRING_IN_FORMAT_ARGS]);
  68
  69 impl<'tcx> LateLintPass<'tcx> for FormatArgs {
  70     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) {
  71         if_chain! {
  72             if let Some(format_args) = FormatArgsExpn::parse(cx, expr);
  73             let expr_expn_data = expr.span.ctxt().outer_expn_data();
  74             let outermost_expn_data = outermost_expn_data(expr_expn_data);
  75             if let Some(macro_def_id) = outermost_expn_data.macro_def_id;
  76             if is_format_macro(cx, macro_def_id);
  77             if let ExpnKind::Macro(_, name) = outermost_expn_data.kind;
  78             then {
  79                 for arg in &format_args.args {
  80                     if arg.format.has_string_formatting() {
  81                         continue;
  82                     }
  83                     if is_aliased(&format_args, arg.param.value.hir_id) {
  84                         continue;
  85                     }
  86                     check_format_in_format_args(cx, outermost_expn_data.call_site, name, arg.param.value);
  87                     check_to_string_in_format_args(cx, name, arg.param.value);
  88                 }
  89             }
  90         }
  91     }
  92 }
  93
  94 fn outermost_expn_data(expn_data: ExpnData) -> ExpnData {
  95     if expn_data.call_site.from_expansion() {
  96         outermost_expn_data(expn_data.call_site.ctxt().outer_expn_data())
  97     } else {
  98         expn_data
  99     }
 100 }
 101
 102 fn check_format_in_format_args(
 103     cx: &LateContext<'_>,
 104     call_site: Span,
 105     name: Symbol,
 106     arg: &Expr<'_>,
 107 ) {
 108     let expn_data = arg.span.ctxt().outer_expn_data();
 109     if expn_data.call_site.from_expansion() {
 110         return;
 111     }
 112     let Some(mac_id) = expn_data.macro_def_id else { return };
 113     if !cx.tcx.is_diagnostic_item(sym::format_macro, mac_id) {
 114         return;
 115     }
 116     span_lint_and_then(
 117         cx,
 118         FORMAT_IN_FORMAT_ARGS,
 119         call_site,
 120         &format!("`format!` in `{}!` args", name),
 121         |diag| {
 122             diag.help(&format!(
 123                 "combine the `format!(..)` arguments with the outer `{}!(..)` call",
 124                 name
 125             ));
 126             diag.help("or consider changing `format!` to `format_args!`");
 127         },
 128     );
 129 }
 130
 131 fn check_to_string_in_format_args(cx: &LateContext<'_>, name: Symbol, value: &Expr<'_>) {
 132     if_chain! {
 133         if !value.span.from_expansion();
 134         if let ExprKind::MethodCall(_, receiver, [], _) = value.kind;
 135         if let Some(method_def_id) = cx.typeck_results().type_dependent_def_id(value.hir_id);
 136         if is_diag_trait_item(cx, method_def_id, sym::ToString);
 137         let receiver_ty = cx.typeck_results().expr_ty(receiver);
 138         if let Some(display_trait_id) = cx.tcx.get_diagnostic_item(sym::Display);
 139         let (n_needed_derefs, target) =
 140             count_needed_derefs(receiver_ty, cx.typeck_results().expr_adjustments(receiver).iter());
 141         if implements_trait(cx, target, display_trait_id, &[]);
 142         if let Some(sized_trait_id) = cx.tcx.lang_items().sized_trait();
 143         if let Some(receiver_snippet) = snippet_opt(cx, receiver.span);
 144         then {
 145             let needs_ref = !implements_trait(cx, receiver_ty, sized_trait_id, &[]);
 146             if n_needed_derefs == 0 && !needs_ref {
 147                 span_lint_and_sugg(
 148                     cx,
 149                     TO_STRING_IN_FORMAT_ARGS,
 150                     value.span.with_lo(receiver.span.hi()),
 151                     &format!(
 152                         "`to_string` applied to a type that implements `Display` in `{}!` args",
 153                         name
 154                     ),
 155                     "remove this",
 156                     String::new(),
 157                     Applicability::MachineApplicable,
 158                 );
 159             } else {
 160                 span_lint_and_sugg(
 161                     cx,
 162                     TO_STRING_IN_FORMAT_ARGS,
 163                     value.span,
 164                     &format!(
 165                         "`to_string` applied to a type that implements `Display` in `{}!` args",
 166                         name
 167                     ),
 168                     "use this",
 169                     format!(
 170                         "{}{:*>width$}{}",
 171                         if needs_ref { "&" } else { "" },
 172                         "",
 173                         receiver_snippet,
 174                         width = n_needed_derefs
 175                     ),
 176                     Applicability::MachineApplicable,
 177                 );
 178             }
 179         }
 180     }
 181 }
 182
 183 // Returns true if `hir_id` is referred to by multiple format params
 184 fn is_aliased(args: &FormatArgsExpn<'_>, hir_id: HirId) -> bool {
 185     args.params().filter(|param| param.value.hir_id == hir_id).at_most_one().is_err()
 186 }
 187
 188 fn count_needed_derefs<'tcx, I>(mut ty: Ty<'tcx>, mut iter: I) -> (usize, Ty<'tcx>)
 189 where
 190     I: Iterator<Item = &'tcx Adjustment<'tcx>>,
 191 {
 192     let mut n_total = 0;
 193     let mut n_needed = 0;
 194     loop {
 195         if let Some(Adjustment { kind: Adjust::Deref(overloaded_deref), target }) = iter.next() {
 196             n_total += 1;
 197             if overloaded_deref.is_some() {
 198                 n_needed = n_total;
 199             }
 200             ty = *target;
 201         } else {
 202             return (n_needed, ty);
 203         }
 204     }
 205 }