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::higher::{FormatArgsArg, FormatArgsExpn, FormatExpn};
   3 use clippy_utils::source::snippet_opt;
   4 use clippy_utils::ty::implements_trait;
   5 use clippy_utils::{is_diag_trait_item, match_def_path, paths};
   6 use if_chain::if_chain;
   7 use rustc_errors::Applicability;
   8 use rustc_hir::{Expr, ExprKind};
   9 use rustc_lint::{LateContext, LateLintPass};
  10 use rustc_middle::ty::adjustment::{Adjust, Adjustment};
  11 use rustc_middle::ty::Ty;
  12 use rustc_session::{declare_lint_pass, declare_tool_lint};
  13 use rustc_span::{sym, ExpnData, ExpnKind, Span, Symbol};
  14
  15 declare_clippy_lint! {
  16     /// ### What it does
  17     /// Detects `format!` within the arguments of another macro that does
  18     /// formatting such as `format!` itself, `write!` or `println!`. Suggests
  19     /// inlining the `format!` call.
  20     ///
  21     /// ### Why is this bad?
  22     /// The recommended code is both shorter and avoids a temporary allocation.
  23     ///
  24     /// ### Example
  25     /// ```rust
  26     /// # use std::panic::Location;
  27     /// println!("error: {}", format!("something failed at {}", Location::caller()));
  28     /// ```
  29     /// Use instead:
  30     /// ```rust
  31     /// # use std::panic::Location;
  32     /// println!("error: something failed at {}", Location::caller());
  33     /// ```
  34     #[clippy::version = "1.58.0"]
  35     pub FORMAT_IN_FORMAT_ARGS,
  36     perf,
  37     "`format!` used in a macro that does formatting"
  38 }
  39
  40 declare_clippy_lint! {
  41     /// ### What it does
  42     /// Checks for [`ToString::to_string`](https://doc.rust-lang.org/std/string/trait.ToString.html#tymethod.to_string)
  43     /// applied to a type that implements [`Display`](https://doc.rust-lang.org/std/fmt/trait.Display.html)
  44     /// in a macro that does formatting.
  45     ///
  46     /// ### Why is this bad?
  47     /// Since the type implements `Display`, the use of `to_string` is
  48     /// unnecessary.
  49     ///
  50     /// ### Example
  51     /// ```rust
  52     /// # use std::panic::Location;
  53     /// println!("error: something failed at {}", Location::caller().to_string());
  54     /// ```
  55     /// Use instead:
  56     /// ```rust
  57     /// # use std::panic::Location;
  58     /// println!("error: something failed at {}", Location::caller());
  59     /// ```
  60     #[clippy::version = "1.58.0"]
  61     pub TO_STRING_IN_FORMAT_ARGS,
  62     perf,
  63     "`to_string` applied to a type that implements `Display` in format args"
  64 }
  65
  66 declare_lint_pass!(FormatArgs => [FORMAT_IN_FORMAT_ARGS, TO_STRING_IN_FORMAT_ARGS]);
  67
  68 const FORMAT_MACRO_PATHS: &[&[&str]] = &[
  69     &paths::FORMAT_ARGS_MACRO,
  70     &paths::ASSERT_EQ_MACRO,
  71     &paths::ASSERT_MACRO,
  72     &paths::ASSERT_NE_MACRO,
  73     &paths::EPRINT_MACRO,
  74     &paths::EPRINTLN_MACRO,
  75     &paths::PRINT_MACRO,
  76     &paths::PRINTLN_MACRO,
  77     &paths::WRITE_MACRO,
  78     &paths::WRITELN_MACRO,
  79 ];
  80
  81 const FORMAT_MACRO_DIAG_ITEMS: &[Symbol] = &[sym::format_macro, sym::std_panic_macro];
  82
  83 impl<'tcx> LateLintPass<'tcx> for FormatArgs {
  84     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) {
  85         if_chain! {
  86             if let Some(format_args) = FormatArgsExpn::parse(expr);
  87             let expr_expn_data = expr.span.ctxt().outer_expn_data();
  88             let outermost_expn_data = outermost_expn_data(expr_expn_data);
  89             if let Some(macro_def_id) = outermost_expn_data.macro_def_id;
  90             if FORMAT_MACRO_PATHS
  91                 .iter()
  92                 .any(|path| match_def_path(cx, macro_def_id, path))
  93                 || FORMAT_MACRO_DIAG_ITEMS
  94                     .iter()
  95                     .any(|diag_item| cx.tcx.is_diagnostic_item(*diag_item, macro_def_id));
  96             if let ExpnKind::Macro(_, name) = outermost_expn_data.kind;
  97             if let Some(args) = format_args.args();
  98             then {
  99                 for (i, arg) in args.iter().enumerate() {
 100                     if !arg.is_display() {
 101                         continue;
 102                     }
 103                     if arg.has_string_formatting() {
 104                         continue;
 105                     }
 106                     if is_aliased(&args, i) {
 107                         continue;
 108                     }
 109                     check_format_in_format_args(cx, outermost_expn_data.call_site, name, arg);
 110                     check_to_string_in_format_args(cx, name, arg);
 111                 }
 112             }
 113         }
 114     }
 115 }
 116
 117 fn outermost_expn_data(expn_data: ExpnData) -> ExpnData {
 118     if expn_data.call_site.from_expansion() {
 119         outermost_expn_data(expn_data.call_site.ctxt().outer_expn_data())
 120     } else {
 121         expn_data
 122     }
 123 }
 124
 125 fn check_format_in_format_args(cx: &LateContext<'_>, call_site: Span, name: Symbol, arg: &FormatArgsArg<'_>) {
 126     if_chain! {
 127         if FormatExpn::parse(arg.value).is_some();
 128         if !arg.value.span.ctxt().outer_expn_data().call_site.from_expansion();
 129         then {
 130             span_lint_and_then(
 131                 cx,
 132                 FORMAT_IN_FORMAT_ARGS,
 133                 call_site,
 134                 &format!("`format!` in `{}!` args", name),
 135                 |diag| {
 136                     diag.help(&format!(
 137                         "combine the `format!(..)` arguments with the outer `{}!(..)` call",
 138                         name
 139                     ));
 140                     diag.help("or consider changing `format!` to `format_args!`");
 141                 },
 142             );
 143         }
 144     }
 145 }
 146
 147 fn check_to_string_in_format_args<'tcx>(cx: &LateContext<'tcx>, name: Symbol, arg: &FormatArgsArg<'tcx>) {
 148     let value = arg.value;
 149     if_chain! {
 150         if !value.span.from_expansion();
 151         if let ExprKind::MethodCall(_, _, [receiver], _) = value.kind;
 152         if let Some(method_def_id) = cx.typeck_results().type_dependent_def_id(value.hir_id);
 153         if is_diag_trait_item(cx, method_def_id, sym::ToString);
 154         let receiver_ty = cx.typeck_results().expr_ty(receiver);
 155         if let Some(display_trait_id) = cx.tcx.get_diagnostic_item(sym::Display);
 156         if let Some(receiver_snippet) = snippet_opt(cx, receiver.span);
 157         then {
 158             let (n_needed_derefs, target) = count_needed_derefs(
 159                 receiver_ty,
 160                 cx.typeck_results().expr_adjustments(receiver).iter(),
 161             );
 162             if implements_trait(cx, target, display_trait_id, &[]) {
 163                 if n_needed_derefs == 0 {
 164                     span_lint_and_sugg(
 165                         cx,
 166                         TO_STRING_IN_FORMAT_ARGS,
 167                         value.span.with_lo(receiver.span.hi()),
 168                         &format!("`to_string` applied to a type that implements `Display` in `{}!` args", name),
 169                         "remove this",
 170                         String::new(),
 171                         Applicability::MachineApplicable,
 172                     );
 173                 } else {
 174                     span_lint_and_sugg(
 175                         cx,
 176                         TO_STRING_IN_FORMAT_ARGS,
 177                         value.span,
 178                         &format!("`to_string` applied to a type that implements `Display` in `{}!` args", name),
 179                         "use this",
 180                         format!("{:*>width$}{}", "", receiver_snippet, width = n_needed_derefs),
 181                         Applicability::MachineApplicable,
 182                     );
 183                 }
 184             }
 185         }
 186     }
 187 }
 188
 189 // Returns true if `args[i]` "refers to" or "is referred to by" another argument.
 190 fn is_aliased(args: &[FormatArgsArg<'_>], i: usize) -> bool {
 191     let value = args[i].value;
 192     args.iter()
 193         .enumerate()
 194         .any(|(j, arg)| i != j && std::ptr::eq(value, arg.value))
 195 }
 196
 197 fn count_needed_derefs<'tcx, I>(mut ty: Ty<'tcx>, mut iter: I) -> (usize, Ty<'tcx>)
 198 where
 199     I: Iterator<Item = &'tcx Adjustment<'tcx>>,
 200 {
 201     let mut n_total = 0;
 202     let mut n_needed = 0;
 203     loop {
 204         if let Some(Adjustment {
 205             kind: Adjust::Deref(overloaded_deref),
 206             target,
 207         }) = iter.next()
 208         {
 209             n_total += 1;
 210             if overloaded_deref.is_some() {
 211                 n_needed = n_total;
 212             }
 213             ty = target;
 214         } else {
 215             return (n_needed, ty);
 216         }
 217     }
 218 }