1 use clippy_utils::diagnostics::{span_lint_and_sugg, span_lint_and_then};
2 use clippy_utils::macros::FormatParamKind::{Implicit, Named, Numbered, Starred};
3 use clippy_utils::macros::{is_format_macro, FormatArgsExpn, FormatParam, FormatParamUsage};
4 use clippy_utils::source::snippet_opt;
5 use clippy_utils::ty::implements_trait;
6 use clippy_utils::{is_diag_trait_item, meets_msrv, msrvs};
7 use if_chain::if_chain;
8 use itertools::Itertools;
9 use rustc_errors::Applicability;
10 use rustc_hir::{Expr, ExprKind, HirId, QPath};
11 use rustc_lint::{LateContext, LateLintPass};
12 use rustc_middle::ty::adjustment::{Adjust, Adjustment};
13 use rustc_middle::ty::Ty;
14 use rustc_semver::RustcVersion;
15 use rustc_session::{declare_tool_lint, impl_lint_pass};
16 use rustc_span::{sym, ExpnData, ExpnKind, Span, Symbol};
18 declare_clippy_lint! {
20 /// Detects `format!` within the arguments of another macro that does
21 /// formatting such as `format!` itself, `write!` or `println!`. Suggests
22 /// inlining the `format!` call.
24 /// ### Why is this bad?
25 /// The recommended code is both shorter and avoids a temporary allocation.
29 /// # use std::panic::Location;
30 /// println!("error: {}", format!("something failed at {}", Location::caller()));
34 /// # use std::panic::Location;
35 /// println!("error: something failed at {}", Location::caller());
37 #[clippy::version = "1.58.0"]
38 pub FORMAT_IN_FORMAT_ARGS,
40 "`format!` used in a macro that does formatting"
43 declare_clippy_lint! {
45 /// Checks for [`ToString::to_string`](https://doc.rust-lang.org/std/string/trait.ToString.html#tymethod.to_string)
46 /// applied to a type that implements [`Display`](https://doc.rust-lang.org/std/fmt/trait.Display.html)
47 /// in a macro that does formatting.
49 /// ### Why is this bad?
50 /// Since the type implements `Display`, the use of `to_string` is
55 /// # use std::panic::Location;
56 /// println!("error: something failed at {}", Location::caller().to_string());
60 /// # use std::panic::Location;
61 /// println!("error: something failed at {}", Location::caller());
63 #[clippy::version = "1.58.0"]
64 pub TO_STRING_IN_FORMAT_ARGS,
66 "`to_string` applied to a type that implements `Display` in format args"
69 declare_clippy_lint! {
71 /// Detect when a variable is not inlined in a format string,
72 /// and suggests to inline it.
74 /// ### Why is this bad?
75 /// Non-inlined code is slightly more difficult to read and understand,
76 /// as it requires arguments to be matched against the format string.
77 /// The inlined syntax, where allowed, is simpler.
84 /// format!("{}", var);
85 /// format!("{v:?}", v = var);
86 /// format!("{0} {0}", var);
87 /// format!("{0:1$}", var, width);
88 /// format!("{:.*}", prec, var);
96 /// format!("{var:?}");
97 /// format!("{var} {var}");
98 /// format!("{var:width$}");
99 /// format!("{var:.prec$}");
102 /// ### Known Problems
104 /// There may be a false positive if the format string is expanded from certain proc macros:
107 /// println!(indoc!("{}"), var);
110 /// If a format string contains a numbered argument that cannot be inlined
111 /// nothing will be suggested, e.g. `println!("{0}={1}", var, 1+2)`.
112 #[clippy::version = "1.65.0"]
113 pub UNINLINED_FORMAT_ARGS,
115 "using non-inlined variables in `format!` calls"
118 impl_lint_pass!(FormatArgs => [FORMAT_IN_FORMAT_ARGS, UNINLINED_FORMAT_ARGS, TO_STRING_IN_FORMAT_ARGS]);
120 pub struct FormatArgs {
121 msrv: Option<RustcVersion>,
126 pub fn new(msrv: Option<RustcVersion>) -> Self {
131 impl<'tcx> LateLintPass<'tcx> for FormatArgs {
132 fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) {
134 if let Some(format_args) = FormatArgsExpn::parse(cx, expr);
135 let expr_expn_data = expr.span.ctxt().outer_expn_data();
136 let outermost_expn_data = outermost_expn_data(expr_expn_data);
137 if let Some(macro_def_id) = outermost_expn_data.macro_def_id;
138 if is_format_macro(cx, macro_def_id);
139 if let ExpnKind::Macro(_, name) = outermost_expn_data.kind;
141 for arg in &format_args.args {
142 if !arg.format.is_default() {
145 if is_aliased(&format_args, arg.param.value.hir_id) {
148 check_format_in_format_args(cx, outermost_expn_data.call_site, name, arg.param.value);
149 check_to_string_in_format_args(cx, name, arg.param.value);
151 if meets_msrv(self.msrv, msrvs::FORMAT_ARGS_CAPTURE) {
152 check_uninlined_args(cx, &format_args, outermost_expn_data.call_site);
158 extract_msrv_attr!(LateContext);
161 fn check_uninlined_args(cx: &LateContext<'_>, args: &FormatArgsExpn<'_>, call_site: Span) {
162 if args.format_string.span.from_expansion() {
166 let mut fixes = Vec::new();
167 // If any of the arguments are referenced by an index number,
168 // and that argument is not a simple variable and cannot be inlined,
169 // we cannot remove any other arguments in the format string,
170 // because the index numbers might be wrong after inlining.
171 // Example of an un-inlinable format: print!("{}{1}", foo, 2)
172 if !args.params().all(|p| check_one_arg(args, &p, &mut fixes)) || fixes.is_empty() {
176 // FIXME: Properly ignore a rare case where the format string is wrapped in a macro.
177 // Example: `format!(indoc!("{}"), foo);`
178 // If inlined, they will cause a compilation error:
179 // > to avoid ambiguity, `format_args!` cannot capture variables
180 // > when the format string is expanded from a macro
181 // @Alexendoo explanation:
182 // > indoc! is a proc macro that is producing a string literal with its span
183 // > set to its input it's not marked as from expansion, and since it's compatible
184 // > tokenization wise clippy_utils::is_from_proc_macro wouldn't catch it either
185 // This might be a relatively expensive test, so do it only we are ready to replace.
186 // See more examples in tests/ui/uninlined_format_args.rs
190 UNINLINED_FORMAT_ARGS,
192 "variables can be used directly in the `format!` string",
194 diag.multipart_suggestion("change this to", fixes, Applicability::MachineApplicable);
199 fn check_one_arg(args: &FormatArgsExpn<'_>, param: &FormatParam<'_>, fixes: &mut Vec<(Span, String)>) -> bool {
200 if matches!(param.kind, Implicit | Starred | Named(_) | Numbered)
201 && let ExprKind::Path(QPath::Resolved(None, path)) = param.value.kind
202 && let [segment] = path.segments
203 && let Some(arg_span) = args.value_with_prev_comma_span(param.value.hir_id)
205 let replacement = match param.usage {
206 FormatParamUsage::Argument => segment.ident.name.to_string(),
207 FormatParamUsage::Width => format!("{}$", segment.ident.name),
208 FormatParamUsage::Precision => format!(".{}$", segment.ident.name),
210 fixes.push((param.span, replacement));
211 fixes.push((arg_span, String::new()));
212 true // successful inlining, continue checking
214 // if we can't inline a numbered argument, we can't continue
215 param.kind != Numbered
219 fn outermost_expn_data(expn_data: ExpnData) -> ExpnData {
220 if expn_data.call_site.from_expansion() {
221 outermost_expn_data(expn_data.call_site.ctxt().outer_expn_data())
227 fn check_format_in_format_args(
228 cx: &LateContext<'_>,
233 let expn_data = arg.span.ctxt().outer_expn_data();
234 if expn_data.call_site.from_expansion() {
237 let Some(mac_id) = expn_data.macro_def_id else { return };
238 if !cx.tcx.is_diagnostic_item(sym::format_macro, mac_id) {
243 FORMAT_IN_FORMAT_ARGS,
245 &format!("`format!` in `{name}!` args"),
248 "combine the `format!(..)` arguments with the outer `{name}!(..)` call"
250 diag.help("or consider changing `format!` to `format_args!`");
255 fn check_to_string_in_format_args(cx: &LateContext<'_>, name: Symbol, value: &Expr<'_>) {
257 if !value.span.from_expansion();
258 if let ExprKind::MethodCall(_, receiver, [], _) = value.kind;
259 if let Some(method_def_id) = cx.typeck_results().type_dependent_def_id(value.hir_id);
260 if is_diag_trait_item(cx, method_def_id, sym::ToString);
261 let receiver_ty = cx.typeck_results().expr_ty(receiver);
262 if let Some(display_trait_id) = cx.tcx.get_diagnostic_item(sym::Display);
263 let (n_needed_derefs, target) =
264 count_needed_derefs(receiver_ty, cx.typeck_results().expr_adjustments(receiver).iter());
265 if implements_trait(cx, target, display_trait_id, &[]);
266 if let Some(sized_trait_id) = cx.tcx.lang_items().sized_trait();
267 if let Some(receiver_snippet) = snippet_opt(cx, receiver.span);
269 let needs_ref = !implements_trait(cx, receiver_ty, sized_trait_id, &[]);
270 if n_needed_derefs == 0 && !needs_ref {
273 TO_STRING_IN_FORMAT_ARGS,
274 value.span.with_lo(receiver.span.hi()),
276 "`to_string` applied to a type that implements `Display` in `{name}!` args"
280 Applicability::MachineApplicable,
285 TO_STRING_IN_FORMAT_ARGS,
288 "`to_string` applied to a type that implements `Display` in `{name}!` args"
292 "{}{:*>n_needed_derefs$}{receiver_snippet}",
293 if needs_ref { "&" } else { "" },
296 Applicability::MachineApplicable,
303 /// Returns true if `hir_id` is referred to by multiple format params
304 fn is_aliased(args: &FormatArgsExpn<'_>, hir_id: HirId) -> bool {
305 args.params().filter(|param| param.value.hir_id == hir_id).at_most_one().is_err()
308 fn count_needed_derefs<'tcx, I>(mut ty: Ty<'tcx>, mut iter: I) -> (usize, Ty<'tcx>)
310 I: Iterator<Item = &'tcx Adjustment<'tcx>>,
313 let mut n_needed = 0;
315 if let Some(Adjustment { kind: Adjust::Deref(overloaded_deref), target }) = iter.next() {
317 if overloaded_deref.is_some() {
322 return (n_needed, ty);