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Add unused_format_specs lint

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This commit is contained in:
Alex Macleod 2022-10-13 12:13:54 +00:00
parent 58ef56e39b
commit 136c2cdb91
13 changed files with 384 additions and 28 deletions
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151
clippy_lints/src/format_args.rs
View file

@ -1,8 +1,10 @@
use clippy_utils::diagnostics::{span_lint_and_sugg, span_lint_and_then};
use clippy_utils::macros::FormatParamKind::{Implicit, Named, Numbered, Starred};
use clippy_utils::macros::{is_format_macro, is_panic, FormatArgsExpn, FormatParam, FormatParamUsage};
use clippy_utils::macros::{
is_format_macro, is_panic, root_macro_call, Count, FormatArg, FormatArgsExpn, FormatParam, FormatParamUsage,
};
use clippy_utils::source::snippet_opt;
use clippy_utils::ty::implements_trait;
use clippy_utils::ty::{implements_trait, is_type_diagnostic_item};
use clippy_utils::{is_diag_trait_item, meets_msrv, msrvs};
use if_chain::if_chain;
use itertools::Itertools;
@ -117,7 +119,43 @@ declare_clippy_lint! {
"using non-inlined variables in `format!` calls"
}
impl_lint_pass!(FormatArgs => [FORMAT_IN_FORMAT_ARGS, UNINLINED_FORMAT_ARGS, TO_STRING_IN_FORMAT_ARGS]);
declare_clippy_lint! {
/// ### What it does
/// Detects [formatting parameters] that have no effect on the output of
/// `format!()`, `println!()` or similar macros.
///
/// ### 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
/// ```rust
/// println!("{:.}", 1.0);
///
/// println!("not padded: {:5}", format_args!("..."));
/// ```
/// Use instead:
/// ```rust
/// println!("{}", 1.0);
///
/// println!("not padded: {}", format_args!("..."));
/// // OR
/// println!("padded: {:5}", format!("..."));
/// ```
///
/// [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"
}
impl_lint_pass!(FormatArgs => [
FORMAT_IN_FORMAT_ARGS,
TO_STRING_IN_FORMAT_ARGS,
UNINLINED_FORMAT_ARGS,
UNUSED_FORMAT_SPECS,
]);
pub struct FormatArgs {
msrv: Option<RustcVersion>,
@ -132,27 +170,26 @@ impl FormatArgs {
impl<'tcx> LateLintPass<'tcx> for FormatArgs {
fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) {
if_chain! {
if let Some(format_args) = FormatArgsExpn::parse(cx, expr);
let expr_expn_data = expr.span.ctxt().outer_expn_data();
let outermost_expn_data = outermost_expn_data(expr_expn_data);
if let Some(macro_def_id) = outermost_expn_data.macro_def_id;
if is_format_macro(cx, macro_def_id);
if let ExpnKind::Macro(_, name) = outermost_expn_data.kind;
then {
for arg in &format_args.args {
if !arg.format.is_default() {
continue;
}
if is_aliased(&format_args, arg.param.value.hir_id) {
continue;
}
check_format_in_format_args(cx, outermost_expn_data.call_site, name, arg.param.value);
check_to_string_in_format_args(cx, name, arg.param.value);
if let Some(format_args) = FormatArgsExpn::parse(cx, expr)
&& let expr_expn_data = expr.span.ctxt().outer_expn_data()
&& let outermost_expn_data = outermost_expn_data(expr_expn_data)
&& let Some(macro_def_id) = outermost_expn_data.macro_def_id
&& is_format_macro(cx, macro_def_id)
&& let ExpnKind::Macro(_, name) = outermost_expn_data.kind
{
for arg in &format_args.args {
check_unused_format_specifier(cx, arg);
if !arg.format.is_default() {
continue;
}
if meets_msrv(self.msrv, msrvs::FORMAT_ARGS_CAPTURE) {
check_uninlined_args(cx, &format_args, outermost_expn_data.call_site, macro_def_id);
if is_aliased(&format_args, arg.param.value.hir_id) {
continue;
}
check_format_in_format_args(cx, outermost_expn_data.call_site, name, arg.param.value);
check_to_string_in_format_args(cx, name, arg.param.value);
}
if meets_msrv(self.msrv, msrvs::FORMAT_ARGS_CAPTURE) {
check_uninlined_args(cx, &format_args, outermost_expn_data.call_site, macro_def_id);
}
}
}
@ -160,6 +197,76 @@ impl<'tcx> LateLintPass<'tcx> for FormatArgs {
extract_msrv_attr!(LateContext);
}
fn check_unused_format_specifier(cx: &LateContext<'_>, arg: &FormatArg<'_>) {
let param_ty = cx.typeck_results().expr_ty(arg.param.value).peel_refs();
if let Count::Implied(Some(mut span)) = arg.format.precision
&& !span.is_empty()
{
span_lint_and_then(
cx,
UNUSED_FORMAT_SPECS,
span,
"empty precision specifier has no effect",
|diag| {
if param_ty.is_floating_point() {
diag.note("a precision specifier is not required to format floats");
}
if arg.format.is_default() {
// If there's no other specifiers remove the `:` too
span = arg.format_span();
}
diag.span_suggestion_verbose(span, "remove the `.`", "", Applicability::MachineApplicable);
},
);
}
if is_type_diagnostic_item(cx, param_ty, sym::Arguments) && !arg.format.is_default_for_trait() {
span_lint_and_then(
cx,
UNUSED_FORMAT_SPECS,
arg.span,
"format specifiers have no effect on `format_args!()`",
|diag| {
let mut suggest_format = |spec, span| {
let message = format!("for the {spec} to apply consider using `format!()`");
if let Some(mac_call) = root_macro_call(arg.param.value.span)
&& cx.tcx.is_diagnostic_item(sym::format_args_macro, mac_call.def_id)
&& arg.span.eq_ctxt(mac_call.span)
{
diag.span_suggestion(
cx.sess().source_map().span_until_char(mac_call.span, '!'),
message,
"format",
Applicability::MaybeIncorrect,
);
} else if let Some(span) = span {
diag.span_help(span, message);
}
};
if !arg.format.width.is_implied() {
suggest_format("width", arg.format.width.span());
}
if !arg.format.precision.is_implied() {
suggest_format("precision", arg.format.precision.span());
}
diag.span_suggestion_verbose(
arg.format_span(),
"if the current behavior is intentional, remove the format specifiers",
"",
Applicability::MaybeIncorrect,
);
},
);
}
}
fn check_uninlined_args(cx: &LateContext<'_>, args: &FormatArgsExpn<'_>, call_site: Span, def_id: DefId) {
if args.format_string.span.from_expansion() {
return;

1
clippy_lints/src/lib.register_all.rs
View file

@ -73,6 +73,7 @@ store.register_group(true, "clippy::all", Some("clippy_all"), vec![
LintId::of(format_args::FORMAT_IN_FORMAT_ARGS),
LintId::of(format_args::TO_STRING_IN_FORMAT_ARGS),
LintId::of(format_args::UNINLINED_FORMAT_ARGS),
LintId::of(format_args::UNUSED_FORMAT_SPECS),
LintId::of(format_impl::PRINT_IN_FORMAT_IMPL),
LintId::of(format_impl::RECURSIVE_FORMAT_IMPL),
LintId::of(formatting::POSSIBLE_MISSING_COMMA),

1
clippy_lints/src/lib.register_complexity.rs
View file

@ -13,6 +13,7 @@ store.register_group(true, "clippy::complexity", Some("clippy_complexity"), vec!
LintId::of(double_parens::DOUBLE_PARENS),
LintId::of(explicit_write::EXPLICIT_WRITE),
LintId::of(format::USELESS_FORMAT),
LintId::of(format_args::UNUSED_FORMAT_SPECS),
LintId::of(functions::TOO_MANY_ARGUMENTS),
LintId::of(int_plus_one::INT_PLUS_ONE),
LintId::of(lifetimes::EXTRA_UNUSED_LIFETIMES),

1
clippy_lints/src/lib.register_lints.rs
View file

@ -164,6 +164,7 @@ store.register_lints(&[
format_args::FORMAT_IN_FORMAT_ARGS,
format_args::TO_STRING_IN_FORMAT_ARGS,
format_args::UNINLINED_FORMAT_ARGS,
format_args::UNUSED_FORMAT_SPECS,
format_impl::PRINT_IN_FORMAT_IMPL,
format_impl::RECURSIVE_FORMAT_IMPL,
format_push_string::FORMAT_PUSH_STRING,