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use clippy_utils::diagnostics::span_lint_and_sugg;
use clippy_utils::macros::{root_macro_call_first_node, FormatArgsExpn};
use clippy_utils::source::snippet_with_applicability;
use clippy_utils::sugg::Sugg;
use if_chain::if_chain;
use rustc_errors::Applicability;
use rustc_hir::{Expr, ExprKind};
use rustc_lint::{LateContext, LateLintPass};
use rustc_middle::ty;
use rustc_session::{declare_lint_pass, declare_tool_lint};
use rustc_span::symbol::kw;
use rustc_span::{sym, Span};
declare_clippy_lint! {
/// ### What it does
/// Checks for the use of `format!("string literal with no
/// argument")` and `format!("{}", foo)` where `foo` is a string.
///
/// ### Why is this bad?
/// There is no point of doing that. `format!("foo")` can
/// be replaced by `"foo".to_owned()` if you really need a `String`. The even
/// worse `&format!("foo")` is often encountered in the wild. `format!("{}",
/// foo)` can be replaced by `foo.clone()` if `foo: String` or `foo.to_owned()`
/// if `foo: &str`.
///
/// ### Examples
/// ```rust
/// let foo = "foo";
/// format!("{}", foo);
/// ```
///
/// Use instead:
/// ```rust
/// let foo = "foo";
/// foo.to_owned();
/// ```
#[clippy::version = "pre 1.29.0"]
pub USELESS_FORMAT,
complexity,
"useless use of `format!`"
}
declare_lint_pass!(UselessFormat => [USELESS_FORMAT]);
impl<'tcx> LateLintPass<'tcx> for UselessFormat {
fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
let (format_args, call_site) = if_chain! {
if let Some(macro_call) = root_macro_call_first_node(cx, expr);
if cx.tcx.is_diagnostic_item(sym::format_macro, macro_call.def_id);
if let Some(format_args) = FormatArgsExpn::find_nested(cx, expr, macro_call.expn);
then {
(format_args, macro_call.span)
} else {
return
}
};
let mut applicability = Applicability::MachineApplicable;
if format_args.args.is_empty() {
match *format_args.format_string.parts {
[] => span_useless_format_empty(cx, call_site, "String::new()".to_owned(), applicability),
[_] => {
// Simulate macro expansion, converting {{ and }} to { and }.
let s_expand = format_args.format_string.snippet.replace("{{", "{").replace("}}", "}");
let sugg = format!("{}.to_string()", s_expand);
span_useless_format(cx, call_site, sugg, applicability);
},
[..] => {},
}
} else if let [arg] = &*format_args.args {
let value = arg.param.value;
if_chain! {
if format_args.format_string.parts == [kw::Empty];
if match cx.typeck_results().expr_ty(value).peel_refs().kind() {
ty::Adt(adt, _) => cx.tcx.is_diagnostic_item(sym::String, adt.did()),
ty::Str => true,
_ => false,
};
if !arg.format.has_string_formatting();
then {
let is_new_string = match value.kind {
ExprKind::Binary(..) => true,
ExprKind::MethodCall(path, ..) => path.ident.name == sym::to_string,
_ => false,
};
let sugg = if is_new_string {
snippet_with_applicability(cx, value.span, "..", &mut applicability).into_owned()
} else {
let sugg = Sugg::hir_with_applicability(cx, value, "<arg>", &mut applicability);
format!("{}.to_string()", sugg.maybe_par())
};
span_useless_format(cx, call_site, sugg, applicability);
}
}
};
}
}
fn span_useless_format_empty(cx: &LateContext<'_>, span: Span, sugg: String, applicability: Applicability) {
span_lint_and_sugg(
cx,
USELESS_FORMAT,
span,
"useless use of `format!`",
"consider using `String::new()`",
sugg,
applicability,
);
}
fn span_useless_format(cx: &LateContext<'_>, span: Span, sugg: String, applicability: Applicability) {
span_lint_and_sugg(
cx,
USELESS_FORMAT,
span,
"useless use of `format!`",
"consider using `.to_string()`",
sugg,
applicability,
);
}
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