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use clippy_utils::diagnostics::span_lint_and_sugg;
use clippy_utils::higher::FormatExpn;
use clippy_utils::last_path_segment;
use clippy_utils::source::{snippet_opt, snippet_with_applicability};
use clippy_utils::sugg::Sugg;
use if_chain::if_chain;
use rustc_errors::Applicability;
use rustc_hir::{BorrowKind, Expr, ExprKind, QPath};
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`.
///
/// **Known problems:** None.
///
/// **Examples:**
/// ```rust
///
/// // Bad
/// let foo = "foo";
/// format!("{}", foo);
///
/// // Good
/// foo.to_owned();
/// ```
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 FormatExpn { call_site, format_args } = match FormatExpn::parse(expr) {
Some(e) if !e.call_site.from_expansion() => e,
_ => return,
};
let mut applicability = Applicability::MachineApplicable;
if format_args.value_args.is_empty() {
if_chain! {
if let [e] = &*format_args.format_string_parts;
if let ExprKind::Lit(lit) = &e.kind;
if let Some(s_src) = snippet_opt(cx, lit.span);
then {
// Simulate macro expansion, converting {{ and }} to { and }.
let s_expand = s_src.replace("{{", "{").replace("}}", "}");
let sugg = format!("{}.to_string()", s_expand);
span_useless_format(cx, call_site, sugg, applicability);
}
}
} else if let [value] = *format_args.value_args {
if_chain! {
if format_args.format_string_symbols == [kw::Empty];
if match cx.typeck_results().expr_ty(value).peel_refs().kind() {
ty::Adt(adt, _) => cx.tcx.is_diagnostic_item(sym::string_type, adt.did),
ty::Str => true,
_ => false,
};
if format_args.args.iter().all(|e| is_display_arg(e));
if format_args.fmt_expr.map_or(true, |e| check_unformatted(e));
then {
let is_new_string = match value.kind {
ExprKind::Binary(..) => true,
ExprKind::MethodCall(path, ..) => path.ident.name.as_str() == "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(cx: &LateContext<'_>, span: Span, mut sugg: String, mut applicability: Applicability) {
// The callsite span contains the statement semicolon for some reason.
if snippet_with_applicability(cx, span, "..", &mut applicability).ends_with(';') {
sugg.push(';');
}
span_lint_and_sugg(
cx,
USELESS_FORMAT,
span,
"useless use of `format!`",
"consider using `.to_string()`",
sugg,
applicability,
);
}
fn is_display_arg(expr: &Expr<'_>) -> bool {
if_chain! {
if let ExprKind::Call(_, [_, fmt]) = expr.kind;
if let ExprKind::Path(QPath::Resolved(_, path)) = fmt.kind;
if let [.., t, _] = path.segments;
if t.ident.name.as_str() == "Display";
then { true } else { false }
}
}
/// Checks if the expression matches
/// ```rust,ignore
/// &[_ {
/// format: _ {
/// width: _::Implied,
/// precision: _::Implied,
/// ...
/// },
/// ...,
/// }]
/// ```
fn check_unformatted(expr: &Expr<'_>) -> bool {
if_chain! {
if let ExprKind::AddrOf(BorrowKind::Ref, _, expr) = expr.kind;
if let ExprKind::Array([expr]) = expr.kind;
// struct `core::fmt::rt::v1::Argument`
if let ExprKind::Struct(_, fields, _) = expr.kind;
if let Some(format_field) = fields.iter().find(|f| f.ident.name == sym::format);
// struct `core::fmt::rt::v1::FormatSpec`
if let ExprKind::Struct(_, fields, _) = format_field.expr.kind;
if let Some(precision_field) = fields.iter().find(|f| f.ident.name == sym::precision);
if let ExprKind::Path(ref precision_path) = precision_field.expr.kind;
if last_path_segment(precision_path).ident.name == sym::Implied;
if let Some(width_field) = fields.iter().find(|f| f.ident.name == sym::width);
if let ExprKind::Path(ref width_qpath) = width_field.expr.kind;
if last_path_segment(width_qpath).ident.name == sym::Implied;
then {
return true;
}
}
false
}
|
