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