1 use clippy_utils::diagnostics::span_lint_and_then;
2 use clippy_utils::{is_slice_of_primitives, sugg::Sugg};
3 use if_chain::if_chain;
4 use rustc_errors::Applicability;
5 use rustc_hir::{Expr, ExprKind};
6 use rustc_lint::{LateContext, LateLintPass};
7 use rustc_session::{declare_lint_pass, declare_tool_lint};
11 /// When sorting primitive values (integers, bools, chars, as well
12 /// as arrays, slices, and tuples of such items), it is better to
13 /// use an unstable sort than a stable sort.
15 /// ### Why is this bad?
16 /// Using a stable sort consumes more memory and cpu cycles. Because
17 /// values which compare equal are identical, preserving their
18 /// relative order (the guarantee that a stable sort provides) means
19 /// nothing, while the extra costs still apply.
23 /// let mut vec = vec![2, 1, 3];
28 /// let mut vec = vec![2, 1, 3];
29 /// vec.sort_unstable();
31 pub STABLE_SORT_PRIMITIVE,
33 "use of sort() when sort_unstable() is equivalent"
36 declare_lint_pass!(StableSortPrimitive => [STABLE_SORT_PRIMITIVE]);
38 /// The three "kinds" of sorts
41 /* The other kinds of lint are currently commented out because they
42 * can map distinct values to equal ones. If the key function is
43 * provably one-to-one, or if the Cmp function conserves equality,
44 * then they could be linted on, but I don't know if we can check
51 /// The name of the stable version of this kind of sort
52 fn stable_name(&self) -> &str {
54 SortingKind::Vanilla => "sort",
55 /* SortingKind::ByKey => "sort_by_key",
56 * SortingKind::ByCmp => "sort_by", */
59 /// The name of the unstable version of this kind of sort
60 fn unstable_name(&self) -> &str {
62 SortingKind::Vanilla => "sort_unstable",
63 /* SortingKind::ByKey => "sort_unstable_by_key",
64 * SortingKind::ByCmp => "sort_unstable_by", */
67 /// Takes the name of a function call and returns the kind of sort
68 /// that corresponds to that function name (or None if it isn't)
69 fn from_stable_name(name: &str) -> Option<SortingKind> {
71 "sort" => Some(SortingKind::Vanilla),
72 // "sort_by" => Some(SortingKind::ByCmp),
73 // "sort_by_key" => Some(SortingKind::ByKey),
79 /// A detected instance of this lint
80 struct LintDetection {
87 fn detect_stable_sort_primitive(cx: &LateContext<'_>, expr: &Expr<'_>) -> Option<LintDetection> {
89 if let ExprKind::MethodCall(method_name, _, args, _) = &expr.kind;
90 if let Some(slice) = &args.get(0);
91 if let Some(method) = SortingKind::from_stable_name(&method_name.ident.name.as_str());
92 if let Some(slice_type) = is_slice_of_primitives(cx, slice);
94 let args_str = args.iter().skip(1).map(|arg| Sugg::hir(cx, arg, "..").to_string()).collect::<Vec<String>>().join(", ");
95 Some(LintDetection { slice_name: Sugg::hir(cx, slice, "..").to_string(), method, method_args: args_str, slice_type })
102 impl LateLintPass<'_> for StableSortPrimitive {
103 fn check_expr(&mut self, cx: &LateContext<'_>, expr: &Expr<'_>) {
104 if let Some(detection) = detect_stable_sort_primitive(cx, expr) {
107 STABLE_SORT_PRIMITIVE,
110 "used `{}` on primitive type `{}`",
111 detection.method.stable_name(),
112 detection.slice_type,
116 diag.span_suggestion(
121 detection.slice_name,
122 detection.method.unstable_name(),
123 detection.method_args,
125 Applicability::MachineApplicable,
128 "an unstable sort would perform faster without any observable difference for this data type",