1 //! calculate cognitive complexity and warn about overly complex functions
3 use clippy_utils::diagnostics::span_lint_and_help;
4 use clippy_utils::source::snippet_opt;
5 use clippy_utils::ty::is_type_diagnostic_item;
6 use clippy_utils::LimitStack;
7 use rustc_ast::ast::Attribute;
8 use rustc_hir::intravisit::{walk_expr, FnKind, Visitor};
9 use rustc_hir::{Body, Expr, ExprKind, FnDecl, HirId};
10 use rustc_lint::{LateContext, LateLintPass, LintContext};
11 use rustc_session::{declare_tool_lint, impl_lint_pass};
12 use rustc_span::source_map::Span;
13 use rustc_span::{sym, BytePos};
15 declare_clippy_lint! {
17 /// Checks for methods with high cognitive complexity.
19 /// ### Why is this bad?
20 /// Methods of high cognitive complexity tend to be hard to
21 /// both read and maintain. Also LLVM will tend to optimize small methods better.
23 /// ### Known problems
24 /// Sometimes it's hard to find a way to reduce the
28 /// You'll see it when you get the warning.
29 #[clippy::version = "1.35.0"]
30 pub COGNITIVE_COMPLEXITY,
32 "functions that should be split up into multiple functions"
35 pub struct CognitiveComplexity {
39 impl CognitiveComplexity {
41 pub fn new(limit: u64) -> Self {
43 limit: LimitStack::new(limit),
48 impl_lint_pass!(CognitiveComplexity => [COGNITIVE_COMPLEXITY]);
50 impl CognitiveComplexity {
51 #[expect(clippy::cast_possible_truncation)]
54 cx: &LateContext<'tcx>,
56 decl: &'tcx FnDecl<'_>,
60 if body_span.from_expansion() {
64 let expr = &body.value;
66 let mut helper = CcHelper { cc: 1, returns: 0 };
67 helper.visit_expr(expr);
68 let CcHelper { cc, returns } = helper;
69 let ret_ty = cx.typeck_results().node_type(expr.hir_id);
70 let ret_adjust = if is_type_diagnostic_item(cx, ret_ty, sym::Result) {
73 #[expect(clippy::integer_division)]
78 // prevent degenerate cases where unreachable code contains `return` statements
79 if rust_cc >= ret_adjust {
80 rust_cc -= ret_adjust;
83 if rust_cc > self.limit.limit() {
84 let fn_span = match kind {
85 FnKind::ItemFn(ident, _, _) | FnKind::Method(ident, _) => ident.span,
87 let header_span = body_span.with_hi(decl.output.span().lo());
88 let pos = snippet_opt(cx, header_span).and_then(|snip| {
89 let low_offset = snip.find('|')?;
90 let high_offset = 1 + snip.get(low_offset + 1..)?.find('|')?;
91 let low = header_span.lo() + BytePos(low_offset as u32);
92 let high = low + BytePos(high_offset as u32 + 1);
97 if let Some((low, high)) = pos {
98 Span::new(low, high, header_span.ctxt(), header_span.parent())
107 COGNITIVE_COMPLEXITY,
110 "the function has a cognitive complexity of ({}/{})",
115 "you could split it up into multiple smaller functions",
121 impl<'tcx> LateLintPass<'tcx> for CognitiveComplexity {
124 cx: &LateContext<'tcx>,
126 decl: &'tcx FnDecl<'_>,
127 body: &'tcx Body<'_>,
131 let def_id = cx.tcx.hir().local_def_id(hir_id);
132 if !cx.tcx.has_attr(def_id.to_def_id(), sym::test) {
133 self.check(cx, kind, decl, body, span);
137 fn enter_lint_attrs(&mut self, cx: &LateContext<'tcx>, attrs: &'tcx [Attribute]) {
138 self.limit.push_attrs(cx.sess(), attrs, "cognitive_complexity");
140 fn exit_lint_attrs(&mut self, cx: &LateContext<'tcx>, attrs: &'tcx [Attribute]) {
141 self.limit.pop_attrs(cx.sess(), attrs, "cognitive_complexity");
150 impl<'tcx> Visitor<'tcx> for CcHelper {
151 fn visit_expr(&mut self, e: &'tcx Expr<'_>) {
154 ExprKind::If(_, _, _) => {
157 ExprKind::Match(_, arms, _) => {
161 self.cc += arms.iter().filter(|arm| arm.guard.is_some()).count() as u64;
163 ExprKind::Ret(_) => self.returns += 1,