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, NestedVisitorMap, Visitor};
9 use rustc_hir::{Body, Expr, ExprKind, FnDecl, HirId};
10 use rustc_lint::{LateContext, LateLintPass, LintContext};
11 use rustc_middle::hir::map::Map;
12 use rustc_session::{declare_tool_lint, impl_lint_pass};
13 use rustc_span::source_map::Span;
14 use rustc_span::{sym, BytePos};
16 declare_clippy_lint! {
17 /// **What it does:** Checks for methods with high cognitive complexity.
19 /// **Why is this bad?** Methods of high cognitive complexity tend to be hard to
20 /// both read and maintain. Also LLVM will tend to optimize small methods better.
22 /// **Known problems:** Sometimes it's hard to find a way to reduce the
25 /// **Example:** No. You'll see it when you get the warning.
26 pub COGNITIVE_COMPLEXITY,
28 "functions that should be split up into multiple functions"
31 pub struct CognitiveComplexity {
35 impl CognitiveComplexity {
37 pub fn new(limit: u64) -> Self {
39 limit: LimitStack::new(limit),
44 impl_lint_pass!(CognitiveComplexity => [COGNITIVE_COMPLEXITY]);
46 impl CognitiveComplexity {
47 #[allow(clippy::cast_possible_truncation)]
50 cx: &LateContext<'tcx>,
52 decl: &'tcx FnDecl<'_>,
56 if body_span.from_expansion() {
60 let expr = &body.value;
62 let mut helper = CcHelper { cc: 1, returns: 0 };
63 helper.visit_expr(expr);
64 let CcHelper { cc, returns } = helper;
65 let ret_ty = cx.typeck_results().node_type(expr.hir_id);
66 let ret_adjust = if is_type_diagnostic_item(cx, ret_ty, sym::result_type) {
69 #[allow(clippy::integer_division)]
74 // prevent degenerate cases where unreachable code contains `return` statements
75 if rust_cc >= ret_adjust {
76 rust_cc -= ret_adjust;
79 if rust_cc > self.limit.limit() {
80 let fn_span = match kind {
81 FnKind::ItemFn(ident, _, _, _) | FnKind::Method(ident, _, _) => ident.span,
83 let header_span = body_span.with_hi(decl.output.span().lo());
84 let pos = snippet_opt(cx, header_span).and_then(|snip| {
85 let low_offset = snip.find('|')?;
86 let high_offset = 1 + snip.get(low_offset + 1..)?.find('|')?;
87 let low = header_span.lo() + BytePos(low_offset as u32);
88 let high = low + BytePos(high_offset as u32 + 1);
93 if let Some((low, high)) = pos {
94 Span::new(low, high, header_span.ctxt())
103 COGNITIVE_COMPLEXITY,
106 "the function has a cognitive complexity of ({}/{})",
111 "you could split it up into multiple smaller functions",
117 impl<'tcx> LateLintPass<'tcx> for CognitiveComplexity {
120 cx: &LateContext<'tcx>,
122 decl: &'tcx FnDecl<'_>,
123 body: &'tcx Body<'_>,
127 let def_id = cx.tcx.hir().local_def_id(hir_id);
128 if !cx.tcx.has_attr(def_id.to_def_id(), sym::test) {
129 self.check(cx, kind, decl, body, span);
133 fn enter_lint_attrs(&mut self, cx: &LateContext<'tcx>, attrs: &'tcx [Attribute]) {
134 self.limit.push_attrs(cx.sess(), attrs, "cognitive_complexity");
136 fn exit_lint_attrs(&mut self, cx: &LateContext<'tcx>, attrs: &'tcx [Attribute]) {
137 self.limit.pop_attrs(cx.sess(), attrs, "cognitive_complexity");
146 impl<'tcx> Visitor<'tcx> for CcHelper {
147 type Map = Map<'tcx>;
149 fn visit_expr(&mut self, e: &'tcx Expr<'_>) {
152 ExprKind::If(_, _, _) => {
155 ExprKind::Match(_, ref arms, _) => {
159 self.cc += arms.iter().filter(|arm| arm.guard.is_some()).count() as u64;
161 ExprKind::Ret(_) => self.returns += 1,
165 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
166 NestedVisitorMap::None