1 //! calculate cyclomatic complexity and warn about overly complex functions
7 use rustc::hir::intravisit::{Visitor, walk_expr};
8 use syntax::ast::Attribute;
10 use syntax::codemap::Span;
12 use utils::{in_macro, LimitStack, span_help_and_lint, paths, match_type};
14 /// **What it does:** Checks for methods with high cyclomatic complexity.
16 /// **Why is this bad?** Methods of high cyclomatic complexity tend to be badly
17 /// readable. Also LLVM will usually optimize small methods better.
19 /// **Known problems:** Sometimes it's hard to find a way to reduce the complexity.
21 /// **Example:** No. You'll see it when you get the warning.
23 pub CYCLOMATIC_COMPLEXITY, Warn,
24 "finds functions that should be split up into multiple functions"
27 pub struct CyclomaticComplexity {
31 impl CyclomaticComplexity {
32 pub fn new(limit: u64) -> Self {
33 CyclomaticComplexity { limit: LimitStack::new(limit) }
37 impl LintPass for CyclomaticComplexity {
38 fn get_lints(&self) -> LintArray {
39 lint_array!(CYCLOMATIC_COMPLEXITY)
43 impl CyclomaticComplexity {
44 fn check<'a, 'tcx>(&mut self, cx: &'a LateContext<'a, 'tcx>, block: &Block, span: Span) {
45 if in_macro(cx, span) {
49 let cfg = CFG::new(cx.tcx, block);
50 let n = cfg.graph.len_nodes() as u64;
51 let e = cfg.graph.len_edges() as u64;
53 // the function has unreachable code, other lints should catch this
57 let mut helper = CCHelper {
64 helper.visit_block(block);
65 let CCHelper { match_arms, divergence, short_circuits, returns, .. } = helper;
66 let ret_ty = cx.tcx.node_id_to_type(block.id);
67 let ret_adjust = if match_type(cx, ret_ty, &paths::RESULT) {
73 if cc + divergence < match_arms + short_circuits {
74 report_cc_bug(cx, cc, match_arms, divergence, short_circuits, ret_adjust, span);
76 let mut rust_cc = cc + divergence - match_arms - short_circuits;
77 // prevent degenerate cases where unreachable code contains `return` statements
78 if rust_cc >= ret_adjust {
79 rust_cc -= ret_adjust;
81 if rust_cc > self.limit.limit() {
82 span_help_and_lint(cx,
83 CYCLOMATIC_COMPLEXITY,
85 &format!("the function has a cyclomatic complexity of {}", rust_cc),
86 "you could split it up into multiple smaller functions");
92 impl LateLintPass for CyclomaticComplexity {
93 fn check_item(&mut self, cx: &LateContext, item: &Item) {
94 if let ItemFn(_, _, _, _, _, ref block) = item.node {
95 if !attr::contains_name(&item.attrs, "test") {
96 self.check(cx, block, item.span);
101 fn check_impl_item(&mut self, cx: &LateContext, item: &ImplItem) {
102 if let ImplItemKind::Method(_, ref block) = item.node {
103 self.check(cx, block, item.span);
107 fn check_trait_item(&mut self, cx: &LateContext, item: &TraitItem) {
108 if let MethodTraitItem(_, Some(ref block)) = item.node {
109 self.check(cx, block, item.span);
113 fn enter_lint_attrs(&mut self, cx: &LateContext, attrs: &[Attribute]) {
114 self.limit.push_attrs(cx.sess(), attrs, "cyclomatic_complexity");
116 fn exit_lint_attrs(&mut self, cx: &LateContext, attrs: &[Attribute]) {
117 self.limit.pop_attrs(cx.sess(), attrs, "cyclomatic_complexity");
121 struct CCHelper<'a, 'gcx: 'a + 'tcx, 'tcx: 'a> {
125 short_circuits: u64, // && and ||
126 tcx: &'a ty::TyCtxt<'a, 'gcx, 'tcx>,
129 impl<'a, 'b, 'tcx, 'gcx> Visitor<'a> for CCHelper<'b, 'gcx, 'tcx> {
130 fn visit_expr(&mut self, e: &'a Expr) {
132 ExprMatch(_, ref arms, _) => {
134 let arms_n: u64 = arms.iter().map(|arm| arm.pats.len() as u64).sum();
136 self.match_arms += arms_n - 2;
139 ExprCall(ref callee, _) => {
141 let ty = self.tcx.node_id_to_type(callee.id);
143 ty::TyFnDef(_, _, ty) |
144 ty::TyFnPtr(ty) if ty.sig.skip_binder().output.diverges() => {
145 self.divergence += 1;
150 ExprClosure(..) => (),
151 ExprBinary(op, _, _) => {
154 BiAnd | BiOr => self.short_circuits += 1,
158 ExprRet(_) => self.returns += 1,
159 _ => walk_expr(self, e),
164 #[cfg(feature="debugging")]
165 fn report_cc_bug(_: &LateContext, cc: u64, narms: u64, div: u64, shorts: u64, returns: u64, span: Span) {
167 "Clippy encountered a bug calculating cyclomatic complexity: cc = {}, arms = {}, \
168 div = {}, shorts = {}, returns = {}. Please file a bug report.",
175 #[cfg(not(feature="debugging"))]
176 fn report_cc_bug(cx: &LateContext, cc: u64, narms: u64, div: u64, shorts: u64, returns: u64, span: Span) {
177 if cx.current_level(CYCLOMATIC_COMPLEXITY) != Level::Allow {
178 cx.sess().span_note_without_error(span,
179 &format!("Clippy encountered a bug calculating cyclomatic complexity \
180 (hide this message with `#[allow(cyclomatic_complexity)]`): \
181 cc = {}, arms = {}, div = {}, shorts = {}, returns = {}. \
182 Please file a bug report.",