2015-11-18 05:35:18 -06:00
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//! calculate cyclomatic complexity and warn about overly complex functions
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use rustc::lint::*;
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use rustc_front::hir::*;
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use rustc::middle::cfg::CFG;
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2015-12-14 07:29:20 -06:00
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use rustc::middle::ty;
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2015-11-18 05:35:18 -06:00
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use syntax::codemap::Span;
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use syntax::attr::*;
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use syntax::ast::Attribute;
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use rustc_front::intravisit::{Visitor, walk_expr};
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2015-12-31 14:39:03 -06:00
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use utils::{in_macro, LimitStack, span_help_and_lint};
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2015-11-18 05:35:18 -06:00
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2016-02-05 17:41:54 -06:00
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/// **What it does:** This lint checks for methods with high cyclomatic complexity
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2015-12-14 15:16:56 -06:00
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///
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/// **Why is this bad?** Methods of high cyclomatic complexity tend to be badly readable. Also LLVM will usually optimize small methods better.
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///
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/// **Known problems:** Sometimes it's hard to find a way to reduce the complexity
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///
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/// **Example:** No. You'll see it when you get the warning.
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2016-02-05 17:13:29 -06:00
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declare_lint! {
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pub CYCLOMATIC_COMPLEXITY, Warn,
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"finds functions that should be split up into multiple functions"
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}
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2015-11-18 05:35:18 -06:00
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pub struct CyclomaticComplexity {
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limit: LimitStack,
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}
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impl CyclomaticComplexity {
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pub fn new(limit: u64) -> Self {
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2016-01-03 22:26:12 -06:00
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CyclomaticComplexity { limit: LimitStack::new(limit) }
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2015-11-18 05:35:18 -06:00
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}
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}
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impl LintPass for CyclomaticComplexity {
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fn get_lints(&self) -> LintArray {
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lint_array!(CYCLOMATIC_COMPLEXITY)
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}
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}
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impl CyclomaticComplexity {
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2015-12-14 07:29:20 -06:00
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fn check<'a, 'tcx>(&mut self, cx: &'a LateContext<'a, 'tcx>, block: &Block, span: Span) {
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if in_macro(cx, span) {
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return;
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}
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2015-11-18 05:35:18 -06:00
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let cfg = CFG::new(cx.tcx, block);
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let n = cfg.graph.len_nodes() as u64;
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let e = cfg.graph.len_edges() as u64;
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let cc = e + 2 - n;
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let mut arm_counter = MatchArmCounter(0);
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arm_counter.visit_block(block);
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2015-12-14 07:29:20 -06:00
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let narms = arm_counter.0;
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let mut diverge_counter = DivergenceCounter(0, &cx.tcx);
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diverge_counter.visit_block(block);
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let divergence = diverge_counter.0;
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if cc + divergence < narms {
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report_cc_bug(cx, cc, narms, divergence, span);
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2015-12-05 02:53:00 -06:00
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} else {
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2015-12-14 07:29:20 -06:00
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let rust_cc = cc + divergence - narms;
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2015-12-05 02:53:00 -06:00
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if rust_cc > self.limit.limit() {
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2016-01-03 22:26:12 -06:00
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span_help_and_lint(cx,
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CYCLOMATIC_COMPLEXITY,
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span,
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2016-02-05 14:54:29 -06:00
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&format!("the function has a cyclomatic complexity of {}", rust_cc),
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"you could split it up into multiple smaller functions");
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2015-12-05 02:53:00 -06:00
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}
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2015-11-18 05:35:18 -06:00
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}
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}
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}
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impl LateLintPass for CyclomaticComplexity {
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fn check_item(&mut self, cx: &LateContext, item: &Item) {
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if let ItemFn(_, _, _, _, _, ref block) = item.node {
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self.check(cx, block, item.span);
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}
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}
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fn check_impl_item(&mut self, cx: &LateContext, item: &ImplItem) {
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if let ImplItemKind::Method(_, ref block) = item.node {
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self.check(cx, block, item.span);
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}
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}
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fn check_trait_item(&mut self, cx: &LateContext, item: &TraitItem) {
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if let MethodTraitItem(_, Some(ref block)) = item.node {
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self.check(cx, block, item.span);
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}
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}
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fn enter_lint_attrs(&mut self, cx: &LateContext, attrs: &[Attribute]) {
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self.limit.push_attrs(cx.sess(), attrs, "cyclomatic_complexity");
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}
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fn exit_lint_attrs(&mut self, cx: &LateContext, attrs: &[Attribute]) {
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self.limit.pop_attrs(cx.sess(), attrs, "cyclomatic_complexity");
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}
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}
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struct MatchArmCounter(u64);
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impl<'a> Visitor<'a> for MatchArmCounter {
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fn visit_expr(&mut self, e: &'a Expr) {
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match e.node {
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ExprMatch(_, ref arms, _) => {
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walk_expr(self, e);
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let arms_n: u64 = arms.iter().map(|arm| arm.pats.len() as u64).sum();
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if arms_n > 1 {
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self.0 += arms_n - 2;
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}
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}
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ExprClosure(..) => {}
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_ => walk_expr(self, e),
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}
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}
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}
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struct DivergenceCounter<'a, 'tcx: 'a>(u64, &'a ty::ctxt<'tcx>);
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impl<'a, 'b, 'tcx> Visitor<'a> for DivergenceCounter<'b, 'tcx> {
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fn visit_expr(&mut self, e: &'a Expr) {
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match e.node {
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ExprCall(ref callee, _) => {
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walk_expr(self, e);
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let ty = self.1.node_id_to_type(callee.id);
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if let ty::TyBareFn(_, ty) = ty.sty {
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if ty.sig.skip_binder().output.diverges() {
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self.0 += 1;
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}
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2015-11-18 05:35:18 -06:00
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}
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2016-01-03 22:26:12 -06:00
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}
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ExprClosure(..) => {}
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2015-11-18 05:35:18 -06:00
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_ => walk_expr(self, e),
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}
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}
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}
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2015-12-05 02:53:00 -06:00
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#[cfg(feature="debugging")]
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2015-12-14 07:29:20 -06:00
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fn report_cc_bug(cx: &LateContext, cc: u64, narms: u64, div: u64, span: Span) {
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cx.sess().span_bug(span,
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&format!("Clippy encountered a bug calculating cyclomatic complexity: cc = {}, arms = {}, \
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div = {}. Please file a bug report.",
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cc,
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narms,
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div));;
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2015-12-05 02:53:00 -06:00
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}
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#[cfg(not(feature="debugging"))]
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fn report_cc_bug(cx: &LateContext, cc: u64, narms: u64, div: u64, span: Span) {
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if cx.current_level(CYCLOMATIC_COMPLEXITY) != Level::Allow {
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2015-12-31 14:39:03 -06:00
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cx.sess().span_note_without_error(span,
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&format!("Clippy encountered a bug calculating cyclomatic complexity \
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2016-01-03 22:26:12 -06:00
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(hide this message with `#[allow(cyclomatic_complexity)]`): cc \
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= {}, arms = {}, div = {}. Please file a bug report.",
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cc,
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narms,
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div));
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2015-12-05 02:53:00 -06:00
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}
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}
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