221 lines
6.7 KiB
Rust
221 lines
6.7 KiB
Rust
//! calculate cyclomatic complexity and warn about overly complex functions
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use rustc::cfg::CFG;
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use rustc::lint::*;
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use rustc::hir::*;
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use rustc::ty;
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use rustc::hir::intravisit::{walk_expr, NestedVisitorMap, Visitor};
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use syntax::ast::{Attribute, NodeId};
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use syntax::codemap::Span;
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use utils::{in_macro, is_allowed, match_type, paths, span_help_and_lint, LimitStack};
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/// **What it does:** Checks for methods with high cyclomatic complexity.
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///
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/// **Why is this bad?** Methods of high cyclomatic complexity tend to be badly
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/// 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
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/// complexity.
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///
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/// **Example:** No. You'll see it when you get the warning.
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declare_clippy_lint! {
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pub CYCLOMATIC_COMPLEXITY,
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complexity,
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"functions that should be split up into multiple functions"
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}
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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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Self {
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limit: LimitStack::new(limit),
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}
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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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fn check<'a, 'tcx: 'a>(&mut self, cx: &'a LateContext<'a, 'tcx>, body: &'tcx Body, span: Span) {
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if in_macro(span) {
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return;
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}
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let cfg = CFG::new(cx.tcx, body);
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let expr = &body.value;
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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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if e + 2 < n {
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// the function has unreachable code, other lints should catch this
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return;
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}
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let cc = e + 2 - n;
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let mut helper = CCHelper {
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match_arms: 0,
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divergence: 0,
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short_circuits: 0,
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returns: 0,
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cx,
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};
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helper.visit_expr(expr);
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let CCHelper {
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match_arms,
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divergence,
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short_circuits,
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returns,
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..
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} = helper;
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let ret_ty = cx.tables.node_id_to_type(expr.hir_id);
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let ret_adjust = if match_type(cx, ret_ty, &paths::RESULT) {
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returns
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} else {
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returns / 2
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};
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if cc + divergence < match_arms + short_circuits {
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report_cc_bug(
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cx,
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cc,
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match_arms,
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divergence,
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short_circuits,
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ret_adjust,
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span,
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body.id().node_id,
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);
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} else {
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let mut rust_cc = cc + divergence - match_arms - short_circuits;
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// prevent degenerate cases where unreachable code contains `return` statements
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if rust_cc >= ret_adjust {
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rust_cc -= ret_adjust;
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}
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if rust_cc > self.limit.limit() {
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span_help_and_lint(
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cx,
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CYCLOMATIC_COMPLEXITY,
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span,
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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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);
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}
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}
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}
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}
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impl<'a, 'tcx> LateLintPass<'a, 'tcx> for CyclomaticComplexity {
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fn check_fn(
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&mut self,
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cx: &LateContext<'a, 'tcx>,
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_: intravisit::FnKind<'tcx>,
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_: &'tcx FnDecl,
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body: &'tcx Body,
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span: Span,
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node_id: NodeId,
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) {
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let def_id = cx.tcx.hir.local_def_id(node_id);
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if !cx.tcx.has_attr(def_id, "test") {
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self.check(cx, body, span);
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}
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}
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fn enter_lint_attrs(&mut self, cx: &LateContext<'a, 'tcx>, attrs: &'tcx [Attribute]) {
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self.limit
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.push_attrs(cx.sess(), attrs, "cyclomatic_complexity");
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}
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fn exit_lint_attrs(&mut self, cx: &LateContext<'a, 'tcx>, attrs: &'tcx [Attribute]) {
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self.limit
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.pop_attrs(cx.sess(), attrs, "cyclomatic_complexity");
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}
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}
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struct CCHelper<'a, 'tcx: 'a> {
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match_arms: u64,
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divergence: u64,
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returns: u64,
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short_circuits: u64, // && and ||
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cx: &'a LateContext<'a, 'tcx>,
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}
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impl<'a, 'tcx> Visitor<'tcx> for CCHelper<'a, 'tcx> {
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fn visit_expr(&mut self, e: &'tcx 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.match_arms += arms_n - 2;
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}
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},
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ExprCall(ref callee, _) => {
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walk_expr(self, e);
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let ty = self.cx.tables.node_id_to_type(callee.hir_id);
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match ty.sty {
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ty::TyFnDef(..) | ty::TyFnPtr(_) => {
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let sig = ty.fn_sig(self.cx.tcx);
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if sig.skip_binder().output().sty == ty::TyNever {
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self.divergence += 1;
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}
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},
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_ => (),
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}
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},
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ExprClosure(.., _) => (),
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ExprBinary(op, _, _) => {
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walk_expr(self, e);
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match op.node {
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BiAnd | BiOr => self.short_circuits += 1,
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_ => (),
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}
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},
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ExprRet(_) => self.returns += 1,
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_ => walk_expr(self, e),
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}
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}
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fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
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NestedVisitorMap::None
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}
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}
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#[cfg(feature = "debugging")]
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#[allow(too_many_arguments)]
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fn report_cc_bug(_: &LateContext, cc: u64, narms: u64, div: u64, shorts: u64, returns: u64, span: Span, _: NodeId) {
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span_bug!(
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span,
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"Clippy encountered a bug calculating cyclomatic complexity: cc = {}, arms = {}, \
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div = {}, shorts = {}, returns = {}. Please file a bug report.",
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cc,
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narms,
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div,
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shorts,
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returns
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);
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}
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#[cfg(not(feature = "debugging"))]
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#[allow(too_many_arguments)]
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fn report_cc_bug(cx: &LateContext, cc: u64, narms: u64, div: u64, shorts: u64, returns: u64, span: Span, id: NodeId) {
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if !is_allowed(cx, CYCLOMATIC_COMPLEXITY, id) {
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cx.sess().span_note_without_error(
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span,
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&format!(
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"Clippy encountered a bug calculating cyclomatic complexity \
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(hide this message with `#[allow(cyclomatic_complexity)]`): \
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cc = {}, arms = {}, div = {}, shorts = {}, returns = {}. \
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Please file a bug report.",
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cc,
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narms,
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div,
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shorts,
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returns
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),
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);
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}
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}
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