rust/clippy_lints/src/cyclomatic_complexity.rs
2018-03-28 15:24:26 +02:00

221 lines
6.7 KiB
Rust

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