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|
//! calculate cognitive complexity and warn about overly complex functions
use clippy_utils::diagnostics::span_lint_and_help;
use clippy_utils::source::snippet_opt;
use clippy_utils::ty::is_type_diagnostic_item;
use clippy_utils::visitors::for_each_expr;
use clippy_utils::{get_async_fn_body, is_async_fn, LimitStack};
use core::ops::ControlFlow;
use rustc_ast::ast::Attribute;
use rustc_hir::intravisit::FnKind;
use rustc_hir::{Body, Expr, ExprKind, FnDecl};
use rustc_lint::{LateContext, LateLintPass, LintContext};
use rustc_session::{declare_tool_lint, impl_lint_pass};
use rustc_span::def_id::LocalDefId;
use rustc_span::source_map::Span;
use rustc_span::{sym, BytePos};
declare_clippy_lint! {
/// ### What it does
/// Checks for methods with high cognitive complexity.
///
/// ### Why is this bad?
/// Methods of high cognitive complexity tend to be hard to
/// both read and maintain. Also LLVM will tend to optimize small methods better.
///
/// ### Known problems
/// Sometimes it's hard to find a way to reduce the
/// complexity.
///
/// ### Example
/// You'll see it when you get the warning.
#[clippy::version = "1.35.0"]
pub COGNITIVE_COMPLEXITY,
nursery,
"functions that should be split up into multiple functions"
}
pub struct CognitiveComplexity {
limit: LimitStack,
}
impl CognitiveComplexity {
#[must_use]
pub fn new(limit: u64) -> Self {
Self {
limit: LimitStack::new(limit),
}
}
}
impl_lint_pass!(CognitiveComplexity => [COGNITIVE_COMPLEXITY]);
impl CognitiveComplexity {
#[expect(clippy::cast_possible_truncation)]
fn check<'tcx>(
&mut self,
cx: &LateContext<'tcx>,
kind: FnKind<'tcx>,
decl: &'tcx FnDecl<'_>,
expr: &'tcx Expr<'_>,
body_span: Span,
) {
if body_span.from_expansion() {
return;
}
let mut cc = 1u64;
let mut returns = 0u64;
let _: Option<!> = for_each_expr(expr, |e| {
match e.kind {
ExprKind::If(_, _, _) => {
cc += 1;
},
ExprKind::Match(_, arms, _) => {
if arms.len() > 1 {
cc += 1;
}
cc += arms.iter().filter(|arm| arm.guard.is_some()).count() as u64;
},
ExprKind::Ret(_) => returns += 1,
_ => {},
}
ControlFlow::Continue(())
});
let ret_ty = cx.typeck_results().node_type(expr.hir_id);
let ret_adjust = if is_type_diagnostic_item(cx, ret_ty, sym::Result) {
returns
} else {
#[expect(clippy::integer_division)]
(returns / 2)
};
// prevent degenerate cases where unreachable code contains `return` statements
if cc >= ret_adjust {
cc -= ret_adjust;
}
if cc > self.limit.limit() {
let fn_span = match kind {
FnKind::ItemFn(ident, _, _) | FnKind::Method(ident, _) => ident.span,
FnKind::Closure => {
let header_span = body_span.with_hi(decl.output.span().lo());
let pos = snippet_opt(cx, header_span).and_then(|snip| {
let low_offset = snip.find('|')?;
let high_offset = 1 + snip.get(low_offset + 1..)?.find('|')?;
let low = header_span.lo() + BytePos(low_offset as u32);
let high = low + BytePos(high_offset as u32 + 1);
Some((low, high))
});
if let Some((low, high)) = pos {
Span::new(low, high, header_span.ctxt(), header_span.parent())
} else {
return;
}
},
};
span_lint_and_help(
cx,
COGNITIVE_COMPLEXITY,
fn_span,
&format!(
"the function has a cognitive complexity of ({cc}/{})",
self.limit.limit()
),
None,
"you could split it up into multiple smaller functions",
);
}
}
}
impl<'tcx> LateLintPass<'tcx> for CognitiveComplexity {
fn check_fn(
&mut self,
cx: &LateContext<'tcx>,
kind: FnKind<'tcx>,
decl: &'tcx FnDecl<'_>,
body: &'tcx Body<'_>,
span: Span,
def_id: LocalDefId,
) {
if !cx.tcx.has_attr(def_id.to_def_id(), sym::test) {
let expr = if is_async_fn(kind) {
match get_async_fn_body(cx.tcx, body) {
Some(b) => b,
None => {
return;
},
}
} else {
body.value
};
self.check(cx, kind, decl, expr, span);
}
}
fn enter_lint_attrs(&mut self, cx: &LateContext<'tcx>, attrs: &'tcx [Attribute]) {
self.limit.push_attrs(cx.sess(), attrs, "cognitive_complexity");
}
fn exit_lint_attrs(&mut self, cx: &LateContext<'tcx>, attrs: &'tcx [Attribute]) {
self.limit.pop_attrs(cx.sess(), attrs, "cognitive_complexity");
}
}
|
