134 lines
4.0 KiB
Rust
134 lines
4.0 KiB
Rust
use clippy_utils::diagnostics::span_lint_and_help;
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use clippy_utils::{is_from_proc_macro, is_in_test_function};
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use rustc_data_structures::fx::FxHashMap;
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use rustc_hir::def_id::LocalDefId;
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use rustc_hir::intravisit::{walk_expr, FnKind, Visitor};
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use rustc_hir::{Body, Expr, ExprKind, FnDecl};
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use rustc_lint::{LateContext, LateLintPass, LintContext};
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use rustc_middle::hir::nested_filter::OnlyBodies;
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use rustc_middle::lint::in_external_macro;
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use rustc_session::impl_lint_pass;
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use rustc_span::Span;
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declare_clippy_lint! {
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/// ### What it does
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/// Checks for functions that are only used once. Does not lint tests.
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///
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/// ### Why is this bad?
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/// It's usually not, splitting a function into multiple parts often improves readability and in
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/// the case of generics, can prevent the compiler from duplicating the function dozens of
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/// time; instead, only duplicating a thunk. But this can prevent segmentation across a
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/// codebase, where many small functions are used only once.
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///
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/// Note: If this lint is used, prepare to allow this a lot.
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///
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/// ### Example
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/// ```no_run
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/// pub fn a<T>(t: &T)
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/// where
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/// T: AsRef<str>,
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/// {
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/// a_inner(t.as_ref())
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/// }
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///
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/// fn a_inner(t: &str) {
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/// /* snip */
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/// }
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///
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/// ```
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/// Use instead:
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/// ```no_run
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/// pub fn a<T>(t: &T)
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/// where
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/// T: AsRef<str>,
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/// {
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/// let t = t.as_ref();
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/// /* snip */
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/// }
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///
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/// ```
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#[clippy::version = "1.72.0"]
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pub SINGLE_CALL_FN,
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restriction,
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"checks for functions that are only used once"
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}
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impl_lint_pass!(SingleCallFn => [SINGLE_CALL_FN]);
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#[derive(Clone)]
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pub struct SingleCallFn {
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pub avoid_breaking_exported_api: bool,
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pub def_id_to_usage: FxHashMap<LocalDefId, (Span, Vec<Span>)>,
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}
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impl<'tcx> LateLintPass<'tcx> for SingleCallFn {
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fn check_fn(
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&mut self,
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cx: &LateContext<'tcx>,
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kind: 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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def_id: LocalDefId,
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) {
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if self.avoid_breaking_exported_api && cx.effective_visibilities.is_exported(def_id)
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|| in_external_macro(cx.sess(), span)
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|| is_in_test_function(cx.tcx, body.value.hir_id)
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|| is_from_proc_macro(cx, &(&kind, body, cx.tcx.local_def_id_to_hir_id(def_id), span))
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{
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return;
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}
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self.def_id_to_usage.insert(def_id, (span, vec![]));
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}
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fn check_crate_post(&mut self, cx: &LateContext<'tcx>) {
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let mut v = FnUsageVisitor {
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cx,
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def_id_to_usage: &mut self.def_id_to_usage,
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};
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cx.tcx.hir().visit_all_item_likes_in_crate(&mut v);
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for usage in self.def_id_to_usage.values() {
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let single_call_fn_span = usage.0;
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if let [caller_span] = *usage.1 {
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span_lint_and_help(
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cx,
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SINGLE_CALL_FN,
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single_call_fn_span,
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"this function is only used once",
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Some(caller_span),
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"used here",
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);
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}
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}
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}
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}
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struct FnUsageVisitor<'a, 'tcx> {
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cx: &'a LateContext<'tcx>,
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def_id_to_usage: &'a mut FxHashMap<LocalDefId, (Span, Vec<Span>)>,
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}
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impl<'a, 'tcx> Visitor<'tcx> for FnUsageVisitor<'a, 'tcx> {
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type NestedFilter = OnlyBodies;
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fn nested_visit_map(&mut self) -> Self::Map {
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self.cx.tcx.hir()
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}
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fn visit_expr(&mut self, expr: &'tcx Expr<'tcx>) {
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let Self { cx, .. } = *self;
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if let ExprKind::Path(qpath) = expr.kind
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&& let res = cx.qpath_res(&qpath, expr.hir_id)
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&& let Some(call_def_id) = res.opt_def_id()
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&& let Some(def_id) = call_def_id.as_local()
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&& let Some(usage) = self.def_id_to_usage.get_mut(&def_id)
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{
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usage.1.push(expr.span);
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}
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walk_expr(self, expr);
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}
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}
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