439 lines
14 KiB
Rust
439 lines
14 KiB
Rust
use reexport::*;
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use rustc::lint::*;
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use rustc::hir::def::Def;
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use rustc::hir::*;
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use rustc::hir::intravisit::{Visitor, walk_ty, walk_ty_param_bound, walk_fn_decl, walk_generics, NestedVisitorMap};
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use std::collections::{HashSet, HashMap};
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use syntax::codemap::Span;
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use utils::{in_external_macro, span_lint, last_path_segment};
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use syntax::symbol::keywords;
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/// **What it does:** Checks for lifetime annotations which can be removed by
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/// relying on lifetime elision.
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///
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/// **Why is this bad?** The additional lifetimes make the code look more
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/// complicated, while there is nothing out of the ordinary going on. Removing
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/// them leads to more readable code.
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///
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/// **Known problems:** Potential false negatives: we bail out if the function
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/// has a `where` clause where lifetimes are mentioned.
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///
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/// **Example:**
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/// ```rust
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/// fn in_and_out<'a>(x: &'a u8, y: u8) -> &'a u8 { x }
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/// ```
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declare_lint! {
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pub NEEDLESS_LIFETIMES,
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Warn,
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"using explicit lifetimes for references in function arguments when elision rules \
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would allow omitting them"
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}
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/// **What it does:** Checks for lifetimes in generics that are never used
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/// anywhere else.
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///
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/// **Why is this bad?** The additional lifetimes make the code look more
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/// complicated, while there is nothing out of the ordinary going on. Removing
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/// them leads to more readable code.
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///
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/// **Known problems:** None.
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///
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/// **Example:**
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/// ```rust
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/// fn unused_lifetime<'a>(x: u8) { .. }
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/// ```
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declare_lint! {
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pub UNUSED_LIFETIMES,
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Warn,
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"unused lifetimes in function definitions"
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}
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#[derive(Copy,Clone)]
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pub struct LifetimePass;
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impl LintPass for LifetimePass {
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fn get_lints(&self) -> LintArray {
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lint_array!(NEEDLESS_LIFETIMES, UNUSED_LIFETIMES)
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}
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}
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impl<'a, 'tcx> LateLintPass<'a, 'tcx> for LifetimePass {
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fn check_item(&mut self, cx: &LateContext<'a, 'tcx>, item: &'tcx Item) {
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if let ItemFn(ref decl, _, _, _, ref generics, id) = item.node {
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check_fn_inner(cx, decl, Some(id), generics, item.span);
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}
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}
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fn check_impl_item(&mut self, cx: &LateContext<'a, 'tcx>, item: &'tcx ImplItem) {
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if let ImplItemKind::Method(ref sig, id) = item.node {
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check_fn_inner(cx, &sig.decl, Some(id), &sig.generics, item.span);
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}
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}
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fn check_trait_item(&mut self, cx: &LateContext<'a, 'tcx>, item: &'tcx TraitItem) {
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if let TraitItemKind::Method(ref sig, ref body) = item.node {
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let body = match *body {
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TraitMethod::Required(_) => None,
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TraitMethod::Provided(id) => Some(id),
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};
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check_fn_inner(cx, &sig.decl, body, &sig.generics, item.span);
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}
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}
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}
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/// The lifetime of a &-reference.
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#[derive(PartialEq, Eq, Hash, Debug)]
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enum RefLt {
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Unnamed,
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Static,
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Named(Name),
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}
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fn check_fn_inner<'a, 'tcx>(
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cx: &LateContext<'a, 'tcx>,
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decl: &'tcx FnDecl,
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body: Option<BodyId>,
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generics: &'tcx Generics,
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span: Span
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) {
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if in_external_macro(cx, span) || has_where_lifetimes(cx, &generics.where_clause) {
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return;
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}
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let mut bounds_lts = Vec::new();
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for typ in &generics.ty_params {
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for bound in &typ.bounds {
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if let TraitTyParamBound(ref trait_ref, _) = *bound {
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let bounds = trait_ref.trait_ref
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.path
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.segments
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.last()
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.expect("a path must have at least one segment")
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.parameters
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.lifetimes();
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for bound in bounds {
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if bound.name != "'static" && !bound.is_elided() {
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return;
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}
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bounds_lts.push(bound);
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}
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}
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}
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}
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if could_use_elision(cx, decl, body, &generics.lifetimes, bounds_lts) {
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span_lint(cx,
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NEEDLESS_LIFETIMES,
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span,
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"explicit lifetimes given in parameter types where they could be elided");
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}
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report_extra_lifetimes(cx, decl, generics);
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}
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fn could_use_elision<'a, 'tcx: 'a>(
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cx: &LateContext<'a, 'tcx>,
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func: &'tcx FnDecl,
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body: Option<BodyId>,
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named_lts: &'tcx [LifetimeDef],
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bounds_lts: Vec<&'tcx Lifetime>
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) -> bool {
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// There are two scenarios where elision works:
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// * no output references, all input references have different LT
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// * output references, exactly one input reference with same LT
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// All lifetimes must be unnamed, 'static or defined without bounds on the
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// level of the current item.
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// check named LTs
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let allowed_lts = allowed_lts_from(named_lts);
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// these will collect all the lifetimes for references in arg/return types
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let mut input_visitor = RefVisitor::new(cx);
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let mut output_visitor = RefVisitor::new(cx);
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// extract lifetimes in input argument types
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for arg in &func.inputs {
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input_visitor.visit_ty(arg);
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}
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// extract lifetimes in output type
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if let Return(ref ty) = func.output {
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output_visitor.visit_ty(ty);
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}
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let input_lts = match input_visitor.into_vec() {
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Some(lts) => lts_from_bounds(lts, bounds_lts.into_iter()),
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None => return false,
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};
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let output_lts = match output_visitor.into_vec() {
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Some(val) => val,
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None => return false,
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};
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if let Some(body_id) = body {
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let mut checker = BodyLifetimeChecker { lifetimes_used_in_body: false };
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checker.visit_expr(&cx.tcx.hir.body(body_id).value);
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if checker.lifetimes_used_in_body {
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return false;
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}
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}
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// check for lifetimes from higher scopes
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for lt in input_lts.iter().chain(output_lts.iter()) {
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if !allowed_lts.contains(lt) {
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return false;
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}
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}
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// no input lifetimes? easy case!
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if input_lts.is_empty() {
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false
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} else if output_lts.is_empty() {
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// no output lifetimes, check distinctness of input lifetimes
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// only unnamed and static, ok
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if input_lts.iter().all(|lt| *lt == RefLt::Unnamed || *lt == RefLt::Static) {
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return false;
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}
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// we have no output reference, so we only need all distinct lifetimes
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input_lts.len() == unique_lifetimes(&input_lts)
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} else {
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// we have output references, so we need one input reference,
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// and all output lifetimes must be the same
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if unique_lifetimes(&output_lts) > 1 {
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return false;
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}
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if input_lts.len() == 1 {
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match (&input_lts[0], &output_lts[0]) {
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(&RefLt::Named(n1), &RefLt::Named(n2)) if n1 == n2 => true,
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(&RefLt::Named(_), &RefLt::Unnamed) => true,
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_ => false, // already elided, different named lifetimes
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// or something static going on
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}
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} else {
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false
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}
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}
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}
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fn allowed_lts_from(named_lts: &[LifetimeDef]) -> HashSet<RefLt> {
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let mut allowed_lts = HashSet::new();
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for lt in named_lts {
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if lt.bounds.is_empty() {
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allowed_lts.insert(RefLt::Named(lt.lifetime.name));
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}
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}
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allowed_lts.insert(RefLt::Unnamed);
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allowed_lts.insert(RefLt::Static);
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allowed_lts
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}
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fn lts_from_bounds<'a, T: Iterator<Item = &'a Lifetime>>(mut vec: Vec<RefLt>, bounds_lts: T) -> Vec<RefLt> {
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for lt in bounds_lts {
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if lt.name != "'static" {
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vec.push(RefLt::Named(lt.name));
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}
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}
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vec
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}
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/// Number of unique lifetimes in the given vector.
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fn unique_lifetimes(lts: &[RefLt]) -> usize {
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lts.iter().collect::<HashSet<_>>().len()
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}
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/// A visitor usable for `rustc_front::visit::walk_ty()`.
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struct RefVisitor<'a, 'tcx: 'a> {
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cx: &'a LateContext<'a, 'tcx>,
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lts: Vec<RefLt>,
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abort: bool,
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}
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impl<'v, 't> RefVisitor<'v, 't> {
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fn new(cx: &'v LateContext<'v, 't>) -> RefVisitor<'v, 't> {
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RefVisitor {
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cx: cx,
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lts: Vec::new(),
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abort: false,
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}
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}
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fn record(&mut self, lifetime: &Option<Lifetime>) {
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if let Some(ref lt) = *lifetime {
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if lt.name == "'static" {
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self.lts.push(RefLt::Static);
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} else if lt.is_elided() {
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self.lts.push(RefLt::Unnamed);
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} else {
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self.lts.push(RefLt::Named(lt.name));
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}
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} else {
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self.lts.push(RefLt::Unnamed);
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}
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}
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fn into_vec(self) -> Option<Vec<RefLt>> {
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if self.abort { None } else { Some(self.lts) }
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}
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fn collect_anonymous_lifetimes(&mut self, qpath: &QPath, ty: &Ty) {
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let last_path_segment = &last_path_segment(qpath).parameters;
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if let AngleBracketedParameters(ref params) = *last_path_segment {
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if params.lifetimes.is_empty() {
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match self.cx.tables.qpath_def(qpath, ty.id) {
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Def::TyAlias(def_id) |
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Def::Struct(def_id) => {
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let generics = self.cx.tcx.generics_of(def_id);
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for _ in generics.regions.as_slice() {
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self.record(&None);
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}
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},
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Def::Trait(def_id) => {
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let trait_def = self.cx.tcx.trait_def(def_id);
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for _ in &self.cx.tcx.generics_of(trait_def.def_id).regions {
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self.record(&None);
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}
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},
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_ => (),
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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> Visitor<'tcx> for RefVisitor<'a, 'tcx> {
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// for lifetimes as parameters of generics
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fn visit_lifetime(&mut self, lifetime: &'tcx Lifetime) {
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self.record(&Some(*lifetime));
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}
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fn visit_ty(&mut self, ty: &'tcx Ty) {
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match ty.node {
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TyRptr(ref lt, _) if lt.is_elided() => {
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self.record(&None);
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},
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TyPath(ref path) => {
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self.collect_anonymous_lifetimes(path, ty);
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},
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TyImplTrait(ref param_bounds) => {
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for bound in param_bounds {
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if let RegionTyParamBound(_) = *bound {
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self.record(&None);
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}
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}
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},
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TyTraitObject(ref bounds, ref lt) => {
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if !lt.is_elided() {
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self.abort = true;
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}
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for bound in bounds {
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self.visit_poly_trait_ref(bound, TraitBoundModifier::None);
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}
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return;
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},
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_ => (),
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}
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walk_ty(self, ty);
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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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/// Are any lifetimes mentioned in the `where` clause? If yes, we don't try to
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/// reason about elision.
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fn has_where_lifetimes<'a, 'tcx: 'a>(cx: &LateContext<'a, 'tcx>, where_clause: &'tcx WhereClause) -> bool {
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for predicate in &where_clause.predicates {
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match *predicate {
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WherePredicate::RegionPredicate(..) => return true,
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WherePredicate::BoundPredicate(ref pred) => {
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// a predicate like F: Trait or F: for<'a> Trait<'a>
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let mut visitor = RefVisitor::new(cx);
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// walk the type F, it may not contain LT refs
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walk_ty(&mut visitor, &pred.bounded_ty);
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if !visitor.lts.is_empty() {
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return true;
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}
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// if the bounds define new lifetimes, they are fine to occur
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let allowed_lts = allowed_lts_from(&pred.bound_lifetimes);
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// now walk the bounds
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for bound in pred.bounds.iter() {
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walk_ty_param_bound(&mut visitor, bound);
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}
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// and check that all lifetimes are allowed
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match visitor.into_vec() {
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None => return false,
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Some(lts) => {
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for lt in lts {
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if !allowed_lts.contains(<) {
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return true;
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}
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}
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},
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}
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},
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WherePredicate::EqPredicate(ref pred) => {
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let mut visitor = RefVisitor::new(cx);
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walk_ty(&mut visitor, &pred.lhs_ty);
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walk_ty(&mut visitor, &pred.rhs_ty);
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if !visitor.lts.is_empty() {
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return true;
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}
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},
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}
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}
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false
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}
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struct LifetimeChecker {
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map: HashMap<Name, Span>,
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}
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impl<'tcx> Visitor<'tcx> for LifetimeChecker {
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// for lifetimes as parameters of generics
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fn visit_lifetime(&mut self, lifetime: &'tcx Lifetime) {
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self.map.remove(&lifetime.name);
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}
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fn visit_lifetime_def(&mut self, _: &'tcx LifetimeDef) {
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// don't actually visit `<'a>` or `<'a: 'b>`
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// we've already visited the `'a` declarations and
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// don't want to spuriously remove them
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// `'b` in `'a: 'b` is useless unless used elsewhere in
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// a non-lifetime bound
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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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fn report_extra_lifetimes<'a, 'tcx: 'a>(cx: &LateContext<'a, 'tcx>, func: &'tcx FnDecl, generics: &'tcx Generics) {
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let hs = generics.lifetimes
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.iter()
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.map(|lt| (lt.lifetime.name, lt.lifetime.span))
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.collect();
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let mut checker = LifetimeChecker { map: hs };
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walk_generics(&mut checker, generics);
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walk_fn_decl(&mut checker, func);
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for &v in checker.map.values() {
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span_lint(cx, UNUSED_LIFETIMES, v, "this lifetime isn't used in the function definition");
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}
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}
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struct BodyLifetimeChecker {
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lifetimes_used_in_body: bool,
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}
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impl<'tcx> Visitor<'tcx> for BodyLifetimeChecker {
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// for lifetimes as parameters of generics
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fn visit_lifetime(&mut self, lifetime: &'tcx Lifetime) {
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if lifetime.name != keywords::Invalid.name() && lifetime.name != "'static" {
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self.lifetimes_used_in_body = true;
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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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