summaryrefslogtreecommitdiffstats
path: root/src/tools/clippy/clippy_lints/src/only_used_in_recursion.rs
diff options
context:
space:
mode:
Diffstat (limited to '')
-rw-r--r--src/tools/clippy/clippy_lints/src/only_used_in_recursion.rs823
1 files changed, 279 insertions, 544 deletions
diff --git a/src/tools/clippy/clippy_lints/src/only_used_in_recursion.rs b/src/tools/clippy/clippy_lints/src/only_used_in_recursion.rs
index 413a740be..6217110a1 100644
--- a/src/tools/clippy/clippy_lints/src/only_used_in_recursion.rs
+++ b/src/tools/clippy/clippy_lints/src/only_used_in_recursion.rs
@@ -1,26 +1,18 @@
-use std::collections::VecDeque;
-
-use clippy_utils::diagnostics::span_lint_and_sugg;
-use clippy_utils::is_lint_allowed;
-use itertools::{izip, Itertools};
-use rustc_ast::{walk_list, Label, Mutability};
-use rustc_data_structures::fx::{FxHashMap, FxHashSet};
+use clippy_utils::diagnostics::span_lint_and_then;
+use clippy_utils::{get_expr_use_or_unification_node, get_parent_node, path_def_id, path_to_local, path_to_local_id};
+use core::cell::Cell;
+use rustc_data_structures::fx::FxHashMap;
use rustc_errors::Applicability;
-use rustc_hir::def::{DefKind, Res};
use rustc_hir::def_id::DefId;
-use rustc_hir::definitions::{DefPathData, DisambiguatedDefPathData};
-use rustc_hir::intravisit::{walk_expr, walk_stmt, FnKind, Visitor};
-use rustc_hir::{
- Arm, Block, Body, Closure, Expr, ExprKind, Guard, HirId, ImplicitSelfKind, Let, Local, Pat, PatKind, Path,
- PathSegment, QPath, Stmt, StmtKind, TyKind, UnOp,
-};
+use rustc_hir::hir_id::HirIdMap;
+use rustc_hir::{Body, Expr, ExprKind, HirId, ImplItem, ImplItemKind, Node, PatKind, TraitItem, TraitItemKind};
use rustc_lint::{LateContext, LateLintPass};
-use rustc_middle::ty;
-use rustc_middle::ty::{Ty, TyCtxt, TypeckResults};
-use rustc_session::{declare_lint_pass, declare_tool_lint};
-use rustc_span::symbol::kw;
-use rustc_span::symbol::Ident;
+use rustc_middle::ty::subst::{GenericArgKind, SubstsRef};
+use rustc_middle::ty::{self, ConstKind};
+use rustc_session::{declare_tool_lint, impl_lint_pass};
+use rustc_span::symbol::{kw, Ident};
use rustc_span::Span;
+use std::iter;
declare_clippy_lint! {
/// ### What it does
@@ -89,572 +81,315 @@ declare_clippy_lint! {
/// ```
#[clippy::version = "1.61.0"]
pub ONLY_USED_IN_RECURSION,
- nursery,
+ complexity,
"arguments that is only used in recursion can be removed"
}
-declare_lint_pass!(OnlyUsedInRecursion => [ONLY_USED_IN_RECURSION]);
-
-impl<'tcx> LateLintPass<'tcx> for OnlyUsedInRecursion {
- fn check_fn(
- &mut self,
- cx: &LateContext<'tcx>,
- kind: FnKind<'tcx>,
- decl: &'tcx rustc_hir::FnDecl<'tcx>,
- body: &'tcx Body<'tcx>,
- _: Span,
- id: HirId,
- ) {
- if is_lint_allowed(cx, ONLY_USED_IN_RECURSION, id) {
- return;
- }
- if let FnKind::ItemFn(ident, ..) | FnKind::Method(ident, ..) = kind {
- let def_id = id.owner.to_def_id();
- let data = cx.tcx.def_path(def_id).data;
-
- if data.len() > 1 {
- match data.get(data.len() - 2) {
- Some(DisambiguatedDefPathData {
- data: DefPathData::Impl,
- disambiguator,
- }) if *disambiguator != 0 => return,
- _ => {},
- }
- }
-
- let has_self = !matches!(decl.implicit_self, ImplicitSelfKind::None);
-
- let ty_res = cx.typeck_results();
- let param_span = body
- .params
- .iter()
- .flat_map(|param| {
- let mut v = Vec::new();
- param.pat.each_binding(|_, hir_id, span, ident| {
- v.push((hir_id, span, ident));
- });
- v
- })
- .skip(if has_self { 1 } else { 0 })
- .filter(|(_, _, ident)| !ident.name.as_str().starts_with('_'))
- .collect_vec();
-
- let params = body.params.iter().map(|param| param.pat).collect();
-
- let mut visitor = SideEffectVisit {
- graph: FxHashMap::default(),
- has_side_effect: FxHashSet::default(),
- ret_vars: Vec::new(),
- contains_side_effect: false,
- break_vars: FxHashMap::default(),
- params,
- fn_ident: ident,
- fn_def_id: def_id,
- is_method: matches!(kind, FnKind::Method(..)),
- has_self,
- ty_res,
- tcx: cx.tcx,
- visited_exprs: FxHashSet::default(),
- };
-
- visitor.visit_expr(&body.value);
- let vars = std::mem::take(&mut visitor.ret_vars);
- // this would set the return variables to side effect
- visitor.add_side_effect(vars);
-
- let mut queue = visitor.has_side_effect.iter().copied().collect::<VecDeque<_>>();
-
- // a simple BFS to check all the variables that have side effect
- while let Some(id) = queue.pop_front() {
- if let Some(next) = visitor.graph.get(&id) {
- for i in next {
- if !visitor.has_side_effect.contains(i) {
- visitor.has_side_effect.insert(*i);
- queue.push_back(*i);
- }
- }
- }
- }
-
- for (id, span, ident) in param_span {
- // if the variable is not used in recursion, it would be marked as unused
- if !visitor.has_side_effect.contains(&id) {
- let mut queue = VecDeque::new();
- let mut visited = FxHashSet::default();
-
- queue.push_back(id);
-
- // a simple BFS to check the graph can reach to itself
- // if it can't, it means the variable is never used in recursion
- while let Some(id) = queue.pop_front() {
- if let Some(next) = visitor.graph.get(&id) {
- for i in next {
- if !visited.contains(i) {
- visited.insert(id);
- queue.push_back(*i);
- }
- }
- }
- }
+impl_lint_pass!(OnlyUsedInRecursion => [ONLY_USED_IN_RECURSION]);
+
+#[derive(Clone, Copy)]
+enum FnKind {
+ Fn,
+ TraitFn,
+ // This is a hack. Ideally we would store a `SubstsRef<'tcx>` type here, but a lint pass must be `'static`.
+ // Substitutions are, however, interned. This allows us to store the pointer as a `usize` when comparing for
+ // equality.
+ ImplTraitFn(usize),
+}
- if visited.contains(&id) {
- span_lint_and_sugg(
- cx,
- ONLY_USED_IN_RECURSION,
- span,
- "parameter is only used in recursion",
- "if this is intentional, prefix with an underscore",
- format!("_{}", ident.name.as_str()),
- Applicability::MaybeIncorrect,
- );
- }
- }
- }
+struct Param {
+ /// The function this is a parameter for.
+ fn_id: DefId,
+ fn_kind: FnKind,
+ /// The index of this parameter.
+ idx: usize,
+ ident: Ident,
+ /// Whether this parameter should be linted. Set by `Params::flag_for_linting`.
+ apply_lint: Cell<bool>,
+ /// All the uses of this parameter.
+ uses: Vec<Usage>,
+}
+impl Param {
+ fn new(fn_id: DefId, fn_kind: FnKind, idx: usize, ident: Ident) -> Self {
+ Self {
+ fn_id,
+ fn_kind,
+ idx,
+ ident,
+ apply_lint: Cell::new(true),
+ uses: Vec::new(),
}
}
}
-pub fn is_primitive(ty: Ty<'_>) -> bool {
- let ty = ty.peel_refs();
- ty.is_primitive() || ty.is_str()
+#[derive(Debug)]
+struct Usage {
+ span: Span,
+ idx: usize,
}
-
-pub fn is_array(ty: Ty<'_>) -> bool {
- let ty = ty.peel_refs();
- ty.is_array() || ty.is_array_slice()
+impl Usage {
+ fn new(span: Span, idx: usize) -> Self {
+ Self { span, idx }
+ }
}
-/// This builds the graph of side effect.
-/// The edge `a -> b` means if `a` has side effect, `b` will have side effect.
-///
-/// There are some example in following code:
-/// ```rust, ignore
-/// let b = 1;
-/// let a = b; // a -> b
-/// let (c, d) = (a, b); // c -> b, d -> b
-///
-/// let e = if a == 0 { // e -> a
-/// c // e -> c
-/// } else {
-/// d // e -> d
-/// };
-/// ```
-pub struct SideEffectVisit<'tcx> {
- graph: FxHashMap<HirId, FxHashSet<HirId>>,
- has_side_effect: FxHashSet<HirId>,
- // bool for if the variable was dereferenced from mutable reference
- ret_vars: Vec<(HirId, bool)>,
- contains_side_effect: bool,
- // break label
- break_vars: FxHashMap<Ident, Vec<(HirId, bool)>>,
- params: Vec<&'tcx Pat<'tcx>>,
- fn_ident: Ident,
- fn_def_id: DefId,
- is_method: bool,
- has_self: bool,
- ty_res: &'tcx TypeckResults<'tcx>,
- tcx: TyCtxt<'tcx>,
- visited_exprs: FxHashSet<HirId>,
+/// The parameters being checked by the lint, indexed by both the parameter's `HirId` and the
+/// `DefId` of the function paired with the parameter's index.
+#[derive(Default)]
+struct Params {
+ params: Vec<Param>,
+ by_id: HirIdMap<usize>,
+ by_fn: FxHashMap<(DefId, usize), usize>,
}
-
-impl<'tcx> Visitor<'tcx> for SideEffectVisit<'tcx> {
- fn visit_stmt(&mut self, s: &'tcx Stmt<'tcx>) {
- match s.kind {
- StmtKind::Local(Local {
- pat, init: Some(init), ..
- }) => {
- self.visit_pat_expr(pat, init, false);
- },
- StmtKind::Item(_) | StmtKind::Expr(_) | StmtKind::Semi(_) => {
- walk_stmt(self, s);
- },
- StmtKind::Local(_) => {},
- }
- self.ret_vars.clear();
+impl Params {
+ fn insert(&mut self, param: Param, id: HirId) {
+ let idx = self.params.len();
+ self.by_id.insert(id, idx);
+ self.by_fn.insert((param.fn_id, param.idx), idx);
+ self.params.push(param);
}
- fn visit_expr(&mut self, ex: &'tcx Expr<'tcx>) {
- if !self.visited_exprs.insert(ex.hir_id) {
- return;
- }
- match ex.kind {
- ExprKind::Array(exprs) | ExprKind::Tup(exprs) => {
- self.ret_vars = exprs
- .iter()
- .flat_map(|expr| {
- self.visit_expr(expr);
- std::mem::take(&mut self.ret_vars)
- })
- .collect();
- },
- ExprKind::Call(callee, args) => self.visit_fn(callee, args),
- ExprKind::MethodCall(path, args, _) => self.visit_method_call(path, args),
- ExprKind::Binary(_, lhs, rhs) => {
- self.visit_bin_op(lhs, rhs);
- },
- ExprKind::Unary(op, expr) => self.visit_un_op(op, expr),
- ExprKind::Let(Let { pat, init, .. }) => self.visit_pat_expr(pat, init, false),
- ExprKind::If(bind, then_expr, else_expr) => {
- self.visit_if(bind, then_expr, else_expr);
- },
- ExprKind::Match(expr, arms, _) => self.visit_match(expr, arms),
- // since analysing the closure is not easy, just set all variables in it to side-effect
- ExprKind::Closure(&Closure { body, .. }) => {
- let body = self.tcx.hir().body(body);
- self.visit_body(body);
- let vars = std::mem::take(&mut self.ret_vars);
- self.add_side_effect(vars);
- },
- ExprKind::Loop(block, label, _, _) | ExprKind::Block(block, label) => {
- self.visit_block_label(block, label);
- },
- ExprKind::Assign(bind, expr, _) => {
- self.visit_assign(bind, expr);
- },
- ExprKind::AssignOp(_, bind, expr) => {
- self.visit_assign(bind, expr);
- self.visit_bin_op(bind, expr);
- },
- ExprKind::Field(expr, _) => {
- self.visit_expr(expr);
- if matches!(self.ty_res.expr_ty(expr).kind(), ty::Ref(_, _, Mutability::Mut)) {
- self.ret_vars.iter_mut().for_each(|(_, b)| *b = true);
- }
- },
- ExprKind::Index(expr, index) => {
- self.visit_expr(expr);
- let mut vars = std::mem::take(&mut self.ret_vars);
- self.visit_expr(index);
- self.ret_vars.append(&mut vars);
-
- if !is_array(self.ty_res.expr_ty(expr)) {
- self.add_side_effect(self.ret_vars.clone());
- } else if matches!(self.ty_res.expr_ty(expr).kind(), ty::Ref(_, _, Mutability::Mut)) {
- self.ret_vars.iter_mut().for_each(|(_, b)| *b = true);
- }
- },
- ExprKind::Break(dest, Some(expr)) => {
- self.visit_expr(expr);
- if let Some(label) = dest.label {
- self.break_vars
- .entry(label.ident)
- .or_insert(Vec::new())
- .append(&mut self.ret_vars);
- }
- self.contains_side_effect = true;
- },
- ExprKind::Ret(Some(expr)) => {
- self.visit_expr(expr);
- let vars = std::mem::take(&mut self.ret_vars);
- self.add_side_effect(vars);
- self.contains_side_effect = true;
- },
- ExprKind::Break(_, None) | ExprKind::Continue(_) | ExprKind::Ret(None) => {
- self.contains_side_effect = true;
- },
- ExprKind::Struct(_, exprs, expr) => {
- let mut ret_vars = exprs
- .iter()
- .flat_map(|field| {
- self.visit_expr(field.expr);
- std::mem::take(&mut self.ret_vars)
- })
- .collect();
-
- walk_list!(self, visit_expr, expr);
- self.ret_vars.append(&mut ret_vars);
- },
- _ => walk_expr(self, ex),
+ fn remove_by_id(&mut self, id: HirId) {
+ if let Some(param) = self.get_by_id_mut(id) {
+ param.uses = Vec::new();
+ let key = (param.fn_id, param.idx);
+ self.by_fn.remove(&key);
+ self.by_id.remove(&id);
}
}
- fn visit_path(&mut self, path: &'tcx Path<'tcx>, _id: HirId) {
- if let Res::Local(id) = path.res {
- self.ret_vars.push((id, false));
- }
+ fn get_by_id_mut(&mut self, id: HirId) -> Option<&mut Param> {
+ self.params.get_mut(*self.by_id.get(&id)?)
}
-}
-impl<'tcx> SideEffectVisit<'tcx> {
- fn visit_assign(&mut self, lhs: &'tcx Expr<'tcx>, rhs: &'tcx Expr<'tcx>) {
- // Just support array and tuple unwrapping for now.
- //
- // ex) `(a, b) = (c, d);`
- // The graph would look like this:
- // a -> c
- // b -> d
- //
- // This would minimize the connection of the side-effect graph.
- match (&lhs.kind, &rhs.kind) {
- (ExprKind::Array(lhs), ExprKind::Array(rhs)) | (ExprKind::Tup(lhs), ExprKind::Tup(rhs)) => {
- // if not, it is a compile error
- debug_assert!(lhs.len() == rhs.len());
- izip!(*lhs, *rhs).for_each(|(lhs, rhs)| self.visit_assign(lhs, rhs));
- },
- // in other assigns, we have to connect all each other
- // because they can be connected somehow
- _ => {
- self.visit_expr(lhs);
- let lhs_vars = std::mem::take(&mut self.ret_vars);
- self.visit_expr(rhs);
- let rhs_vars = std::mem::take(&mut self.ret_vars);
- self.connect_assign(&lhs_vars, &rhs_vars, false);
- },
- }
+ fn get_by_fn(&self, id: DefId, idx: usize) -> Option<&Param> {
+ self.params.get(*self.by_fn.get(&(id, idx))?)
}
- fn visit_block_label(&mut self, block: &'tcx Block<'tcx>, label: Option<Label>) {
- self.visit_block(block);
- let _ = label.and_then(|label| {
- self.break_vars
- .remove(&label.ident)
- .map(|mut break_vars| self.ret_vars.append(&mut break_vars))
- });
- }
-
- fn visit_bin_op(&mut self, lhs: &'tcx Expr<'tcx>, rhs: &'tcx Expr<'tcx>) {
- self.visit_expr(lhs);
- let mut ret_vars = std::mem::take(&mut self.ret_vars);
- self.visit_expr(rhs);
- self.ret_vars.append(&mut ret_vars);
-
- // the binary operation between non primitive values are overloaded operators
- // so they can have side-effects
- if !is_primitive(self.ty_res.expr_ty(lhs)) || !is_primitive(self.ty_res.expr_ty(rhs)) {
- self.ret_vars.iter().for_each(|id| {
- self.has_side_effect.insert(id.0);
- });
- self.contains_side_effect = true;
- }
+ fn clear(&mut self) {
+ self.params.clear();
+ self.by_id.clear();
+ self.by_fn.clear();
}
- fn visit_un_op(&mut self, op: UnOp, expr: &'tcx Expr<'tcx>) {
- self.visit_expr(expr);
- let ty = self.ty_res.expr_ty(expr);
- // dereferencing a reference has no side-effect
- if !is_primitive(ty) && !matches!((op, ty.kind()), (UnOp::Deref, ty::Ref(..))) {
- self.add_side_effect(self.ret_vars.clone());
- }
-
- if matches!((op, ty.kind()), (UnOp::Deref, ty::Ref(_, _, Mutability::Mut))) {
- self.ret_vars.iter_mut().for_each(|(_, b)| *b = true);
+ /// Sets the `apply_lint` flag on each parameter.
+ fn flag_for_linting(&mut self) {
+ // Stores the list of parameters currently being resolved. Needed to avoid cycles.
+ let mut eval_stack = Vec::new();
+ for param in &self.params {
+ self.try_disable_lint_for_param(param, &mut eval_stack);
}
}
- fn visit_pat_expr(&mut self, pat: &'tcx Pat<'tcx>, expr: &'tcx Expr<'tcx>, connect_self: bool) {
- match (&pat.kind, &expr.kind) {
- (PatKind::Tuple(pats, _), ExprKind::Tup(exprs)) => {
- self.ret_vars = izip!(*pats, *exprs)
- .flat_map(|(pat, expr)| {
- self.visit_pat_expr(pat, expr, connect_self);
- std::mem::take(&mut self.ret_vars)
- })
- .collect();
- },
- (PatKind::Slice(front_exprs, _, back_exprs), ExprKind::Array(exprs)) => {
- let mut vars = izip!(*front_exprs, *exprs)
- .flat_map(|(pat, expr)| {
- self.visit_pat_expr(pat, expr, connect_self);
- std::mem::take(&mut self.ret_vars)
- })
- .collect();
- self.ret_vars = izip!(back_exprs.iter().rev(), exprs.iter().rev())
- .flat_map(|(pat, expr)| {
- self.visit_pat_expr(pat, expr, connect_self);
- std::mem::take(&mut self.ret_vars)
- })
- .collect();
- self.ret_vars.append(&mut vars);
- },
- _ => {
- let mut lhs_vars = Vec::new();
- pat.each_binding(|_, id, _, _| lhs_vars.push((id, false)));
- self.visit_expr(expr);
- let rhs_vars = std::mem::take(&mut self.ret_vars);
- self.connect_assign(&lhs_vars, &rhs_vars, connect_self);
- self.ret_vars = rhs_vars;
- },
+ // Use by calling `flag_for_linting`.
+ fn try_disable_lint_for_param(&self, param: &Param, eval_stack: &mut Vec<usize>) -> bool {
+ if !param.apply_lint.get() {
+ true
+ } else if param.uses.is_empty() {
+ // Don't lint on unused parameters.
+ param.apply_lint.set(false);
+ true
+ } else if eval_stack.contains(&param.idx) {
+ // Already on the evaluation stack. Returning false will continue to evaluate other dependencies.
+ false
+ } else {
+ eval_stack.push(param.idx);
+ // Check all cases when used at a different parameter index.
+ // Needed to catch cases like: `fn f(x: u32, y: u32) { f(y, x) }`
+ for usage in param.uses.iter().filter(|u| u.idx != param.idx) {
+ if self
+ .get_by_fn(param.fn_id, usage.idx)
+ // If the parameter can't be found, then it's used for more than just recursion.
+ .map_or(true, |p| self.try_disable_lint_for_param(p, eval_stack))
+ {
+ param.apply_lint.set(false);
+ eval_stack.pop();
+ return true;
+ }
+ }
+ eval_stack.pop();
+ false
}
}
+}
- fn visit_fn(&mut self, callee: &'tcx Expr<'tcx>, args: &'tcx [Expr<'tcx>]) {
- self.visit_expr(callee);
- let mut ret_vars = std::mem::take(&mut self.ret_vars);
- self.add_side_effect(ret_vars.clone());
-
- let mut is_recursive = false;
-
- if_chain! {
- if !self.has_self;
- if let ExprKind::Path(QPath::Resolved(_, path)) = callee.kind;
- if let Res::Def(DefKind::Fn, def_id) = path.res;
- if self.fn_def_id == def_id;
- then {
- is_recursive = true;
- }
- }
+#[derive(Default)]
+pub struct OnlyUsedInRecursion {
+ /// Track the top-level body entered. Needed to delay reporting when entering nested bodies.
+ entered_body: Option<HirId>,
+ params: Params,
+}
- if_chain! {
- if !self.has_self && self.is_method;
- if let ExprKind::Path(QPath::TypeRelative(ty, segment)) = callee.kind;
- if segment.ident == self.fn_ident;
- if let TyKind::Path(QPath::Resolved(_, path)) = ty.kind;
- if let Res::SelfTy{ .. } = path.res;
- then {
- is_recursive = true;
- }
+impl<'tcx> LateLintPass<'tcx> for OnlyUsedInRecursion {
+ fn check_body(&mut self, cx: &LateContext<'tcx>, body: &'tcx Body<'tcx>) {
+ if body.value.span.from_expansion() {
+ return;
}
-
- if is_recursive {
- izip!(self.params.clone(), args).for_each(|(pat, expr)| {
- self.visit_pat_expr(pat, expr, true);
- self.ret_vars.clear();
- });
- } else {
- // This would set arguments used in closure that does not have side-effect.
- // Closure itself can be detected whether there is a side-effect, but the
- // value of variable that is holding closure can change.
- // So, we just check the variables.
- self.ret_vars = args
- .iter()
- .flat_map(|expr| {
- self.visit_expr(expr);
- std::mem::take(&mut self.ret_vars)
- })
- .collect_vec()
- .into_iter()
- .map(|id| {
- self.has_side_effect.insert(id.0);
- id
- })
- .collect();
- self.contains_side_effect = true;
+ // `skip_params` is either `0` or `1` to skip the `self` parameter in trait functions.
+ // It can't be renamed, and it can't be removed without removing it from multiple functions.
+ let (fn_id, fn_kind, skip_params) = match get_parent_node(cx.tcx, body.value.hir_id) {
+ Some(Node::Item(i)) => (i.def_id.to_def_id(), FnKind::Fn, 0),
+ Some(Node::TraitItem(&TraitItem {
+ kind: TraitItemKind::Fn(ref sig, _),
+ def_id,
+ ..
+ })) => (
+ def_id.to_def_id(),
+ FnKind::TraitFn,
+ usize::from(sig.decl.implicit_self.has_implicit_self()),
+ ),
+ Some(Node::ImplItem(&ImplItem {
+ kind: ImplItemKind::Fn(ref sig, _),
+ def_id,
+ ..
+ })) => {
+ #[allow(trivial_casts)]
+ if let Some(Node::Item(item)) = get_parent_node(cx.tcx, cx.tcx.hir().local_def_id_to_hir_id(def_id))
+ && let Some(trait_ref) = cx.tcx.impl_trait_ref(item.def_id)
+ && let Some(trait_item_id) = cx.tcx.associated_item(def_id).trait_item_def_id
+ {
+ (
+ trait_item_id,
+ FnKind::ImplTraitFn(cx.tcx.erase_regions(trait_ref.substs) as *const _ as usize),
+ usize::from(sig.decl.implicit_self.has_implicit_self()),
+ )
+ } else {
+ (def_id.to_def_id(), FnKind::Fn, 0)
+ }
+ },
+ _ => return,
+ };
+ body.params
+ .iter()
+ .enumerate()
+ .skip(skip_params)
+ .filter_map(|(idx, p)| match p.pat.kind {
+ PatKind::Binding(_, id, ident, None) if !ident.as_str().starts_with('_') => {
+ Some((id, Param::new(fn_id, fn_kind, idx, ident)))
+ },
+ _ => None,
+ })
+ .for_each(|(id, param)| self.params.insert(param, id));
+ if self.entered_body.is_none() {
+ self.entered_body = Some(body.value.hir_id);
}
-
- self.ret_vars.append(&mut ret_vars);
}
- fn visit_method_call(&mut self, path: &'tcx PathSegment<'tcx>, args: &'tcx [Expr<'tcx>]) {
- if_chain! {
- if self.is_method;
- if path.ident == self.fn_ident;
- if let ExprKind::Path(QPath::Resolved(_, path)) = args.first().unwrap().kind;
- if let Res::Local(..) = path.res;
- let ident = path.segments.last().unwrap().ident;
- if ident.name == kw::SelfLower;
- then {
- izip!(self.params.clone(), args.iter())
- .for_each(|(pat, expr)| {
- self.visit_pat_expr(pat, expr, true);
- self.ret_vars.clear();
- });
- } else {
- self.ret_vars = args
- .iter()
- .flat_map(|expr| {
- self.visit_expr(expr);
- std::mem::take(&mut self.ret_vars)
- })
- .collect_vec()
- .into_iter()
- .map(|a| {
- self.has_side_effect.insert(a.0);
- a
- })
- .collect();
- self.contains_side_effect = true;
+ fn check_expr(&mut self, cx: &LateContext<'tcx>, e: &'tcx Expr<'tcx>) {
+ if let Some(id) = path_to_local(e)
+ && let Some(param) = self.params.get_by_id_mut(id)
+ {
+ let typeck = cx.typeck_results();
+ let span = e.span;
+ let mut e = e;
+ loop {
+ match get_expr_use_or_unification_node(cx.tcx, e) {
+ None | Some((Node::Stmt(_), _)) => return,
+ Some((Node::Expr(parent), child_id)) => match parent.kind {
+ // Recursive call. Track which index the parameter is used in.
+ ExprKind::Call(callee, args)
+ if path_def_id(cx, callee).map_or(false, |id| {
+ id == param.fn_id
+ && has_matching_substs(param.fn_kind, typeck.node_substs(callee.hir_id))
+ }) =>
+ {
+ if let Some(idx) = args.iter().position(|arg| arg.hir_id == child_id) {
+ param.uses.push(Usage::new(span, idx));
+ }
+ return;
+ },
+ ExprKind::MethodCall(_, receiver, args, _)
+ if typeck.type_dependent_def_id(parent.hir_id).map_or(false, |id| {
+ id == param.fn_id
+ && has_matching_substs(param.fn_kind, typeck.node_substs(parent.hir_id))
+ }) =>
+ {
+ if let Some(idx) = iter::once(receiver).chain(args).position(|arg| arg.hir_id == child_id) {
+ param.uses.push(Usage::new(span, idx));
+ }
+ return;
+ },
+ // Assignment to a parameter is fine.
+ ExprKind::Assign(lhs, _, _) | ExprKind::AssignOp(_, lhs, _) if lhs.hir_id == child_id => {
+ return;
+ },
+ // Parameter update e.g. `x = x + 1`
+ ExprKind::Assign(lhs, rhs, _) | ExprKind::AssignOp(_, lhs, rhs)
+ if rhs.hir_id == child_id && path_to_local_id(lhs, id) =>
+ {
+ return;
+ },
+ // Side-effect free expressions. Walk to the parent expression.
+ ExprKind::Binary(_, lhs, rhs)
+ if typeck.expr_ty(lhs).is_primitive() && typeck.expr_ty(rhs).is_primitive() =>
+ {
+ e = parent;
+ continue;
+ },
+ ExprKind::Unary(_, arg) if typeck.expr_ty(arg).is_primitive() => {
+ e = parent;
+ continue;
+ },
+ ExprKind::AddrOf(..) | ExprKind::Cast(..) => {
+ e = parent;
+ continue;
+ },
+ // Only allow field accesses without auto-deref
+ ExprKind::Field(..) if typeck.adjustments().get(child_id).is_none() => {
+ e = parent;
+ continue
+ }
+ _ => (),
+ },
+ _ => (),
+ }
+ self.params.remove_by_id(id);
+ return;
}
}
}
- fn visit_if(&mut self, bind: &'tcx Expr<'tcx>, then_expr: &'tcx Expr<'tcx>, else_expr: Option<&'tcx Expr<'tcx>>) {
- let contains_side_effect = self.contains_side_effect;
- self.contains_side_effect = false;
- self.visit_expr(bind);
- let mut vars = std::mem::take(&mut self.ret_vars);
- self.visit_expr(then_expr);
- let mut then_vars = std::mem::take(&mut self.ret_vars);
- walk_list!(self, visit_expr, else_expr);
- if self.contains_side_effect {
- self.add_side_effect(vars.clone());
- }
- self.contains_side_effect |= contains_side_effect;
- self.ret_vars.append(&mut vars);
- self.ret_vars.append(&mut then_vars);
- }
-
- fn visit_match(&mut self, expr: &'tcx Expr<'tcx>, arms: &'tcx [Arm<'tcx>]) {
- self.visit_expr(expr);
- let mut expr_vars = std::mem::take(&mut self.ret_vars);
- self.ret_vars = arms
- .iter()
- .flat_map(|arm| {
- let contains_side_effect = self.contains_side_effect;
- self.contains_side_effect = false;
- // this would visit `expr` multiple times
- // but couldn't think of a better way
- self.visit_pat_expr(arm.pat, expr, false);
- let mut vars = std::mem::take(&mut self.ret_vars);
- let _ = arm.guard.as_ref().map(|guard| {
- self.visit_expr(match guard {
- Guard::If(expr) | Guard::IfLet(Let { init: expr, .. }) => expr,
- });
- vars.append(&mut self.ret_vars);
- });
- self.visit_expr(arm.body);
- if self.contains_side_effect {
- self.add_side_effect(vars.clone());
- self.add_side_effect(expr_vars.clone());
+ fn check_body_post(&mut self, cx: &LateContext<'tcx>, body: &'tcx Body<'tcx>) {
+ if self.entered_body == Some(body.value.hir_id) {
+ self.entered_body = None;
+ self.params.flag_for_linting();
+ for param in &self.params.params {
+ if param.apply_lint.get() {
+ span_lint_and_then(
+ cx,
+ ONLY_USED_IN_RECURSION,
+ param.ident.span,
+ "parameter is only used in recursion",
+ |diag| {
+ if param.ident.name != kw::SelfLower {
+ diag.span_suggestion(
+ param.ident.span,
+ "if this is intentional, prefix it with an underscore",
+ format!("_{}", param.ident.name),
+ Applicability::MaybeIncorrect,
+ );
+ }
+ diag.span_note(
+ param.uses.iter().map(|x| x.span).collect::<Vec<_>>(),
+ "parameter used here",
+ );
+ },
+ );
}
- self.contains_side_effect |= contains_side_effect;
- vars.append(&mut self.ret_vars);
- vars
- })
- .collect();
- self.ret_vars.append(&mut expr_vars);
- }
-
- fn connect_assign(&mut self, lhs: &[(HirId, bool)], rhs: &[(HirId, bool)], connect_self: bool) {
- // if mutable dereference is on assignment it can have side-effect
- // (this can lead to parameter mutable dereference and change the original value)
- // too hard to detect whether this value is from parameter, so this would all
- // check mutable dereference assignment to side effect
- lhs.iter().filter(|(_, b)| *b).for_each(|(id, _)| {
- self.has_side_effect.insert(*id);
- self.contains_side_effect = true;
- });
-
- // there is no connection
- if lhs.is_empty() || rhs.is_empty() {
- return;
- }
-
- // by connected rhs in cycle, the connections would decrease
- // from `n * m` to `n + m`
- // where `n` and `m` are length of `lhs` and `rhs`.
-
- // unwrap is possible since rhs is not empty
- let rhs_first = rhs.first().unwrap();
- for (id, _) in lhs.iter() {
- if connect_self || *id != rhs_first.0 {
- self.graph
- .entry(*id)
- .or_insert_with(FxHashSet::default)
- .insert(rhs_first.0);
}
+ self.params.clear();
}
-
- let rhs = rhs.iter();
- izip!(rhs.clone().cycle().skip(1), rhs).for_each(|(from, to)| {
- if connect_self || from.0 != to.0 {
- self.graph.entry(from.0).or_insert_with(FxHashSet::default).insert(to.0);
- }
- });
}
+}
- fn add_side_effect(&mut self, v: Vec<(HirId, bool)>) {
- for (id, _) in v {
- self.has_side_effect.insert(id);
- self.contains_side_effect = true;
- }
+fn has_matching_substs(kind: FnKind, substs: SubstsRef<'_>) -> bool {
+ match kind {
+ FnKind::Fn => true,
+ FnKind::TraitFn => substs.iter().enumerate().all(|(idx, subst)| match subst.unpack() {
+ GenericArgKind::Lifetime(_) => true,
+ GenericArgKind::Type(ty) => matches!(*ty.kind(), ty::Param(ty) if ty.index as usize == idx),
+ GenericArgKind::Const(c) => matches!(c.kind(), ConstKind::Param(c) if c.index as usize == idx),
+ }),
+ #[allow(trivial_casts)]
+ FnKind::ImplTraitFn(expected_substs) => substs as *const _ as usize == expected_substs,
}
}
generated by cgit v1.2.3 (git 2.39.1) at 2024-07-28 01:07:25 +0000