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Implement uninit_vec lint #7682
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452181c
Implement uninit_vec lint
Qwaz b8ba726
Fix clippy lints
Qwaz 759200b
Handle PR feedbacks first round
Qwaz fdc06d9
Improve error messages
Qwaz fec20bf
Add #allow attribute to suppress FP #7698
Qwaz dd9c8d3
Extract get_vec_init_kind and share it
Qwaz b1aa306
Address PR comments
Qwaz de0d2b1
Add testcases
Qwaz 2181387
Improved error message for set_len() on empty Vec
Qwaz 03fed75
Address internal lints
Qwaz 4ed3a4f
Update lint description for new() and default()
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,221 @@ | ||
| use clippy_utils::diagnostics::{span_lint, span_lint_and_then}; | ||
| use clippy_utils::higher::{get_vec_init_kind, VecInitKind}; | ||
| use clippy_utils::ty::{is_type_diagnostic_item, is_uninit_value_valid_for_ty}; | ||
| use clippy_utils::{is_lint_allowed, path_to_local_id, peel_hir_expr_while, SpanlessEq}; | ||
| use rustc_hir::{Block, Expr, ExprKind, HirId, PatKind, PathSegment, Stmt, StmtKind}; | ||
| use rustc_lint::{LateContext, LateLintPass}; | ||
| use rustc_middle::lint::in_external_macro; | ||
| use rustc_middle::ty; | ||
| use rustc_session::{declare_lint_pass, declare_tool_lint}; | ||
| use rustc_span::{sym, Span}; | ||
|
|
||
| // TODO: add `ReadBuf` (RFC 2930) in "How to fix" once it is available in std | ||
| declare_clippy_lint! { | ||
| /// ### What it does | ||
| /// Checks for `set_len()` call that creates `Vec` with uninitialized elements. | ||
| /// This is commonly caused by calling `set_len()` right after after calling | ||
| /// `with_capacity()` or `reserve()`. | ||
| /// | ||
| /// ### Why is this bad? | ||
| /// It creates a `Vec` with uninitialized data, which leads to | ||
| /// undefined behavior with most safe operations. | ||
| /// | ||
| /// Notably, uninitialized `Vec<u8>` must not be used with generic `Read`. | ||
| /// | ||
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|
||
| /// ### Known Problems | ||
| /// This lint only checks directly adjacent statements. | ||
| /// | ||
| /// ### Example | ||
| /// ```rust,ignore | ||
| /// let mut vec: Vec<u8> = Vec::with_capacity(1000); | ||
| /// unsafe { vec.set_len(1000); } | ||
| /// reader.read(&mut vec); // undefined behavior! | ||
| /// ``` | ||
| /// | ||
| /// ### How to fix? | ||
| /// 1. Use an initialized buffer: | ||
| /// ```rust,ignore | ||
| /// let mut vec: Vec<u8> = vec![0; 1000]; | ||
| /// reader.read(&mut vec); | ||
| /// ``` | ||
| /// 2. Wrap the content in `MaybeUninit`: | ||
| /// ```rust,ignore | ||
| /// let mut vec: Vec<MaybeUninit<T>> = Vec::with_capacity(1000); | ||
| /// vec.set_len(1000); // `MaybeUninit` can be uninitialized | ||
| /// ``` | ||
| /// 3. If you are on nightly, `Vec::spare_capacity_mut()` is available: | ||
| /// ```rust,ignore | ||
| /// let mut vec: Vec<u8> = Vec::with_capacity(1000); | ||
| /// let remaining = vec.spare_capacity_mut(); // `&mut [MaybeUninit<u8>]` | ||
| /// // perform initialization with `remaining` | ||
| /// vec.set_len(...); // Safe to call `set_len()` on initialized part | ||
| /// ``` | ||
| pub UNINIT_VEC, | ||
| correctness, | ||
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|
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| "Vec with uninitialized data" | ||
| } | ||
|
|
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| declare_lint_pass!(UninitVec => [UNINIT_VEC]); | ||
|
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| // FIXME: update to a visitor-based implementation. | ||
| // Threads: https://github.com/rust-lang/rust-clippy/pull/7682#discussion_r710998368 | ||
| impl<'tcx> LateLintPass<'tcx> for UninitVec { | ||
| fn check_block(&mut self, cx: &LateContext<'tcx>, block: &'tcx Block<'_>) { | ||
| if !in_external_macro(cx.tcx.sess, block.span) { | ||
| for w in block.stmts.windows(2) { | ||
| if let StmtKind::Expr(expr) | StmtKind::Semi(expr) = w[1].kind { | ||
| handle_uninit_vec_pair(cx, &w[0], expr); | ||
| } | ||
| } | ||
|
|
||
| if let (Some(stmt), Some(expr)) = (block.stmts.last(), block.expr) { | ||
| handle_uninit_vec_pair(cx, stmt, expr); | ||
| } | ||
| } | ||
| } | ||
| } | ||
|
|
||
| fn handle_uninit_vec_pair( | ||
| cx: &LateContext<'tcx>, | ||
| maybe_init_or_reserve: &'tcx Stmt<'tcx>, | ||
| maybe_set_len: &'tcx Expr<'tcx>, | ||
| ) { | ||
| if_chain! { | ||
| if let Some(vec) = extract_init_or_reserve_target(cx, maybe_init_or_reserve); | ||
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|
||
| if let Some((set_len_self, call_span)) = extract_set_len_self(cx, maybe_set_len); | ||
| if vec.location.eq_expr(cx, set_len_self); | ||
| if let ty::Ref(_, vec_ty, _) = cx.typeck_results().expr_ty_adjusted(set_len_self).kind(); | ||
| if let ty::Adt(_, substs) = vec_ty.kind(); | ||
| // `#[allow(...)]` attribute can be set on enclosing unsafe block of `set_len()` | ||
| if !is_lint_allowed(cx, UNINIT_VEC, maybe_set_len.hir_id); | ||
| then { | ||
| if vec.has_capacity() { | ||
| // with_capacity / reserve -> set_len | ||
|
|
||
| // Check T of Vec<T> | ||
| if !is_uninit_value_valid_for_ty(cx, substs.type_at(0)) { | ||
| // FIXME: #7698, false positive of the internal lints | ||
| #[allow(clippy::collapsible_span_lint_calls)] | ||
| span_lint_and_then( | ||
| cx, | ||
| UNINIT_VEC, | ||
| vec![call_span, maybe_init_or_reserve.span], | ||
| "calling `set_len()` immediately after reserving a buffer creates uninitialized values", | ||
| |diag| { | ||
| diag.help("initialize the buffer or wrap the content in `MaybeUninit`"); | ||
| }, | ||
| ); | ||
| } | ||
| } else { | ||
| // new / default -> set_len | ||
| span_lint( | ||
| cx, | ||
| UNINIT_VEC, | ||
| vec![call_span, maybe_init_or_reserve.span], | ||
| "calling `set_len()` on empty `Vec` creates out-of-bound values", | ||
| ); | ||
| } | ||
| } | ||
| } | ||
| } | ||
|
|
||
| /// The target `Vec` that is initialized or reserved | ||
| #[derive(Clone, Copy)] | ||
| struct TargetVec<'tcx> { | ||
| location: VecLocation<'tcx>, | ||
| /// `None` if `reserve()` | ||
| init_kind: Option<VecInitKind>, | ||
| } | ||
|
|
||
| impl TargetVec<'_> { | ||
| pub fn has_capacity(self) -> bool { | ||
| !matches!(self.init_kind, Some(VecInitKind::New | VecInitKind::Default)) | ||
| } | ||
| } | ||
|
|
||
| #[derive(Clone, Copy)] | ||
| enum VecLocation<'tcx> { | ||
| Local(HirId), | ||
| Expr(&'tcx Expr<'tcx>), | ||
| } | ||
|
|
||
| impl<'tcx> VecLocation<'tcx> { | ||
| pub fn eq_expr(self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) -> bool { | ||
| match self { | ||
| VecLocation::Local(hir_id) => path_to_local_id(expr, hir_id), | ||
| VecLocation::Expr(self_expr) => SpanlessEq::new(cx).eq_expr(self_expr, expr), | ||
| } | ||
| } | ||
| } | ||
|
|
||
| /// Finds the target location where the result of `Vec` initialization is stored | ||
| /// or `self` expression for `Vec::reserve()`. | ||
| fn extract_init_or_reserve_target<'tcx>(cx: &LateContext<'tcx>, stmt: &'tcx Stmt<'tcx>) -> Option<TargetVec<'tcx>> { | ||
| match stmt.kind { | ||
| StmtKind::Local(local) => { | ||
| if_chain! { | ||
| if let Some(init_expr) = local.init; | ||
| if let PatKind::Binding(_, hir_id, _, None) = local.pat.kind; | ||
| if let Some(init_kind) = get_vec_init_kind(cx, init_expr); | ||
| then { | ||
| return Some(TargetVec { | ||
| location: VecLocation::Local(hir_id), | ||
| init_kind: Some(init_kind), | ||
| }) | ||
| } | ||
| } | ||
| }, | ||
| StmtKind::Expr(expr) | StmtKind::Semi(expr) => match expr.kind { | ||
| ExprKind::Assign(lhs, rhs, _span) => { | ||
| if let Some(init_kind) = get_vec_init_kind(cx, rhs) { | ||
| return Some(TargetVec { | ||
| location: VecLocation::Expr(lhs), | ||
| init_kind: Some(init_kind), | ||
| }); | ||
| } | ||
| }, | ||
| ExprKind::MethodCall(path, _, [self_expr, _], _) if is_reserve(cx, path, self_expr) => { | ||
| return Some(TargetVec { | ||
| location: VecLocation::Expr(self_expr), | ||
| init_kind: None, | ||
| }); | ||
| }, | ||
| _ => (), | ||
| }, | ||
| StmtKind::Item(_) => (), | ||
| } | ||
| None | ||
| } | ||
|
|
||
| fn is_reserve(cx: &LateContext<'_>, path: &PathSegment<'_>, self_expr: &Expr<'_>) -> bool { | ||
| is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(self_expr).peel_refs(), sym::Vec) | ||
| && path.ident.name.as_str() == "reserve" | ||
| } | ||
|
|
||
| /// Returns self if the expression is `Vec::set_len()` | ||
| fn extract_set_len_self(cx: &LateContext<'_>, expr: &'tcx Expr<'_>) -> Option<(&'tcx Expr<'tcx>, Span)> { | ||
| // peel unsafe blocks in `unsafe { vec.set_len() }` | ||
| let expr = peel_hir_expr_while(expr, |e| { | ||
| if let ExprKind::Block(block, _) = e.kind { | ||
| // Extract the first statement/expression | ||
| match (block.stmts.get(0).map(|stmt| &stmt.kind), block.expr) { | ||
| (None, Some(expr)) => Some(expr), | ||
| (Some(StmtKind::Expr(expr) | StmtKind::Semi(expr)), _) => Some(expr), | ||
| _ => None, | ||
| } | ||
| } else { | ||
| None | ||
| } | ||
| }); | ||
| match expr.kind { | ||
| ExprKind::MethodCall(path, _, [self_expr, _], _) => { | ||
| let self_type = cx.typeck_results().expr_ty(self_expr).peel_refs(); | ||
| if is_type_diagnostic_item(cx, self_type, sym::Vec) && path.ident.name.as_str() == "set_len" { | ||
| Some((self_expr, expr.span)) | ||
| } else { | ||
| None | ||
| } | ||
| }, | ||
| _ => None, | ||
| } | ||
| } | ||
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