--- /dev/null
+use crate::utils::sugg::Sugg;
+use crate::utils::{get_enclosing_block, match_qpath, span_lint_and_then, SpanlessEq};
+use if_chain::if_chain;
+use rustc_ast::ast::LitKind;
+use rustc_errors::Applicability;
+use rustc_hir::intravisit::{walk_block, walk_expr, walk_stmt, NestedVisitorMap, Visitor};
+use rustc_hir::{BindingAnnotation, Block, Expr, ExprKind, HirId, PatKind, QPath, Stmt, StmtKind};
+use rustc_lint::{LateContext, LateLintPass, Lint};
+use rustc_middle::hir::map::Map;
+use rustc_session::{declare_lint_pass, declare_tool_lint};
+use rustc_span::symbol::Symbol;
+
+declare_clippy_lint! {
+ /// **What it does:** Checks slow zero-filled vector initialization
+ ///
+ /// **Why is this bad?** These structures are non-idiomatic and less efficient than simply using
+ /// `vec![0; len]`.
+ ///
+ /// **Known problems:** None.
+ ///
+ /// **Example:**
+ /// ```rust
+ /// # use core::iter::repeat;
+ /// # let len = 4;
+ ///
+ /// // Bad
+ /// let mut vec1 = Vec::with_capacity(len);
+ /// vec1.resize(len, 0);
+ ///
+ /// let mut vec2 = Vec::with_capacity(len);
+ /// vec2.extend(repeat(0).take(len));
+ ///
+ /// // Good
+ /// let mut vec1 = vec![0; len];
+ /// let mut vec2 = vec![0; len];
+ /// ```
+ pub SLOW_VECTOR_INITIALIZATION,
+ perf,
+ "slow vector initialization"
+}
+
+declare_lint_pass!(SlowVectorInit => [SLOW_VECTOR_INITIALIZATION]);
+
+/// `VecAllocation` contains data regarding a vector allocated with `with_capacity` and then
+/// assigned to a variable. For example, `let mut vec = Vec::with_capacity(0)` or
+/// `vec = Vec::with_capacity(0)`
+struct VecAllocation<'tcx> {
+ /// Symbol of the local variable name
+ variable_name: Symbol,
+
+ /// Reference to the expression which allocates the vector
+ allocation_expr: &'tcx Expr<'tcx>,
+
+ /// Reference to the expression used as argument on `with_capacity` call. This is used
+ /// to only match slow zero-filling idioms of the same length than vector initialization.
+ len_expr: &'tcx Expr<'tcx>,
+}
+
+/// Type of slow initialization
+enum InitializationType<'tcx> {
+ /// Extend is a slow initialization with the form `vec.extend(repeat(0).take(..))`
+ Extend(&'tcx Expr<'tcx>),
+
+ /// Resize is a slow initialization with the form `vec.resize(.., 0)`
+ Resize(&'tcx Expr<'tcx>),
+}
+
+impl<'tcx> LateLintPass<'tcx> for SlowVectorInit {
+ fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
+ // Matches initialization on reassignements. For example: `vec = Vec::with_capacity(100)`
+ if_chain! {
+ if let ExprKind::Assign(ref left, ref right, _) = expr.kind;
+
+ // Extract variable name
+ if let ExprKind::Path(QPath::Resolved(_, ref path)) = left.kind;
+ if let Some(variable_name) = path.segments.get(0);
+
+ // Extract len argument
+ if let Some(ref len_arg) = Self::is_vec_with_capacity(right);
+
+ then {
+ let vi = VecAllocation {
+ variable_name: variable_name.ident.name,
+ allocation_expr: right,
+ len_expr: len_arg,
+ };
+
+ Self::search_initialization(cx, vi, expr.hir_id);
+ }
+ }
+ }
+
+ fn check_stmt(&mut self, cx: &LateContext<'tcx>, stmt: &'tcx Stmt<'_>) {
+ // Matches statements which initializes vectors. For example: `let mut vec = Vec::with_capacity(10)`
+ if_chain! {
+ if let StmtKind::Local(ref local) = stmt.kind;
+ if let PatKind::Binding(BindingAnnotation::Mutable, .., variable_name, None) = local.pat.kind;
+ if let Some(ref init) = local.init;
+ if let Some(ref len_arg) = Self::is_vec_with_capacity(init);
+
+ then {
+ let vi = VecAllocation {
+ variable_name: variable_name.name,
+ allocation_expr: init,
+ len_expr: len_arg,
+ };
+
+ Self::search_initialization(cx, vi, stmt.hir_id);
+ }
+ }
+ }
+}
+
+impl SlowVectorInit {
+ /// Checks if the given expression is `Vec::with_capacity(..)`. It will return the expression
+ /// of the first argument of `with_capacity` call if it matches or `None` if it does not.
+ fn is_vec_with_capacity<'tcx>(expr: &Expr<'tcx>) -> Option<&'tcx Expr<'tcx>> {
+ if_chain! {
+ if let ExprKind::Call(ref func, ref args) = expr.kind;
+ if let ExprKind::Path(ref path) = func.kind;
+ if match_qpath(path, &["Vec", "with_capacity"]);
+ if args.len() == 1;
+
+ then {
+ return Some(&args[0]);
+ }
+ }
+
+ None
+ }
+
+ /// Search initialization for the given vector
+ fn search_initialization<'tcx>(cx: &LateContext<'tcx>, vec_alloc: VecAllocation<'tcx>, parent_node: HirId) {
+ let enclosing_body = get_enclosing_block(cx, parent_node);
+
+ if enclosing_body.is_none() {
+ return;
+ }
+
+ let mut v = VectorInitializationVisitor {
+ cx,
+ vec_alloc,
+ slow_expression: None,
+ initialization_found: false,
+ };
+
+ v.visit_block(enclosing_body.unwrap());
+
+ if let Some(ref allocation_expr) = v.slow_expression {
+ Self::lint_initialization(cx, allocation_expr, &v.vec_alloc);
+ }
+ }
+
+ fn lint_initialization<'tcx>(
+ cx: &LateContext<'tcx>,
+ initialization: &InitializationType<'tcx>,
+ vec_alloc: &VecAllocation<'_>,
+ ) {
+ match initialization {
+ InitializationType::Extend(e) | InitializationType::Resize(e) => Self::emit_lint(
+ cx,
+ e,
+ vec_alloc,
+ "slow zero-filling initialization",
+ SLOW_VECTOR_INITIALIZATION,
+ ),
+ };
+ }
+
+ fn emit_lint<'tcx>(
+ cx: &LateContext<'tcx>,
+ slow_fill: &Expr<'_>,
+ vec_alloc: &VecAllocation<'_>,
+ msg: &str,
+ lint: &'static Lint,
+ ) {
+ let len_expr = Sugg::hir(cx, vec_alloc.len_expr, "len");
+
+ span_lint_and_then(cx, lint, slow_fill.span, msg, |diag| {
+ diag.span_suggestion(
+ vec_alloc.allocation_expr.span,
+ "consider replace allocation with",
+ format!("vec![0; {}]", len_expr),
+ Applicability::Unspecified,
+ );
+ });
+ }
+}
+
+/// `VectorInitializationVisitor` searches for unsafe or slow vector initializations for the given
+/// vector.
+struct VectorInitializationVisitor<'a, 'tcx> {
+ cx: &'a LateContext<'tcx>,
+
+ /// Contains the information.
+ vec_alloc: VecAllocation<'tcx>,
+
+ /// Contains the slow initialization expression, if one was found.
+ slow_expression: Option<InitializationType<'tcx>>,
+
+ /// `true` if the initialization of the vector has been found on the visited block.
+ initialization_found: bool,
+}
+
+impl<'a, 'tcx> VectorInitializationVisitor<'a, 'tcx> {
+ /// Checks if the given expression is extending a vector with `repeat(0).take(..)`
+ fn search_slow_extend_filling(&mut self, expr: &'tcx Expr<'_>) {
+ if_chain! {
+ if self.initialization_found;
+ if let ExprKind::MethodCall(ref path, _, ref args, _) = expr.kind;
+ if let ExprKind::Path(ref qpath_subj) = args[0].kind;
+ if match_qpath(&qpath_subj, &[&*self.vec_alloc.variable_name.as_str()]);
+ if path.ident.name == sym!(extend);
+ if let Some(ref extend_arg) = args.get(1);
+ if self.is_repeat_take(extend_arg);
+
+ then {
+ self.slow_expression = Some(InitializationType::Extend(expr));
+ }
+ }
+ }
+
+ /// Checks if the given expression is resizing a vector with 0
+ fn search_slow_resize_filling(&mut self, expr: &'tcx Expr<'_>) {
+ if_chain! {
+ if self.initialization_found;
+ if let ExprKind::MethodCall(ref path, _, ref args, _) = expr.kind;
+ if let ExprKind::Path(ref qpath_subj) = args[0].kind;
+ if match_qpath(&qpath_subj, &[&*self.vec_alloc.variable_name.as_str()]);
+ if path.ident.name == sym!(resize);
+ if let (Some(ref len_arg), Some(fill_arg)) = (args.get(1), args.get(2));
+
+ // Check that is filled with 0
+ if let ExprKind::Lit(ref lit) = fill_arg.kind;
+ if let LitKind::Int(0, _) = lit.node;
+
+ // Check that len expression is equals to `with_capacity` expression
+ if SpanlessEq::new(self.cx).eq_expr(len_arg, self.vec_alloc.len_expr);
+
+ then {
+ self.slow_expression = Some(InitializationType::Resize(expr));
+ }
+ }
+ }
+
+ /// Returns `true` if give expression is `repeat(0).take(...)`
+ fn is_repeat_take(&self, expr: &Expr<'_>) -> bool {
+ if_chain! {
+ if let ExprKind::MethodCall(ref take_path, _, ref take_args, _) = expr.kind;
+ if take_path.ident.name == sym!(take);
+
+ // Check that take is applied to `repeat(0)`
+ if let Some(ref repeat_expr) = take_args.get(0);
+ if Self::is_repeat_zero(repeat_expr);
+
+ // Check that len expression is equals to `with_capacity` expression
+ if let Some(ref len_arg) = take_args.get(1);
+ if SpanlessEq::new(self.cx).eq_expr(len_arg, self.vec_alloc.len_expr);
+
+ then {
+ return true;
+ }
+ }
+
+ false
+ }
+
+ /// Returns `true` if given expression is `repeat(0)`
+ fn is_repeat_zero(expr: &Expr<'_>) -> bool {
+ if_chain! {
+ if let ExprKind::Call(ref fn_expr, ref repeat_args) = expr.kind;
+ if let ExprKind::Path(ref qpath_repeat) = fn_expr.kind;
+ if match_qpath(&qpath_repeat, &["repeat"]);
+ if let Some(ref repeat_arg) = repeat_args.get(0);
+ if let ExprKind::Lit(ref lit) = repeat_arg.kind;
+ if let LitKind::Int(0, _) = lit.node;
+
+ then {
+ return true
+ }
+ }
+
+ false
+ }
+}
+
+impl<'a, 'tcx> Visitor<'tcx> for VectorInitializationVisitor<'a, 'tcx> {
+ type Map = Map<'tcx>;
+
+ fn visit_stmt(&mut self, stmt: &'tcx Stmt<'_>) {
+ if self.initialization_found {
+ match stmt.kind {
+ StmtKind::Expr(ref expr) | StmtKind::Semi(ref expr) => {
+ self.search_slow_extend_filling(expr);
+ self.search_slow_resize_filling(expr);
+ },
+ _ => (),
+ }
+
+ self.initialization_found = false;
+ } else {
+ walk_stmt(self, stmt);
+ }
+ }
+
+ fn visit_block(&mut self, block: &'tcx Block<'_>) {
+ if self.initialization_found {
+ if let Some(ref s) = block.stmts.get(0) {
+ self.visit_stmt(s)
+ }
+
+ self.initialization_found = false;
+ } else {
+ walk_block(self, block);
+ }
+ }
+
+ fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
+ // Skip all the expressions previous to the vector initialization
+ if self.vec_alloc.allocation_expr.hir_id == expr.hir_id {
+ self.initialization_found = true;
+ }
+
+ walk_expr(self, expr);
+ }
+
+ fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
+ NestedVisitorMap::None
+ }
+}
projects / rustc.git / blobdiff