diff --git a/clippy_lints/src/lib.rs b/clippy_lints/src/lib.rs index 2dbe448c950..cf754d48667 100644 --- a/clippy_lints/src/lib.rs +++ b/clippy_lints/src/lib.rs @@ -190,6 +190,7 @@ pub mod replace_consts; pub mod returns; pub mod serde_api; pub mod shadow; +pub mod slow_vector_initialization; pub mod strings; pub mod suspicious_trait_impl; pub mod swap; @@ -459,6 +460,7 @@ pub fn register_plugins(reg: &mut rustc_plugin::Registry<'_>, conf: &Conf) { reg.register_late_lint_pass(box non_copy_const::NonCopyConst); reg.register_late_lint_pass(box ptr_offset_with_cast::Pass); reg.register_late_lint_pass(box redundant_clone::RedundantClone); + reg.register_late_lint_pass(box slow_vector_initialization::Pass); reg.register_lint_group("clippy::restriction", Some("clippy_restriction"), vec![ arithmetic::FLOAT_ARITHMETIC, @@ -980,6 +982,7 @@ pub fn register_plugins(reg: &mut rustc_plugin::Registry<'_>, conf: &Conf) { methods::SINGLE_CHAR_PATTERN, misc::CMP_OWNED, mutex_atomic::MUTEX_ATOMIC, + slow_vector_initialization::SLOW_VECTOR_INITIALIZATION, trivially_copy_pass_by_ref::TRIVIALLY_COPY_PASS_BY_REF, types::BOX_VEC, vec::USELESS_VEC, diff --git a/clippy_lints/src/slow_vector_initialization.rs b/clippy_lints/src/slow_vector_initialization.rs new file mode 100644 index 00000000000..52855031a5a --- /dev/null +++ b/clippy_lints/src/slow_vector_initialization.rs @@ -0,0 +1,304 @@ +// Copyright 2014-2018 The Rust Project Developers. See the COPYRIGHT +// file at the top-level directory of this distribution. +// +// Licensed under the Apache License, Version 2.0 or the MIT license +// , at your +// option. This file may not be copied, modified, or distributed +// except according to those terms. + +use crate::rustc::hir::intravisit::{walk_expr, NestedVisitorMap, Visitor}; +use crate::rustc::lint::{LateContext, LateLintPass, LintArray, LintPass}; +use crate::rustc::{declare_tool_lint, lint_array}; +use crate::rustc::hir::*; +use if_chain::if_chain; +use crate::syntax_pos::symbol::Symbol; +use crate::syntax::ast::{LitKind, NodeId}; +use crate::syntax::source_map::Span; +use crate::utils::{match_qpath, span_lint_and_then, SpanlessEq}; +use crate::utils::get_enclosing_block; +use crate::rustc_errors::{Applicability}; + +/// **What it does:** Checks slow zero-filled vector initialization +/// +/// **Why is this bad?** This structures are non-idiomatic and less efficient than simply using +/// `vec![len; 0]`. +/// +/// **Known problems:** None. +/// +/// **Example:** +/// ```rust +/// let mut vec1 = Vec::with_capacity(len); +/// vec1.resize(len, 0); +/// +/// let mut vec2 = Vec::with_capacity(len); +/// vec2.extend(repeat(0).take(len)) +/// ``` +declare_clippy_lint! { + pub SLOW_VECTOR_INITIALIZATION, + perf, + "slow or unsafe vector initialization" +} + +#[derive(Copy, Clone, Default)] +pub struct Pass; + +impl LintPass for Pass { + fn get_lints(&self) -> LintArray { + lint_array!(SLOW_VECTOR_INITIALIZATION) + } +} + +/// VecInitialization contains data regarding a vector initialized 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 VecInitialization<'tcx> { + /// Symbol of the local variable name + variable_name: Symbol, + + /// Reference to the expression which initializes the vector + initialization_expr: &'tcx Expr, + + /// 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, +} + +/// Type of slow initialization +enum InitializationType<'tcx> { + /// Extend is a slow initialization with the form `vec.extend(repeat(0).take(..))` + Extend(&'tcx Expr), + + /// Resize is a slow initialization with the form `vec.resize(.., 0)` + Resize(&'tcx Expr), +} + +impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Pass { + fn check_expr(&mut self, cx: &LateContext<'a, '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.node; + + // Extract variable name + if let ExprKind::Path(QPath::Resolved(_, ref path)) = left.node; + if let Some(variable_name) = path.segments.get(0); + + // Extract len argument + if let Some(ref len_arg) = Pass::is_vec_with_capacity(right); + + then { + let vi = VecInitialization { + variable_name: variable_name.ident.name, + initialization_expr: right, + len_expr: len_arg, + }; + + Pass::search_slow_zero_filling(cx, vi, expr.id, expr.span); + } + } + } + + fn check_stmt(&mut self, cx: &LateContext<'a, 'tcx>, stmt: &'tcx Stmt) { + // Matches statements which initializes vectors. For example: `let mut vec = Vec::with_capacity(10)` + if_chain! { + if let StmtKind::Decl(ref decl, _) = stmt.node; + if let DeclKind::Local(ref local) = decl.node; + if let PatKind::Binding(BindingAnnotation::Mutable, _, variable_name, None) = local.pat.node; + if let Some(ref init) = local.init; + if let Some(ref len_arg) = Pass::is_vec_with_capacity(init); + + then { + let vi = VecInitialization { + variable_name: variable_name.name, + initialization_expr: init, + len_expr: len_arg, + }; + + Pass::search_slow_zero_filling(cx, vi, stmt.node.id(), stmt.span); + } + } + } +} + +impl Pass { + /// 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(expr: &Expr) -> Option<&Expr> { + if_chain! { + if let ExprKind::Call(ref func, ref args) = expr.node; + if let ExprKind::Path(ref path) = func.node; + if match_qpath(path, &["Vec", "with_capacity"]); + if args.len() == 1; + + then { + return Some(&args[0]); + } + } + + None + } + + /// Search for slow zero filling vector initialization for the given vector + fn search_slow_zero_filling<'tcx>( + cx: &LateContext<'_, 'tcx>, + vec_initialization: VecInitialization<'tcx>, + parent_node: NodeId, + parent_span: Span + ) { + let enclosing_body = get_enclosing_block(cx, parent_node); + + if enclosing_body.is_none() { + return; + } + + let mut v = SlowInitializationVisitor { + cx, + vec_ini: vec_initialization, + slow_expression: None, + initialization_found: false, + }; + + v.visit_block(enclosing_body.unwrap()); + + if let Some(ref repeat_expr) = v.slow_expression { + span_lint_and_then( + cx, + SLOW_VECTOR_INITIALIZATION, + parent_span, + "detected slow zero-filling initialization", + |db| { + db.span_suggestion_with_applicability(v.vec_ini.initialization_expr.span, "consider replacing with", "vec![0; ..]".to_string(), Applicability::Unspecified); + + match repeat_expr { + InitializationType::Extend(e) => { + db.span_note(e.span, "extended here with .. 0"); + }, + InitializationType::Resize(e) => { + db.span_note(e.span, "resize here with .. 0"); + } + } + } + ); + } + } +} + +/// SlowInitializationVisitor searches for slow zero filling vector initialization, for the given +/// vector. +struct SlowInitializationVisitor<'a, 'tcx: 'a> { + cx: &'a LateContext<'a, 'tcx>, + + /// Contains the information + vec_ini: VecInitialization<'tcx>, + + /// Contains, if found, the slow initialization expression + slow_expression: Option>, + + /// true if the initialization of the vector has been found on the visited block + initialization_found: bool, +} + +impl<'a, 'tcx> SlowInitializationVisitor<'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.node; + if let ExprKind::Path(ref qpath_subj) = args[0].node; + if match_qpath(&qpath_subj, &[&self.vec_ini.variable_name.to_string()]); + if path.ident.name == "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.node; + if let ExprKind::Path(ref qpath_subj) = args[0].node; + if match_qpath(&qpath_subj, &[&self.vec_ini.variable_name.to_string()]); + if path.ident.name == "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.node; + 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_ini.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.node; + if take_path.ident.name == "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_ini.len_expr); + + then { + return true; + } + } + + false + } + + /// Returns `true` if given expression is `repeat(0)` + fn is_repeat_zero(&self, expr: &Expr) -> bool { + if_chain! { + if let ExprKind::Call(ref fn_expr, ref repeat_args) = expr.node; + if let ExprKind::Path(ref qpath_repeat) = fn_expr.node; + if match_qpath(&qpath_repeat, &["repeat"]); + if let Some(ref repeat_arg) = repeat_args.get(0); + if let ExprKind::Lit(ref lit) = repeat_arg.node; + if let LitKind::Int(0, _) = lit.node; + + then { + return true + } + } + + false + } +} + +impl<'a, 'tcx> Visitor<'tcx> for SlowInitializationVisitor<'a, 'tcx> { + fn visit_expr(&mut self, expr: &'tcx Expr) { + // Stop the search if we already found a slow zero-filling initialization + if self.slow_expression.is_some() { + return + } + + // Skip all the expressions previous to the vector initialization + if self.vec_ini.initialization_expr.id == expr.id { + self.initialization_found = true; + } + + self.search_slow_extend_filling(expr); + self.search_slow_resize_filling(expr); + + walk_expr(self, expr); + } + + fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> { + NestedVisitorMap::None + } +} diff --git a/tests/ui/slow_vector_initialization.rs b/tests/ui/slow_vector_initialization.rs new file mode 100644 index 00000000000..f79abe8327e --- /dev/null +++ b/tests/ui/slow_vector_initialization.rs @@ -0,0 +1,63 @@ +// Copyright 2014-2018 The Rust Project Developers. See the COPYRIGHT +// file at the top-level directory of this distribution. +// +// Licensed under the Apache License, Version 2.0 or the MIT license +// , at your +// option. This file may not be copied, modified, or distributed +// except according to those terms. + +use std::iter::repeat; + +fn main() { + resize_vector(); + extend_vector(); + mixed_extend_resize_vector(); +} + +fn extend_vector() { + // Extend with constant expression + let len = 300; + let mut vec1 = Vec::with_capacity(len); + vec1.extend(repeat(0).take(len)); + + // Extend with len expression + let mut vec2 = Vec::with_capacity(len - 10); + vec2.extend(repeat(0).take(len - 10)); + + // Extend with mismatching expression should not be warned + let mut vec3 = Vec::with_capacity(24322); + vec3.extend(repeat(0).take(2)); +} + +fn mixed_extend_resize_vector() { + // Mismatching len + let mut mismatching_len = Vec::with_capacity(30); + + // Slow initialization + let mut resized_vec = Vec::with_capacity(30); + let mut extend_vec = Vec::with_capacity(30); + + resized_vec.resize(30, 0); + mismatching_len.extend(repeat(0).take(40)); + extend_vec.extend(repeat(0).take(30)); +} + +fn resize_vector() { + // Resize with constant expression + let len = 300; + let mut vec1 = Vec::with_capacity(len); + vec1.resize(len, 0); + + // Resize mismatch len + let mut vec2 = Vec::with_capacity(200); + vec2.resize(10, 0); + + // Resize with len expression + let mut vec3 = Vec::with_capacity(len - 10); + vec3.resize(len - 10, 0); + + // Reinitialization should be warned + vec1 = Vec::with_capacity(10); + vec1.resize(10, 0); +} diff --git a/tests/ui/slow_vector_initialization.stderr b/tests/ui/slow_vector_initialization.stderr new file mode 100644 index 00000000000..4941794d541 --- /dev/null +++ b/tests/ui/slow_vector_initialization.stderr @@ -0,0 +1,101 @@ +error: detected slow zero-filling initialization + --> $DIR/slow_vector_initialization.rs:21:5 + | +21 | let mut vec1 = Vec::with_capacity(len); + | ^^^^^^^^^^^^^^^-----------------------^ + | | + | help: consider replacing with: `vec![0; ..]` + | + = note: `-D clippy::slow-vector-initialization` implied by `-D warnings` +note: extended here with .. 0 + --> $DIR/slow_vector_initialization.rs:22:5 + | +22 | vec1.extend(repeat(0).take(len)); + | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +error: detected slow zero-filling initialization + --> $DIR/slow_vector_initialization.rs:25:5 + | +25 | let mut vec2 = Vec::with_capacity(len - 10); + | ^^^^^^^^^^^^^^^----------------------------^ + | | + | help: consider replacing with: `vec![0; ..]` + | +note: extended here with .. 0 + --> $DIR/slow_vector_initialization.rs:26:5 + | +26 | vec2.extend(repeat(0).take(len - 10)); + | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +error: detected slow zero-filling initialization + --> $DIR/slow_vector_initialization.rs:38:5 + | +38 | let mut resized_vec = Vec::with_capacity(30); + | ^^^^^^^^^^^^^^^^^^^^^^----------------------^ + | | + | help: consider replacing with: `vec![0; ..]` + | +note: resize here with .. 0 + --> $DIR/slow_vector_initialization.rs:41:5 + | +41 | resized_vec.resize(30, 0); + | ^^^^^^^^^^^^^^^^^^^^^^^^^ + +error: detected slow zero-filling initialization + --> $DIR/slow_vector_initialization.rs:39:5 + | +39 | let mut extend_vec = Vec::with_capacity(30); + | ^^^^^^^^^^^^^^^^^^^^^----------------------^ + | | + | help: consider replacing with: `vec![0; ..]` + | +note: extended here with .. 0 + --> $DIR/slow_vector_initialization.rs:43:5 + | +43 | extend_vec.extend(repeat(0).take(30)); + | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +error: detected slow zero-filling initialization + --> $DIR/slow_vector_initialization.rs:49:5 + | +49 | let mut vec1 = Vec::with_capacity(len); + | ^^^^^^^^^^^^^^^-----------------------^ + | | + | help: consider replacing with: `vec![0; ..]` + | +note: resize here with .. 0 + --> $DIR/slow_vector_initialization.rs:50:5 + | +50 | vec1.resize(len, 0); + | ^^^^^^^^^^^^^^^^^^^ + +error: detected slow zero-filling initialization + --> $DIR/slow_vector_initialization.rs:57:5 + | +57 | let mut vec3 = Vec::with_capacity(len - 10); + | ^^^^^^^^^^^^^^^----------------------------^ + | | + | help: consider replacing with: `vec![0; ..]` + | +note: resize here with .. 0 + --> $DIR/slow_vector_initialization.rs:58:5 + | +58 | vec3.resize(len - 10, 0); + | ^^^^^^^^^^^^^^^^^^^^^^^^ + +error: detected slow zero-filling initialization + --> $DIR/slow_vector_initialization.rs:61:5 + | +61 | vec1 = Vec::with_capacity(10); + | ^^^^^^^---------------------- + | | + | help: consider replacing with: `vec![0; ..]` + | +note: resize here with .. 0 + --> $DIR/slow_vector_initialization.rs:62:5 + | +62 | vec1.resize(10, 0); + | ^^^^^^^^^^^^^^^^^^ + +error: aborting due to 7 previous errors + diff --git a/tests/ui/slow_vector_initialization.stdout b/tests/ui/slow_vector_initialization.stdout new file mode 100644 index 00000000000..e69de29bb2d