src/tools/clippy/clippy_lints/src/slow_vector_initialization.rs - toolchain/rustc - Git at Google

 use clippy_utils::diagnostics::span_lint_and_then;
 use clippy_utils::macros::root_macro_call;
 use clippy_utils::sugg::Sugg;
 use clippy_utils::{
     get_enclosing_block, is_expr_path_def_path, is_integer_literal, is_path_diagnostic_item, path_to_local,
     path_to_local_id, paths, SpanlessEq,
 };
 use rustc_errors::Applicability;
 use rustc_hir::intravisit::{walk_block, walk_expr, walk_stmt, Visitor};
 use rustc_hir::{BindingAnnotation, Block, Expr, ExprKind, HirId, PatKind, Stmt, StmtKind};
 use rustc_lint::{LateContext, LateLintPass};
 use rustc_session::declare_lint_pass;
 use rustc_span::symbol::sym;

 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]`.
     ///
     /// Specifically, for `vec![0; len]`, the compiler can use a specialized type of allocation
     /// that also zero-initializes the allocated memory in the same call
     /// (see: [alloc_zeroed](https://doc.rust-lang.org/stable/std/alloc/trait.GlobalAlloc.html#method.alloc_zeroed)).
     ///
     /// Writing `Vec::new()` followed by `vec.resize(len, 0)` is suboptimal because,
     /// while it does do the same number of allocations,
     /// it involves two operations for allocating and initializing.
     /// The `resize` call first allocates memory (since `Vec::new()` did not), and only *then* zero-initializes it.
     ///
     /// ### Example
     /// ```no_run
     /// # use core::iter::repeat;
     /// # let len = 4;
     /// let mut vec1 = Vec::new();
     /// vec1.resize(len, 0);
     ///
     /// let mut vec2 = Vec::with_capacity(len);
     /// vec2.resize(len, 0);
     ///
     /// let mut vec3 = Vec::with_capacity(len);
     /// vec3.extend(repeat(0).take(len));
     /// ```
     ///
     /// Use instead:
     /// ```no_run
     /// # let len = 4;
     /// let mut vec1 = vec![0; len];
     /// let mut vec2 = vec![0; len];
     /// let mut vec3 = vec![0; len];
     /// ```
     #[clippy::version = "1.32.0"]
     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> {
     /// `HirId` of the variable
     local_id: HirId,

     /// 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.
     size_expr: InitializedSize<'tcx>,
 }

 /// Initializer for the creation of the vector.
 ///
 /// When `Vec::with_capacity(size)` is found, the `size` expression will be in
 /// `InitializedSize::Initialized`.
 ///
 /// Otherwise, for `Vec::new()` calls, there is no allocation initializer yet, so
 /// `InitializedSize::Uninitialized` is used.
 /// Later, when a call to `.resize(size, 0)` or similar is found, it's set
 /// to `InitializedSize::Initialized(size)`.
 ///
 /// Since it will be set to `InitializedSize::Initialized(size)` when a slow initialization is
 /// found, it is always safe to "unwrap" it at lint time.
 enum InitializedSize<'tcx> {
     Initialized(&'tcx Expr<'tcx>),
     Uninitialized,
 }

 /// 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 reassignments. For example: `vec = Vec::with_capacity(100)`
         if let ExprKind::Assign(left, right, _) = expr.kind
             && let Some(local_id) = path_to_local(left)
             && let Some(size_expr) = Self::as_vec_initializer(cx, right)
         {
             let vi = VecAllocation {
                 local_id,
                 allocation_expr: right,
                 size_expr,
             };

             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)`
         // or `Vec::new()`
         if let StmtKind::Let(local) = stmt.kind
             && let PatKind::Binding(BindingAnnotation::MUT, local_id, _, None) = local.pat.kind
             && let Some(init) = local.init
             && let Some(size_expr) = Self::as_vec_initializer(cx, init)
         {
             let vi = VecAllocation {
                 local_id,
                 allocation_expr: init,
                 size_expr,
             };

             Self::search_initialization(cx, vi, stmt.hir_id);
         }
     }
 }

 impl SlowVectorInit {
     /// Looks for `Vec::with_capacity(size)` or `Vec::new()` calls and returns the initialized size,
     /// if any. More specifically, it returns:
     /// - `Some(InitializedSize::Initialized(size))` for `Vec::with_capacity(size)`
     /// - `Some(InitializedSize::Uninitialized)` for `Vec::new()`
     /// - `None` for other, unrelated kinds of expressions
     fn as_vec_initializer<'tcx>(cx: &LateContext<'_>, expr: &'tcx Expr<'tcx>) -> Option<InitializedSize<'tcx>> {
         // Generally don't warn if the vec initializer comes from an expansion, except for the vec! macro.
         // This lets us still warn on `vec![]`, while ignoring other kinds of macros that may output an
         // empty vec
         if expr.span.from_expansion()
             && root_macro_call(expr.span).map(|m| m.def_id) != cx.tcx.get_diagnostic_item(sym::vec_macro)
         {
             return None;
         }

         if let ExprKind::Call(func, [len_expr]) = expr.kind
             && is_expr_path_def_path(cx, func, &paths::VEC_WITH_CAPACITY)
         {
             Some(InitializedSize::Initialized(len_expr))
         } else if matches!(expr.kind, ExprKind::Call(func, _) if is_expr_path_def_path(cx, func, &paths::VEC_NEW)) {
             Some(InitializedSize::Uninitialized)
         } else {
             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");
             },
         };
     }

     fn emit_lint(cx: &LateContext<'_>, slow_fill: &Expr<'_>, vec_alloc: &VecAllocation<'_>, msg: &str) {
         let len_expr = Sugg::hir(
             cx,
             match vec_alloc.size_expr {
                 InitializedSize::Initialized(expr) => expr,
                 InitializedSize::Uninitialized => unreachable!("size expression must be set by this point"),
             },
             "len",
         );

         span_lint_and_then(cx, SLOW_VECTOR_INITIALIZATION, slow_fill.span, msg, |diag| {
             diag.span_suggestion(
                 vec_alloc.allocation_expr.span.source_callsite(),
                 "consider replacing this 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 self.initialization_found
             && let ExprKind::MethodCall(path, self_arg, [extend_arg], _) = expr.kind
             && path_to_local_id(self_arg, self.vec_alloc.local_id)
             && path.ident.name == sym!(extend)
             && self.is_repeat_take(extend_arg)
         {
             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<'tcx>) {
         if self.initialization_found
             && let ExprKind::MethodCall(path, self_arg, [len_arg, fill_arg], _) = expr.kind
             && path_to_local_id(self_arg, self.vec_alloc.local_id)
             && path.ident.name == sym!(resize)
             // Check that is filled with 0
             && is_integer_literal(fill_arg, 0)
         {
             let is_matching_resize = if let InitializedSize::Initialized(size_expr) = self.vec_alloc.size_expr {
                 // If we have a size expression, check that it is equal to what's passed to `resize`
                 SpanlessEq::new(self.cx).eq_expr(len_arg, size_expr)
                     || matches!(len_arg.kind, ExprKind::MethodCall(path, ..) if path.ident.as_str() == "capacity")
             } else {
                 self.vec_alloc.size_expr = InitializedSize::Initialized(len_arg);
                 true
             };

             if is_matching_resize {
                 self.slow_expression = Some(InitializationType::Resize(expr));
             }
         }
     }

     /// Returns `true` if give expression is `repeat(0).take(...)`
     fn is_repeat_take(&mut self, expr: &'tcx Expr<'tcx>) -> bool {
         if let ExprKind::MethodCall(take_path, recv, [len_arg, ..], _) = expr.kind
             && take_path.ident.name == sym!(take)
             // Check that take is applied to `repeat(0)`
             && self.is_repeat_zero(recv)
         {
             if let InitializedSize::Initialized(size_expr) = self.vec_alloc.size_expr {
                 // Check that len expression is equals to `with_capacity` expression
                 return SpanlessEq::new(self.cx).eq_expr(len_arg, size_expr)
                     || matches!(len_arg.kind, ExprKind::MethodCall(path, ..) if path.ident.as_str() == "capacity");
             }

             self.vec_alloc.size_expr = InitializedSize::Initialized(len_arg);
             return true;
         }

         false
     }

     /// Returns `true` if given expression is `repeat(0)`
     fn is_repeat_zero(&self, expr: &Expr<'_>) -> bool {
         if let ExprKind::Call(fn_expr, [repeat_arg]) = expr.kind
             && is_path_diagnostic_item(self.cx, fn_expr, sym::iter_repeat)
             && is_integer_literal(repeat_arg, 0)
         {
             true
         } else {
             false
         }
     }
 }

 impl<'a, 'tcx> Visitor<'tcx> for VectorInitializationVisitor<'a, 'tcx> {
     fn visit_stmt(&mut self, stmt: &'tcx Stmt<'_>) {
         if self.initialization_found {
             match stmt.kind {
                 StmtKind::Expr(expr) | StmtKind::Semi(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(s) = block.stmts.first() {
                 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);
     }
 }
	use clippy_utils::diagnostics::span_lint_and_then;
	use clippy_utils::macros::root_macro_call;
	use clippy_utils::sugg::Sugg;
	use clippy_utils::{
	get_enclosing_block, is_expr_path_def_path, is_integer_literal, is_path_diagnostic_item, path_to_local,
	path_to_local_id, paths, SpanlessEq,
	};
	use rustc_errors::Applicability;
	use rustc_hir::intravisit::{walk_block, walk_expr, walk_stmt, Visitor};
	use rustc_hir::{BindingAnnotation, Block, Expr, ExprKind, HirId, PatKind, Stmt, StmtKind};
	use rustc_lint::{LateContext, LateLintPass};
	use rustc_session::declare_lint_pass;
	use rustc_span::symbol::sym;

	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]`.
	///
	/// Specifically, for `vec![0; len]`, the compiler can use a specialized type of allocation
	/// that also zero-initializes the allocated memory in the same call
	/// (see: [alloc_zeroed](https://doc.rust-lang.org/stable/std/alloc/trait.GlobalAlloc.html#method.alloc_zeroed)).
	///
	/// Writing `Vec::new()` followed by `vec.resize(len, 0)` is suboptimal because,
	/// while it does do the same number of allocations,
	/// it involves two operations for allocating and initializing.
	/// The `resize` call first allocates memory (since `Vec::new()` did not), and only then zero-initializes it.
	///
	/// ### Example
	/// ```no_run
	/// # use core::iter::repeat;
	/// # let len = 4;
	/// let mut vec1 = Vec::new();
	/// vec1.resize(len, 0);
	///
	/// let mut vec2 = Vec::with_capacity(len);
	/// vec2.resize(len, 0);
	///
	/// let mut vec3 = Vec::with_capacity(len);
	/// vec3.extend(repeat(0).take(len));
	/// ```
	///
	/// Use instead:
	/// ```no_run
	/// # let len = 4;
	/// let mut vec1 = vec![0; len];
	/// let mut vec2 = vec![0; len];
	/// let mut vec3 = vec![0; len];
	/// ```
	#[clippy::version = "1.32.0"]
	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> {
	/// `HirId` of the variable
	local_id: HirId,

	/// 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.
	size_expr: InitializedSize<'tcx>,
	}

	/// Initializer for the creation of the vector.
	///
	/// When `Vec::with_capacity(size)` is found, the `size` expression will be in
	/// `InitializedSize::Initialized`.
	///
	/// Otherwise, for `Vec::new()` calls, there is no allocation initializer yet, so
	/// `InitializedSize::Uninitialized` is used.
	/// Later, when a call to `.resize(size, 0)` or similar is found, it's set
	/// to `InitializedSize::Initialized(size)`.
	///
	/// Since it will be set to `InitializedSize::Initialized(size)` when a slow initialization is
	/// found, it is always safe to "unwrap" it at lint time.
	enum InitializedSize<'tcx> {
	Initialized(&'tcx Expr<'tcx>),
	Uninitialized,
	}

	/// 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 reassignments. For example: `vec = Vec::with_capacity(100)`
	if let ExprKind::Assign(left, right, _) = expr.kind
	&& let Some(local_id) = path_to_local(left)
	&& let Some(size_expr) = Self::as_vec_initializer(cx, right)
	{
	let vi = VecAllocation {
	local_id,
	allocation_expr: right,
	size_expr,
	};

	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)`
	// or `Vec::new()`
	if let StmtKind::Let(local) = stmt.kind
	&& let PatKind::Binding(BindingAnnotation::MUT, local_id, _, None) = local.pat.kind
	&& let Some(init) = local.init
	&& let Some(size_expr) = Self::as_vec_initializer(cx, init)
	{
	let vi = VecAllocation {
	local_id,
	allocation_expr: init,
	size_expr,
	};

	Self::search_initialization(cx, vi, stmt.hir_id);
	}
	}
	}

	impl SlowVectorInit {
	/// Looks for `Vec::with_capacity(size)` or `Vec::new()` calls and returns the initialized size,
	/// if any. More specifically, it returns:
	/// - `Some(InitializedSize::Initialized(size))` for `Vec::with_capacity(size)`
	/// - `Some(InitializedSize::Uninitialized)` for `Vec::new()`
	/// - `None` for other, unrelated kinds of expressions
	fn as_vec_initializer<'tcx>(cx: &LateContext<'_>, expr: &'tcx Expr<'tcx>) -> Option<InitializedSize<'tcx>> {
	// Generally don't warn if the vec initializer comes from an expansion, except for the vec! macro.
	// This lets us still warn on `vec![]`, while ignoring other kinds of macros that may output an
	// empty vec
	if expr.span.from_expansion()
	&& root_macro_call(expr.span).map(\|m\| m.def_id) != cx.tcx.get_diagnostic_item(sym::vec_macro)
	{
	return None;
	}

	if let ExprKind::Call(func, [len_expr]) = expr.kind
	&& is_expr_path_def_path(cx, func, &paths::VEC_WITH_CAPACITY)
	{
	Some(InitializedSize::Initialized(len_expr))
	} else if matches!(expr.kind, ExprKind::Call(func, _) if is_expr_path_def_path(cx, func, &paths::VEC_NEW)) {
	Some(InitializedSize::Uninitialized)
	} else {
	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");
	},
	};
	}

	fn emit_lint(cx: &LateContext<'_>, slow_fill: &Expr<'_>, vec_alloc: &VecAllocation<'_>, msg: &str) {
	let len_expr = Sugg::hir(
	cx,
	match vec_alloc.size_expr {
	InitializedSize::Initialized(expr) => expr,
	InitializedSize::Uninitialized => unreachable!("size expression must be set by this point"),
	},
	"len",
	);

	span_lint_and_then(cx, SLOW_VECTOR_INITIALIZATION, slow_fill.span, msg, \|diag\| {
	diag.span_suggestion(
	vec_alloc.allocation_expr.span.source_callsite(),
	"consider replacing this 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 self.initialization_found
	&& let ExprKind::MethodCall(path, self_arg, [extend_arg], _) = expr.kind
	&& path_to_local_id(self_arg, self.vec_alloc.local_id)
	&& path.ident.name == sym!(extend)
	&& self.is_repeat_take(extend_arg)
	{
	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<'tcx>) {
	if self.initialization_found
	&& let ExprKind::MethodCall(path, self_arg, [len_arg, fill_arg], _) = expr.kind
	&& path_to_local_id(self_arg, self.vec_alloc.local_id)
	&& path.ident.name == sym!(resize)
	// Check that is filled with 0
	&& is_integer_literal(fill_arg, 0)
	{
	let is_matching_resize = if let InitializedSize::Initialized(size_expr) = self.vec_alloc.size_expr {
	// If we have a size expression, check that it is equal to what's passed to `resize`
	SpanlessEq::new(self.cx).eq_expr(len_arg, size_expr)
	\|\| matches!(len_arg.kind, ExprKind::MethodCall(path, ..) if path.ident.as_str() == "capacity")
	} else {
	self.vec_alloc.size_expr = InitializedSize::Initialized(len_arg);
	true
	};

	if is_matching_resize {
	self.slow_expression = Some(InitializationType::Resize(expr));
	}
	}
	}

	/// Returns `true` if give expression is `repeat(0).take(...)`
	fn is_repeat_take(&mut self, expr: &'tcx Expr<'tcx>) -> bool {
	if let ExprKind::MethodCall(take_path, recv, [len_arg, ..], _) = expr.kind
	&& take_path.ident.name == sym!(take)
	// Check that take is applied to `repeat(0)`
	&& self.is_repeat_zero(recv)
	{
	if let InitializedSize::Initialized(size_expr) = self.vec_alloc.size_expr {
	// Check that len expression is equals to `with_capacity` expression
	return SpanlessEq::new(self.cx).eq_expr(len_arg, size_expr)
	\|\| matches!(len_arg.kind, ExprKind::MethodCall(path, ..) if path.ident.as_str() == "capacity");
	}

	self.vec_alloc.size_expr = InitializedSize::Initialized(len_arg);
	return true;
	}

	false
	}

	/// Returns `true` if given expression is `repeat(0)`
	fn is_repeat_zero(&self, expr: &Expr<'_>) -> bool {
	if let ExprKind::Call(fn_expr, [repeat_arg]) = expr.kind
	&& is_path_diagnostic_item(self.cx, fn_expr, sym::iter_repeat)
	&& is_integer_literal(repeat_arg, 0)
	{
	true
	} else {
	false
	}
	}
	}

	impl<'a, 'tcx> Visitor<'tcx> for VectorInitializationVisitor<'a, 'tcx> {
	fn visit_stmt(&mut self, stmt: &'tcx Stmt<'_>) {
	if self.initialization_found {
	match stmt.kind {
	StmtKind::Expr(expr) \| StmtKind::Semi(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(s) = block.stmts.first() {
	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);
	}
	}