--- /dev/null
+use crate::utils::{
+ is_type_diagnostic_item, match_def_path, path_to_local, path_to_local_id, paths, snippet, span_lint_and_sugg,
+};
+use if_chain::if_chain;
+use rustc_ast::ast::LitKind;
+use rustc_errors::Applicability;
+use rustc_hir::{BindingAnnotation, Block, Expr, ExprKind, HirId, Local, PatKind, QPath, Stmt, StmtKind};
+use rustc_lint::{LateContext, LateLintPass, LintContext};
+use rustc_middle::lint::in_external_macro;
+use rustc_session::{declare_tool_lint, impl_lint_pass};
+use rustc_span::{symbol::sym, Span};
+use std::convert::TryInto;
+
+declare_clippy_lint! {
+ /// **What it does:** Checks for calls to `push` immediately after creating a new `Vec`.
+ ///
+ /// **Why is this bad?** The `vec![]` macro is both more performant and easier to read than
+ /// multiple `push` calls.
+ ///
+ /// **Known problems:** None.
+ ///
+ /// **Example:**
+ ///
+ /// ```rust
+ /// let mut v = Vec::new();
+ /// v.push(0);
+ /// ```
+ /// Use instead:
+ /// ```rust
+ /// let v = vec![0];
+ /// ```
+ pub VEC_INIT_THEN_PUSH,
+ perf,
+ "`push` immediately after `Vec` creation"
+}
+
+impl_lint_pass!(VecInitThenPush => [VEC_INIT_THEN_PUSH]);
+
+#[derive(Default)]
+pub struct VecInitThenPush {
+ searcher: Option<VecPushSearcher>,
+}
+
+#[derive(Clone, Copy)]
+enum VecInitKind {
+ New,
+ WithCapacity(u64),
+}
+struct VecPushSearcher {
+ local_id: HirId,
+ init: VecInitKind,
+ lhs_is_local: bool,
+ lhs_span: Span,
+ err_span: Span,
+ found: u64,
+}
+impl VecPushSearcher {
+ fn display_err(&self, cx: &LateContext<'_>) {
+ match self.init {
+ _ if self.found == 0 => return,
+ VecInitKind::WithCapacity(x) if x > self.found => return,
+ _ => (),
+ };
+
+ let mut s = if self.lhs_is_local {
+ String::from("let ")
+ } else {
+ String::new()
+ };
+ s.push_str(&snippet(cx, self.lhs_span, ".."));
+ s.push_str(" = vec![..];");
+
+ span_lint_and_sugg(
+ cx,
+ VEC_INIT_THEN_PUSH,
+ self.err_span,
+ "calls to `push` immediately after creation",
+ "consider using the `vec![]` macro",
+ s,
+ Applicability::HasPlaceholders,
+ );
+ }
+}
+
+impl LateLintPass<'_> for VecInitThenPush {
+ fn check_block(&mut self, _: &LateContext<'tcx>, _: &'tcx Block<'tcx>) {
+ self.searcher = None;
+ }
+
+ fn check_local(&mut self, cx: &LateContext<'tcx>, local: &'tcx Local<'tcx>) {
+ if_chain! {
+ if !in_external_macro(cx.sess(), local.span);
+ if let Some(init) = local.init;
+ if let PatKind::Binding(BindingAnnotation::Mutable, id, _, None) = local.pat.kind;
+ if let Some(init_kind) = get_vec_init_kind(cx, init);
+ then {
+ self.searcher = Some(VecPushSearcher {
+ local_id: id,
+ init: init_kind,
+ lhs_is_local: true,
+ lhs_span: local.ty.map_or(local.pat.span, |t| local.pat.span.to(t.span)),
+ err_span: local.span,
+ found: 0,
+ });
+ }
+ }
+ }
+
+ fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
+ if self.searcher.is_none() {
+ if_chain! {
+ if !in_external_macro(cx.sess(), expr.span);
+ if let ExprKind::Assign(left, right, _) = expr.kind;
+ if let Some(id) = path_to_local(left);
+ if let Some(init_kind) = get_vec_init_kind(cx, right);
+ then {
+ self.searcher = Some(VecPushSearcher {
+ local_id: id,
+ init: init_kind,
+ lhs_is_local: false,
+ lhs_span: left.span,
+ err_span: expr.span,
+ found: 0,
+ });
+ }
+ }
+ }
+ }
+
+ fn check_stmt(&mut self, cx: &LateContext<'tcx>, stmt: &'tcx Stmt<'_>) {
+ if let Some(searcher) = self.searcher.take() {
+ if_chain! {
+ if let StmtKind::Expr(expr) | StmtKind::Semi(expr) = stmt.kind;
+ if let ExprKind::MethodCall(path, _, [self_arg, _], _) = expr.kind;
+ if path_to_local_id(self_arg, searcher.local_id);
+ if path.ident.name.as_str() == "push";
+ then {
+ self.searcher = Some(VecPushSearcher {
+ found: searcher.found + 1,
+ err_span: searcher.err_span.to(stmt.span),
+ .. searcher
+ });
+ } else {
+ searcher.display_err(cx);
+ }
+ }
+ }
+ }
+
+ fn check_block_post(&mut self, cx: &LateContext<'tcx>, _: &'tcx Block<'tcx>) {
+ if let Some(searcher) = self.searcher.take() {
+ searcher.display_err(cx);
+ }
+ }
+}
+
+fn get_vec_init_kind<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) -> Option<VecInitKind> {
+ if let ExprKind::Call(func, args) = expr.kind {
+ match func.kind {
+ ExprKind::Path(QPath::TypeRelative(ty, name))
+ if is_type_diagnostic_item(cx, cx.typeck_results().node_type(ty.hir_id), sym::vec_type) =>
+ {
+ if name.ident.name == sym::new {
+ return Some(VecInitKind::New);
+ } else if name.ident.name.as_str() == "with_capacity" {
+ return args.get(0).and_then(|arg| {
+ if_chain! {
+ if let ExprKind::Lit(lit) = &arg.kind;
+ if let LitKind::Int(num, _) = lit.node;
+ then {
+ Some(VecInitKind::WithCapacity(num.try_into().ok()?))
+ } else {
+ None
+ }
+ }
+ });
+ }
+ }
+ ExprKind::Path(QPath::Resolved(_, path))
+ if match_def_path(cx, path.res.opt_def_id()?, &paths::DEFAULT_TRAIT_METHOD)
+ && is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(expr), sym::vec_type) =>
+ {
+ return Some(VecInitKind::New);
+ }
+ _ => (),
+ }
+ }
+ None
+}
projects / rustc.git / blobdiff