409 lines
14 KiB
Rust
409 lines
14 KiB
Rust
use clippy_utils::diagnostics::span_lint_and_then;
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use clippy_utils::source::snippet;
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use clippy_utils::{contains_name, higher, iter_input_pats};
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use rustc_hir::intravisit::FnKind;
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use rustc_hir::{
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Block, Body, Expr, ExprKind, FnDecl, Guard, HirId, Local, MutTy, Pat, PatKind, Path, QPath, StmtKind, Ty, TyKind,
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UnOp,
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};
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use rustc_lint::{LateContext, LateLintPass, LintContext};
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use rustc_middle::lint::in_external_macro;
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use rustc_middle::ty;
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use rustc_session::{declare_lint_pass, declare_tool_lint};
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use rustc_span::source_map::Span;
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use rustc_span::symbol::Symbol;
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declare_clippy_lint! {
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/// ### What it does
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/// Checks for bindings that shadow other bindings already in
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/// scope, while just changing reference level or mutability.
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///
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/// ### Why is this bad?
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/// Not much, in fact it's a very common pattern in Rust
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/// code. Still, some may opt to avoid it in their code base, they can set this
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/// lint to `Warn`.
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///
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/// ### Known problems
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/// This lint, as the other shadowing related lints,
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/// currently only catches very simple patterns.
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///
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/// ### Example
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/// ```rust
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/// # let x = 1;
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/// // Bad
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/// let x = &x;
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///
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/// // Good
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/// let y = &x; // use different variable name
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/// ```
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pub SHADOW_SAME,
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restriction,
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"rebinding a name to itself, e.g., `let mut x = &mut x`"
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}
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declare_clippy_lint! {
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/// ### What it does
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/// Checks for bindings that shadow other bindings already in
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/// scope, while reusing the original value.
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///
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/// ### Why is this bad?
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/// Not too much, in fact it's a common pattern in Rust
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/// code. Still, some argue that name shadowing like this hurts readability,
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/// because a value may be bound to different things depending on position in
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/// the code.
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///
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/// ### Known problems
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/// This lint, as the other shadowing related lints,
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/// currently only catches very simple patterns.
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///
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/// ### Example
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/// ```rust
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/// let x = 2;
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/// let x = x + 1;
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/// ```
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/// use different variable name:
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/// ```rust
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/// let x = 2;
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/// let y = x + 1;
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/// ```
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pub SHADOW_REUSE,
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restriction,
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"rebinding a name to an expression that re-uses the original value, e.g., `let x = x + 1`"
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}
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declare_clippy_lint! {
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/// ### What it does
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/// Checks for bindings that shadow other bindings already in
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/// scope, either without a initialization or with one that does not even use
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/// the original value.
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///
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/// ### Why is this bad?
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/// Name shadowing can hurt readability, especially in
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/// large code bases, because it is easy to lose track of the active binding at
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/// any place in the code. This can be alleviated by either giving more specific
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/// names to bindings or introducing more scopes to contain the bindings.
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///
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/// ### Known problems
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/// This lint, as the other shadowing related lints,
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/// currently only catches very simple patterns. Note that
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/// `allow`/`warn`/`deny`/`forbid` attributes only work on the function level
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/// for this lint.
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///
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/// ### Example
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/// ```rust
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/// # let y = 1;
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/// # let z = 2;
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/// let x = y;
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///
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/// // Bad
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/// let x = z; // shadows the earlier binding
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///
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/// // Good
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/// let w = z; // use different variable name
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/// ```
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pub SHADOW_UNRELATED,
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pedantic,
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"rebinding a name without even using the original value"
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}
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declare_lint_pass!(Shadow => [SHADOW_SAME, SHADOW_REUSE, SHADOW_UNRELATED]);
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impl<'tcx> LateLintPass<'tcx> for Shadow {
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fn check_fn(
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&mut self,
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cx: &LateContext<'tcx>,
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_: FnKind<'tcx>,
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decl: &'tcx FnDecl<'_>,
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body: &'tcx Body<'_>,
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_: Span,
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_: HirId,
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) {
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if in_external_macro(cx.sess(), body.value.span) {
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return;
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}
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check_fn(cx, decl, body);
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}
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}
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fn check_fn<'tcx>(cx: &LateContext<'tcx>, decl: &'tcx FnDecl<'_>, body: &'tcx Body<'_>) {
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let mut bindings = Vec::with_capacity(decl.inputs.len());
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for arg in iter_input_pats(decl, body) {
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if let PatKind::Binding(.., ident, _) = arg.pat.kind {
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bindings.push((ident.name, ident.span));
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}
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}
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check_expr(cx, &body.value, &mut bindings);
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}
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fn check_block<'tcx>(cx: &LateContext<'tcx>, block: &'tcx Block<'_>, bindings: &mut Vec<(Symbol, Span)>) {
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let len = bindings.len();
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for stmt in block.stmts {
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match stmt.kind {
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StmtKind::Local(local) => check_local(cx, local, bindings),
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StmtKind::Expr(e) | StmtKind::Semi(e) => check_expr(cx, e, bindings),
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StmtKind::Item(..) => {},
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}
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}
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if let Some(o) = block.expr {
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check_expr(cx, o, bindings);
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}
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bindings.truncate(len);
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}
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fn check_local<'tcx>(cx: &LateContext<'tcx>, local: &'tcx Local<'_>, bindings: &mut Vec<(Symbol, Span)>) {
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if in_external_macro(cx.sess(), local.span) {
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return;
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}
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if higher::is_from_for_desugar(local) {
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return;
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}
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let Local {
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pat,
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ref ty,
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ref init,
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span,
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..
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} = *local;
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if let Some(t) = *ty {
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check_ty(cx, t, bindings);
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}
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if let Some(o) = *init {
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check_expr(cx, o, bindings);
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check_pat(cx, pat, Some(o), span, bindings);
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} else {
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check_pat(cx, pat, None, span, bindings);
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}
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}
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fn is_binding(cx: &LateContext<'_>, pat_id: HirId) -> bool {
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let var_ty = cx.typeck_results().node_type_opt(pat_id);
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var_ty.map_or(false, |var_ty| !matches!(var_ty.kind(), ty::Adt(..)))
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}
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fn check_pat<'tcx>(
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cx: &LateContext<'tcx>,
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pat: &'tcx Pat<'_>,
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init: Option<&'tcx Expr<'_>>,
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span: Span,
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bindings: &mut Vec<(Symbol, Span)>,
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) {
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// TODO: match more stuff / destructuring
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match pat.kind {
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PatKind::Binding(.., ident, ref inner) => {
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let name = ident.name;
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if is_binding(cx, pat.hir_id) {
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let mut new_binding = true;
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for tup in bindings.iter_mut() {
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if tup.0 == name {
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lint_shadow(cx, name, span, pat.span, init, tup.1);
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tup.1 = ident.span;
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new_binding = false;
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break;
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}
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}
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if new_binding {
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bindings.push((name, ident.span));
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}
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}
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if let Some(p) = *inner {
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check_pat(cx, p, init, span, bindings);
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}
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},
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PatKind::Struct(_, pfields, _) => {
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if let Some(init_struct) = init {
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if let ExprKind::Struct(_, efields, _) = init_struct.kind {
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for field in pfields {
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let name = field.ident.name;
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let efield = efields
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.iter()
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.find_map(|f| if f.ident.name == name { Some(&*f.expr) } else { None });
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check_pat(cx, field.pat, efield, span, bindings);
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}
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} else {
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for field in pfields {
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check_pat(cx, field.pat, init, span, bindings);
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}
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}
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} else {
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for field in pfields {
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check_pat(cx, field.pat, None, span, bindings);
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}
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}
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},
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PatKind::Tuple(inner, _) => {
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if let Some(init_tup) = init {
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if let ExprKind::Tup(tup) = init_tup.kind {
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for (i, p) in inner.iter().enumerate() {
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check_pat(cx, p, Some(&tup[i]), p.span, bindings);
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}
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} else {
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for p in inner {
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check_pat(cx, p, init, span, bindings);
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}
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}
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} else {
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for p in inner {
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check_pat(cx, p, None, span, bindings);
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}
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}
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},
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PatKind::Box(inner) => {
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if let Some(initp) = init {
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if let ExprKind::Box(inner_init) = initp.kind {
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check_pat(cx, inner, Some(inner_init), span, bindings);
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} else {
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check_pat(cx, inner, init, span, bindings);
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}
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} else {
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check_pat(cx, inner, init, span, bindings);
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}
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},
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PatKind::Ref(inner, _) => check_pat(cx, inner, init, span, bindings),
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// PatVec(Vec<P<Pat>>, Option<P<Pat>>, Vec<P<Pat>>),
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_ => (),
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}
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}
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fn lint_shadow<'tcx>(
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cx: &LateContext<'tcx>,
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name: Symbol,
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span: Span,
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pattern_span: Span,
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init: Option<&'tcx Expr<'_>>,
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prev_span: Span,
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) {
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if let Some(expr) = init {
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if is_self_shadow(name, expr) {
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span_lint_and_then(
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cx,
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SHADOW_SAME,
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span,
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&format!(
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"`{}` is shadowed by itself in `{}`",
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snippet(cx, pattern_span, "_"),
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snippet(cx, expr.span, "..")
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),
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|diag| {
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diag.span_note(prev_span, "previous binding is here");
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},
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);
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} else if contains_name(name, expr) {
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span_lint_and_then(
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cx,
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SHADOW_REUSE,
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pattern_span,
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&format!(
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"`{}` is shadowed by `{}` which reuses the original value",
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snippet(cx, pattern_span, "_"),
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snippet(cx, expr.span, "..")
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),
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|diag| {
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diag.span_note(expr.span, "initialization happens here");
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diag.span_note(prev_span, "previous binding is here");
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},
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);
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} else {
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span_lint_and_then(
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cx,
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SHADOW_UNRELATED,
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pattern_span,
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&format!("`{}` is being shadowed", snippet(cx, pattern_span, "_")),
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|diag| {
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diag.span_note(expr.span, "initialization happens here");
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diag.span_note(prev_span, "previous binding is here");
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},
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);
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}
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} else {
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span_lint_and_then(
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cx,
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SHADOW_UNRELATED,
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span,
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&format!("`{}` shadows a previous declaration", snippet(cx, pattern_span, "_")),
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|diag| {
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diag.span_note(prev_span, "previous binding is here");
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},
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);
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}
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}
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fn check_expr<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>, bindings: &mut Vec<(Symbol, Span)>) {
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if in_external_macro(cx.sess(), expr.span) {
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return;
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}
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match expr.kind {
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ExprKind::Unary(_, e) | ExprKind::Field(e, _) | ExprKind::AddrOf(_, _, e) | ExprKind::Box(e) => {
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check_expr(cx, e, bindings);
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},
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ExprKind::Block(block, _) | ExprKind::Loop(block, ..) => check_block(cx, block, bindings),
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// ExprKind::Call
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// ExprKind::MethodCall
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ExprKind::Array(v) | ExprKind::Tup(v) => {
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for e in v {
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check_expr(cx, e, bindings);
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}
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},
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ExprKind::If(cond, then, ref otherwise) => {
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check_expr(cx, cond, bindings);
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check_expr(cx, then, bindings);
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if let Some(o) = *otherwise {
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check_expr(cx, o, bindings);
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}
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},
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ExprKind::Match(init, arms, _) => {
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check_expr(cx, init, bindings);
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let len = bindings.len();
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for arm in arms {
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check_pat(cx, arm.pat, Some(init), arm.pat.span, bindings);
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// This is ugly, but needed to get the right type
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if let Some(ref guard) = arm.guard {
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match guard {
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Guard::If(if_expr) => check_expr(cx, if_expr, bindings),
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Guard::IfLet(guard_pat, guard_expr) => {
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check_pat(cx, guard_pat, Some(*guard_expr), guard_pat.span, bindings);
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check_expr(cx, guard_expr, bindings);
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},
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}
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}
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check_expr(cx, arm.body, bindings);
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bindings.truncate(len);
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}
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},
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_ => (),
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}
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}
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fn check_ty<'tcx>(cx: &LateContext<'tcx>, ty: &'tcx Ty<'_>, bindings: &mut Vec<(Symbol, Span)>) {
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match ty.kind {
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TyKind::Slice(sty) => check_ty(cx, sty, bindings),
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TyKind::Array(fty, ref anon_const) => {
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check_ty(cx, fty, bindings);
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check_expr(cx, &cx.tcx.hir().body(anon_const.body).value, bindings);
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},
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TyKind::Ptr(MutTy { ty: mty, .. }) | TyKind::Rptr(_, MutTy { ty: mty, .. }) => check_ty(cx, mty, bindings),
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TyKind::Tup(tup) => {
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for t in tup {
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check_ty(cx, t, bindings);
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}
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},
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TyKind::Typeof(ref anon_const) => check_expr(cx, &cx.tcx.hir().body(anon_const.body).value, bindings),
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_ => (),
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}
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}
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fn is_self_shadow(name: Symbol, expr: &Expr<'_>) -> bool {
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match expr.kind {
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ExprKind::Box(inner) | ExprKind::AddrOf(_, _, inner) => is_self_shadow(name, inner),
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ExprKind::Block(block, _) => {
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block.stmts.is_empty() && block.expr.as_ref().map_or(false, |e| is_self_shadow(name, e))
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},
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ExprKind::Unary(op, inner) => (UnOp::Deref == op) && is_self_shadow(name, inner),
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ExprKind::Path(QPath::Resolved(_, path)) => path_eq_name(name, path),
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_ => false,
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}
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}
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fn path_eq_name(name: Symbol, path: &Path<'_>) -> bool {
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!path.is_global() && path.segments.len() == 1 && path.segments[0].ident.name == name
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}
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