83 lines
3.2 KiB
Rust
83 lines
3.2 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::ty::walk_ptrs_ty_depth;
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use clippy_utils::{match_def_path, paths};
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use if_chain::if_chain;
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use rustc_errors::Applicability;
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use rustc_hir::{BorrowKind, Expr, ExprKind};
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use rustc_lint::{LateContext, LateLintPass};
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use rustc_session::{declare_lint_pass, declare_tool_lint};
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declare_clippy_lint! {
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/// ### What it does
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/// Checks for calls of `mem::discriminant()` on a non-enum type.
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///
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/// ### Why is this bad?
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/// The value of `mem::discriminant()` on non-enum types
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/// is unspecified.
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///
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/// ### Example
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/// ```rust
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/// use std::mem;
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///
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/// mem::discriminant(&"hello");
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/// mem::discriminant(&&Some(2));
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/// ```
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pub MEM_DISCRIMINANT_NON_ENUM,
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correctness,
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"calling `mem::descriminant` on non-enum type"
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}
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declare_lint_pass!(MemDiscriminant => [MEM_DISCRIMINANT_NON_ENUM]);
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impl<'tcx> LateLintPass<'tcx> for MemDiscriminant {
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fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
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if_chain! {
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if let ExprKind::Call(func, func_args) = expr.kind;
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// is `mem::discriminant`
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if let ExprKind::Path(ref func_qpath) = func.kind;
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if let Some(def_id) = cx.qpath_res(func_qpath, func.hir_id).opt_def_id();
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if match_def_path(cx, def_id, &paths::MEM_DISCRIMINANT);
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// type is non-enum
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let ty_param = cx.typeck_results().node_substs(func.hir_id).type_at(0);
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if !ty_param.is_enum();
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then {
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span_lint_and_then(
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cx,
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MEM_DISCRIMINANT_NON_ENUM,
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expr.span,
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&format!("calling `mem::discriminant` on non-enum type `{}`", ty_param),
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|diag| {
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// if this is a reference to an enum, suggest dereferencing
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let (base_ty, ptr_depth) = walk_ptrs_ty_depth(ty_param);
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if ptr_depth >= 1 && base_ty.is_enum() {
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let param = &func_args[0];
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// cancel out '&'s first
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let mut derefs_needed = ptr_depth;
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let mut cur_expr = param;
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while derefs_needed > 0 {
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if let ExprKind::AddrOf(BorrowKind::Ref, _, inner_expr) = cur_expr.kind {
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derefs_needed -= 1;
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cur_expr = inner_expr;
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} else {
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break;
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}
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}
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let derefs = "*".repeat(derefs_needed);
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diag.span_suggestion(
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param.span,
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"try dereferencing",
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format!("{}{}", derefs, snippet(cx, cur_expr.span, "<param>")),
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Applicability::MachineApplicable,
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);
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}
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},
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)
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}
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}
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}
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}
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