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New lint: detect unnecessary struct building
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,84 @@ | ||
| use clippy_utils::{diagnostics::span_lint_and_sugg, get_parent_expr, path_to_local, source::snippet, ty::is_copy}; | ||
| use rustc_hir::*; | ||
| use rustc_lint::{LateContext, LateLintPass}; | ||
| use rustc_session::{declare_lint_pass, declare_tool_lint}; | ||
|
|
||
| declare_clippy_lint! { | ||
| /// ### What it does | ||
| /// Checks for initialization of a `struct` by copying a base without setting | ||
| /// any field. | ||
| /// | ||
| /// ### Why is this bad? | ||
| /// Readibility suffers from unnecessary struct building. | ||
| /// | ||
| /// ### Example | ||
| /// ```rust | ||
| /// struct S { s: String } | ||
| /// | ||
| /// let a = S { s: String::from("Hello, world!") }; | ||
| /// let b = S { ..a }; | ||
| /// ``` | ||
| /// Use instead: | ||
| /// ```rust | ||
| /// struct S { s: String } | ||
| /// | ||
| /// let a = S { s: String::from("Hello, world!") }; | ||
| /// let b = a; | ||
| /// ``` | ||
| #[clippy::version = "1.70.0"] | ||
| pub UNNECESSARY_STRUCT, | ||
| complexity, | ||
| "struct built from a base that can be written mode concisely" | ||
| } | ||
| declare_lint_pass!(UnnecessaryStruct => [UNNECESSARY_STRUCT]); | ||
|
|
||
| impl LateLintPass<'_> for UnnecessaryStruct { | ||
| fn check_expr(&mut self, cx: &LateContext<'_>, expr: &Expr<'_>) { | ||
| if let ExprKind::Struct(_, &[], Some(base)) = expr.kind { | ||
| if let Some(parent) = get_parent_expr(cx, expr) && | ||
| let parent_ty = cx.typeck_results().expr_ty_adjusted(parent) && | ||
| parent_ty.is_any_ptr() | ||
| { | ||
| if is_copy(cx, cx.typeck_results().expr_ty(expr)) && path_to_local(base).is_some() { | ||
| // When the type implements `Copy`, a reference to the new struct works on the | ||
| // copy. Using the original would borrow it. | ||
| return; | ||
| } | ||
|
|
||
| if parent_ty.is_mutable_ptr() && !is_mutable(cx, base) { | ||
| // The original can be used in a mutable reference context only if it is mutable. | ||
| return; | ||
| } | ||
| } | ||
|
|
||
| // TODO: do not propose to replace *XX if XX is not Copy | ||
| if let ExprKind::Unary(UnOp::Deref, target) = base.kind && | ||
| matches!(target.kind, ExprKind::Path(..)) && | ||
| !is_copy(cx, cx.typeck_results().expr_ty(expr)) | ||
| { | ||
| // `*base` cannot be used instead of the struct in the general case if it is not Copy. | ||
| return; | ||
| } | ||
|
|
||
| span_lint_and_sugg( | ||
| cx, | ||
| UNNECESSARY_STRUCT, | ||
| expr.span, | ||
| "unnecessary struct building", | ||
| "replace with", | ||
| snippet(cx, base.span, "..").into_owned(), | ||
| rustc_errors::Applicability::MachineApplicable, | ||
| ); | ||
| } | ||
| } | ||
| } | ||
|
|
||
| fn is_mutable(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool { | ||
| if let Some(hir_id) = path_to_local(expr) && | ||
| let Node::Pat(pat) = cx.tcx.hir().get(hir_id) | ||
| { | ||
| matches!(pat.kind, PatKind::Binding(BindingAnnotation::MUT, ..)) | ||
| } else { | ||
| true | ||
| } | ||
| } |
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