use clippy_utils::diagnostics::{span_lint_hir, span_lint_hir_and_then};
+use clippy_utils::is_lint_allowed;
use clippy_utils::source::snippet_opt;
use clippy_utils::ty::has_drop;
use rustc_errors::Applicability;
use rustc_hir::def::{DefKind, Res};
-use rustc_hir::{BinOpKind, BlockCheckMode, Expr, ExprKind, Stmt, StmtKind, UnsafeSource};
+use rustc_hir::{is_range_literal, BinOpKind, BlockCheckMode, Expr, ExprKind, PatKind, Stmt, StmtKind, UnsafeSource};
use rustc_lint::{LateContext, LateLintPass};
use rustc_session::{declare_lint_pass, declare_tool_lint};
use std::ops::Deref;
/// Checks for statements which have no effect.
///
/// ### Why is this bad?
- /// Similar to dead code, these statements are actually
+ /// Unlike dead code, these statements are actually
/// executed. However, as they have no effect, all they do is make the code less
/// readable.
///
"statements with no effect"
}
+declare_clippy_lint! {
+ /// ### What it does
+ /// Checks for binding to underscore prefixed variable without side-effects.
+ ///
+ /// ### Why is this bad?
+ /// Unlike dead code, these bindings are actually
+ /// executed. However, as they have no effect and shouldn't be used further on, all they
+ /// do is make the code less readable.
+ ///
+ /// ### Known problems
+ /// Further usage of this variable is not checked, which can lead to false positives if it is
+ /// used later in the code.
+ ///
+ /// ### Example
+ /// ```rust,ignore
+ /// let _i_serve_no_purpose = 1;
+ /// ```
+ pub NO_EFFECT_UNDERSCORE_BINDING,
+ pedantic,
+ "binding to `_` prefixed variable with no side-effect"
+}
+
declare_clippy_lint! {
/// ### What it does
/// Checks for expression statements that can be reduced to a
"outer expressions with no effect"
}
+declare_lint_pass!(NoEffect => [NO_EFFECT, UNNECESSARY_OPERATION, NO_EFFECT_UNDERSCORE_BINDING]);
+
+impl<'tcx> LateLintPass<'tcx> for NoEffect {
+ fn check_stmt(&mut self, cx: &LateContext<'tcx>, stmt: &'tcx Stmt<'_>) {
+ if check_no_effect(cx, stmt) {
+ return;
+ }
+ check_unnecessary_operation(cx, stmt);
+ }
+}
+
+fn check_no_effect(cx: &LateContext<'tcx>, stmt: &'tcx Stmt<'_>) -> bool {
+ if let StmtKind::Semi(expr) = stmt.kind {
+ if has_no_effect(cx, expr) {
+ span_lint_hir(cx, NO_EFFECT, expr.hir_id, stmt.span, "statement with no effect");
+ return true;
+ }
+ } else if let StmtKind::Local(local) = stmt.kind {
+ if_chain! {
+ if !is_lint_allowed(cx, NO_EFFECT_UNDERSCORE_BINDING, local.hir_id);
+ if let Some(init) = local.init;
+ if !local.pat.span.from_expansion();
+ if has_no_effect(cx, init);
+ if let PatKind::Binding(_, _, ident, _) = local.pat.kind;
+ if ident.name.to_ident_string().starts_with('_');
+ then {
+ span_lint_hir(
+ cx,
+ NO_EFFECT_UNDERSCORE_BINDING,
+ init.hir_id,
+ stmt.span,
+ "binding to `_` prefixed variable with no side-effect"
+ );
+ return true;
+ }
+ }
+ }
+ false
+}
+
fn has_no_effect(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
if expr.span.from_expansion() {
return false;
ExprKind::Call(callee, args) => {
if let ExprKind::Path(ref qpath) = callee.kind {
let res = cx.qpath_res(qpath, callee.hir_id);
- match res {
- Res::Def(DefKind::Struct | DefKind::Variant | DefKind::Ctor(..), ..) => {
- !has_drop(cx, cx.typeck_results().expr_ty(expr))
- && args.iter().all(|arg| has_no_effect(cx, arg))
- },
- _ => false,
+ let def_matched = matches!(
+ res,
+ Res::Def(DefKind::Struct | DefKind::Variant | DefKind::Ctor(..), ..)
+ );
+ if def_matched || is_range_literal(expr) {
+ !has_drop(cx, cx.typeck_results().expr_ty(expr)) && args.iter().all(|arg| has_no_effect(cx, arg))
+ } else {
+ false
}
} else {
false
}
}
-declare_lint_pass!(NoEffect => [NO_EFFECT, UNNECESSARY_OPERATION]);
-
-impl<'tcx> LateLintPass<'tcx> for NoEffect {
- fn check_stmt(&mut self, cx: &LateContext<'tcx>, stmt: &'tcx Stmt<'_>) {
- if let StmtKind::Semi(expr) = stmt.kind {
- if has_no_effect(cx, expr) {
- span_lint_hir(cx, NO_EFFECT, expr.hir_id, stmt.span, "statement with no effect");
- } else if let Some(reduced) = reduce_expression(cx, expr) {
+fn check_unnecessary_operation(cx: &LateContext<'tcx>, stmt: &'tcx Stmt<'_>) {
+ if_chain! {
+ if let StmtKind::Semi(expr) = stmt.kind;
+ if let Some(reduced) = reduce_expression(cx, expr);
+ if !&reduced.iter().any(|e| e.span.from_expansion());
+ then {
+ if let ExprKind::Index(..) = &expr.kind {
+ let snippet;
+ if let (Some(arr), Some(func)) = (snippet_opt(cx, reduced[0].span), snippet_opt(cx, reduced[1].span)) {
+ snippet = format!("assert!({}.len() > {});", &arr, &func);
+ } else {
+ return;
+ }
+ span_lint_hir_and_then(
+ cx,
+ UNNECESSARY_OPERATION,
+ expr.hir_id,
+ stmt.span,
+ "unnecessary operation",
+ |diag| {
+ diag.span_suggestion(
+ stmt.span,
+ "statement can be written as",
+ snippet,
+ Applicability::MaybeIncorrect,
+ );
+ },
+ );
+ } else {
let mut snippet = String::new();
for e in reduced {
- if e.span.from_expansion() {
- return;
- }
if let Some(snip) = snippet_opt(cx, e.span) {
snippet.push_str(&snip);
snippet.push(';');
UNNECESSARY_OPERATION,
expr.hir_id,
stmt.span,
- "statement can be reduced",
+ "unnecessary operation",
|diag| {
- diag.span_suggestion(stmt.span, "replace it with", snippet, Applicability::MachineApplicable);
+ diag.span_suggestion(
+ stmt.span,
+ "statement can be reduced to",
+ snippet,
+ Applicability::MachineApplicable,
+ );
},
);
}
projects / rust.git / blobdiff