187 lines
6.3 KiB
Rust
187 lines
6.3 KiB
Rust
use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
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use rustc::hir::def::Def;
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use rustc::hir::{Expr, Expr_, Stmt, StmtSemi, BlockCheckMode, UnsafeSource, BiAnd, BiOr};
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use utils::{in_macro, span_lint, snippet_opt, span_lint_and_then};
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use std::ops::Deref;
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/// **What it does:** Checks for statements which have no effect.
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///
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/// **Why is this bad?** Similar to dead code, these statements are actually
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/// executed. However, as they have no effect, all they do is make the code less
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/// readable.
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///
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/// **Known problems:** None.
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///
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/// **Example:**
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/// ```rust
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/// 0;
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/// ```
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declare_lint! {
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pub NO_EFFECT,
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Warn,
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"statements with no effect"
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}
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/// **What it does:** Checks for expression statements that can be reduced to a
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/// sub-expression.
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///
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/// **Why is this bad?** Expressions by themselves often have no side-effects.
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/// Having such expressions reduces readability.
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///
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/// **Known problems:** None.
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///
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/// **Example:**
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/// ```rust
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/// compute_array()[0];
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/// ```
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declare_lint! {
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pub UNNECESSARY_OPERATION,
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Warn,
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"outer expressions with no effect"
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}
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fn has_no_effect(cx: &LateContext, expr: &Expr) -> bool {
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if in_macro(cx, expr.span) {
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return false;
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}
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match expr.node {
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Expr_::ExprLit(..) |
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Expr_::ExprClosure(..) |
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Expr_::ExprPath(..) => true,
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Expr_::ExprIndex(ref a, ref b) |
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Expr_::ExprBinary(_, ref a, ref b) => has_no_effect(cx, a) && has_no_effect(cx, b),
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Expr_::ExprArray(ref v) |
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Expr_::ExprTup(ref v) => v.iter().all(|val| has_no_effect(cx, val)),
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Expr_::ExprRepeat(ref inner, _) |
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Expr_::ExprCast(ref inner, _) |
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Expr_::ExprType(ref inner, _) |
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Expr_::ExprUnary(_, ref inner) |
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Expr_::ExprField(ref inner, _) |
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Expr_::ExprTupField(ref inner, _) |
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Expr_::ExprAddrOf(_, ref inner) |
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Expr_::ExprBox(ref inner) => has_no_effect(cx, inner),
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Expr_::ExprStruct(_, ref fields, ref base) => {
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fields.iter().all(|field| has_no_effect(cx, &field.expr)) &&
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match *base {
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Some(ref base) => has_no_effect(cx, base),
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None => true,
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}
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},
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Expr_::ExprCall(ref callee, ref args) => {
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if let Expr_::ExprPath(ref qpath) = callee.node {
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let def = cx.tables.qpath_def(qpath, callee.id);
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match def {
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Def::Struct(..) |
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Def::Variant(..) |
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Def::StructCtor(..) |
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Def::VariantCtor(..) => args.iter().all(|arg| has_no_effect(cx, arg)),
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_ => false,
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}
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} else {
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false
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}
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},
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Expr_::ExprBlock(ref block) => {
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block.stmts.is_empty() &&
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if let Some(ref expr) = block.expr {
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has_no_effect(cx, expr)
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} else {
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false
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}
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},
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_ => false,
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}
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}
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#[derive(Copy, Clone)]
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pub struct Pass;
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impl LintPass for Pass {
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fn get_lints(&self) -> LintArray {
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lint_array!(NO_EFFECT, UNNECESSARY_OPERATION)
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}
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}
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impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Pass {
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fn check_stmt(&mut self, cx: &LateContext<'a, 'tcx>, stmt: &'tcx Stmt) {
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if let StmtSemi(ref expr, _) = stmt.node {
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if has_no_effect(cx, expr) {
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span_lint(cx, NO_EFFECT, stmt.span, "statement with no effect");
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} else if let Some(reduced) = reduce_expression(cx, expr) {
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let mut snippet = String::new();
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for e in reduced {
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if in_macro(cx, e.span) {
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return;
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}
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if let Some(snip) = snippet_opt(cx, e.span) {
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snippet.push_str(&snip);
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snippet.push(';');
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} else {
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return;
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}
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}
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span_lint_and_then(cx,
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UNNECESSARY_OPERATION,
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stmt.span,
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"statement can be reduced",
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|db| { db.span_suggestion(stmt.span, "replace it with", snippet); });
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}
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}
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}
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}
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fn reduce_expression<'a>(cx: &LateContext, expr: &'a Expr) -> Option<Vec<&'a Expr>> {
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if in_macro(cx, expr.span) {
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return None;
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}
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match expr.node {
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Expr_::ExprIndex(ref a, ref b) => Some(vec![&**a, &**b]),
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Expr_::ExprBinary(ref binop, ref a, ref b) if binop.node != BiAnd && binop.node != BiOr => {
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Some(vec![&**a, &**b])
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},
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Expr_::ExprArray(ref v) |
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Expr_::ExprTup(ref v) => Some(v.iter().collect()),
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Expr_::ExprRepeat(ref inner, _) |
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Expr_::ExprCast(ref inner, _) |
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Expr_::ExprType(ref inner, _) |
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Expr_::ExprUnary(_, ref inner) |
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Expr_::ExprField(ref inner, _) |
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Expr_::ExprTupField(ref inner, _) |
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Expr_::ExprAddrOf(_, ref inner) |
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Expr_::ExprBox(ref inner) => reduce_expression(cx, inner).or_else(|| Some(vec![inner])),
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Expr_::ExprStruct(_, ref fields, ref base) => {
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Some(fields.iter().map(|f| &f.expr).chain(base).map(Deref::deref).collect())
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},
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Expr_::ExprCall(ref callee, ref args) => {
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if let Expr_::ExprPath(ref qpath) = callee.node {
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let def = cx.tables.qpath_def(qpath, callee.id);
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match def {
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Def::Struct(..) |
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Def::Variant(..) |
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Def::StructCtor(..) |
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Def::VariantCtor(..) => Some(args.iter().collect()),
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_ => None,
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}
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} else {
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None
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}
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},
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Expr_::ExprBlock(ref block) => {
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if block.stmts.is_empty() {
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block.expr.as_ref().and_then(|e| {
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match block.rules {
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BlockCheckMode::UnsafeBlock(UnsafeSource::UserProvided) => None,
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BlockCheckMode::DefaultBlock => Some(vec![&**e]),
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// in case of compiler-inserted signaling blocks
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_ => reduce_expression(cx, e),
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}
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})
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} else {
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None
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}
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},
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_ => None,
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}
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}
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