2018-05-30 03:15:50 -05:00
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use crate::utils::{has_drop, in_macro, snippet_opt, span_lint, span_lint_and_sugg};
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2018-12-29 09:04:45 -06:00
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use rustc::hir::def::Def;
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use rustc::hir::{BinOpKind, BlockCheckMode, Expr, ExprKind, Stmt, StmtKind, UnsafeSource};
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use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
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use rustc::{declare_tool_lint, lint_array};
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use rustc_errors::Applicability;
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2016-05-13 09:43:47 -05:00
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use std::ops::Deref;
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2015-10-28 11:50:00 -05:00
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2016-08-06 02:55:04 -05:00
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/// **What it does:** Checks for statements which have no effect.
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2015-12-14 15:16:56 -06:00
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///
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2016-08-06 02:55:04 -05:00
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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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2015-12-14 15:16:56 -06:00
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///
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/// **Known problems:** None.
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///
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2016-07-15 17:25:44 -05:00
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/// **Example:**
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/// ```rust
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/// 0;
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/// ```
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2018-03-28 08:24:26 -05:00
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declare_clippy_lint! {
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2015-10-28 11:50:00 -05:00
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pub NO_EFFECT,
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2018-03-28 08:24:26 -05:00
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complexity,
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2015-10-28 11:50:00 -05:00
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"statements with no effect"
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}
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2016-08-06 02:55:04 -05:00
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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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2016-05-13 09:43:47 -05:00
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///
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2016-08-06 02:55:04 -05:00
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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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2016-05-13 09:43:47 -05:00
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///
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/// **Known problems:** None.
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///
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2016-07-15 17:25:44 -05:00
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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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2018-03-28 08:24:26 -05:00
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declare_clippy_lint! {
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2016-05-13 09:43:47 -05:00
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pub UNNECESSARY_OPERATION,
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2018-03-28 08:24:26 -05:00
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complexity,
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2016-05-13 09:43:47 -05:00
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"outer expressions with no effect"
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}
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2018-07-23 06:01:12 -05:00
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fn has_no_effect(cx: &LateContext<'_, '_>, expr: &Expr) -> bool {
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2017-03-31 17:14:04 -05:00
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if in_macro(expr.span) {
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2015-10-28 11:50:00 -05:00
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return false;
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}
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match expr.node {
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2018-07-12 02:30:57 -05:00
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ExprKind::Lit(..) | ExprKind::Closure(.., _) => true,
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2018-12-09 05:19:21 -06:00
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ExprKind::Path(..) => !has_drop(cx, cx.tables.expr_ty(expr)),
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2018-07-12 02:30:57 -05:00
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ExprKind::Index(ref a, ref b) | ExprKind::Binary(_, ref a, ref b) => {
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2017-09-05 04:33:04 -05:00
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has_no_effect(cx, a) && has_no_effect(cx, b)
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},
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2018-07-12 02:30:57 -05:00
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ExprKind::Array(ref v) | ExprKind::Tup(ref v) => v.iter().all(|val| has_no_effect(cx, val)),
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2018-11-27 14:14:15 -06:00
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ExprKind::Repeat(ref inner, _)
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| ExprKind::Cast(ref inner, _)
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| ExprKind::Type(ref inner, _)
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| ExprKind::Unary(_, ref inner)
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| ExprKind::Field(ref inner, _)
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| ExprKind::AddrOf(_, ref inner)
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| ExprKind::Box(ref inner) => has_no_effect(cx, inner),
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2018-07-12 02:30:57 -05:00
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ExprKind::Struct(_, ref fields, ref base) => {
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2018-12-09 05:19:21 -06:00
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!has_drop(cx, cx.tables.expr_ty(expr))
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2018-11-27 14:14:15 -06:00
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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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2016-12-20 11:21:30 -06:00
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},
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2018-11-27 14:14:15 -06:00
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ExprKind::Call(ref callee, ref args) => {
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if let ExprKind::Path(ref qpath) = callee.node {
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let def = cx.tables.qpath_def(qpath, callee.hir_id);
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match def {
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Def::Struct(..) | Def::Variant(..) | Def::StructCtor(..) | Def::VariantCtor(..) => {
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2018-12-09 05:19:21 -06:00
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!has_drop(cx, cx.tables.expr_ty(expr)) && args.iter().all(|arg| has_no_effect(cx, arg))
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2018-11-27 14:14:15 -06:00
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},
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_ => false,
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}
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2017-09-05 04:33:04 -05:00
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} else {
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false
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}
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2016-12-20 11:21:30 -06:00
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},
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2018-11-27 14:14:15 -06:00
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ExprKind::Block(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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2015-10-28 11:50:00 -05:00
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_ => false,
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}
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}
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#[derive(Copy, Clone)]
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2016-06-10 09:17:20 -05:00
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pub struct Pass;
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2015-10-28 11:50:00 -05:00
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2016-06-10 09:17:20 -05:00
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impl LintPass for Pass {
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2015-10-28 11:50:00 -05:00
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fn get_lints(&self) -> LintArray {
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2016-05-13 09:43:47 -05:00
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lint_array!(NO_EFFECT, UNNECESSARY_OPERATION)
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2015-10-28 11:50:00 -05:00
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}
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2019-01-26 13:40:55 -06:00
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fn name(&self) -> &'static str {
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"NoEffect"
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}
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2015-10-28 11:50:00 -05:00
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}
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2016-12-07 06:13:40 -06:00
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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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2019-01-20 04:21:30 -06:00
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if let StmtKind::Semi(ref expr) = stmt.node {
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2015-10-28 11:50:00 -05:00
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if has_no_effect(cx, expr) {
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2016-01-03 22:26:12 -06:00
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span_lint(cx, NO_EFFECT, stmt.span, "statement with no effect");
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2016-05-13 09:43:47 -05:00
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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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2017-03-31 17:14:04 -05:00
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if in_macro(e.span) {
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2016-05-13 09:43:47 -05:00
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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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2017-08-09 02:30:56 -05:00
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span_lint_and_sugg(
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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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"replace it with",
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snippet,
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2018-11-27 08:13:57 -06:00
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Applicability::MachineApplicable,
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2017-08-09 02:30:56 -05:00
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);
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2016-05-13 09:43:47 -05:00
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}
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}
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}
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}
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2018-07-23 06:01:12 -05:00
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fn reduce_expression<'a>(cx: &LateContext<'_, '_>, expr: &'a Expr) -> Option<Vec<&'a Expr>> {
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2017-03-31 17:14:04 -05:00
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if in_macro(expr.span) {
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2016-05-13 09:43:47 -05:00
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return None;
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}
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match expr.node {
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2018-07-12 02:30:57 -05:00
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ExprKind::Index(ref a, ref b) => Some(vec![&**a, &**b]),
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2018-07-12 02:50:09 -05:00
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ExprKind::Binary(ref binop, ref a, ref b) if binop.node != BinOpKind::And && binop.node != BinOpKind::Or => {
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2016-12-29 17:00:55 -06:00
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Some(vec![&**a, &**b])
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},
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2018-07-12 02:30:57 -05:00
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ExprKind::Array(ref v) | ExprKind::Tup(ref v) => Some(v.iter().collect()),
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2018-11-27 14:14:15 -06:00
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ExprKind::Repeat(ref inner, _)
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| ExprKind::Cast(ref inner, _)
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| ExprKind::Type(ref inner, _)
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| ExprKind::Unary(_, ref inner)
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| ExprKind::Field(ref inner, _)
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| ExprKind::AddrOf(_, ref inner)
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| ExprKind::Box(ref inner) => reduce_expression(cx, inner).or_else(|| Some(vec![inner])),
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ExprKind::Struct(_, ref fields, ref base) => {
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2018-12-09 05:19:21 -06:00
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if has_drop(cx, cx.tables.expr_ty(expr)) {
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2018-11-27 14:14:15 -06:00
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None
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} else {
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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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2017-09-18 14:07:33 -05:00
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},
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2018-11-27 14:14:15 -06:00
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ExprKind::Call(ref callee, ref args) => {
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if let ExprKind::Path(ref qpath) = callee.node {
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let def = cx.tables.qpath_def(qpath, callee.hir_id);
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match def {
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Def::Struct(..) | Def::Variant(..) | Def::StructCtor(..) | Def::VariantCtor(..)
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2018-12-09 05:19:21 -06:00
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if !has_drop(cx, cx.tables.expr_ty(expr)) =>
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2018-11-27 14:14:15 -06:00
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{
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Some(args.iter().collect())
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},
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_ => None,
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}
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} else {
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None
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2016-05-13 09:43:47 -05:00
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}
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2016-12-20 11:21:30 -06:00
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},
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2018-07-12 02:30:57 -05:00
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ExprKind::Block(ref block, _) => {
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2016-05-13 09:43:47 -05:00
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if block.stmts.is_empty() {
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2016-06-05 18:42:39 -05:00
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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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2016-05-13 09:43:47 -05:00
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})
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} else {
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None
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2015-10-28 11:50:00 -05:00
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}
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2016-12-20 11:21:30 -06:00
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},
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2016-05-13 09:43:47 -05:00
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_ => None,
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2015-10-28 11:50:00 -05:00
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}
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}
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