bjoernager/rust
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Do not suggest ; if expression is side effect free

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When a tail expression isn't unit, we previously always suggested adding
a trailing `;` to turn it into a statement. This suggestion isn't
appropriate for any expression that doesn't have side-effects, as the
user will have likely wanted to call something else or do something with
the resulting value, instead of just discarding it.
This commit is contained in:
Esteban Küber 2021-02-04 17:36:06 -08:00
parent 020edd91a9
commit d669882f38
11 changed files with 92 additions and 51 deletions
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58
compiler/rustc_hir/src/hir.rs
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@ -1,5 +1,6 @@
// ignore-tidy-filelength
use crate::def::{DefKind, Namespace, Res};
use crate::def::{CtorKind, DefKind, Namespace, Res};
use crate::def_id::DefId;
crate use crate::hir_id::HirId;
use crate::{itemlikevisit, LangItem};
@ -1554,6 +1555,63 @@ impl Expr<'_> {
}
expr
}
pub fn can_have_side_effects(&self) -> bool {
match self.peel_drop_temps().kind {
ExprKind::Path(_) | ExprKind::Lit(_) => false,
ExprKind::Type(base, _)
| ExprKind::Unary(_, base)
| ExprKind::Field(base, _)
| ExprKind::Index(base, _)
| ExprKind::AddrOf(.., base)
| ExprKind::Cast(base, _) => {
// This isn't exactly true for `Index` and all `Unnary`, but we are using this
// method exclusively for diagnostics and there's a *cultural* pressure against
// them being used only for its side-effects.
base.can_have_side_effects()
}
ExprKind::Struct(_, fields, init) => fields
.iter()
.map(|field| field.expr)
.chain(init.into_iter())
.all(|e| e.can_have_side_effects()),
ExprKind::Array(args)
| ExprKind::Tup(args)
| ExprKind::Call(
Expr {
kind:
ExprKind::Path(QPath::Resolved(
None,
Path { res: Res::Def(DefKind::Ctor(_, CtorKind::Fn), _), .. },
)),
..
},
args,
) => args.iter().all(|arg| arg.can_have_side_effects()),
ExprKind::If(..)
| ExprKind::Match(..)
| ExprKind::MethodCall(..)
| ExprKind::Call(..)
| ExprKind::Closure(..)
| ExprKind::Block(..)
| ExprKind::Repeat(..)
| ExprKind::Break(..)
| ExprKind::Continue(..)
| ExprKind::Ret(..)
| ExprKind::Loop(..)
| ExprKind::Assign(..)
| ExprKind::InlineAsm(..)
| ExprKind::LlvmInlineAsm(..)
| ExprKind::AssignOp(..)
| ExprKind::ConstBlock(..)
| ExprKind::Box(..)
| ExprKind::Binary(..)
| ExprKind::Yield(..)
| ExprKind::DropTemps(..)
| ExprKind::Err => true,
}
}
}
/// Checks if the specified expression is a built-in range literal.