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needless_late_init: ignore if let, let mut and significant drops

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This commit is contained in:
Alex Macleod 2022-04-01 18:23:47 +01:00
parent 9938daf5bc
commit 1d1fecff0f
8 changed files with 221 additions and 139 deletions
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66
clippy_lints/src/matches/redundant_pattern_match.rs
View file

@ -2,17 +2,16 @@ use super::REDUNDANT_PATTERN_MATCHING;
use clippy_utils::diagnostics::span_lint_and_then;
use clippy_utils::source::snippet;
use clippy_utils::sugg::Sugg;
use clippy_utils::ty::{implements_trait, is_type_diagnostic_item, is_type_lang_item, match_type};
use clippy_utils::ty::needs_ordered_drop;
use clippy_utils::{higher, match_def_path};
use clippy_utils::{is_lang_ctor, is_trait_method, paths};
use if_chain::if_chain;
use rustc_ast::ast::LitKind;
use rustc_data_structures::fx::FxHashSet;
use rustc_errors::Applicability;
use rustc_hir::LangItem::{OptionNone, PollPending};
use rustc_hir::{
intravisit::{walk_expr, Visitor},
Arm, Block, Expr, ExprKind, LangItem, Node, Pat, PatKind, QPath, UnOp,
Arm, Block, Expr, ExprKind, Node, Pat, PatKind, QPath, UnOp,
};
use rustc_lint::LateContext;
use rustc_middle::ty::{self, subst::GenericArgKind, DefIdTree, Ty};
@ -32,59 +31,6 @@ pub(super) fn check<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
}
}
/// Checks if the drop order for a type matters. Some std types implement drop solely to
/// deallocate memory. For these types, and composites containing them, changing the drop order
/// won't result in any observable side effects.
fn type_needs_ordered_drop<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> bool {
type_needs_ordered_drop_inner(cx, ty, &mut FxHashSet::default())
}
fn type_needs_ordered_drop_inner<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>, seen: &mut FxHashSet<Ty<'tcx>>) -> bool {
if !seen.insert(ty) {
return false;
}
if !ty.needs_drop(cx.tcx, cx.param_env) {
false
} else if !cx
.tcx
.lang_items()
.drop_trait()
.map_or(false, |id| implements_trait(cx, ty, id, &[]))
{
// This type doesn't implement drop, so no side effects here.
// Check if any component type has any.
match ty.kind() {
ty::Tuple(fields) => fields.iter().any(|ty| type_needs_ordered_drop_inner(cx, ty, seen)),
ty::Array(ty, _) => type_needs_ordered_drop_inner(cx, *ty, seen),
ty::Adt(adt, subs) => adt
.all_fields()
.map(|f| f.ty(cx.tcx, subs))
.any(|ty| type_needs_ordered_drop_inner(cx, ty, seen)),
_ => true,
}
}
// Check for std types which implement drop, but only for memory allocation.
else if is_type_diagnostic_item(cx, ty, sym::Vec)
|| is_type_lang_item(cx, ty, LangItem::OwnedBox)
|| is_type_diagnostic_item(cx, ty, sym::Rc)
|| is_type_diagnostic_item(cx, ty, sym::Arc)
|| is_type_diagnostic_item(cx, ty, sym::cstring_type)
|| is_type_diagnostic_item(cx, ty, sym::BTreeMap)
|| is_type_diagnostic_item(cx, ty, sym::LinkedList)
|| match_type(cx, ty, &paths::WEAK_RC)
|| match_type(cx, ty, &paths::WEAK_ARC)
{
// Check all of the generic arguments.
if let ty::Adt(_, subs) = ty.kind() {
subs.types().any(|ty| type_needs_ordered_drop_inner(cx, ty, seen))
} else {
true
}
} else {
true
}
}
// Extract the generic arguments out of a type
fn try_get_generic_ty(ty: Ty<'_>, index: usize) -> Option<Ty<'_>> {
if_chain! {
@ -115,7 +61,7 @@ fn temporaries_need_ordered_drop<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<
// e.g. In `(String::new(), 0).1` the string is a temporary value.
ExprKind::AddrOf(_, _, expr) | ExprKind::Field(expr, _) => {
if !matches!(expr.kind, ExprKind::Path(_)) {
if type_needs_ordered_drop(self.cx, self.cx.typeck_results().expr_ty(expr)) {
if needs_ordered_drop(self.cx, self.cx.typeck_results().expr_ty(expr)) {
self.res = true;
} else {
self.visit_expr(expr);
@ -126,7 +72,7 @@ fn temporaries_need_ordered_drop<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<
// e.g. In `(vec![0])[0]` the vector is a temporary value.
ExprKind::Index(base, index) => {
if !matches!(base.kind, ExprKind::Path(_)) {
if type_needs_ordered_drop(self.cx, self.cx.typeck_results().expr_ty(base)) {
if needs_ordered_drop(self.cx, self.cx.typeck_results().expr_ty(base)) {
self.res = true;
} else {
self.visit_expr(base);
@ -143,7 +89,7 @@ fn temporaries_need_ordered_drop<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<
.typeck_results()
.type_dependent_def_id(expr.hir_id)
.map_or(false, |id| self.cx.tcx.fn_sig(id).skip_binder().inputs()[0].is_ref());
if self_by_ref && type_needs_ordered_drop(self.cx, self.cx.typeck_results().expr_ty(self_arg)) {
if self_by_ref && needs_ordered_drop(self.cx, self.cx.typeck_results().expr_ty(self_arg)) {
self.res = true;
} else {
self.visit_expr(self_arg);
@ -243,7 +189,7 @@ fn find_sugg_for_if_let<'tcx>(
// scrutinee would be, so they have to be considered as well.
// e.g. in `if let Some(x) = foo.lock().unwrap().baz.as_ref() { .. }` the lock will be held
// for the duration if body.
let needs_drop = type_needs_ordered_drop(cx, check_ty) || temporaries_need_ordered_drop(cx, let_expr);
let needs_drop = needs_ordered_drop(cx, check_ty) || temporaries_need_ordered_drop(cx, let_expr);
// check that `while_let_on_iterator` lint does not trigger
if_chain! {

40
clippy_lints/src/needless_late_init.rs
View file

@ -1,10 +1,14 @@
use clippy_utils::diagnostics::span_lint_and_then;
use clippy_utils::path_to_local;
use clippy_utils::source::snippet_opt;
use clippy_utils::visitors::{expr_visitor, is_local_used};
use clippy_utils::ty::needs_ordered_drop;
use clippy_utils::visitors::{expr_visitor, expr_visitor_no_bodies, is_local_used};
use rustc_errors::Applicability;
use rustc_hir::intravisit::Visitor;
use rustc_hir::{Block, Expr, ExprKind, HirId, Local, LocalSource, MatchSource, Node, Pat, PatKind, Stmt, StmtKind};
use rustc_hir::{
BindingAnnotation, Block, Expr, ExprKind, HirId, Local, LocalSource, MatchSource, Node, Pat, PatKind, Stmt,
StmtKind,
};
use rustc_lint::{LateContext, LateLintPass};
use rustc_session::{declare_lint_pass, declare_tool_lint};
use rustc_span::Span;
@ -73,6 +77,31 @@ fn contains_assign_expr<'tcx>(cx: &LateContext<'tcx>, stmt: &'tcx Stmt<'tcx>) ->
seen
}
fn contains_let(cond: &Expr<'_>) -> bool {
let mut seen = false;
expr_visitor_no_bodies(|expr| {
if let ExprKind::Let(_) = expr.kind {
seen = true;
}
!seen
})
.visit_expr(cond);
seen
}
fn stmt_needs_ordered_drop(cx: &LateContext<'_>, stmt: &Stmt<'_>) -> bool {
let StmtKind::Local(local) = stmt.kind else { return false };
!local.pat.walk_short(|pat| {
if let PatKind::Binding(.., None) = pat.kind {
!needs_ordered_drop(cx, cx.typeck_results().pat_ty(pat))
} else {
true
}
})
}
#[derive(Debug)]
struct LocalAssign {
lhs_id: HirId,
@ -187,11 +216,14 @@ fn first_usage<'tcx>(
local_stmt_id: HirId,
block: &'tcx Block<'tcx>,
) -> Option<Usage<'tcx>> {
let significant_drop = needs_ordered_drop(cx, cx.typeck_results().node_type(binding_id));
block
.stmts
.iter()
.skip_while(|stmt| stmt.hir_id != local_stmt_id)
.skip(1)
.take_while(|stmt| !significant_drop || !stmt_needs_ordered_drop(cx, stmt))
.find(|&stmt| is_local_used(cx, stmt, binding_id))
.and_then(|stmt| match stmt.kind {
StmtKind::Expr(expr) => Some(Usage {
@ -258,7 +290,7 @@ fn check<'tcx>(
},
);
},
ExprKind::If(_, then_expr, Some(else_expr)) => {
ExprKind::If(cond, then_expr, Some(else_expr)) if !contains_let(cond) => {
let (applicability, suggestions) = assignment_suggestions(cx, binding_id, [then_expr, else_expr])?;
span_lint_and_then(
@ -338,7 +370,7 @@ impl<'tcx> LateLintPass<'tcx> for NeedlessLateInit {
if let Local {
init: None,
pat: &Pat {
kind: PatKind::Binding(_, binding_id, _, None),
kind: PatKind::Binding(BindingAnnotation::Unannotated, binding_id, _, None),
..
},
source: LocalSource::Normal,

71
clippy_utils/src/ty.rs
View file

@ -3,11 +3,11 @@
#![allow(clippy::module_name_repetitions)]
use rustc_ast::ast::Mutability;
use rustc_data_structures::fx::FxHashMap;
use rustc_data_structures::fx::{FxHashMap, FxHashSet};
use rustc_hir as hir;
use rustc_hir::def::{CtorKind, DefKind, Res};
use rustc_hir::def_id::DefId;
use rustc_hir::{Expr, TyKind, Unsafety};
use rustc_hir::{Expr, LangItem, TyKind, Unsafety};
use rustc_infer::infer::TyCtxtInferExt;
use rustc_lint::LateContext;
use rustc_middle::mir::interpret::{ConstValue, Scalar};
@ -22,7 +22,7 @@ use rustc_trait_selection::infer::InferCtxtExt;
use rustc_trait_selection::traits::query::normalize::AtExt;
use std::iter;
use crate::{match_def_path, must_use_attr, path_res};
use crate::{match_def_path, must_use_attr, path_res, paths};
// Checks if the given type implements copy.
pub fn is_copy<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> bool {
@ -83,6 +83,20 @@ pub fn get_associated_type<'tcx>(
})
}
/// Get the diagnostic name of a type, e.g. `sym::HashMap`. To check if a type
/// implements a trait marked with a diagnostic item use [`implements_trait`].
///
/// For a further exploitation what diagnostic items are see [diagnostic items] in
/// rustc-dev-guide.
///
/// [Diagnostic Items]: https://rustc-dev-guide.rust-lang.org/diagnostics/diagnostic-items.html
pub fn get_type_diagnostic_name(cx: &LateContext<'_>, ty: Ty<'_>) -> Option<Symbol> {
match ty.kind() {
ty::Adt(adt, _) => cx.tcx.get_diagnostic_name(adt.did()),
_ => None,
}
}
/// Returns true if ty has `iter` or `iter_mut` methods
pub fn has_iter_method(cx: &LateContext<'_>, probably_ref_ty: Ty<'_>) -> Option<Symbol> {
// FIXME: instead of this hard-coded list, we should check if `<adt>::iter`
@ -319,6 +333,57 @@ pub fn match_type(cx: &LateContext<'_>, ty: Ty<'_>, path: &[&str]) -> bool {
}
}
/// Checks if the drop order for a type matters. Some std types implement drop solely to
/// deallocate memory. For these types, and composites containing them, changing the drop order
/// won't result in any observable side effects.
pub fn needs_ordered_drop<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> bool {
fn needs_ordered_drop_inner<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>, seen: &mut FxHashSet<Ty<'tcx>>) -> bool {
if !seen.insert(ty) {
return false;
}
if !ty.has_significant_drop(cx.tcx, cx.param_env) {
false
}
// Check for std types which implement drop, but only for memory allocation.
else if is_type_lang_item(cx, ty, LangItem::OwnedBox)
|| matches!(
get_type_diagnostic_name(cx, ty),
Some(sym::HashSet | sym::Rc | sym::Arc | sym::cstring_type)
)
|| match_type(cx, ty, &paths::WEAK_RC)
|| match_type(cx, ty, &paths::WEAK_ARC)
{
// Check all of the generic arguments.
if let ty::Adt(_, subs) = ty.kind() {
subs.types().any(|ty| needs_ordered_drop_inner(cx, ty, seen))
} else {
true
}
} else if !cx
.tcx
.lang_items()
.drop_trait()
.map_or(false, |id| implements_trait(cx, ty, id, &[]))
{
// This type doesn't implement drop, so no side effects here.
// Check if any component type has any.
match ty.kind() {
ty::Tuple(fields) => fields.iter().any(|ty| needs_ordered_drop_inner(cx, ty, seen)),
ty::Array(ty, _) => needs_ordered_drop_inner(cx, *ty, seen),
ty::Adt(adt, subs) => adt
.all_fields()
.map(|f| f.ty(cx.tcx, subs))
.any(|ty| needs_ordered_drop_inner(cx, ty, seen)),
_ => true,
}
} else {
true
}
}
needs_ordered_drop_inner(cx, ty, &mut FxHashSet::default())
}
/// Peels off all references on the type. Returns the underlying type and the number of references
/// removed.
pub fn peel_mid_ty_refs(ty: Ty<'_>) -> (Ty<'_>, usize) {

74
tests/ui/needless_late_init.rs
View file

@ -1,5 +1,15 @@
#![allow(unused)]
#![allow(clippy::let_unit_value)]
#![feature(let_chains)]
#![allow(unused, clippy::nonminimal_bool, clippy::let_unit_value)]
use std::collections::{BTreeMap, BTreeSet, HashMap, HashSet};
use std::rc::Rc;
struct SignificantDrop;
impl std::ops::Drop for SignificantDrop {
fn drop(&mut self) {
println!("dropped");
}
}
fn main() {
let a;
@ -18,13 +28,6 @@ fn main() {
b = "five"
}
let c;
if let Some(n) = Some(5) {
c = n;
} else {
c = -50;
}
let d;
if true {
let temp = 5;
@ -37,7 +40,7 @@ fn main() {
if true {
e = format!("{} {}", a, b);
} else {
e = format!("{}", c);
e = format!("{}", n);
}
let f;
@ -53,7 +56,27 @@ fn main() {
panic!();
}
println!("{}", a);
// Drop order only matters if both are significant
let x;
let y = SignificantDrop;
x = 1;
let x;
let y = 1;
x = SignificantDrop;
let x;
// types that should be considered insignificant
let y = 1;
let y = "2";
let y = String::new();
let y = vec![3.0];
let y = HashMap::<usize, usize>::new();
let y = BTreeMap::<usize, usize>::new();
let y = HashSet::<usize>::new();
let y = BTreeSet::<usize>::new();
let y = Box::new(4);
x = SignificantDrop;
}
async fn in_async() -> &'static str {
@ -177,5 +200,32 @@ fn does_not_lint() {
}
in_macro!();
println!("{}", x);
// ignore if-lets - https://github.com/rust-lang/rust-clippy/issues/8613
let x;
if let Some(n) = Some("v") {
x = 1;
} else {
x = 2;
}
let x;
if true && let Some(n) = Some("let chains too") {
x = 1;
} else {
x = 2;
}
// ignore mut bindings
// https://github.com/shepmaster/twox-hash/blob/b169c16d86eb8ea4a296b0acb9d00ca7e3c3005f/src/sixty_four.rs#L88-L93
// https://github.com/dtolnay/thiserror/blob/21c26903e29cb92ba1a7ff11e82ae2001646b60d/tests/test_generics.rs#L91-L100
let mut x: usize;
x = 1;
x = 2;
x = 3;
// should not move the declaration if `x` has a significant drop, and there
// is another binding with a significant drop between it and the first usage
let x;
let y = SignificantDrop;
x = SignificantDrop;
}

72
tests/ui/needless_late_init.stderr
View file

@ -1,5 +1,5 @@
error: unneeded late initialization
--> $DIR/needless_late_init.rs:5:5
--> $DIR/needless_late_init.rs:15:5
|
LL | let a;
| ^^^^^^
@ -21,7 +21,7 @@ LL | };
| +
error: unneeded late initialization
--> $DIR/needless_late_init.rs:14:5
--> $DIR/needless_late_init.rs:24:5
|
LL | let b;
| ^^^^^^
@ -42,28 +42,7 @@ LL | };
| +
error: unneeded late initialization
--> $DIR/needless_late_init.rs:21:5
|
LL | let c;
| ^^^^^^
|
help: declare `c` here
|
LL | let c = if let Some(n) = Some(5) {
| +++++++
help: remove the assignments from the branches
|
LL ~ n
LL | } else {
LL ~ -50
|
help: add a semicolon after the `if` expression
|
LL | };
| +
error: unneeded late initialization
--> $DIR/needless_late_init.rs:28:5
--> $DIR/needless_late_init.rs:31:5
|
LL | let d;
| ^^^^^^
@ -84,7 +63,7 @@ LL | };
| +
error: unneeded late initialization
--> $DIR/needless_late_init.rs:36:5
--> $DIR/needless_late_init.rs:39:5
|
LL | let e;
| ^^^^^^
@ -97,7 +76,7 @@ help: remove the assignments from the branches
|
LL ~ format!("{} {}", a, b)
LL | } else {
LL ~ format!("{}", c)
LL ~ format!("{}", n)
|
help: add a semicolon after the `if` expression
|
@ -105,7 +84,7 @@ LL | };
| +
error: unneeded late initialization
--> $DIR/needless_late_init.rs:43:5
--> $DIR/needless_late_init.rs:46:5
|
LL | let f;
| ^^^^^^
@ -121,7 +100,7 @@ LL + 1 => "three",
|
error: unneeded late initialization
--> $DIR/needless_late_init.rs:49:5
--> $DIR/needless_late_init.rs:52:5
|
LL | let g: usize;
| ^^^^^^^^^^^^^
@ -140,9 +119,42 @@ help: add a semicolon after the `if` expression
LL | };
| +
error: unneeded late initialization
--> $DIR/needless_late_init.rs:60:5
|
LL | let x;
| ^^^^^^
|
help: declare `x` here
|
LL | let x = 1;
| ~~~~~
error: unneeded late initialization
--> $DIR/needless_late_init.rs:64:5
|
LL | let x;
| ^^^^^^
|
help: declare `x` here
|
LL | let x = SignificantDrop;
| ~~~~~
error: unneeded late initialization
--> $DIR/needless_late_init.rs:68:5
|
LL | let x;
| ^^^^^^
|
help: declare `x` here
|
LL | let x = SignificantDrop;
| ~~~~~
error: unneeded late initialization
--> $DIR/needless_late_init.rs:87:5
|
LL | let a;
| ^^^^^^
|
@ -162,7 +174,7 @@ LL | };
| +
error: unneeded late initialization
--> $DIR/needless_late_init.rs:81:5
--> $DIR/needless_late_init.rs:104:5
|
LL | let a;
| ^^^^^^
@ -182,5 +194,5 @@ help: add a semicolon after the `match` expression
LL | };
| +
error: aborting due to 9 previous errors
error: aborting due to 11 previous errors

8
tests/ui/needless_late_init_fixable.fixed
View file

@ -15,11 +15,5 @@ fn main() {
let d: usize = 1;
let mut e = 1;
e = 2;
let h = format!("{}", e);
println!("{}", a);
let e = format!("{}", d);
}

10
tests/ui/needless_late_init_fixable.rs
View file

@ -14,12 +14,6 @@ fn main() {
let d: usize;
d = 1;
let mut e;
e = 1;
e = 2;
let h;
h = format!("{}", e);
println!("{}", a);
let e;
e = format!("{}", d);
}

19
tests/ui/needless_late_init_fixable.stderr
View file

@ -46,24 +46,13 @@ LL | let d: usize = 1;
error: unneeded late initialization
--> $DIR/needless_late_init_fixable.rs:17:5
|
LL | let mut e;
| ^^^^^^^^^^
LL | let e;
| ^^^^^^
|
help: declare `e` here
|
LL | let mut e = 1;
| ~~~~~~~~~
error: unneeded late initialization
--> $DIR/needless_late_init_fixable.rs:21:5
|
LL | let h;
| ^^^^^^
|
help: declare `h` here
|
LL | let h = format!("{}", e);
LL | let e = format!("{}", d);
| ~~~~~
error: aborting due to 6 previous errors
error: aborting due to 5 previous errors