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Auto merge of #5536 - rail-rain:fix_manual_memcpy, r=phansch

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Fix the bugs of `manual_memcpy`, simplify the suggestion and refactor it

While I’m working on the long procrastinated work to expand `manual_memcpy`(#1670), I found a few minor bugs and probably unidiomatic or old coding style. There is a brief explanation of changes to the behaviour this PR will make below. And, I have a questoin: do I need to add tests for the first and second fixed bugs? I thought it might be too rare cases to include the tests for those. I added for the last one though.

* Bug fix
  * It negates resulted offsets (`src/dst_offset`) when `offset` is subtraction by 0. This PR will remove any subtraction by 0 as a part of minification.

    ```rust
    for i in 0..5 {
        dst[i - 0] = src[i];
    }
    ```

    ```diff
     warning: it looks like you're manually copying between slices
       --> src/main.rs:2:14
        |
    LL  |     for i in 0..5 {
    -   |              ^^^^ help: try replacing the loop by: `dst[..-5].clone_from_slice(&src[..5])`
    +   |              ^^^^ help: try replacing the loop by: `dst[..5].clone_from_slice(&src[..5])`
        |
    ```
  * It prints `RangeTo` or `RangeFull` when both of `end` and `offset` are 0, which have different meaning. This PR will print 0. I could reject the cases `end` is 0, but I thought I won’t catch other cases `reverse_range_loop` will trigger, and it’s over to catch every such cases.

    ```rust
    for i in 0..0 {
        dst[i] = src[i];
    }
    ```

    ```diff
     warning: it looks like you're manually copying between slices
       --> src/main.rs:2:14
        |
     LL |     for i in 0..0 {
    -   |              ^^^^ help: try replacing the loop by: `dst.clone_from_slice(&src[..])`
    +   |              ^^^^ help: try replacing the loop by: `dst[..0].clone_from_slice(&src[..0])`
        |
    ```
  * it prints four dots when `end` is `None`. This PR will ignore any `for` loops without `end` because a `for` loop that takes `RangeFrom` as its argument and contains indexing without the statements or the expressions that end loops such as `break` will definitely panic, and `manual_memcpy` should ignore the loops with such control flow.

    ```rust
    fn manual_copy(src: &[u32], dst: &mut [u32]) {
        for i in 0.. {
            dst[i] = src[i];
        }
    }
    ```

    ```diff
    -warning: it looks like you're manually copying between slices
    -  --> src/main.rs:2:14
    -   |
    -LL |     for i in 0.. {
    -   |              ^^^ help: try replacing the loop by: `dst[....].clone_from_slice(&src[....])`
    -   |
    ```
* Simplification of the suggestion

  * It prints 0 when `start` or `end` and `offset` are same (from #3323). This PR will use `RangeTo`

changelog: fixed the bugs of `manual_memcpy` and also simplify the suggestion.
This commit is contained in:
bors 2020-05-02 08:11:48 +00:00
commit e3b8c41d0d
3 changed files with 206 additions and 188 deletions
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355
clippy_lints/src/loops.rs
View File

@ -10,7 +10,6 @@
};
use crate::utils::{is_type_diagnostic_item, qpath_res, same_tys, sext, sugg};
use if_chain::if_chain;
use itertools::Itertools;
use rustc_ast::ast;
use rustc_data_structures::fx::{FxHashMap, FxHashSet};
use rustc_errors::Applicability;
@ -772,40 +771,48 @@ fn check_for_loop<'a, 'tcx>(
fn same_var<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &Expr<'_>, var: HirId) -> bool {
if_chain! {
if let ExprKind::Path(ref qpath) = expr.kind;
if let QPath::Resolved(None, ref path) = *qpath;
if let ExprKind::Path(qpath) = &expr.kind;
if let QPath::Resolved(None, path) = qpath;
if path.segments.len() == 1;
if let Res::Local(local_id) = qpath_res(cx, qpath, expr.hir_id);
// our variable!
if local_id == var;
then {
return true;
// our variable!
local_id == var
} else {
false
}
}
}
false
#[derive(Clone, Copy)]
enum OffsetSign {
Positive,
Negative,
}
struct Offset {
value: String,
negate: bool,
sign: OffsetSign,
}
impl Offset {
fn negative(s: String) -> Self {
Self { value: s, negate: true }
}
fn positive(s: String) -> Self {
fn negative(value: String) -> Self {
Self {
value: s,
negate: false,
value,
sign: OffsetSign::Negative,
}
}
fn positive(value: String) -> Self {
Self {
value,
sign: OffsetSign::Positive,
}
}
}
struct FixedOffsetVar {
var_name: String,
struct FixedOffsetVar<'hir> {
var: &'hir Expr<'hir>,
offset: Offset,
}
@ -819,10 +826,20 @@ fn is_slice_like<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, ty: Ty<'_>) -> bool {
is_slice || is_type_diagnostic_item(cx, ty, sym!(vec_type)) || is_type_diagnostic_item(cx, ty, sym!(vecdeque_type))
}
fn get_fixed_offset_var<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &Expr<'_>, var: HirId) -> Option<FixedOffsetVar> {
fn fetch_cloned_expr<'tcx>(expr: &'tcx Expr<'tcx>) -> &'tcx Expr<'tcx> {
if_chain! {
if let ExprKind::MethodCall(method, _, args) = expr.kind;
if method.ident.name == sym!(clone);
if args.len() == 1;
if let Some(arg) = args.get(0);
then { arg } else { expr }
}
}
fn get_offset<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, idx: &Expr<'_>, var: HirId) -> Option<Offset> {
fn extract_offset<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, e: &Expr<'_>, var: HirId) -> Option<String> {
match e.kind {
ExprKind::Lit(ref l) => match l.node {
match &e.kind {
ExprKind::Lit(l) => match l.node {
ast::LitKind::Int(x, _ty) => Some(x.to_string()),
_ => None,
},
@ -831,14 +848,8 @@ fn extract_offset<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, e: &Expr<'_>, var: HirId
}
}
if let ExprKind::Index(ref seqexpr, ref idx) = expr.kind {
let ty = cx.tables.expr_ty(seqexpr);
if !is_slice_like(cx, ty) {
return None;
}
let offset = match idx.kind {
ExprKind::Binary(op, ref lhs, ref rhs) => match op.node {
match idx.kind {
ExprKind::Binary(op, lhs, rhs) => match op.node {
BinOpKind::Add => {
let offset_opt = if same_var(cx, lhs, var) {
extract_offset(cx, rhs, var)
@ -853,93 +864,123 @@ fn extract_offset<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, e: &Expr<'_>, var: HirId
BinOpKind::Sub if same_var(cx, lhs, var) => extract_offset(cx, rhs, var).map(Offset::negative),
_ => None,
},
ExprKind::Path(..) => {
if same_var(cx, idx, var) {
Some(Offset::positive("0".into()))
ExprKind::Path(..) if same_var(cx, idx, var) => Some(Offset::positive("0".into())),
_ => None,
}
}
fn get_assignments<'tcx>(body: &'tcx Expr<'tcx>) -> impl Iterator<Item = Option<(&'tcx Expr<'tcx>, &'tcx Expr<'tcx>)>> {
fn get_assignment<'tcx>(e: &'tcx Expr<'tcx>) -> Option<(&'tcx Expr<'tcx>, &'tcx Expr<'tcx>)> {
if let ExprKind::Assign(lhs, rhs, _) = e.kind {
Some((lhs, rhs))
} else {
None
}
}
// This is one of few ways to return different iterators
// derived from: https://stackoverflow.com/questions/29760668/conditionally-iterate-over-one-of-several-possible-iterators/52064434#52064434
let mut iter_a = None;
let mut iter_b = None;
if let ExprKind::Block(b, _) = body.kind {
let Block { stmts, expr, .. } = *b;
iter_a = stmts
.iter()
.filter_map(|stmt| match stmt.kind {
StmtKind::Local(..) | StmtKind::Item(..) => None,
StmtKind::Expr(e) | StmtKind::Semi(e) => Some(e),
})
.chain(expr.into_iter())
.map(get_assignment)
.into()
} else {
iter_b = Some(get_assignment(body))
}
iter_a.into_iter().flatten().chain(iter_b.into_iter())
}
fn build_manual_memcpy_suggestion<'a, 'tcx>(
cx: &LateContext<'a, 'tcx>,
start: &Expr<'_>,
end: &Expr<'_>,
limits: ast::RangeLimits,
dst_var: FixedOffsetVar<'_>,
src_var: FixedOffsetVar<'_>,
) -> String {
fn print_sum(arg1: &str, arg2: &Offset) -> String {
match (arg1, &arg2.value[..], arg2.sign) {
("0", "0", _) => "0".into(),
("0", x, OffsetSign::Positive) | (x, "0", _) => x.into(),
("0", x, OffsetSign::Negative) => format!("-{}", x),
(x, y, OffsetSign::Positive) => format!("({} + {})", x, y),
(x, y, OffsetSign::Negative) => {
if x == y {
"0".into()
} else {
format!("({} - {})", x, y)
}
},
_ => None,
}
}
fn print_offset(start_str: &str, inline_offset: &Offset) -> String {
let offset = print_sum(start_str, inline_offset);
if offset.as_str() == "0" {
"".into()
} else {
offset
}
}
let print_limit = |end: &Expr<'_>, offset: Offset, var: &Expr<'_>| {
if_chain! {
if let ExprKind::MethodCall(method, _, len_args) = end.kind;
if method.ident.name == sym!(len);
if len_args.len() == 1;
if let Some(arg) = len_args.get(0);
if var_def_id(cx, arg) == var_def_id(cx, var);
then {
match offset.sign {
OffsetSign::Negative => format!("({} - {})", snippet(cx, end.span, "<src>.len()"), offset.value),
OffsetSign::Positive => "".into(),
}
} else {
let end_str = match limits {
ast::RangeLimits::Closed => {
let end = sugg::Sugg::hir(cx, end, "<count>");
format!("{}", end + sugg::ONE)
},
ast::RangeLimits::HalfOpen => format!("{}", snippet(cx, end.span, "..")),
};
offset.map(|o| FixedOffsetVar {
var_name: snippet_opt(cx, seqexpr.span).unwrap_or_else(|| "???".into()),
offset: o,
})
print_sum(&end_str, &offset)
}
}
};
let start_str = snippet(cx, start.span, "").to_string();
let dst_offset = print_offset(&start_str, &dst_var.offset);
let dst_limit = print_limit(end, dst_var.offset, dst_var.var);
let src_offset = print_offset(&start_str, &src_var.offset);
let src_limit = print_limit(end, src_var.offset, src_var.var);
let dst_var_name = snippet_opt(cx, dst_var.var.span).unwrap_or_else(|| "???".into());
let src_var_name = snippet_opt(cx, src_var.var.span).unwrap_or_else(|| "???".into());
let dst = if dst_offset == "" && dst_limit == "" {
dst_var_name
} else {
None
}
}
format!("{}[{}..{}]", dst_var_name, dst_offset, dst_limit)
};
fn fetch_cloned_fixed_offset_var<'a, 'tcx>(
cx: &LateContext<'a, 'tcx>,
expr: &Expr<'_>,
var: HirId,
) -> Option<FixedOffsetVar> {
if_chain! {
if let ExprKind::MethodCall(ref method, _, ref args) = expr.kind;
if method.ident.name == sym!(clone);
if args.len() == 1;
if let Some(arg) = args.get(0);
then {
return get_fixed_offset_var(cx, arg, var);
format!(
"{}.clone_from_slice(&{}[{}..{}])",
dst, src_var_name, src_offset, src_limit
)
}
}
get_fixed_offset_var(cx, expr, var)
}
fn get_indexed_assignments<'a, 'tcx>(
cx: &LateContext<'a, 'tcx>,
body: &Expr<'_>,
var: HirId,
) -> Vec<(FixedOffsetVar, FixedOffsetVar)> {
fn get_assignment<'a, 'tcx>(
cx: &LateContext<'a, 'tcx>,
e: &Expr<'_>,
var: HirId,
) -> Option<(FixedOffsetVar, FixedOffsetVar)> {
if let ExprKind::Assign(ref lhs, ref rhs, _) = e.kind {
match (
get_fixed_offset_var(cx, lhs, var),
fetch_cloned_fixed_offset_var(cx, rhs, var),
) {
(Some(offset_left), Some(offset_right)) => {
// Source and destination must be different
if offset_left.var_name == offset_right.var_name {
None
} else {
Some((offset_left, offset_right))
}
},
_ => None,
}
} else {
None
}
}
if let ExprKind::Block(ref b, _) = body.kind {
let Block {
ref stmts, ref expr, ..
} = **b;
stmts
.iter()
.map(|stmt| match stmt.kind {
StmtKind::Local(..) | StmtKind::Item(..) => None,
StmtKind::Expr(ref e) | StmtKind::Semi(ref e) => Some(get_assignment(cx, e, var)),
})
.chain(expr.as_ref().into_iter().map(|e| Some(get_assignment(cx, &*e, var))))
.filter_map(|op| op)
.collect::<Option<Vec<_>>>()
.unwrap_or_default()
} else {
get_assignment(cx, body, var).into_iter().collect()
}
}
/// Checks for for loops that sequentially copy items from one slice-like
/// object to another.
fn detect_manual_memcpy<'a, 'tcx>(
@ -951,93 +992,43 @@ fn detect_manual_memcpy<'a, 'tcx>(
) {
if let Some(higher::Range {
start: Some(start),
ref end,
end: Some(end),
limits,
}) = higher::range(cx, arg)
{
// the var must be a single name
if let PatKind::Binding(_, canonical_id, _, _) = pat.kind {
let print_sum = |arg1: &Offset, arg2: &Offset| -> String {
match (&arg1.value[..], arg1.negate, &arg2.value[..], arg2.negate) {
("0", _, "0", _) => "".into(),
("0", _, x, false) | (x, false, "0", false) => x.into(),
("0", _, x, true) | (x, false, "0", true) => format!("-{}", x),
(x, false, y, false) => format!("({} + {})", x, y),
(x, false, y, true) => {
if x == y {
"0".into()
} else {
format!("({} - {})", x, y)
}
},
(x, true, y, false) => {
if x == y {
"0".into()
} else {
format!("({} - {})", y, x)
}
},
(x, true, y, true) => format!("-({} + {})", x, y),
}
};
let print_limit = |end: &Option<&Expr<'_>>, offset: Offset, var_name: &str| {
if let Some(end) = *end {
if_chain! {
if let ExprKind::MethodCall(ref method, _, ref len_args) = end.kind;
if method.ident.name == sym!(len);
if len_args.len() == 1;
if let Some(arg) = len_args.get(0);
if snippet(cx, arg.span, "??") == var_name;
then {
return if offset.negate {
format!("({} - {})", snippet(cx, end.span, "<src>.len()"), offset.value)
} else {
String::new()
};
}
}
let end_str = match limits {
ast::RangeLimits::Closed => {
let end = sugg::Sugg::hir(cx, end, "<count>");
format!("{}", end + sugg::ONE)
},
ast::RangeLimits::HalfOpen => format!("{}", snippet(cx, end.span, "..")),
};
print_sum(&Offset::positive(end_str), &offset)
} else {
"..".into()
}
};
// The only statements in the for loops can be indexed assignments from
// indexed retrievals.
let manual_copies = get_indexed_assignments(cx, body, canonical_id);
let big_sugg = get_assignments(body)
.map(|o| {
o.and_then(|(lhs, rhs)| {
let rhs = fetch_cloned_expr(rhs);
if_chain! {
if let ExprKind::Index(seqexpr_left, idx_left) = lhs.kind;
if let ExprKind::Index(seqexpr_right, idx_right) = rhs.kind;
if is_slice_like(cx, cx.tables.expr_ty(seqexpr_left))
&& is_slice_like(cx, cx.tables.expr_ty(seqexpr_right));
if let Some(offset_left) = get_offset(cx, &idx_left, canonical_id);
if let Some(offset_right) = get_offset(cx, &idx_right, canonical_id);
let big_sugg = manual_copies
.into_iter()
.map(|(dst_var, src_var)| {
let start_str = Offset::positive(snippet(cx, start.span, "").to_string());
let dst_offset = print_sum(&start_str, &dst_var.offset);
let dst_limit = print_limit(end, dst_var.offset, &dst_var.var_name);
let src_offset = print_sum(&start_str, &src_var.offset);
let src_limit = print_limit(end, src_var.offset, &src_var.var_name);
let dst = if dst_offset == "" && dst_limit == "" {
dst_var.var_name
// Source and destination must be different
if var_def_id(cx, seqexpr_left) != var_def_id(cx, seqexpr_right);
then {
Some((FixedOffsetVar { var: seqexpr_left, offset: offset_left },
FixedOffsetVar { var: seqexpr_right, offset: offset_right }))
} else {
format!("{}[{}..{}]", dst_var.var_name, dst_offset, dst_limit)
};
format!(
"{}.clone_from_slice(&{}[{}..{}])",
dst, src_var.var_name, src_offset, src_limit
)
None
}
}
})
.join("\n ");
})
.map(|o| o.map(|(dst, src)| build_manual_memcpy_suggestion(cx, start, end, limits, dst, src)))
.collect::<Option<Vec<_>>>()
.filter(|v| !v.is_empty())
.map(|v| v.join("\n "));
if !big_sugg.is_empty() {
if let Some(big_sugg) = big_sugg {
span_lint_and_sugg(
cx,
MANUAL_MEMCPY,

15
tests/ui/manual_memcpy.rs
View File

@ -98,6 +98,21 @@ fn index(&self, _: usize) -> &i32 {
for i in from..from + 3 {
dst[i] = src[i - from];
}
#[allow(clippy::identity_op)]
for i in 0..5 {
dst[i - 0] = src[i];
}
#[allow(clippy::reverse_range_loop)]
for i in 0..0 {
dst[i] = src[i];
}
// `RangeTo` `for` loop - don't trigger lint
for i in 0.. {
dst[i] = src[i];
}
}
#[warn(clippy::needless_range_loop, clippy::manual_memcpy)]

20
tests/ui/manual_memcpy.stderr
View File

@ -58,19 +58,31 @@ error: it looks like you're manually copying between slices
--> $DIR/manual_memcpy.rs:94:14
|
LL | for i in from..from + src.len() {
| ^^^^^^^^^^^^^^^^^^^^^^ help: try replacing the loop by: `dst[from..from + src.len()].clone_from_slice(&src[0..(from + src.len() - from)])`
| ^^^^^^^^^^^^^^^^^^^^^^ help: try replacing the loop by: `dst[from..from + src.len()].clone_from_slice(&src[..(from + src.len() - from)])`
error: it looks like you're manually copying between slices
--> $DIR/manual_memcpy.rs:98:14
|
LL | for i in from..from + 3 {
| ^^^^^^^^^^^^^^ help: try replacing the loop by: `dst[from..from + 3].clone_from_slice(&src[0..(from + 3 - from)])`
| ^^^^^^^^^^^^^^ help: try replacing the loop by: `dst[from..from + 3].clone_from_slice(&src[..(from + 3 - from)])`
error: it looks like you're manually copying between slices
--> $DIR/manual_memcpy.rs:105:14
--> $DIR/manual_memcpy.rs:103:14
|
LL | for i in 0..5 {
| ^^^^ help: try replacing the loop by: `dst[..5].clone_from_slice(&src[..5])`
error: it looks like you're manually copying between slices
--> $DIR/manual_memcpy.rs:108:14
|
LL | for i in 0..0 {
| ^^^^ help: try replacing the loop by: `dst[..0].clone_from_slice(&src[..0])`
error: it looks like you're manually copying between slices
--> $DIR/manual_memcpy.rs:120:14
|
LL | for i in 0..src.len() {
| ^^^^^^^^^^^^ help: try replacing the loop by: `dst[..src.len()].clone_from_slice(&src[..])`
error: aborting due to 11 previous errors
error: aborting due to 13 previous errors