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Auto merge of #6187 - geoffreycopin:master, r=ebroto
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Lint unnecessary int-to-int and float-to-float casts

This is an implementation of a lint that detects unnecessary casts of number literals, as discussed here:
#6116

---

changelog: lint unnecessary as-casts of literals when they could be written using literal syntax.
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@bors
bors committed Oct 24, 2020
2 parents bf1c6f9 + d46edd9 commit 4a2d09a
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Showing 6 changed files with 189 additions and 44 deletions.
66 changes: 54 additions & 12 deletions clippy_lints/src/types.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -11,7 +11,7 @@ use rustc_hir as hir;
use rustc_hir::intravisit::{walk_body, walk_expr, walk_ty, FnKind, NestedVisitorMap, Visitor};
use rustc_hir::{
BinOpKind, Block, Body, Expr, ExprKind, FnDecl, FnRetTy, FnSig, GenericArg, GenericParamKind, HirId, ImplItem,
ImplItemKind, Item, ItemKind, Lifetime, Local, MatchSource, MutTy, Mutability, Node, QPath, Stmt, StmtKind,
ImplItemKind, Item, ItemKind, Lifetime, Lit, Local, MatchSource, MutTy, Mutability, Node, QPath, Stmt, StmtKind,
TraitFn, TraitItem, TraitItemKind, TyKind, UnOp,
};
use rustc_lint::{LateContext, LateLintPass, LintContext};
Expand Down Expand Up @@ -1224,7 +1224,8 @@ declare_clippy_lint! {
}

declare_clippy_lint! {
/// **What it does:** Checks for casts to the same type.
/// **What it does:** Checks for casts to the same type, casts of int literals to integer types
/// and casts of float literals to float types.
///
/// **Why is this bad?** It's just unnecessary.
///
Expand All @@ -1233,6 +1234,14 @@ declare_clippy_lint! {
/// **Example:**
/// ```rust
/// let _ = 2i32 as i32;
/// let _ = 0.5 as f32;
/// ```
///
/// Better:
///
/// ```rust
/// let _ = 2_i32;
/// let _ = 0.5_f32;
/// ```
pub UNNECESSARY_CAST,
complexity,
Expand Down Expand Up @@ -1598,7 +1607,9 @@ impl<'tcx> LateLintPass<'tcx> for Casts {
if let ExprKind::Cast(ref ex, _) = expr.kind {
let (cast_from, cast_to) = (cx.typeck_results().expr_ty(ex), cx.typeck_results().expr_ty(expr));
lint_fn_to_numeric_cast(cx, expr, ex, cast_from, cast_to);
if let ExprKind::Lit(ref lit) = ex.kind {
if let Some(lit) = get_numeric_literal(ex) {
let literal_str = snippet_opt(cx, ex.span).unwrap_or_default();

if_chain! {
if let LitKind::Int(n, _) = lit.node;
if let Some(src) = snippet_opt(cx, lit.span);
Expand All @@ -1608,19 +1619,19 @@ impl<'tcx> LateLintPass<'tcx> for Casts {
let to_nbits = fp_ty_mantissa_nbits(cast_to);
if from_nbits != 0 && to_nbits != 0 && from_nbits <= to_nbits && num_lit.is_decimal();
then {
span_lint_and_sugg(
cx,
UNNECESSARY_CAST,
expr.span,
&format!("casting integer literal to `{}` is unnecessary", cast_to),
"try",
format!("{}_{}", n, cast_to),
Applicability::MachineApplicable,
);
let literal_str = if is_unary_neg(ex) { format!("-{}", num_lit.integer) } else { num_lit.integer.into() };
show_unnecessary_cast(cx, expr, &literal_str, cast_from, cast_to);
return;
}
}

match lit.node {
LitKind::Int(_, LitIntType::Unsuffixed) if cast_to.is_integral() => {
show_unnecessary_cast(cx, expr, &literal_str, cast_from, cast_to);
},
LitKind::Float(_, LitFloatType::Unsuffixed) if cast_to.is_floating_point() => {
show_unnecessary_cast(cx, expr, &literal_str, cast_from, cast_to);
},
LitKind::Int(_, LitIntType::Unsuffixed) | LitKind::Float(_, LitFloatType::Unsuffixed) => {},
_ => {
if cast_from.kind() == cast_to.kind() && !in_external_macro(cx.sess(), expr.span) {
Expand All @@ -1646,6 +1657,37 @@ impl<'tcx> LateLintPass<'tcx> for Casts {
}
}

fn is_unary_neg(expr: &Expr<'_>) -> bool {
matches!(expr.kind, ExprKind::Unary(UnOp::UnNeg, _))
}

fn get_numeric_literal<'e>(expr: &'e Expr<'e>) -> Option<&'e Lit> {
match expr.kind {
ExprKind::Lit(ref lit) => Some(lit),
ExprKind::Unary(UnOp::UnNeg, e) => {
if let ExprKind::Lit(ref lit) = e.kind {
Some(lit)
} else {
None
}
},
_ => None,
}
}

fn show_unnecessary_cast(cx: &LateContext<'_>, expr: &Expr<'_>, literal_str: &str, cast_from: Ty<'_>, cast_to: Ty<'_>) {
let literal_kind_name = if cast_from.is_integral() { "integer" } else { "float" };
span_lint_and_sugg(
cx,
UNNECESSARY_CAST,
expr.span,
&format!("casting {} literal to `{}` is unnecessary", literal_kind_name, cast_to),
"try",
format!("{}_{}", literal_str, cast_to),
Applicability::MachineApplicable,
);
}

fn lint_numeric_casts<'tcx>(
cx: &LateContext<'tcx>,
expr: &Expr<'tcx>,
Expand Down
1 change: 1 addition & 0 deletions tests/ui/eq_op.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -6,6 +6,7 @@
#[allow(clippy::no_effect, unused_variables, clippy::unnecessary_operation, clippy::short_circuit_statement)]
#[allow(clippy::nonminimal_bool)]
#[allow(unused)]
#[allow(clippy::unnecessary_cast)]
fn main() {
// simple values and comparisons
1 == 1;
Expand Down
54 changes: 27 additions & 27 deletions tests/ui/eq_op.stderr
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Original file line number Diff line number Diff line change
@@ -1,163 +1,163 @@
error: equal expressions as operands to `==`
--> $DIR/eq_op.rs:11:5
--> $DIR/eq_op.rs:12:5
|
LL | 1 == 1;
| ^^^^^^
|
= note: `-D clippy::eq-op` implied by `-D warnings`

error: equal expressions as operands to `==`
--> $DIR/eq_op.rs:12:5
--> $DIR/eq_op.rs:13:5
|
LL | "no" == "no";
| ^^^^^^^^^^^^

error: equal expressions as operands to `!=`
--> $DIR/eq_op.rs:14:5
--> $DIR/eq_op.rs:15:5
|
LL | false != false;
| ^^^^^^^^^^^^^^

error: equal expressions as operands to `<`
--> $DIR/eq_op.rs:15:5
--> $DIR/eq_op.rs:16:5
|
LL | 1.5 < 1.5;
| ^^^^^^^^^

error: equal expressions as operands to `>=`
--> $DIR/eq_op.rs:16:5
--> $DIR/eq_op.rs:17:5
|
LL | 1u64 >= 1u64;
| ^^^^^^^^^^^^

error: equal expressions as operands to `&`
--> $DIR/eq_op.rs:19:5
--> $DIR/eq_op.rs:20:5
|
LL | (1 as u64) & (1 as u64);
| ^^^^^^^^^^^^^^^^^^^^^^^

error: equal expressions as operands to `^`
--> $DIR/eq_op.rs:20:5
--> $DIR/eq_op.rs:21:5
|
LL | 1 ^ ((((((1))))));
| ^^^^^^^^^^^^^^^^^

error: equal expressions as operands to `<`
--> $DIR/eq_op.rs:23:5
--> $DIR/eq_op.rs:24:5
|
LL | (-(2) < -(2));
| ^^^^^^^^^^^^^

error: equal expressions as operands to `==`
--> $DIR/eq_op.rs:24:5
--> $DIR/eq_op.rs:25:5
|
LL | ((1 + 1) & (1 + 1) == (1 + 1) & (1 + 1));
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error: equal expressions as operands to `&`
--> $DIR/eq_op.rs:24:6
--> $DIR/eq_op.rs:25:6
|
LL | ((1 + 1) & (1 + 1) == (1 + 1) & (1 + 1));
| ^^^^^^^^^^^^^^^^^

error: equal expressions as operands to `&`
--> $DIR/eq_op.rs:24:27
--> $DIR/eq_op.rs:25:27
|
LL | ((1 + 1) & (1 + 1) == (1 + 1) & (1 + 1));
| ^^^^^^^^^^^^^^^^^

error: equal expressions as operands to `==`
--> $DIR/eq_op.rs:25:5
--> $DIR/eq_op.rs:26:5
|
LL | (1 * 2) + (3 * 4) == 1 * 2 + 3 * 4;
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error: equal expressions as operands to `!=`
--> $DIR/eq_op.rs:28:5
--> $DIR/eq_op.rs:29:5
|
LL | ([1] != [1]);
| ^^^^^^^^^^^^

error: equal expressions as operands to `!=`
--> $DIR/eq_op.rs:29:5
--> $DIR/eq_op.rs:30:5
|
LL | ((1, 2) != (1, 2));
| ^^^^^^^^^^^^^^^^^^

error: equal expressions as operands to `==`
--> $DIR/eq_op.rs:33:5
--> $DIR/eq_op.rs:34:5
|
LL | 1 + 1 == 2;
| ^^^^^^^^^^

error: equal expressions as operands to `==`
--> $DIR/eq_op.rs:34:5
--> $DIR/eq_op.rs:35:5
|
LL | 1 - 1 == 0;
| ^^^^^^^^^^

error: equal expressions as operands to `-`
--> $DIR/eq_op.rs:34:5
--> $DIR/eq_op.rs:35:5
|
LL | 1 - 1 == 0;
| ^^^^^

error: equal expressions as operands to `-`
--> $DIR/eq_op.rs:36:5
--> $DIR/eq_op.rs:37:5
|
LL | 1 - 1;
| ^^^^^

error: equal expressions as operands to `/`
--> $DIR/eq_op.rs:37:5
--> $DIR/eq_op.rs:38:5
|
LL | 1 / 1;
| ^^^^^

error: equal expressions as operands to `&&`
--> $DIR/eq_op.rs:38:5
--> $DIR/eq_op.rs:39:5
|
LL | true && true;
| ^^^^^^^^^^^^

error: equal expressions as operands to `||`
--> $DIR/eq_op.rs:40:5
--> $DIR/eq_op.rs:41:5
|
LL | true || true;
| ^^^^^^^^^^^^

error: equal expressions as operands to `&&`
--> $DIR/eq_op.rs:46:5
--> $DIR/eq_op.rs:47:5
|
LL | a == b && b == a;
| ^^^^^^^^^^^^^^^^

error: equal expressions as operands to `&&`
--> $DIR/eq_op.rs:47:5
--> $DIR/eq_op.rs:48:5
|
LL | a != b && b != a;
| ^^^^^^^^^^^^^^^^

error: equal expressions as operands to `&&`
--> $DIR/eq_op.rs:48:5
--> $DIR/eq_op.rs:49:5
|
LL | a < b && b > a;
| ^^^^^^^^^^^^^^

error: equal expressions as operands to `&&`
--> $DIR/eq_op.rs:49:5
--> $DIR/eq_op.rs:50:5
|
LL | a <= b && b >= a;
| ^^^^^^^^^^^^^^^^

error: equal expressions as operands to `==`
--> $DIR/eq_op.rs:52:5
--> $DIR/eq_op.rs:53:5
|
LL | a == a;
| ^^^^^^

error: equal expressions as operands to `/`
--> $DIR/eq_op.rs:62:20
--> $DIR/eq_op.rs:63:20
|
LL | const D: u32 = A / A;
| ^^^^^
Expand Down
19 changes: 17 additions & 2 deletions tests/ui/unnecessary_cast_fixable.fixed
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Original file line number Diff line number Diff line change
Expand Up @@ -8,16 +8,31 @@ fn main() {
100_f32;
100_f64;
100_f64;
let _ = -100_f32;
let _ = -100_f64;
let _ = -100_f64;
// Should not trigger
#[rustfmt::skip]
let v = vec!(1);
&v as &[i32];
1.0 as f64;
1 as u64;
0x10 as f32;
0o10 as f32;
0b10 as f32;
0x11 as f64;
0o11 as f64;
0b11 as f64;

1_u32;
0x10_i32;
0b10_usize;
0o73_u16;
1_000_000_000_u32;

1.0_f64;
0.5_f32;

1.0 as u16;

let _ = -1_i32;
let _ = -1.0_f32;
}
19 changes: 17 additions & 2 deletions tests/ui/unnecessary_cast_fixable.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -8,16 +8,31 @@ fn main() {
100 as f32;
100 as f64;
100_i32 as f64;
let _ = -100 as f32;
let _ = -100 as f64;
let _ = -100_i32 as f64;
// Should not trigger
#[rustfmt::skip]
let v = vec!(1);
&v as &[i32];
1.0 as f64;
1 as u64;
0x10 as f32;
0o10 as f32;
0b10 as f32;
0x11 as f64;
0o11 as f64;
0b11 as f64;

1 as u32;
0x10 as i32;
0b10 as usize;
0o73 as u16;
1_000_000_000 as u32;

1.0 as f64;
0.5 as f32;

1.0 as u16;

let _ = -1 as i32;
let _ = -1.0 as f32;
}
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