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michaelsproulmichaelsproul
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Restriction lint for function pointer casts
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‎CHANGELOG.md

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@@ -2727,6 +2727,7 @@ Released 2018-09-13
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[`float_cmp_const`]: https://rust-lang.github.io/rust-clippy/master/index.html#float_cmp_const
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[`float_equality_without_abs`]: https://rust-lang.github.io/rust-clippy/master/index.html#float_equality_without_abs
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[`fn_address_comparisons`]: https://rust-lang.github.io/rust-clippy/master/index.html#fn_address_comparisons
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[`fn_cast`]: https://rust-lang.github.io/rust-clippy/master/index.html#fn_cast
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[`fn_params_excessive_bools`]: https://rust-lang.github.io/rust-clippy/master/index.html#fn_params_excessive_bools
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[`fn_to_numeric_cast`]: https://rust-lang.github.io/rust-clippy/master/index.html#fn_to_numeric_cast
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[`fn_to_numeric_cast_with_truncation`]: https://rust-lang.github.io/rust-clippy/master/index.html#fn_to_numeric_cast_with_truncation

‎clippy_lints/src/casts/fn_cast.rs

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@@ -0,0 +1,34 @@
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use clippy_utils::diagnostics::span_lint_and_sugg;
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use clippy_utils::source::snippet_with_applicability;
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use rustc_errors::Applicability;
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use rustc_hir::Expr;
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use rustc_lint::LateContext;
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use rustc_middle::ty::{self, Ty};
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use super::FN_CAST;
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pub(super) fn check(cx: &LateContext<'_>, expr: &Expr<'_>, cast_expr: &Expr<'_>, cast_from: Ty<'_>, cast_to: Ty<'_>) {
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// We allow casts from any function type to any function type.
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match cast_to.kind() {
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ty::FnDef(..) | ty::FnPtr(..) => return,
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_ => { /* continue to checks */ },
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}
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match cast_from.kind() {
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ty::FnDef(..) | ty::FnPtr(_) => {
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let mut applicability = Applicability::MaybeIncorrect;
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let from_snippet = snippet_with_applicability(cx, cast_expr.span, "x", &mut applicability);
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span_lint_and_sugg(
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cx,
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FN_CAST,
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expr.span,
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&format!("casting function pointer `{}` to `{}`", from_snippet, cast_to),
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"did you mean to invoke the function?",
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format!("{}() as {}", from_snippet, cast_to),
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applicability,
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);
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},
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_ => {},
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}
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}

‎clippy_lints/src/casts/mod.rs

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@@ -6,6 +6,7 @@ mod cast_ptr_alignment;
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mod cast_ref_to_mut;
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mod cast_sign_loss;
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mod char_lit_as_u8;
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mod fn_cast;
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mod fn_to_numeric_cast;
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mod fn_to_numeric_cast_with_truncation;
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mod ptr_as_ptr;
@@ -251,6 +252,42 @@ declare_clippy_lint! {
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"casting a function pointer to a numeric type not wide enough to store the address"
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}
253254

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declare_clippy_lint! {
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/// ### What it does
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/// Checks for casts of a function pointer to any non-function type.
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///
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/// ### Why is this bad?
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/// Casting a function pointer can have surprising results and can occur accidentally if
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/// parantheses are omitted from a function call. If you aren't doing anything low-level with
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/// function pointers then you can opt-out of casting functions to avoid mistakes.
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/// Alternatively, you can use this lint to audit all uses of function pointer casts in your
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/// code.
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///
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/// ### Example
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/// ```rust
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/// // Bad: fn1 is cast as `usize`
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/// fn fn1() -> u16 {
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/// 1
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/// };
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/// let _ = fn1 as usize;
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///
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/// // Good: maybe you intended to call the function?
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/// fn fn2() -> u16 {
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/// 1
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/// };
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/// let _ = fn2() as usize;
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///
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/// // Good: maybe you intended to cast it to a function type?
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/// fn fn3() -> u16 {
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/// 1
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/// }
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/// let _ = fn3 as fn() -> u16;
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/// ```
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pub FN_CAST,
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restriction,
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"casting a function pointer to any non-function type"
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}
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declare_clippy_lint! {
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/// ### What it does
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/// Checks for casts of `&T` to `&mut T` anywhere in the code.
@@ -360,6 +397,7 @@ impl_lint_pass!(Casts => [
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CAST_REF_TO_MUT,
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CAST_PTR_ALIGNMENT,
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UNNECESSARY_CAST,
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FN_CAST,
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FN_TO_NUMERIC_CAST,
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FN_TO_NUMERIC_CAST_WITH_TRUNCATION,
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CHAR_LIT_AS_U8,
@@ -385,6 +423,7 @@ impl<'tcx> LateLintPass<'tcx> for Casts {
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return;
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}
387425

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fn_cast::check(cx, expr, cast_expr, cast_from, cast_to);
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fn_to_numeric_cast::check(cx, expr, cast_expr, cast_from, cast_to);
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fn_to_numeric_cast_with_truncation::check(cx, expr, cast_expr, cast_from, cast_to);
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if cast_from.is_numeric() && cast_to.is_numeric() && !in_external_macro(cx.sess(), expr.span) {

‎clippy_lints/src/lib.rs

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@@ -570,6 +570,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
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casts::CAST_REF_TO_MUT,
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casts::CAST_SIGN_LOSS,
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casts::CHAR_LIT_AS_U8,
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casts::FN_CAST,
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casts::FN_TO_NUMERIC_CAST,
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casts::FN_TO_NUMERIC_CAST_WITH_TRUNCATION,
575576
casts::PTR_AS_PTR,
@@ -1018,6 +1019,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
10181019
LintId::of(as_conversions::AS_CONVERSIONS),
10191020
LintId::of(asm_syntax::INLINE_ASM_X86_ATT_SYNTAX),
10201021
LintId::of(asm_syntax::INLINE_ASM_X86_INTEL_SYNTAX),
1022+
LintId::of(casts::FN_CAST),
10211023
LintId::of(create_dir::CREATE_DIR),
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LintId::of(dbg_macro::DBG_MACRO),
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LintId::of(default_numeric_fallback::DEFAULT_NUMERIC_FALLBACK),

‎tests/ui/fn_cast.rs

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@@ -0,0 +1,76 @@
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#![warn(clippy::fn_cast)]
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#![allow(clippy::fn_to_numeric_cast, clippy::fn_to_numeric_cast_with_truncation)]
3+
4+
fn foo() -> u8 {
5+
0
6+
}
7+
8+
fn generic_foo<T>(x: T) -> T {
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x
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}
11+
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trait Trait {
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fn static_method() -> u32 {
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2
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}
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}
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struct Struct;
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impl Trait for Struct {}
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fn fn_pointer_to_integer() {
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let _ = foo as i8;
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let _ = foo as i16;
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let _ = foo as i32;
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let _ = foo as i64;
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let _ = foo as i128;
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let _ = foo as isize;
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let _ = foo as u8;
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let _ = foo as u16;
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let _ = foo as u32;
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let _ = foo as u64;
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let _ = foo as u128;
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let _ = foo as usize;
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}
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38+
fn static_method_to_integer() {
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let _ = Struct::static_method as usize;
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}
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fn fn_with_fn_arg(f: fn(i32) -> u32) -> usize {
43+
f as usize
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}
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fn fn_with_generic_static_trait_method<T: Trait>() -> usize {
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T::static_method as usize
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}
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fn closure_to_fn_to_integer() {
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let clos = |x| x * 2_u32;
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let _ = (clos as fn(u32) -> u32) as usize;
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}
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fn fn_to_raw_ptr() {
57+
let _ = foo as *const ();
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}
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fn cast_fn_to_self() {
61+
// Casting to the same function pointer type should be permitted.
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let _ = foo as fn() -> u8;
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}
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fn cast_generic_to_concrete() {
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// Casting to a more concrete function pointer type should be permitted.
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let _ = generic_foo as fn(usize) -> usize;
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}
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fn cast_closure_to_fn() {
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// Casting a closure to a function pointer should be permitted.
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let id = |x| x;
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let _ = id as fn(usize) -> usize;
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}
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fn main() {}

‎tests/ui/fn_cast.stderr

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error: casting function pointer `foo` to `i8`
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--> $DIR/fn_cast.rs:23:13
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|
4+
LL | let _ = foo as i8;
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| ^^^^^^^^^ help: did you mean to invoke the function?: `foo() as i8`
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|
7+
= note: `-D clippy::fn-cast` implied by `-D warnings`
8+
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error: casting function pointer `foo` to `i16`
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--> $DIR/fn_cast.rs:24:13
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|
12+
LL | let _ = foo as i16;
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| ^^^^^^^^^^ help: did you mean to invoke the function?: `foo() as i16`
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15+
error: casting function pointer `foo` to `i32`
16+
--> $DIR/fn_cast.rs:25:13
17+
|
18+
LL | let _ = foo as i32;
19+
| ^^^^^^^^^^ help: did you mean to invoke the function?: `foo() as i32`
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21+
error: casting function pointer `foo` to `i64`
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--> $DIR/fn_cast.rs:26:13
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|
24+
LL | let _ = foo as i64;
25+
| ^^^^^^^^^^ help: did you mean to invoke the function?: `foo() as i64`
26+
27+
error: casting function pointer `foo` to `i128`
28+
--> $DIR/fn_cast.rs:27:13
29+
|
30+
LL | let _ = foo as i128;
31+
| ^^^^^^^^^^^ help: did you mean to invoke the function?: `foo() as i128`
32+
33+
error: casting function pointer `foo` to `isize`
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--> $DIR/fn_cast.rs:28:13
35+
|
36+
LL | let _ = foo as isize;
37+
| ^^^^^^^^^^^^ help: did you mean to invoke the function?: `foo() as isize`
38+
39+
error: casting function pointer `foo` to `u8`
40+
--> $DIR/fn_cast.rs:30:13
41+
|
42+
LL | let _ = foo as u8;
43+
| ^^^^^^^^^ help: did you mean to invoke the function?: `foo() as u8`
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error: casting function pointer `foo` to `u16`
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--> $DIR/fn_cast.rs:31:13
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|
48+
LL | let _ = foo as u16;
49+
| ^^^^^^^^^^ help: did you mean to invoke the function?: `foo() as u16`
50+
51+
error: casting function pointer `foo` to `u32`
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--> $DIR/fn_cast.rs:32:13
53+
|
54+
LL | let _ = foo as u32;
55+
| ^^^^^^^^^^ help: did you mean to invoke the function?: `foo() as u32`
56+
57+
error: casting function pointer `foo` to `u64`
58+
--> $DIR/fn_cast.rs:33:13
59+
|
60+
LL | let _ = foo as u64;
61+
| ^^^^^^^^^^ help: did you mean to invoke the function?: `foo() as u64`
62+
63+
error: casting function pointer `foo` to `u128`
64+
--> $DIR/fn_cast.rs:34:13
65+
|
66+
LL | let _ = foo as u128;
67+
| ^^^^^^^^^^^ help: did you mean to invoke the function?: `foo() as u128`
68+
69+
error: casting function pointer `foo` to `usize`
70+
--> $DIR/fn_cast.rs:35:13
71+
|
72+
LL | let _ = foo as usize;
73+
| ^^^^^^^^^^^^ help: did you mean to invoke the function?: `foo() as usize`
74+
75+
error: casting function pointer `Struct::static_method` to `usize`
76+
--> $DIR/fn_cast.rs:39:13
77+
|
78+
LL | let _ = Struct::static_method as usize;
79+
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: did you mean to invoke the function?: `Struct::static_method() as usize`
80+
81+
error: casting function pointer `f` to `usize`
82+
--> $DIR/fn_cast.rs:43:5
83+
|
84+
LL | f as usize
85+
| ^^^^^^^^^^ help: did you mean to invoke the function?: `f() as usize`
86+
87+
error: casting function pointer `T::static_method` to `usize`
88+
--> $DIR/fn_cast.rs:47:5
89+
|
90+
LL | T::static_method as usize
91+
| ^^^^^^^^^^^^^^^^^^^^^^^^^ help: did you mean to invoke the function?: `T::static_method() as usize`
92+
93+
error: casting function pointer `(clos as fn(u32) -> u32)` to `usize`
94+
--> $DIR/fn_cast.rs:53:13
95+
|
96+
LL | let _ = (clos as fn(u32) -> u32) as usize;
97+
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: did you mean to invoke the function?: `(clos as fn(u32) -> u32)() as usize`
98+
99+
error: casting function pointer `foo` to `*const ()`
100+
--> $DIR/fn_cast.rs:57:13
101+
|
102+
LL | let _ = foo as *const ();
103+
| ^^^^^^^^^^^^^^^^ help: did you mean to invoke the function?: `foo() as *const ()`
104+
105+
error: aborting due to 17 previous errors
106+

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