Add support for 'extern const fn'
This works just as you might expect - an 'extern const fn' is a 'const fn' that is callable from foreign code. Currently, panicking is not allowed in consts. When RFC 2345 is stabilized, then panicking in an 'extern const fn' will produce a compile-time error when invoked at compile time, and an abort when invoked at runtime. Since this is extending the language (we're allowing the `const` keyword in a new context), I believe that this will need an FCP. However, it's a very minor change, so I didn't think that filing an RFC was necessary. This will allow libc (and other FFI crates) to make many functions `const`, without having to give up on making them `extern` as well.
This commit is contained in:
Aaron Hill
parent
7130fc54e0
commit
73b50d211b
18 changed files with 302 additions and 21 deletions
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@ -519,6 +519,9 @@ declare_features! (
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/// Allows the use of or-patterns (e.g., `0 | 1`).
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(active, or_patterns, "1.38.0", Some(54883), None),
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/// Allows the definition of `const extern fn` and `const unsafe extern fn`.
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(active, const_extern_fn, "1.40.0", Some(64926), None),
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// -------------------------------------------------------------------------
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// feature-group-end: actual feature gates
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// -------------------------------------------------------------------------
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@ -821,6 +821,7 @@ pub fn check_crate(krate: &ast::Crate,
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gate_all!(async_closure, "async closures are unstable");
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gate_all!(yields, generators, "yield syntax is experimental");
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gate_all!(or_patterns, "or-patterns syntax is experimental");
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gate_all!(const_extern_fn, "`const extern fn` definitions are unstable");
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visit::walk_crate(&mut visitor, krate);
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}
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@ -57,6 +57,8 @@ pub struct GatedSpans {
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pub yields: Lock<Vec<Span>>,
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/// Spans collected for gating `or_patterns`, e.g. `Some(Foo | Bar)`.
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pub or_patterns: Lock<Vec<Span>>,
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/// Spans collected for gating `const_extern_fn`, e.g. `const extern fn foo`.
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pub const_extern_fn: Lock<Vec<Span>>,
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}
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/// Info about a parsing session.
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@ -1486,6 +1486,15 @@ impl<'a> Parser<'a> {
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Ok(())
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}
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/// Parses `extern` followed by an optional ABI string, or nothing.
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fn parse_extern_abi(&mut self) -> PResult<'a, Abi> {
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if self.eat_keyword(kw::Extern) {
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Ok(self.parse_opt_abi()?.unwrap_or(Abi::C))
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} else {
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Ok(Abi::Rust)
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}
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}
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/// Parses a string as an ABI spec on an extern type or module. Consumes
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/// the `extern` keyword, if one is found.
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fn parse_opt_abi(&mut self) -> PResult<'a, Option<Abi>> {
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@ -149,17 +149,23 @@ impl<'a> Parser<'a> {
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}
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if self.eat_keyword(kw::Const) {
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let const_span = self.prev_span;
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if self.check_keyword(kw::Fn)
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|| (self.check_keyword(kw::Unsafe)
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&& self.is_keyword_ahead(1, &[kw::Fn])) {
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if [kw::Fn, kw::Unsafe, kw::Extern].iter().any(|k| self.check_keyword(*k)) {
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// CONST FUNCTION ITEM
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let unsafety = self.parse_unsafety();
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self.bump();
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if self.check_keyword(kw::Extern) {
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self.sess.gated_spans.const_extern_fn.borrow_mut().push(
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lo.to(self.token.span)
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);
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}
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let abi = self.parse_extern_abi()?;
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let header = FnHeader {
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unsafety,
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asyncness: respan(const_span, IsAsync::NotAsync),
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constness: respan(const_span, Constness::Const),
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abi: Abi::Rust,
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abi,
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};
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return self.parse_item_fn(lo, visibility, attrs, header);
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}
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@ -257,11 +263,7 @@ impl<'a> Parser<'a> {
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self.bump(); // `unsafe`
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// `{` is also expected after `unsafe`; in case of error, include it in the diagnostic.
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self.check(&token::OpenDelim(token::Brace));
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let abi = if self.eat_keyword(kw::Extern) {
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self.parse_opt_abi()?.unwrap_or(Abi::C)
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} else {
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Abi::Rust
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};
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let abi = self.parse_extern_abi()?;
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self.expect_keyword(kw::Fn)?;
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let fn_span = self.prev_span;
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let header = FnHeader {
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@ -834,11 +836,7 @@ impl<'a> Parser<'a> {
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let (constness, unsafety, abi) = if is_const_fn {
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(respan(const_span, Constness::Const), unsafety, Abi::Rust)
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} else {
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let abi = if self.eat_keyword(kw::Extern) {
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self.parse_opt_abi()?.unwrap_or(Abi::C)
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} else {
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Abi::Rust
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};
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let abi = self.parse_extern_abi()?;
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(respan(self.prev_span, Constness::NotConst), unsafety, abi)
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};
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if !self.eat_keyword(kw::Fn) {
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@ -1278,14 +1276,30 @@ impl<'a> Parser<'a> {
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// Treat `const` as `static` for error recovery, but don't add it to expected tokens.
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if self.check_keyword(kw::Static) || self.token.is_keyword(kw::Const) {
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if self.token.is_keyword(kw::Const) {
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self.diagnostic()
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.struct_span_err(self.token.span, "extern items cannot be `const`")
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.span_suggestion(
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let mut err = self
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.struct_span_err(self.token.span, "extern items cannot be `const`");
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// The user wrote 'const fn'
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if self.is_keyword_ahead(1, &[kw::Fn, kw::Unsafe]) {
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err.emit();
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// Consume `const`
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self.bump();
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// Consume `unsafe` if present, since `extern` blocks
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// don't allow it. This will leave behind a plain 'fn'
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self.eat_keyword(kw::Unsafe);
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// Treat 'const fn` as a plain `fn` for error recovery purposes.
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// We've already emitted an error, so compilation is guaranteed
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// to fail
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return Ok(self.parse_item_foreign_fn(visibility, lo, attrs, extern_sp)?);
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}
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err.span_suggestion(
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self.token.span,
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"try using a static value",
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"static".to_owned(),
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Applicability::MachineApplicable
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).emit();
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);
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err.emit();
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}
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self.bump(); // `static` or `const`
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return Ok(self.parse_item_foreign_static(visibility, lo, attrs)?);
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@ -196,6 +196,7 @@ symbols! {
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console,
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const_compare_raw_pointers,
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const_constructor,
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const_extern_fn,
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const_fn,
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const_fn_union,
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const_generics,
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@ -0,0 +1,23 @@
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#![feature(const_extern_fn)]
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extern "C" {
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fn regular_in_block();
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}
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const extern fn bar() {
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unsafe {
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regular_in_block();
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//~^ ERROR: cannot call functions with `"C"` abi in `min_const_fn`
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}
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}
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extern fn regular() {}
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const extern fn foo() {
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unsafe {
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regular();
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//~^ ERROR: cannot call functions with `"C"` abi in `min_const_fn`
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}
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}
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fn main() {}
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@ -0,0 +1,21 @@
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error[E0723]: cannot call functions with `"C"` abi in `min_const_fn`
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--> $DIR/const-extern-fn-call-extern-fn.rs:9:9
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LL | regular_in_block();
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| ^^^^^^^^^^^^^^^^^^
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= note: for more information, see issue https://github.com/rust-lang/rust/issues/57563
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= help: add `#![feature(const_fn)]` to the crate attributes to enable
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error[E0723]: cannot call functions with `"C"` abi in `min_const_fn`
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--> $DIR/const-extern-fn-call-extern-fn.rs:18:9
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LL | regular();
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| ^^^^^^^^^
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= note: for more information, see issue https://github.com/rust-lang/rust/issues/57563
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= help: add `#![feature(const_fn)]` to the crate attributes to enable
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error: aborting due to 2 previous errors
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For more information about this error, try `rustc --explain E0723`.
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@ -0,0 +1,13 @@
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#![feature(const_extern_fn)]
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const extern fn unsize(x: &[u8; 3]) -> &[u8] { x }
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//~^ ERROR unsizing casts are not allowed in const fn
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const unsafe extern "C" fn closure() -> fn() { || {} }
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//~^ ERROR function pointers in const fn are unstable
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const unsafe extern fn use_float() { 1.0 + 1.0; }
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//~^ ERROR only int, `bool` and `char` operations are stable in const fn
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const extern "C" fn ptr_cast(val: *const u8) { val as usize; }
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//~^ ERROR casting pointers to ints is unstable in const fn
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fn main() {}
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@ -0,0 +1,39 @@
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error[E0723]: unsizing casts are not allowed in const fn
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--> $DIR/const-extern-fn-min-const-fn.rs:3:48
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LL | const extern fn unsize(x: &[u8; 3]) -> &[u8] { x }
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| ^
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= note: for more information, see issue https://github.com/rust-lang/rust/issues/57563
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= help: add `#![feature(const_fn)]` to the crate attributes to enable
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error[E0723]: function pointers in const fn are unstable
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--> $DIR/const-extern-fn-min-const-fn.rs:5:41
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LL | const unsafe extern "C" fn closure() -> fn() { || {} }
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| ^^^^
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= note: for more information, see issue https://github.com/rust-lang/rust/issues/57563
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= help: add `#![feature(const_fn)]` to the crate attributes to enable
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error[E0723]: only int, `bool` and `char` operations are stable in const fn
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--> $DIR/const-extern-fn-min-const-fn.rs:7:38
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LL | const unsafe extern fn use_float() { 1.0 + 1.0; }
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| ^^^^^^^^^
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= note: for more information, see issue https://github.com/rust-lang/rust/issues/57563
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= help: add `#![feature(const_fn)]` to the crate attributes to enable
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error[E0723]: casting pointers to ints is unstable in const fn
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--> $DIR/const-extern-fn-min-const-fn.rs:9:48
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LL | const extern "C" fn ptr_cast(val: *const u8) { val as usize; }
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| ^^^^^^^^^^^^
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= note: for more information, see issue https://github.com/rust-lang/rust/issues/57563
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= help: add `#![feature(const_fn)]` to the crate attributes to enable
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error: aborting due to 4 previous errors
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For more information about this error, try `rustc --explain E0723`.
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@ -0,0 +1,10 @@
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#![feature(const_extern_fn)]
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const unsafe extern fn foo() -> usize { 5 }
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fn main() {
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let a: [u8; foo()];
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//~^ ERROR call to unsafe function is unsafe and requires unsafe function or block
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foo();
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//~^ ERROR call to unsafe function is unsafe and requires unsafe function or block
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}
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@ -0,0 +1,19 @@
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error[E0133]: call to unsafe function is unsafe and requires unsafe function or block
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--> $DIR/const-extern-fn-requires-unsafe.rs:8:5
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LL | foo();
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| ^^^^^ call to unsafe function
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= note: consult the function's documentation for information on how to avoid undefined behavior
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error[E0133]: call to unsafe function is unsafe and requires unsafe function or block
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--> $DIR/const-extern-fn-requires-unsafe.rs:6:17
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LL | let a: [u8; foo()];
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| ^^^^^ call to unsafe function
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= note: consult the function's documentation for information on how to avoid undefined behavior
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error: aborting due to 2 previous errors
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For more information about this error, try `rustc --explain E0133`.
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35
src/test/ui/consts/const-extern-fn/const-extern-fn.rs
Normal file
35
src/test/ui/consts/const-extern-fn/const-extern-fn.rs
Normal file
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@ -0,0 +1,35 @@
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// run-pass
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#![feature(const_extern_fn)]
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const extern fn foo1(val: u8) -> u8 {
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val + 1
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}
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const extern "C" fn foo2(val: u8) -> u8 {
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val + 1
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}
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const unsafe extern fn bar1(val: bool) -> bool {
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!val
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}
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const unsafe extern "C" fn bar2(val: bool) -> bool {
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!val
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}
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fn main() {
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let a: [u8; foo1(25) as usize] = [0; 26];
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let b: [u8; foo2(25) as usize] = [0; 26];
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assert_eq!(a, b);
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let bar1_res = unsafe { bar1(false) };
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let bar2_res = unsafe { bar2(false) };
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assert!(bar1_res);
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assert_eq!(bar1_res, bar2_res);
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let _foo1_cast: extern fn(u8) -> u8 = foo1;
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let _foo2_cast: extern fn(u8) -> u8 = foo2;
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let _bar1_cast: unsafe extern fn(bool) -> bool = bar1;
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let _bar2_cast: unsafe extern fn(bool) -> bool = bar2;
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}
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@ -0,0 +1,12 @@
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// Check that `const extern fn` and `const unsafe extern fn` are feature-gated.
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#[cfg(FALSE)] const extern fn foo1() {} //~ ERROR `const extern fn` definitions are unstable
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#[cfg(FALSE)] const extern "C" fn foo2() {} //~ ERROR `const extern fn` definitions are unstable
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#[cfg(FALSE)] const extern "Rust" fn foo3() {} //~ ERROR `const extern fn` definitions are unstable
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#[cfg(FALSE)] const unsafe extern fn bar1() {} //~ ERROR `const extern fn` definitions are unstable
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#[cfg(FALSE)] const unsafe extern "C" fn bar2() {}
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//~^ ERROR `const extern fn` definitions are unstable
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#[cfg(FALSE)] const unsafe extern "Rust" fn bar3() {}
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//~^ ERROR `const extern fn` definitions are unstable
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fn main() {}
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@ -0,0 +1,57 @@
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error[E0658]: `const extern fn` definitions are unstable
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--> $DIR/feature-gate-const_extern_fn.rs:3:15
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LL | #[cfg(FALSE)] const extern fn foo1() {}
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| ^^^^^^^^^^^^
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= note: for more information, see https://github.com/rust-lang/rust/issues/64926
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= help: add `#![feature(const_extern_fn)]` to the crate attributes to enable
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error[E0658]: `const extern fn` definitions are unstable
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--> $DIR/feature-gate-const_extern_fn.rs:4:15
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LL | #[cfg(FALSE)] const extern "C" fn foo2() {}
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| ^^^^^^^^^^^^
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= note: for more information, see https://github.com/rust-lang/rust/issues/64926
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= help: add `#![feature(const_extern_fn)]` to the crate attributes to enable
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error[E0658]: `const extern fn` definitions are unstable
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--> $DIR/feature-gate-const_extern_fn.rs:5:15
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LL | #[cfg(FALSE)] const extern "Rust" fn foo3() {}
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| ^^^^^^^^^^^^
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|
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= note: for more information, see https://github.com/rust-lang/rust/issues/64926
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= help: add `#![feature(const_extern_fn)]` to the crate attributes to enable
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error[E0658]: `const extern fn` definitions are unstable
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--> $DIR/feature-gate-const_extern_fn.rs:6:15
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LL | #[cfg(FALSE)] const unsafe extern fn bar1() {}
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| ^^^^^^^^^^^^^^^^^^^
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|
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= note: for more information, see https://github.com/rust-lang/rust/issues/64926
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= help: add `#![feature(const_extern_fn)]` to the crate attributes to enable
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error[E0658]: `const extern fn` definitions are unstable
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--> $DIR/feature-gate-const_extern_fn.rs:7:15
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|
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LL | #[cfg(FALSE)] const unsafe extern "C" fn bar2() {}
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| ^^^^^^^^^^^^^^^^^^^
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|
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= note: for more information, see https://github.com/rust-lang/rust/issues/64926
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= help: add `#![feature(const_extern_fn)]` to the crate attributes to enable
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error[E0658]: `const extern fn` definitions are unstable
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--> $DIR/feature-gate-const_extern_fn.rs:9:15
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|
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LL | #[cfg(FALSE)] const unsafe extern "Rust" fn bar3() {}
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| ^^^^^^^^^^^^^^^^^^^
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|
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= note: for more information, see https://github.com/rust-lang/rust/issues/64926
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= help: add `#![feature(const_extern_fn)]` to the crate attributes to enable
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error: aborting due to 6 previous errors
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For more information about this error, try `rustc --explain E0658`.
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8
src/test/ui/parser/no-const-fn-in-extern-block.rs
Normal file
8
src/test/ui/parser/no-const-fn-in-extern-block.rs
Normal file
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@ -0,0 +1,8 @@
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extern {
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const fn foo();
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//~^ ERROR extern items cannot be `const`
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const unsafe fn bar();
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//~^ ERROR extern items cannot be `const`
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}
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fn main() {}
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14
src/test/ui/parser/no-const-fn-in-extern-block.stderr
Normal file
14
src/test/ui/parser/no-const-fn-in-extern-block.stderr
Normal file
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@ -0,0 +1,14 @@
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error: extern items cannot be `const`
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--> $DIR/no-const-fn-in-extern-block.rs:2:5
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LL | const fn foo();
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| ^^^^^
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error: extern items cannot be `const`
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--> $DIR/no-const-fn-in-extern-block.rs:4:5
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LL | const unsafe fn bar();
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| ^^^^^
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error: aborting due to 2 previous errors
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@ -8,9 +8,9 @@ LL | let _: unsafe extern "rust-intrinsic" fn(isize) -> usize = std::mem::tr
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| help: use parentheses to call this function: `std::mem::transmute(...)`
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= note: expected type `unsafe extern "rust-intrinsic" fn(isize) -> usize`
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found type `unsafe extern "rust-intrinsic" fn(_) -> _ {std::intrinsics::transmute::<_, _>}`
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found type `unsafe extern "rust-intrinsic" fn(_) -> _ {std::mem::transmute::<_, _>}`
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error[E0606]: casting `unsafe extern "rust-intrinsic" fn(_) -> _ {std::intrinsics::transmute::<_, _>}` as `unsafe extern "rust-intrinsic" fn(isize) -> usize` is invalid
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error[E0606]: casting `unsafe extern "rust-intrinsic" fn(_) -> _ {std::mem::transmute::<_, _>}` as `unsafe extern "rust-intrinsic" fn(isize) -> usize` is invalid
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--> $DIR/reify-intrinsic.rs:11:13
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LL | let _ = std::mem::transmute as unsafe extern "rust-intrinsic" fn(isize) -> usize;
|
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|
|
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Loading…
Add table
Reference in a new issue