primitive docs should show core/alloc/std accessibility

[cuviper]

In #61851, I tried to generate primitive docs in core, similar to those in std. My main motivation was to clearly see what f64 methods are available in core alone, under #[no_std], since a lot of them require std and libm support. However, I had trouble making that work because of broken documentation links between core and std-specific methods.

So I think instead, rustdoc could put some kind of marker on primitive methods to indicate what crate added them, so the accessibility is known. Apart from floating point, there are also a few slice methods that are only added in alloc. Maybe there are more that I don't know yet!

[Mark-Simulacrum]

I'm going to move this to T-doc as I personally don't think we should special case things even more in rustdoc (and it seems much simpler to just add a line to the primitive docs in the relevant files today).

[Mark-Simulacrum]

Ah, I missed that this is about methods, not types. In that case yeah this probably needs to be in rustdoc (and I guess only applies to primitives since those bypass coherence).

[jyn514]

Maybe there are more that I don't know yet!

rust/src/librustdoc/clean/types.rs

Lines 1313 to 1355 in 6cc268e

	map! {
	Isize => single(lang_items.isize_impl()),
	I8 => single(lang_items.i8_impl()),
	I16 => single(lang_items.i16_impl()),
	I32 => single(lang_items.i32_impl()),
	I64 => single(lang_items.i64_impl()),
	I128 => single(lang_items.i128_impl()),
	Usize => single(lang_items.usize_impl()),
	U8 => single(lang_items.u8_impl()),
	U16 => single(lang_items.u16_impl()),
	U32 => single(lang_items.u32_impl()),
	U64 => single(lang_items.u64_impl()),
	U128 => single(lang_items.u128_impl()),
	F32 => both(lang_items.f32_impl(), lang_items.f32_runtime_impl()),
	F64 => both(lang_items.f64_impl(), lang_items.f64_runtime_impl()),
	Char => single(lang_items.char_impl()),
	Bool => single(lang_items.bool_impl()),
	Str => both(lang_items.str_impl(), lang_items.str_alloc_impl()),
	Slice => {
	lang_items
	.slice_impl()
	.into_iter()
	.chain(lang_items.slice_u8_impl())
	.chain(lang_items.slice_alloc_impl())
	.chain(lang_items.slice_u8_alloc_impl())
	.collect()
	},
	Array => single(lang_items.array_impl()),
	Tuple => smallvec![],
	Unit => smallvec![],
	RawPointer => {
	lang_items
	.const_ptr_impl()
	.into_iter()
	.chain(lang_items.mut_ptr_impl())
	.chain(lang_items.const_slice_ptr_impl())
	.chain(lang_items.mut_slice_ptr_impl())
	.collect()
	},
	Reference => smallvec![],
	Fn => smallvec![],
	Never => smallvec![],
	}

[jyn514]

Rustdoc could do this by checking def_id.krate for each of these impls. I think this should go on the impl block itself, not the method, since it's impossible for the same impl to span multiple crates.