duplicate note on platform_intrinsics feature gate

[matthiaskrgr]

I tried this code:

#![feature(platform_intrinsics)]

pub fn main() {}

note the duplicate = note: using it is strongly discouraged

warning: the feature `platform_intrinsics` is internal to the compiler or standard library
 --> 688E28C68796BD785ADEA37D96B0DC202A82E2B0FF1F2A33B2A9C36992515DA4.rs:1:12
  |
1 | #![feature(platform_intrinsics)]
  |            ^^^^^^^^^^^^^^^^^^^
  |
  = note: using it is strongly discouraged
  = note: using it is strongly discouraged
  = note: `#[warn(internal_features)]` on by default

warning: 1 warning emitted

rustc 1.74.0-nightly (8ce4540bd 2023-09-29)
binary: rustc
commit-hash: 8ce4540bd6fe7d58d4bc05f1b137d61937d3cf72
commit-date: 2023-09-29
host: x86_64-unknown-linux-gnu
release: 1.74.0-nightly
LLVM version: 17.0.2

[workingjubilee]

feature, not a bug: we want people to be very strongly discouraged, so we say it twice.

[Noratrieb]

the more repetions, the more discouraged. lang_items should go up to 10.

[matthiaskrgr]

Maybe we should print it in an infinite loop, just to be on the save side? 😇

[workingjubilee]

https://www.youtube.com/watch?v=sq_Fm7qfRQk

[meysam81]

This is happening on rustc 1.75.0-nightly (e0d7ed1f4 2023-10-01) as well.

[gurry]

@rustbot claim

The source of the problem is the decorator for BuiltinInternalFeatures which is adding two children to the Diagnostic instead of one. I'm trying to dig further and decipher the marco-generated decorator code here:

rust/compiler/rustc_macros/src/diagnostics/diagnostic.rs

Lines 122 to 134 in 2e7e0fb

	let implementation = builder.each_variant(&mut structure, |mut builder, variant| {
	let preamble = builder.preamble(variant);
	let body = builder.body(variant);
	let diag = &builder.parent.diag;
	let formatting_init = &builder.formatting_init;
	quote! {
	#preamble
	#formatting_init
	#body
	#diag
	}
	});

I also noticed that the behaviour seems to differ across gates. E.g. building this:

#![feature(custom_mir)]
#![feature(platform_intrinsics)]

pub fn main() {}

emits one note for custom_mir and two notes for platform_intrinsics:

warning: the feature `custom_mir` is internal to the compiler or standard library
 --> ../test.rs:1:12
  |
1 | #![feature(custom_mir)]
  |            ^^^^^^^^^^
  |
  = note: using it is strongly discouraged
  = note: `#[warn(internal_features)]` on by default

warning: the feature `platform_intrinsics` is internal to the compiler or standard library
 --> ../test.rs:2:12
  |
2 | #![feature(platform_intrinsics)]
  |            ^^^^^^^^^^^^^^^^^^^
  |
  = note: using it is strongly discouraged
  = note: using it is strongly discouraged

warning: 2 warnings emitted

Not sure what's different about these gates.

I'm new to this area, so if you can provide any pointers based on the above, please do.

[gurry]

This program tests all the internal gates:

#![feature(allocator_internals)]
#![feature(allow_internal_unsafe)]
#![feature(allow_internal_unstable)]
#![feature(compiler_builtins)]
#![feature(custom_mir)]
#![feature(intrinsics)]
#![feature(lang_items)]
#![feature(omit_gdb_pretty_printer_section)]
#![feature(prelude_import)]
#![feature(profiler_runtime)]
#![feature(rustc_attrs)]
#![feature(staged_api)]
#![feature(test_2018_feature)]
#![feature(test_unstable_lint)]
#![feature(unsafe_pin_internals)]
#![feature(link_llvm_intrinsics)]
#![feature(needs_panic_runtime)]
#![feature(panic_runtime)]
#![feature(platform_intrinsics)]
#![feature(rustc_allow_const_fn_unstable)]
#![feature(rustdoc_internals)]

pub fn main() {}

It produces the following output:

warning: the feature `allocator_internals` is internal to the compiler or standard library
 --> ../test.rs:1:12
  |
1 | #![feature(allocator_internals)]
  |            ^^^^^^^^^^^^^^^^^^^
  |
  = note: using it is strongly discouraged
  = note: `#[warn(internal_features)]` on by default

warning: the feature `allow_internal_unsafe` is internal to the compiler or standard library
 --> ../test.rs:2:12
  |
2 | #![feature(allow_internal_unsafe)]
  |            ^^^^^^^^^^^^^^^^^^^^^
  |
  = note: using it is strongly discouraged

warning: the feature `allow_internal_unstable` is internal to the compiler or standard library
 --> ../test.rs:3:12
  |
3 | #![feature(allow_internal_unstable)]
  |            ^^^^^^^^^^^^^^^^^^^^^^^
  |
  = note: using it is strongly discouraged

warning: the feature `compiler_builtins` is internal to the compiler or standard library
 --> ../test.rs:4:12
  |
4 | #![feature(compiler_builtins)]
  |            ^^^^^^^^^^^^^^^^^
  |
  = note: using it is strongly discouraged

warning: the feature `custom_mir` is internal to the compiler or standard library
 --> ../test.rs:5:12
  |
5 | #![feature(custom_mir)]
  |            ^^^^^^^^^^
  |
  = note: using it is strongly discouraged

warning: the feature `intrinsics` is internal to the compiler or standard library
 --> ../test.rs:6:12
  |
6 | #![feature(intrinsics)]
  |            ^^^^^^^^^^
  |
  = note: using it is strongly discouraged

warning: the feature `lang_items` is internal to the compiler or standard library
 --> ../test.rs:7:12
  |
7 | #![feature(lang_items)]
  |            ^^^^^^^^^^
  |
  = note: using it is strongly discouraged

warning: the feature `omit_gdb_pretty_printer_section` is internal to the compiler or standard library
 --> ../test.rs:8:12
  |
8 | #![feature(omit_gdb_pretty_printer_section)]
  |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  |
  = note: using it is strongly discouraged

warning: the feature `prelude_import` is internal to the compiler or standard library
 --> ../test.rs:9:12
  |
9 | #![feature(prelude_import)]
  |            ^^^^^^^^^^^^^^
  |
  = note: using it is strongly discouraged

warning: the feature `profiler_runtime` is internal to the compiler or standard library
  --> ../test.rs:10:12
   |
10 | #![feature(profiler_runtime)]
   |            ^^^^^^^^^^^^^^^^
   |
   = note: using it is strongly discouraged

warning: the feature `rustc_attrs` is internal to the compiler or standard library
  --> ../test.rs:11:12
   |
11 | #![feature(rustc_attrs)]
   |            ^^^^^^^^^^^
   |
   = note: using it is strongly discouraged

warning: the feature `staged_api` is internal to the compiler or standard library
  --> ../test.rs:12:12
   |
12 | #![feature(staged_api)]
   |            ^^^^^^^^^^
   |
   = note: using it is strongly discouraged

warning: the feature `test_2018_feature` is internal to the compiler or standard library
  --> ../test.rs:13:12
   |
13 | #![feature(test_2018_feature)]
   |            ^^^^^^^^^^^^^^^^^
   |
   = note: using it is strongly discouraged

warning: the feature `test_unstable_lint` is internal to the compiler or standard library
  --> ../test.rs:14:12
   |
14 | #![feature(test_unstable_lint)]
   |            ^^^^^^^^^^^^^^^^^^
   |
   = note: using it is strongly discouraged

warning: the feature `unsafe_pin_internals` is internal to the compiler or standard library
  --> ../test.rs:15:12
   |
15 | #![feature(unsafe_pin_internals)]
   |            ^^^^^^^^^^^^^^^^^^^^
   |
   = note: using it is strongly discouraged

warning: the feature `link_llvm_intrinsics` is internal to the compiler or standard library
  --> ../test.rs:16:12
   |
16 | #![feature(link_llvm_intrinsics)]
   |            ^^^^^^^^^^^^^^^^^^^^
   |
   = note: using it is strongly discouraged
   = note: using it is strongly discouraged

warning: the feature `needs_panic_runtime` is internal to the compiler or standard library
  --> ../test.rs:17:12
   |
17 | #![feature(needs_panic_runtime)]
   |            ^^^^^^^^^^^^^^^^^^^
   |
   = note: using it is strongly discouraged
   = note: using it is strongly discouraged

warning: the feature `panic_runtime` is internal to the compiler or standard library
  --> ../test.rs:18:12
   |
18 | #![feature(panic_runtime)]
   |            ^^^^^^^^^^^^^
   |
   = note: using it is strongly discouraged
   = note: using it is strongly discouraged

warning: the feature `platform_intrinsics` is internal to the compiler or standard library
  --> ../test.rs:19:12
   |
19 | #![feature(platform_intrinsics)]
   |            ^^^^^^^^^^^^^^^^^^^
   |
   = note: using it is strongly discouraged
   = note: using it is strongly discouraged

warning: the feature `rustc_allow_const_fn_unstable` is internal to the compiler or standard library
  --> ../test.rs:20:12
   |
20 | #![feature(rustc_allow_const_fn_unstable)]
   |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: using it is strongly discouraged
   = note: using it is strongly discouraged

warning: the feature `rustdoc_internals` is internal to the compiler or standard library
  --> ../test.rs:21:12
   |
21 | #![feature(rustdoc_internals)]
   |            ^^^^^^^^^^^^^^^^^
   |
   = note: using it is strongly discouraged
   = note: using it is strongly discouraged

error: module has missing stability attribute
  --> ../test.rs:1:1
   |
1  | / #![feature(allocator_internals)]
2  | | #![feature(allow_internal_unsafe)]
3  | | #![feature(allow_internal_unstable)]
4  | | #![feature(compiler_builtins)]
...  |
22 | |
23 | | pub fn main() {}
   | |________________^

error: function has missing stability attribute
  --> ../test.rs:23:1
   |
23 | pub fn main() {}
   | ^^^^^^^^^^^^^^^^

error: aborting due to 2 previous errors; 21 warnings emitted

Of the 21 internal gates, only the last 6 result in duplicate notes.

[matthiaskrgr]

These should be more, there's a file somewhere that defines all the features but I can't check it right now on mobile

[Noratrieb]

I think that should be all of them. This is super weird indeed, no idea

[gurry]

Thanks @matthiaskrgr & @Nilstrieb.

I found what's different about gates with duplicate notes: they all have an associated issue.

Here's the full list grepped from compiler/rustc_feature/src/active.rs:

(internal, allocator_internals, "1.20.0", None, None),
(internal, allow_internal_unsafe, "1.0.0", None, None),
(internal, allow_internal_unstable, "1.0.0", None, None),
(internal, compiler_builtins, "1.13.0", None, None),
(internal, custom_mir, "1.65.0", None, None),
(internal, intrinsics, "1.0.0", None, None),
(internal, lang_items, "1.0.0", None, None),
(internal, omit_gdb_pretty_printer_section, "1.5.0", None, None),
(internal, prelude_import, "1.2.0", None, None),
(internal, profiler_runtime, "1.18.0", None, None),
(internal, rustc_attrs, "1.0.0", None, None),
(internal, staged_api, "1.0.0", None, None),
(internal, test_2018_feature, "1.31.0", None, Some(Edition::Edition2018)),
(internal, test_unstable_lint, "1.60.0", None, None),
(internal, unsafe_pin_internals, "1.60.0", None, None),
(internal, link_llvm_intrinsics, "1.0.0", Some(29602), None),
(internal, needs_panic_runtime, "1.10.0", Some(32837), None),
(internal, panic_runtime, "1.10.0", Some(32837), None),
(internal, platform_intrinsics, "1.4.0", Some(27731), None),
(internal, rustc_allow_const_fn_unstable, "1.49.0", Some(69399), None),
(internal, rustdoc_internals, "1.58.0", Some(90418), None),

Notice that the second last field in the last 6 lines is Some unlike the rest where it is None. Apparently having an associated issue causes this problem.

[gurry]

The root cause is the note being passed on this line:

rust/compiler/rustc_lint/src/builtin.rs

Line 2276 in 2e7e0fb

BuiltinInternalFeatures { name, note },

Its value is Some(...) for gates that have an associated issue and None for others. Since BuiltinInternalFeatures already has a #[note] attribute:

rust/compiler/rustc_lint/src/lints.rs

Line 412 in 2e7e0fb

#[note]

this results in duplicates.

The solution is to always pass None for internal gates.