"error: module has missing stability attribute" is insufficiently explained

[jruderman]

Given the following code (playground):

#![feature(slice_from_ptr_range)]
#![feature(slice_ptr_get)]
#![feature(staged_api)]
#![feature(stmt_expr_attributes)]
#![feature(strict_provenance)]

fn foo() {}
fn bar() {}

The current output points to the entire file and doesn't tell me what I did wrong:

error: module has missing stability attribute
 --> src/lib.rs:1:1
  |
1 | / #![feature(slice_from_ptr_range)]
2 | | #![feature(slice_ptr_get)]
3 | | #![feature(staged_api)]
4 | | #![feature(stmt_expr_attributes)]
... |
7 | | fn foo() {}
8 | | fn bar() {}
  | |___________^

If I understand the feature correctly, the output should be:

error: expected at least one pub item in this module to be marked as stable or unstable
note: expected because of `#![feature(staged_api)]` on line 3

[fmease]

If I understand the feature correctly, the output should be: error: expected at least one pub item in this module to be marked as stable or unstable

No, with module has missing stability attribute the compiler means the current module (in this case the root module, the crate root). E.g. if you add #![stable(feature = "…", since = "…")] below or above the other inner attributes, the error will go away.

How is this used? For example, libtest is unconditionally unstable, libstd is stable unless restricted_std is enabled.

Not sure how the current error message could be improved since it is correct and relatively clear already.

[jruderman]

Well, it confused me! I had to binary-search to even figure out that #![feature(staged_api)] was the line triggering it.

[fmease]

Well, it confused me!

Can't argue against that. Admittedly, the massive span is a bit useless / misleading, even though it's technically correct.

I remember this used to be the same problem with E0601 (missing main function) which used to highlight the entire file. Nowadays, we shrink the span to an empty one in this case and add a label suggesting to add a function.

We could basically do the same for the staged_api case.

@rustbot claim

[fmease]

Any (uncaught) misuses of internal feature are considered to be the fault of the user and not a bug in rustc. I'm closing this as works as intended / not planned as per MCP 620.