Replace - with _ in fluent slugs to improve developer workflows
This is a proposal to smoothen the compiler contribution experience in the face of the move to fluent.
## Context
The fluent project has introduced a layer of abstraction to compiler errors. Previously, people would write down error messages directly in the same file the code was located to emit them. Now, there is a slug that connects the code in the compiler to the error message in the ftl file.
You can look at 7ef610c003 to see an example of the changes:
Old:
```Rust
let msg = format!(
"bounds on `{}` are most likely incorrect, consider instead \
using `{}` to detect whether a type can be trivially dropped",
predicate,
cx.tcx.def_path_str(needs_drop)
);
lint.build(&msg).emit();
```
New (Rust side):
```Rust
lint.build(fluent::lint::drop_trait_constraints)
.set_arg("predicate", predicate)
.set_arg("needs_drop", cx.tcx.def_path_str(needs_drop))
.emit();
```
New (Fluent side):
```fluent
lint-drop-trait-constraints =
bounds on `{$predicate}` are most likely incorrect, consider instead using `{$needs_drop}` to detect whether a type can be trivially dropped
```
You will note that in the ftl file, the slug is slightly different from the slug in the Rust file: The ftl slug uses `-` (e.g. `lint-drop-trait-constraints`) while the rust slug uses `::` and `_` (e.g. `lint::drop_trait_constraints`). This choice was probably done due to:
* Rust not accepting `-` in identifiers (as it is an operator)
* fluent not supporting the `:` character in slug names (parse error upon attempts)
* all official fluent documentation using `-` instead of `_`
## The problem
The two different types of slugs, one with `-`, and one with `_`, cause difficulties for contributors. Imagine you don't have perfect knowledge of where stuff is in the compiler (i would say this is most people), and you encounter an error for which you think there is something you could improve that is not just a rewording.
So you want to find out where in the compiler's code that error is being emitted. The best way is via grepping.
1. you grep for the message in the compiler's source code. You discover the ftl file and find out the slug for that error.
2. That slug however contains `-` instead of `_`, so you have to manually translate the `-`'s into `_`s, and furthermore either remove the leading module name, or replace the first `-` with a `::`.
3. you do a second grep to get to the emitting location in the compiler's code.
This translation difficulty in step 2 appears also in the other direction when you want to figure out what some code in the compiler is doing and use error messages to help your understanding. Comments and variable names are way less exposed to users so [are more likely going to lie](cc3c5d2700) than error messages.
I think that at least the `-`→`_` translation which makes up most of step 2 can be removed at low cost.
## The solution
If you look closely, the practice of fluent to use `-` is only a stylistic choice and it is not enforced by fluent implementations, neither the playground nor the one the rust compiler uses, that slugs may not contain `_`. Thus, we can in fact migrate the ftl side to `_`. So now we'll have slugs like `lint_drop_trait_constraints` on the ftl side. You only have to do one replacement now to get to the Rust slug: remove the first `_` and place a `::` in its stead. I would argue that this change is in fact useful as it allows you to control whether you want to look at the rust side of things or the ftl side of things via changing the query string only: with an increased number of translations checked into the repository, grepping for raw slugs will return the slug in many ftl files, so an explicit step to look for the source code is always useful. In the other direction (rust to fluent), you don't need a translation at all any more, as you can just take the final piece of the slug (e.g. `drop_trait_constraints`) and grep for that. The PR also adds enforcement to forbid usage of `_` in slug names. Internal slug names (those leading with a `-`) are exempt from that enforcement.
As another workflow that benefits from this change, people who add new errors don't have to do that `-` conversion either.
| Before/After | Fluent slug | Rust slug (no change) |
|--|--|--|
| Before | `lint-drop-trait-constraints` | `lint::drop_trait_constraints`|
| After | `lint_drop_trait_constraints` | `lint::drop_trait_constraints`|
Note that I've suggested this previously in the translation thread on zulip. I think it's important to think about non-translator contribution impact of fluent. I have certainly plans for more improvements, but this is a good first step.
``@rustbot`` label A-diagnostics
Having to replace - with _ (and vice versa) makes the slugs less greppable
and thus constitutes a contributor roadblock.
Result of running this repeatedly up until reaching a fixpoint:
find compiler/rustc_error_messages/locales/en-US/ -type f -exec sed -i 's/\(.+\)-\(.*\)=/\1_\2=/' {} \;
Plus some fixes to update usages of slugs leading with -.
Some command-line options accessible through `sess.opts` are best
accessed through wrapper functions on `Session`, `TyCtxt` or otherwise,
rather than through field access on the option struct in the `Session`.
Adds a new lint which triggers on those options that should be accessed
through a wrapper function so that this is prohibited. Options are
annotated with a new attribute `rustc_lint_opt_deny_field_access` which
can specify the error message (i.e. "use this other function instead")
to be emitted.
A simpler alternative would be to simply rename the options in the
option type so that it is clear they should not be used, however this
doesn't prevent uses, just discourages them. Another alternative would
be to make the option fields private, and adding accessor functions on
the option types, however the wrapper functions sometimes rely on
additional state from `Session` or `TyCtxt` which wouldn't be available
in an function on the option type, so the accessor would simply make the
field available and its use would be discouraged too.
Signed-off-by: David Wood <david.wood@huawei.com>
Improve the function pointer docs
This is #97842 but for function pointers instead of tuples. The concept is basically the same.
* Reduce duplicate impls; show `fn (T₁, T₂, …, Tₙ)` and include a sentence saying that there exists up to twelve of them.
* Show `Copy` and `Clone`.
* Show auto traits like `Send` and `Sync`, and blanket impls like `Any`.
https://notriddle.com/notriddle-rustdoc-test/std/primitive.fn.html
Apply the `#[rustc_lint_diagnostics]` attribute to
`LintDiagnosticBuilder::build` so that diagnostic migration lints will
trigger for it.
Signed-off-by: David Wood <david.wood@huawei.com>
