coverage: Remove all unstable support for MC/DC instrumentation
Preliminary support for a partial implementation of “Modified Condition/Decision Coverage” instrumentation was added behind the unstable flag `-Zcoverage-options=mcdc` in 2024. These are the most substantial PRs involved:
- rust-lang/rust#123409
- rust-lang/rust#126733
At the time, I accepted these PRs with relatively modest scrutiny, because I did not want to stand in the way of independent work on MC/DC instrumentation. My hope was that ongoing work by interested contributors would lead to the code becoming clearer and more maintainable over time.
---
However, that MC/DC code has proven itself to be a major burden on overall maintenance of coverage instrumentation, and a major obstacle to other planned improvements, such as internal changes needed for proper support of macro expansion regions.
I have also become reluctant to accept any further MC/DC-related changes that would increase this burden.
That tension has resulted in an unhappy impasse. On one hand, the present MC/DC implementation is not yet complete, and shows little sign of being complete at an acceptable level of code quality in the foreseeable future. On the other hand, the continued existence of this partial MC/DC implementation is imposing serious maintenance burdens on every other aspect of coverage instrumentation, and is preventing some of the very improvements that would make it easier to accept expanded MC/DC support in the future.
While I know this will be disappointing to some, I think the healthy way forward is accept that I made the wrong call in accepting the current implementation, and to remove it entirely from the compiler.
Add support for `ty::Instance` path shortening in diagnostics
Make `ty::Instance` able to use `short_string` and usable in structured errors directly. Remove some ad-hoc type shortening logic.
Simplify dead code lint
This PR scratches a few itches I had when looking at that code.
The perf improvement comes from keeping the `scanned` set through several marking phases. This pretty much divides by 2 the number of HIR traversals.
`Printer` cleanups
The trait `Printer` is implemented by six types, and the sub-trait `PrettyPrinter` is implemented by three of those types. The traits and the impls are complex and a bit of a mess. This PR starts to clean them up.
r? ``@davidtwco``
Return a struct with named fields from `hash_owner_nodes`
While looking through this code for other reasons, I noticed a nice opportunity to return a struct with named fields instead of a tuple. The first patch also introduces an early-return to flatten the rest of `hash_owner_nodes`.
There are further changes that could potentially be made here (renaming things, `Option<Hashes>` instead of optional fields), but I'm not deeply familiar with this code so I didn't want to disturb the calling code too much.
It's a cryptic macro that makes some things slightly more concise in
`PrettyPrinter`. E.g. if you declare `define_scope_printer!(p)` in a
scope you can then call `p! to get these transformations:
```
p!("foo"); --> write!(p, "foo")?;
p!(print(ty)); --> ty.print(p)?;
p!(method(args)); --> p.method(args)?;
```
You can also chain calls, e.g.:
```
p!("foo", print(ty)); --> write!(p, "foo")?; ty.print(p)?;
```
Ultimately this doesn't seem worth it. The macro definition is hard to
read, the call sites are hard to read, `define_scope_printer!` is pretty
gross, and the code size reductions are small. Tellingly, many normal
`write!` and `print` calls are sprinkled throughout the code, probably
because people have made modifications and didn't want to use or
understand how to use `p!`.
This commit removes it.
Currently they are mostly named `cx`, which is a terrible name for a
type that impls `Printer`/`PrettyPrinter`, and is easy to confuse with
other types like `TyCtxt`. This commit changes them to `p`. A couple of
existing `p` variables had to be renamed to make way.
Improve formatting of doc code blocks
We don't currently apply automatic formatting to doc comment code blocks. As a
result, it has built up various idiosyncracies, which make such automatic
formatting difficult. Some of those idiosyncracies also make things harder for
human readers or other tools.
This PR makes a few improvements to doc code formatting, in the hopes of making
future automatic formatting easier, as well as in many cases providing net
readability improvements.
I would suggest reading each commit separately, as each commit contains one
class of changes.
Remove the witness type from coroutine *args* (without actually removing the type)
This does as much of rust-lang/rust#144157 as we can without having to break rust-lang/rust#143545 and/or introduce some better way of handling higher ranked assumptions.
Namely, it:
* Stalls coroutines based off of the *coroutine* type rather than the witness type.
* Reworks the dtorck constraint hack to not rely on the witness type.
* Removes the witness type from the args of the coroutine, eagerly creating the type for nested obligations when needed (auto/clone impls).
I'll experiment with actually removing the witness type in a follow-up.
r? lcnr
Deduplicate `IntTy`/`UintTy`/`FloatTy`.
There are identical definitions in `rustc_type_ir` and `rustc_ast`. This commit removes them and places a single definition in `rustc_ast_ir`. This requires adding `rust_span` as a dependency of `rustc_ast_ir`, but means a bunch of silly conversion functions can be removed.
r? `@fmease`
There are identical definitions in `rustc_type_ir` and `rustc_ast`. This
commit removes them and places a single definition in `rustc_ast_ir`.
This requires adding `rust_span` as a dependency of `rustc_ast_ir`, but
means a bunch of silly conversion functions can be removed.
The one annoying wrinkle is that the old version had differences in
their `Debug` impls, e.g. one printed `u32` while the other printed
`U32`. Some compiler error messages rely on the former (yuk), and some
clippy output depends on the latter. So the commit also changes clippy
to not rely on `Debug` and just implement what it needs itself.
Currently there is `Ty` and `BoundTy`, and `Region` and `BoundRegion`,
and `Const` and... `BoundVar`. An annoying inconsistency.
This commit repurposes the existing `BoundConst`, which was barely used,
so it's the partner to `Const`. Unlike `BoundTy`/`BoundRegion` it lacks
a `kind` field but it's still nice to have because it makes the const
code more similar to the ty/region code everywhere.
The commit also removes `impl From<BoundVar> for BoundTy`, which has a
single use and doesn't seem worth it.
These changes fix the "FIXME: We really should have a separate
`BoundConst` for consts".
Type folders can only modify a few "types of interest": `Binder`, `Ty`,
`Predicate`, `Clauses`, `Region`, `Const`. Likewise for type visitors,
but they can also visit errors (via `ErrorGuaranteed`).
Currently the impls of `try_super_fold_with`, `super_fold_with`, and
`super_visit_with` do more than they need to -- they fold/visit values
that cannot contain any types of interest.
This commit removes those unnecessary fold/visit operations, which makes
these impls more similar to the impls for `Ty`. It also removes the
now-unnecessary derived impls for the no-longer-visited types.
Rollup of 3 pull requests
Successful merges:
- rust-lang/rust#144657 (fix: Only "close the window" when its the last annotated file)
- rust-lang/rust#144665 (Re-block SRoA on SIMD types)
- rust-lang/rust#144713 (`rustc_middle::ty` cleanups)
r? `@ghost`
`@rustbot` modify labels: rollup
Stuart Cook