This permits all coercions to be performed in casts, but adds lints to warn in those cases.
Part of this patch moves cast checking to a later stage of type checking. We acquire obligations to check casts as part of type checking where we previously checked them. Once we have type checked a function or module, then we check any cast obligations which have been acquired. That means we have more type information available to check casts (this was crucial to making coercions work properly in place of some casts), but it means that casts cannot feed input into type inference.
[breaking change]
* Adds two new lints for trivial casts and trivial numeric casts, these are warn by default, but can cause errors if you build with warnings as errors. Previously, trivial numeric casts and casts to trait objects were allowed.
* The unused casts lint has gone.
* Interactions between casting and type inference have changed in subtle ways. Two ways this might manifest are:
- You may need to 'direct' casts more with extra type information, for example, in some cases where `foo as _ as T` succeeded, you may now need to specify the type for `_`
- Casts do not influence inference of integer types. E.g., the following used to type check:
```
let x = 42;
let y = &x as *const u32;
```
Because the cast would inform inference that `x` must have type `u32`. This no longer applies and the compiler will fallback to `i32` for `x` and thus there will be a type error in the cast. The solution is to add more type information:
```
let x: u32 = 42;
let y = &x as *const u32;
```
This changes the type of some public constants/statics in libunicode.
Notably some `&'static &'static [(char, char)]` have changed
to `&'static [(char, char)]`. The regexp crate seems to be the
sole user of these, yet this is technically a [breaking-change]
Previously every auto-serialized tags are strongly typed. However
this is not strictly required, and instead it can be exploited
to provide the optimal encoding for smaller integers. This commit
repurposes `EsI8`/`EsU8` through `EsI64`/`EsU64` tags to represent
*any* integers with given ranges: It is now possible to encode
`42u64` as two bytes `EsU8 0x2a`, for example.
There are some limitations:
* It does not apply to non-auto-serialized tags for obvious reasons.
Fortunately, we have already eliminated the biggest source of
such tag in favor of auto-serialized tags: `tag_table_id`.
* Bigger tags cannot be used to represent smaller types.
* Signed tags and unsigned tags do not mix.
We try to move the data when the length can be encoded in
the much smaller number of bytes. This interferes with indices and
type abbreviations however, so this commit introduces a public
interface to get and mark a "stable" (i.e. not affected by
relaxation) position of the current pointer.
The relaxation logic only moves a small data, currently at most
256 bytes, as moving the data can be costly. There might be
further opportunities to allow more relaxation by moving fields
around, which I didn't seriously try.
They replace the existing `EsEnumVid`, `EsVecLen` and `EsMapLen`
tags altogether; the meaning of them can be easily inferred
from the enclosing tag. It also has an added benefit of
encodings for smaller variant ids or lengths being more compact
(5 bytes to 2 bytes).
For the reference, while it is designed to be selectively enabled,
it was essentially enabled throughout every snapshot and nightly
as far as I can tell. This makes the usefulness of `EsLabel` itself
questionable, as it was quite rare that `EsLabel` broke the build.
It had consumed about 20~30% of metadata (!) and so this should be
a huge win.
It doesn't serve any useful purpose. It *might* be useful when
there are some tags that are generated by `Encodable` and
not delimited by any tags, but IIUC it's not the case.
Previous:
<-------------------- len1 ------------------->
EsEnum <len1> EsEnumVid <vid> EsEnumBody <len2> <arg1> <arg2>
<--- len2 -->
Now:
<----------- len1 ---------->
EsEnum <len1> EsEnumVid <vid> <arg1> <arg2>
Many auto-serialization tags are fixed-size (note: many ordinary
tags are also fixed-size but for now this commit ignores them),
so having an explicit length is a waste. This moves any
auto-serialization tags with an implicit length before other tags,
so a test for them is easy. A preliminary experiment shows this
has at least 1% gain over the status quo.
EBML tags are encoded in a variable-length unsigned int (vuint),
which is clever but causes some tags to be encoded in two bytes
while there are really about 180 tags or so. Assuming that there
wouldn't be, say, over 1,000 tags in the future, we can use much
more efficient encoding scheme. The new scheme should support
at most 4,096 tags anyway.
This also flattens a scattered tag namespace (did you know that
0xa9 is followed by 0xb0?) and makes a room for autoserialized tags
in 0x00 through 0x1f.
This changes the type of some public constants/statics in libunicode.
Notably some `&'static &'static [(char, char)]` have changed
to `&'static [(char, char)]`. The regexp crate seems to be the
sole user of these, yet this is technically a [breaking-change]
This commit renames the features for the `std::old_io` and `std::old_path`
modules to `old_io` and `old_path` to help facilitate migration to the new APIs.
This is a breaking change as crates which mention the old feature names now need
to be renamed to use the new feature names.
[breaking-change]
There are a number of holes that the stability lint did not previously cover,
including:
* Types
* Bounds on type parameters on functions and impls
* Where clauses
* Imports
* Patterns (structs and enums)
These holes have all been fixed by overriding the `visit_path` function on the
AST visitor instead of a few specialized cases. This change also necessitated a
few stability changes:
* The `collections::fmt` module is now stable (it was already supposed to be).
* The `thread_local:👿:Key` type is now stable (it was already supposed to
be).
* The `std::rt::{begin_unwind, begin_unwind_fmt}` functions are now stable.
These are required via the `panic!` macro.
* The `std::old_io::stdio::{println, println_args}` functions are now stable.
These are required by the `print!` and `println!` macros.
* The `ops::{FnOnce, FnMut, Fn}` traits are now `#[stable]`. This is required to
make bounds with these traits stable. Note that manual implementations of
these traits are still gated by default, this stability only allows bounds
such as `F: FnOnce()`.
Additionally, the compiler now has special logic to ignore its own generated
`__test` module for the `--test` harness in terms of stability.
Closes#8962Closes#16360Closes#20327
[breaking-change]
In preparation for upcoming changes to the `Writer` trait (soon to be called
`Write`) this commit renames the current `write` method to `write_all` to match
the semantics of the upcoming `write_all` method. The `write` method will be
repurposed to return a `usize` indicating how much data was written which
differs from the current `write` semantics. In order to head off as much
unintended breakage as possible, the method is being deprecated now in favor of
a new name.
[breaking-change]
