Add more *-unwind ABI variants
The following *-unwind ABIs are now supported:
- "C-unwind"
- "cdecl-unwind"
- "stdcall-unwind"
- "fastcall-unwind"
- "vectorcall-unwind"
- "thiscall-unwind"
- "aapcs-unwind"
- "win64-unwind"
- "sysv64-unwind"
- "system-unwind"
cc `@rust-lang/wg-ffi-unwind`
Currently, it can be `None` if the conversion from `OsString` fails, in
which case all searches will skip over the `SearchPathFile`.
The commit changes things so that the `SearchPathFile` just doesn't get
created in the first place. Same behaviour, but slightly simpler code.
rustdoc: Pre-calculate traits that are in scope for doc links
This eliminates one more late use of resolver (part of #83761).
At early doc link resolution time we go through parent modules of items from the current crate, reexports of items from other crates, trait items, and impl items collected by `collect-intra-doc-links` pass, determine traits that are in scope in each such module, and put those traits into a map used by later rustdoc passes.
r? `@jyn514`
Store a `Symbol` instead of an `Ident` in `AssocItem`
This is the same idea as #92533, but for `AssocItem` instead
of `VariantDef`/`FieldDef`.
With this change, we no longer have any uses of
`#[stable_hasher(project(...))]`
`Decoder` has two impls:
- opaque: this impl is already partly infallible, i.e. in some places it
currently panics on failure (e.g. if the input is too short, or on a
bad `Result` discriminant), and in some places it returns an error
(e.g. on a bad `Option` discriminant). The number of places where
either happens is surprisingly small, just because the binary
representation has very little redundancy and a lot of input reading
can occur even on malformed data.
- json: this impl is fully fallible, but it's only used (a) for the
`.rlink` file production, and there's a `FIXME` comment suggesting it
should change to a binary format, and (b) in a few tests in
non-fundamental ways. Indeed #85993 is open to remove it entirely.
And the top-level places in the compiler that call into decoding just
abort on error anyway. So the fallibility is providing little value, and
getting rid of it leads to some non-trivial performance improvements.
Much of this commit is pretty boring and mechanical. Some notes about
a few interesting parts:
- The commit removes `Decoder::{Error,error}`.
- `InternIteratorElement::intern_with`: the impl for `T` now has the same
optimization for small counts that the impl for `Result<T, E>` has,
because it's now much hotter.
- Decodable impls for SmallVec, LinkedList, VecDeque now all use
`collect`, which is nice; the one for `Vec` uses unsafe code, because
that gave better perf on some benchmarks.
This is the same idea as #92533, but for `AssocItem` instead
of `VariantDef`/`FieldDef`.
With this change, we no longer have any uses of
`#[stable_hasher(project(...))]`
Implement raw-dylib support for windows-gnu
Add support for `#[link(kind = "raw-dylib")]` on windows-gnu targets. Work around binutils's linker's inability to read import libraries produced by LLVM by calling out to the binutils `dlltool` utility to create an import library from a temporary .DEF file; this approach is effectively a slightly refined version of `@mati865's` earlier attempt at this strategy in PR #88801. (In particular, this attempt at this strategy adds support for `#[link_ordinal(...)]` as well.)
In support of #58713.
Implement `#[rustc_must_implement_one_of]` attribute
This PR adds a new attribute — `#[rustc_must_implement_one_of]` that allows changing the "minimal complete definition" of a trait. It's similar to GHC's minimal `{-# MINIMAL #-}` pragma, though `#[rustc_must_implement_one_of]` is weaker atm.
Such attribute was long wanted. It can be, for example, used in `Read` trait to make transitions to recently added `read_buf` easier:
```rust
#[rustc_must_implement_one_of(read, read_buf)]
pub trait Read {
fn read(&mut self, buf: &mut [u8]) -> Result<usize> {
let mut buf = ReadBuf::new(buf);
self.read_buf(&mut buf)?;
Ok(buf.filled_len())
}
fn read_buf(&mut self, buf: &mut ReadBuf<'_>) -> Result<()> {
default_read_buf(|b| self.read(b), buf)
}
}
impl Read for Ty0 {}
//^ This will fail to compile even though all `Read` methods have default implementations
// Both of these will compile just fine
impl Read for Ty1 {
fn read(&mut self, buf: &mut [u8]) -> Result<usize> { /* ... */ }
}
impl Read for Ty2 {
fn read_buf(&mut self, buf: &mut ReadBuf<'_>) -> Result<()> { /* ... */ }
}
```
For now, this is implemented as an internal attribute to start experimenting on the design of this feature. In the future we may want to extend it:
- Allow arbitrary requirements like `a | (b & c)`
- Allow multiple requirements like
- ```rust
#[rustc_must_implement_one_of(a, b)]
#[rustc_must_implement_one_of(c, d)]
```
- Make it appear in rustdoc documentation
- Change the syntax?
- Etc
Eventually, we should make an RFC and make this (or rather similar) attribute public.
---
I'm fairly new to compiler development and not at all sure if the implementation makes sense, but at least it passes tests :)
rustc_metadata: Stop passing `CrateMetadataRef` by reference (step 1)
It's already a (fat) reference.
Double referencing it creates lifetime issues for its methods that want to return iterators.
---
Extracted from https://github.com/rust-lang/rust/pull/92245 for a perf run.
The PR changes a lot of symbol names due to function signature changes, so it's hard to do differential profiling, let's spend some machine time instead.
The field is also renamed from `ident` to `name. In most cases,
we don't actually need the `Span`. A new `ident` method is added
to `VariantDef` and `FieldDef`, which constructs the full `Ident`
using `tcx.def_ident_span()`. This method is used in the cases
where we actually need an `Ident`.
This makes incremental compilation properly track changes
to the `Span`, without all of the invalidations caused by storing
a `Span` directly via an `Ident`.
rustdoc: Introduce a resolver cache for sharing data between early doc link resolution and later passes
The refactoring parts of https://github.com/rust-lang/rust/pull/88679, shouldn't cause any slowdowns.
r? `@jyn514`
rustc_metadata: Optimize and document module children decoding
The first commit limits the item in the `item_children`/`each_child_of_item` query to modules (in name resolution sense) and adds a corresponding assertion.
The `associated_item_def_ids` query collecting children of traits and impls specifically now uses a simplified implementation not decoding unnecessary data instead of `each_child_of_item`, this gives a nice performance improvement.
The second commit does some renaming that clarifies the terminology used for all items in a module vs `use` items only.
By avoiding formatting and allocations in the no-ident case, and by making the span mandatory if the ident exists.
Use the optimized `opt_item_ident` to cleanup `fn each_child_of_item`
Stabilize -Z symbol-mangling-version=v0 as -C symbol-mangling-version=v0
This allows selecting `v0` symbol-mangling without an unstable option. Selecting `legacy` still requires -Z unstable-options.
This does not change the default symbol-mangling-version. See https://github.com/rust-lang/rust/pull/89917 for a pull request changing the default. Rationale, from #89917:
Rust's current mangling scheme depends on compiler internals; loses information about generic parameters (and other things) which makes for a worse experience when using external tools that need to interact with Rust symbol names; is inconsistent; and can contain . characters which aren't universally supported. Therefore, Rust has defined its own symbol mangling scheme which is defined in terms of the Rust language, not the compiler implementation; encodes information about generic parameters in a reversible way; has a consistent definition; and generates symbols that only use the characters A-Z, a-z, 0-9, and _.
Support for the new Rust symbol mangling scheme has been added to upstream tools that will need to interact with Rust symbols (e.g. debuggers).
This pull request allows enabling the new v0 symbol-mangling-version.
See #89917 for references to the implementation of v0, and for references to the tool changes to decode Rust symbols.
Remove effect of `#[no_link]` attribute on name resolution
Previously it hid all non-macro names from other crates.
This has no relation to linking and can change name resolution behavior in some cases (e.g. glob conflicts), in addition to just producing the "unresolved name" errors.
I can kind of understand the possible reasoning behind the current behavior - if you can use names from a `no_link` crates then you can use, for example, functions too, but whether it will actually work or produce link-time errors will depend on random factors like inliner behavior.
(^^^ This is not the actual reason why the current behavior exist, I've looked through git history and it's mostly accidental.)
I think this risk is ok for such an obscure attribute, and we don't need to specifically prevent use of non-macro items from such crates.
(I'm not actually sure why would anyone use `#[no_link]` on a crate, even if it's macro only, if you aware of any use cases, please share. IIRC, at some point it was used for crates implementing custom derives - the now removed legacy ones, not the current proc macros.)
Extracted from https://github.com/rust-lang/rust/pull/91795.
This allows selecting `v0` symbol-mangling without an unstable option.
Selecting `legacy` still requires -Z unstable-options.
Continue supporting -Z symbol-mangling-version for compatibility for
now, but show a deprecation warning for it.
Import `SourceFile`s from crate before decoding foreign `Span`
Fixes#92163Fixes#92014
When writing to the incremental cache, we encode all `Span`s
we encounter, regardless of whether or not their `SourceFile`
comes from the local crate, or from a foreign crate.
When we decode a `Span`, we use the `StableSourceFileId` we encoded
to locate the matching `SourceFile` in the current session. If this
id corresponds to a `SourceFile` from another crate, then we need to
have already imported that `SourceFile` into our current session.
This usually happens automatically during resolution / macro expansion,
when we try to resolve definitions from other crates. In certain cases,
however, we may try to load a `Span` from a transitive dependency
without having ever imported the `SourceFile`s from that crate, leading
to an ICE.
This PR fixes the issue by enconding the `SourceFile`'s `CrateNum`
when we encode a `Span`. During decoding, we call `imported_source_files()`
when we encounter a foreign `CrateNum`, which ensure that all
`SourceFile`s from that crate are imported into the current session.
rustc_metadata: Encode list of all crate's traits into metadata
While working on https://github.com/rust-lang/rust/pull/88679 I noticed that rustdoc is casually doing something quite expensive, something that is used only for error reporting in rustc - collecting all traits from all crates in the dependency tree.
This PR trades some minor extra time spent by metadata encoder in rustc for major gains for rustdoc (and for rustc runs with errors, which execute the `all_traits` query for better diagnostics).
rustc_metadata: Switch crate data iteration from a callback to iterator
The iteration looks more conventional this way, and some allocations are avoided.
rustc_metadata: Merge `get_ctor_def_id` and `get_ctor_kind`
Also avoid decoding the whole `ty::AssocItem` to get a `has_self` flag.
A small optimization and cleanup extracted from https://github.com/rust-lang/rust/pull/89059.
Fixes#92163Fixes#92014
When writing to the incremental cache, we encode all `Span`s
we encounter, regardless of whether or not their `SourceFile`
comes from the local crate, or from a foreign crate.
When we decode a `Span`, we use the `StableSourceFileId` we encoded
to locate the matching `SourceFile` in the current session. If this
id corresponds to a `SourceFile` from another crate, then we need to
have already imported that `SourceFile` into our current session.
This usually happens automatically during resolution / macro expansion,
when we try to resolve definitions from other crates. In certain cases,
however, we may try to load a `Span` from a transitive dependency
without having ever imported the `SourceFile`s from that crate, leading
to an ICE.
This PR fixes the issue by calling `imported_source_files()`
when we encounter a `SourceFile` with a foreign `CrateNum`.
This ensures that all `SourceFile`s from that crate are imported
into the current session.
Remove `SymbolStr`
This was originally proposed in https://github.com/rust-lang/rust/pull/74554#discussion_r466203544. As well as removing the icky `SymbolStr` type, it allows the removal of a lot of `&` and `*` occurrences.
Best reviewed one commit at a time.
r? `@oli-obk`
Previously it hid all non-macro names from other crates.
This has no relation to linking and can change name resolution behavior in some cases (e.g. glob conflicts), in addition to just producing the "unresolved name" errors
By changing `as_str()` to take `&self` instead of `self`, we can just
return `&str`. We're still lying about lifetimes, but it's a smaller lie
than before, where `SymbolStr` contained a (fake) `&'static str`!
replace dynamic library module with libloading
This PR deletes the `rustc_metadata::dynamic_lib` module in favor of the popular and better tested [`libloading` crate](https://github.com/nagisa/rust_libloading/).
We don't benefit from `libloading`'s symbol lifetimes since we end up leaking the loaded library in all cases, but the call-sites look much nicer by improving error handling and abstracting away some transmutes. We also can remove `rustc_metadata`'s direct dependencies on `libc` and `winapi`.
This PR also adds an exception for `libloading` (and its license) to tidy, so this will need sign-off from the compiler team.
Bump rmeta version to fix rustc_serialize ICE
#91407 changed the serialization format which leads to ICEs for nightly users such as #91663 and linked issues. The issue can be solved by running `cargo clean`. But bumping the metadata version should lead to the cached files being discarded, avoiding the issue entirely.
#91407 changed the serialization format which leads to ICEs for nightly users such as #91663 and linked issue.
Bumping the metadata version should lead to the cached files being discarded instead.
Record more artifact sizes during self-profiling.
This PR adds artifact size recording for
- "linked artifacts" (executables, RLIBs, dylibs, static libs)
- object files
- dwo files
- assembly files
- crate metadata
- LLVM bitcode files
- LLVM IR files
- codegen unit size estimates
Currently the identifiers emitted for these are hard-coded as string literals. Is it worth adding constants to https://github.com/rust-lang/measureme/blob/master/measureme/src/rustc.rs instead? We don't do that for query names and the like -- but artifact kinds might be more stable than query names.
Type inference for inline consts
Fixes#78132Fixes#78174Fixes#81857Fixes#89964
Perform type checking/inference of inline consts in the same context as the outer def, similar to what is currently done to closure.
Doing so would require `closure_base_def_id` of the inline const to return the outer def, and since `closure_base_def_id` can be called on non-local crate (and thus have no HIR available), a new `DefKind` is created for inline consts.
The type of the generated anon const can capture lifetime of outer def, so we couldn't just use the typeck result as the type of the inline const's def. Closure has a similar issue, and it uses extra type params `CK, CS, U` to capture closure kind, input/output signature and upvars. I use a similar approach for inline consts, letting it have an extra type param `R`, and then `typeof(InlineConst<[paremt generics], R>)` would just be `R`. In borrowck region requirements are also propagated to the outer MIR body just like it's currently done for closure.
With this PR, inline consts in expression position are quitely usable now; however the usage in pattern position is still incomplete -- since those does not remain in the MIR borrowck couldn't verify the lifetime there. I have left an ignored test as a FIXME.
Some disucssions can be found on [this Zulip thread](https://rust-lang.zulipchat.com/#narrow/stream/260443-project-const-generics/topic/inline.20consts.20typeck).
cc `````@spastorino````` `````@lcnr`````
r? `````@nikomatsakis`````
`````@rustbot````` label A-inference F-inline_const T-compiler
Improve error when an .rlib can't be parsed
This usually describes either an error in the compiler itself or some
sort of IO error. Either way, we should report it to the user rather
than just saying "crate not found".
This only gives an error if the crate couldn't be loaded at all - if the
compiler finds another .rlib or .rmeta file which was valid, it will
continue to compile the crate.
Example output:
```
error[E0785]: found invalid metadata files for crate `foo`
--> bar.rs:3:24
|
3 | println!("{}", foo::FOO_11_49[0]);
| ^^^
|
= warning: failed to parse rlib '/home/joshua/test-rustdoc/libfoo.rlib': Invalid archive extended name offset
```
cc `@ehuss`
This usually describes either an error in the compiler itself or some
sort of IO error. Either way, we should report it to the user rather
than just saying "crate not found".
This only gives an error if the crate couldn't be loaded at all - if the
compiler finds another .rlib or .rmeta file which was valid, it will
continue to compile the crate.
Example output:
```
error[E0785]: found invalid metadata files for crate `foo`
--> bar.rs:3:24
|
3 | println!("{}", foo::FOO_11_49[0]);
| ^^^
|
= warning: failed to parse rlib '/home/joshua/test-rustdoc/libfoo.rlib': Invalid archive extended name offset
```
TraitKind -> Trait
TyAliasKind -> TyAlias
ImplKind -> Impl
FnKind -> Fn
All `*Kind`s in AST are supposed to be enums.
Tuple structs are converted to braced structs for the types above, and fields are reordered in syntactic order.
Also, mutable AST visitor now correctly visit spans in defaultness, unsafety, impl polarity and constness.
Improve and test cross-crate hygiene
- Decode the parent expansion for traits and enums in `rustc_resolve`, this was already being used for resolution in typeck
- Avoid suggesting importing names with def-site hygiene, since it's often not useful
- Add more tests
r? `@petrochenkov`
Adopt let_else across the compiler
This performs a substitution of code following the pattern:
```
let <id> = if let <pat> = ... { identity } else { ... : ! };
```
To simplify it to:
```
let <pat> = ... { identity } else { ... : ! };
```
By adopting the `let_else` feature (cc #87335).
The PR also updates the syn crate because the currently used version of the crate doesn't support `let_else` syntax yet.
Note: Generally I'm the person who *removes* usages of unstable features from the compiler, not adds more usages of them, but in this instance I think it hopefully helps the feature get stabilized sooner and in a better state. I have written a [comment](https://github.com/rust-lang/rust/issues/87335#issuecomment-944846205) on the tracking issue about my experience and what I feel could be improved before stabilization of `let_else`.
polymorphization: shims and predicates
Supersedes #75737 and #75414. This pull request includes up some changes to polymorphization which hadn't landed previously and gets stage2 bootstrapping and the test suite passing when polymorphization is enabled. There are still issues with `type_id` and polymorphization to investigate but this should get polymorphization in a reasonable state to work on.
- #75737 and #75414 both worked but were blocked on having the rest of the test suite pass (with polymorphization enabled) with and without the PRs. It makes more sense to just land these so that the changes are in.
- #75737's changes remove the restriction of `InstanceDef::Item` on polymorphization, so that shims can now be polymorphized. This won't have much of an effect until polymorphization's analysis is more advanced, but it doesn't hurt.
- #75414's changes remove all logic which marks parameters as used based on their presence in predicates - given #75675, this will enable more polymorphization and avoid the symbol clashes that predicate logic previously sidestepped.
- Polymorphization now explicitly checks (and skips) foreign items, this is necessary for stage2 bootstrapping to work when polymorphization is enabled.
- The conditional determining the emission of a note adding context to a post-monomorphization error has been modified. Polymorphization results in `optimized_mir` running for shims during collection where that wouldn't happen previously, some errors are emitted during `optimized_mir` and these were considered post-monomorphization errors with the existing logic (more errors and shims have a `DefId` coming from the std crate, not the local crate), adding a note that resulted in tests failing. It isn't particularly feasible to change where polymorphization runs or prevent it from using `optimized_mir`, so it seemed more reasonable to not change the conditional.
- `characteristic_def_id_of_type` was being invoked during partitioning for self types of impl blocks which had projections that depended on the value of unused generic parameters of a function - this caused a ICE in a debuginfo test. If partitioning is enabled and the instance needs substitution then this is skipped. That test still fails for me locally, but not with an ICE, but it fails in a fresh checkout too, so 🤷♂️.
r? `@lcnr`
This performs a substitution of code following the pattern:
let <id> = if let <pat> = ... { identity } else { ... : ! };
To simplify it to:
let <pat> = ... { identity } else { ... : ! };
By adopting the let_else feature.
Only dylib and rlib candidates were included in the error. I think the
reason is that at the time this error was originally implemented, rmeta
crate sources were represented different from dylib and rlib sources.
I wrote up more detailed analysis in [this comment][1].
The new version of the code is also a bit easier to read and should be
more robust to future changes since it uses `CrateSources::paths()`.
[1]: https://github.com/rust-lang/rust/pull/88675#issuecomment-935282436
Correct decoding of foreign expansions during incr. comp.
Fixes https://github.com/rust-lang/rust/issues/74946
The original issue was due to a wrong assertion in `expn_hash_to_expn_id`.
The secondary issue was due to a mismatch between the encoding and decoding paths for expansions that are created after the TyCtxt is created.
Implement `#[link_ordinal(n)]`
Allows the use of `#[link_ordinal(n)]` with `#[link(kind = "raw-dylib")]`, allowing Rust to link against DLLs that export symbols by ordinal rather than by name. As long as the ordinal matches, the name of the function in Rust is not required to match the name of the corresponding function in the exporting DLL.
Part of #58713.
Make an initial guess for metadata size to reduce buffer resizes
When reading metadata, the compiler starts with a `Vec::new()`, which will need to grow repeatedly as the metadata gets decompressed into it. Reduce the number of resizes by starting out at the size of the compressed data.
Rework HIR API to make invocations of the hir_crate query harder.
`hir_crate` forces the recomputation of queries that depend on it.
This PR aims at avoiding useless invocations of `hir_crate` by making dependent code go through `tcx.hir()`.
This commit removes the restriction of `InstanceDef::Item` on
polymorphization, so that shims can now be polymorphized.
Signed-off-by: David Wood <david.wood@huawei.com>
fix non_blanket_impls iteration order
We sometimes iterate over all `non_blanket_impls`, not sure if this is observable outside
of error messages (i.e. as incremental bugs). This should fix the underlying issue of #86986.
second attempt of #88718
r? `@nikomatsakis`
Migrate in-tree crates to 2021
This replaces #89075 (cherry picking some of the commits from there), and closes#88637 and fixes#89074.
It excludes a migration of the library crates for now (see tidy diff) because we have some pending bugs around macro spans to fix there.
I instrumented bootstrap during the migration to make sure all crates moved from 2018 to 2021 had the compatibility warnings applied first.
Originally, the intent was to support cargo fix --edition within bootstrap, but this proved fairly difficult to pull off. We'd need to architect the check functionality to support running cargo check and cargo fix within the same x.py invocation, and only resetting sysroots on check. Further, it was found that cargo fix doesn't behave too well with "not quite workspaces", such as Clippy which has several crates. Bootstrap runs with --manifest-path ... for all the tools, and this makes cargo fix only attempt migration for that crate. We can't use e.g. --workspace due to needing to maintain sysroots for different phases of compilation appropriately.
It is recommended to skip the mass migration of Cargo.toml's to 2021 for review purposes; you can also use `git diff d6cd2c6c87 -I'^edition = .20...$'` to ignore the edition = 2018/21 lines in the diff.
This also adjusts the lint docs generation to accept (and ignore) an allow
attribute, rather than expecting the documentation to be immediately followed by
the lint name.
This encoding allows for random access without an expensive upfront decoding
state which in turn allows simplifying the DefPathIndex lookup logic without
regressing performance.
Add -Z panic-in-drop={unwind,abort} command-line option
This PR changes `Drop` to abort if an unwinding panic attempts to escape it, making the process abort instead. This has several benefits:
- The current behavior when unwinding out of `Drop` is very unintuitive and easy to miss: unwinding continues, but the remaining drops in scope are simply leaked.
- A lot of unsafe code doesn't expect drops to unwind, which can lead to unsoundness:
- https://github.com/servo/rust-smallvec/issues/14
- https://github.com/bluss/arrayvec/issues/3
- There is a code size and compilation time cost to this: LLVM needs to generate extra landing pads out of all calls in a drop implementation. This can compound when functions are inlined since unwinding will then continue on to process drops in the callee, which can itself unwind, etc.
- Initial measurements show a 3% size reduction and up to 10% compilation time reduction on some crates (`syn`).
One thing to note about `-Z panic-in-drop=abort` is that *all* crates must be built with this option for it to be sound since it makes the compiler assume that dropping `Box<dyn Any>` will never unwind.
cc https://github.com/rust-lang/lang-team/issues/97
generic_const_exprs: use thir for abstract consts instead of mir
Changes `AbstractConst` building to use `thir` instead of `mir` so that there's less chance of consts unifying when they shouldn't because lowering to mir dropped information (see `abstract-consts-as-cast-5.rs` test)
r? `@lcnr`
Encode spans relative to the enclosing item
The aim of this PR is to avoid recomputing queries when code is moved without modification.
MCP at https://github.com/rust-lang/compiler-team/issues/443
This is achieved by :
1. storing the HIR owner LocalDefId information inside the span;
2. encoding and decoding spans relative to the enclosing item in the incremental on-disk cache;
3. marking a dependency to the `source_span(LocalDefId)` query when we translate a span from the short (`Span`) representation to its explicit (`SpanData`) representation.
Since all client code uses `Span`, step 3 ensures that all manipulations
of span byte positions actually create the dependency edge between
the caller and the `source_span(LocalDefId)`.
This query return the actual absolute span of the parent item.
As a consequence, any source code motion that changes the absolute byte position of a node will either:
- modify the distance to the parent's beginning, so change the relative span's hash;
- dirty `source_span`, and trigger the incremental recomputation of all code that
depends on the span's absolute byte position.
With this scheme, I believe the dependency tracking to be accurate.
For the moment, the spans are marked during lowering.
I'd rather do this during def-collection,
but the AST MutVisitor is not practical enough just yet.
The only difference is that we attach macro-expanded spans
to their expansion point instead of the macro itself.
CrateLocator refactorings
This makes the `CrateLocator` a lot cleaner IMHO and much more self-contained. The last commit removes `extra_filename` from the crate metadata. This is an **insta-stable** change as it allows a crate like `libfoo-abc.rlib` to be used as dependency and then be renamed as `libfoo-bcd.rlib` while still being found as indirect dependency. This may reduce performance when there are a lot of versions of the same crate available as the extra filename won't be used to do an early rejection of crates before trying to load metadata, but it makes the logic to find the right filename a lot cleaner.
