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[AVR] Changed data_layout
This change is required when
https://github.com/llvm/llvm-project/commit/97f0ff0c80407adee693436b44e55ededfcd5435
gets included in the Rust llvm tree, because it changes the AVR data-layout
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Handle macros with multiple kinds, and improve errors
(I recommend reviewing this commit-by-commit.)
Switch to a bitflags `MacroKinds` to support macros with more than one kind
Review everything that uses `MacroKind`, and switch anything that could refer to more than one kind to use `MacroKinds`.
Add a new `SyntaxExtensionKind::MacroRules` for `macro_rules!` macros, using the concrete `MacroRulesMacroExpander` type, and have it track which kinds it can handle. Eliminate the separate optional `attr_ext`, now that a `SyntaxExtension` can handle multiple macro kinds.
This also avoids the need to downcast when calling methods on `MacroRulesMacroExpander`, such as `get_unused_rule`.
Integrate macro kind checking into name resolution's `sub_namespace_match`, so that we only find a macro if it's the right type, and eliminate the special-case hack for attributes.
This allows detecting and report macro kind mismatches early, and more precisely, improving various error messages. In particular, this eliminates the case in `failed_to_match_macro` to check for a function-like invocation of a macro with no function-like rules.
Instead, macro kind mismatches now result in an unresolved macro, and we detect this case in `unresolved_macro_suggestions`, which now carefully distinguishes between a kind mismatch and other errors.
This also handles cases of forward-referenced attributes and cyclic attributes.
----
In this PR, I've minimally fixed up `rustdoc` so that it compiles and passes tests. This is just the minimal necessary fixes to handle the switch to `MacroKinds`, and it only works for macros that don't actually have multiple kinds. This will panic (with a `todo!`) if it encounters a macro with multiple kinds.
rustdoc needs further fixes to handle macros with multiple kinds, and to handle attributes and derive macros that aren't proc macros. I'd appreciate some help from a rustdoc expert on that.
----
r? ````````@petrochenkov````````
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r=davidtwco
Add aarch64_be-unknown-none-softfloat target
This adds a new target for bare-metal big endian ARM64 without FPU. We want to use this in [the Hermit unikernel](https://github.com/hermit-os/kernel) because big endian ARM64 is the most accessible big endian architecture for us and it can be supported with our existing aarch64 code. I have compiled our kernel and bootloader with this target and they work as expected in QEMU.
Regarding the [tier 3 target policy](https://doc.rust-lang.org/rustc/target-tier-policy.html#tier-3-target-policy):
> - A tier 3 target must have a designated developer or developers (the "target maintainers") on record to be CCed when issues arise regarding the target. (The mechanism to track and CC such developers may evolve over time.)
The maintainer(s) (currently just me) are listed in the markdown document that documents the target.
> - Targets must use naming consistent with any existing targets; for instance, a target for the same CPU or OS as an existing Rust target should use the same name for that CPU or OS. Targets should normally use the same names and naming conventions as used elsewhere in the broader ecosystem beyond Rust (such as in other toolchains), unless they have a very good reason to diverge. Changing the name of a target can be highly disruptive, especially once the target reaches a higher tier, so getting the name right is important even for a tier 3 target.
> - Target names should not introduce undue confusion or ambiguity unless absolutely necessary to maintain ecosystem compatibility. For example, if the name of the target makes people extremely likely to form incorrect beliefs about what it targets, the name should be changed or augmented to disambiguate it.
> - If possible, use only letters, numbers, dashes and underscores for the name. Periods (.) are known to cause issues in Cargo.
The target name is consistent with the existing `aarch64-unknown-none-softfloat` target and the existing big endian aarch64 targets like `aarch64_be-unknown-linux-gnu`.
> - Tier 3 targets may have unusual requirements to build or use, but must not create legal issues or impose onerous legal terms for the Rust project or for Rust developers or users.
> - The target must not introduce license incompatibilities.
> - Anything added to the Rust repository must be under the standard Rust license (MIT OR Apache-2.0).
> - The target must not cause the Rust tools or libraries built for any other host (even when supporting cross-compilation to the target) to depend on any new dependency less permissive than the Rust licensing policy. This applies whether the dependency is a Rust crate that would require adding new license exceptions (as specified by the tidy tool in the rust-lang/rust repository), or whether the dependency is a native library or binary. In other words, the introduction of the target must not cause a user installing or running a version of Rust or the Rust tools to be subject to any new license requirements.
> - Compiling, linking, and emitting functional binaries, libraries, or other code for the target (whether hosted on the target itself or cross-compiling from another target) must not depend on proprietary (non-FOSS) libraries. Host tools built for the target itself may depend on the ordinary runtime libraries supplied by the platform and commonly used by other applications built for the target, but those libraries must not be required for code generation for the target; cross-compilation to the target must not require such libraries at all. For instance, rustc built for the target may depend on a common proprietary C runtime library or console output library, but must not depend on a proprietary code generation library or code optimization library. Rust's license permits such combinations, but the Rust project has no interest in maintaining such combinations within the scope of Rust itself, even at tier 3.
> - "onerous" here is an intentionally subjective term. At a minimum, "onerous" legal/licensing terms include but are not limited to: non-disclosure requirements, non-compete requirements, contributor license agreements (CLAs) or equivalent, "non-commercial"/"research-only"/etc terms, requirements conditional on the employer or employment of any particular Rust developers, revocable terms, any requirements that create liability for the Rust project or its developers or users, or any requirements that adversely affect the livelihood or prospects of the Rust project or its developers or users.
There are no licensing issues and any toolchain that can compile for `aarch64-unknown-none-softfloat` can also compile for `aarch64_be-unknown-none-softfloat` (well, at least GCC and LLVM). No proprietary components are required.
> - Neither this policy nor any decisions made regarding targets shall create any binding agreement or estoppel by any party. If any member of an approving Rust team serves as one of the maintainers of a target, or has any legal or employment requirement (explicit or implicit) that might affect their decisions regarding a target, they must recuse themselves from any approval decisions regarding the target's tier status, though they may otherwise participate in discussions.
> - This requirement does not prevent part or all of this policy from being cited in an explicit contract or work agreement (e.g. to implement or maintain support for a target). This requirement exists to ensure that a developer or team responsible for reviewing and approving a target does not face any legal threats or obligations that would prevent them from freely exercising their judgment in such approval, even if such judgment involves subjective matters or goes beyond the letter of these requirements.
Ack.
> - Tier 3 targets should attempt to implement as much of the standard libraries as possible and appropriate (core for most targets, alloc for targets that can support dynamic memory allocation, std for targets with an operating system or equivalent layer of system-provided functionality), but may leave some code unimplemented (either unavailable or stubbed out as appropriate), whether because the target makes it impossible to implement or challenging to implement. The authors of pull requests are not obligated to avoid calling any portions of the standard library on the basis of a tier 3 target not implementing those portions.
This target does not implement std and is equivalent to `aarch64-unknown-none-softfloat` in all these regards.
> - The target must provide documentation for the Rust community explaining how to build for the target, using cross-compilation if possible. If the target supports running binaries, or running tests (even if they do not pass), the documentation must explain how to run such binaries or tests for the target, using emulation if possible or dedicated hardware if necessary.
Ack, that is part of the markdown document.
> - Tier 3 targets must not impose burden on the authors of pull requests, or other developers in the community, to maintain the target. In particular, do not post comments (automated or manual) on a PR that derail or suggest a block on the PR based on a tier 3 target. Do not send automated messages or notifications (via any medium, including via ```@)``` to a PR author or others involved with a PR regarding a tier 3 target, unless they have opted into such messages.
> - Backlinks such as those generated by the issue/PR tracker when linking to an issue or PR are not considered a violation of this policy, within reason. However, such messages (even on a separate repository) must not generate notifications to anyone involved with a PR who has not requested such notifications.
Ack.
> - Patches adding or updating tier 3 targets must not break any existing tier 2 or tier 1 target, and must not knowingly break another tier 3 target without approval of either the compiler team or the maintainers of the other tier 3 target.
> - In particular, this may come up when working on closely related targets, such as variations of the same architecture with different features. Avoid introducing unconditional uses of features that another variation of the target may not have; use conditional compilation or runtime detection, as appropriate, to let each target run code supported by that target.
This doesn't break any existing targets.
> - Tier 3 targets must be able to produce assembly using at least one of rustc's supported backends from any host target. (Having support in a fork of the backend is not sufficient, it must be upstream.)
The LLVM backend works.
> - If a tier 3 target stops meeting these requirements, or the target maintainers no longer have interest or time, or the target shows no signs of activity and has not built for some time, or removing the target would improve the quality of the Rust codebase, we may post a PR to remove it; any such PR will be CCed to the target maintainers (and potentially other people who have previously worked on the target), to check potential interest in improving the situation.
Ack.
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search graph: lazily update parent goals
Based on top of rust-lang/rust#143054. In the search graph only the last entry is actually mutable and all other entries get lazily mutated when popping child goals.
This simplifies a bunch of possible future optimizations:
- We can try evaluating nested goals and entirely ignore discard their evaluation by simply not calling `fn update_parent_goal`
- Because we only lazily update, tracking the "impact" of a nested goal is easy. The necessary information *has to be* integrated in the `StackEntry` of the current goal, as there is otherwise no way to influence its parents. This makes it easier to avoid rerunning cycle heads if they have only been used in candidates which don't impact the final result of a goal.
r? `````````@compiler-errors````````` `````````@BoxyUwU`````````
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More `Printer` cleanups
A sequel to rust-lang/rust#144776.
r? ```@davidtwco```
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aarch64: Make `outline-atomics` a known target feature
This is a feature used by LLVM that is enabled for our `aarch64-linux` targets, which we would like to configure on in `std`. Thus, mark `outline-atomics` a known feature. It is left unstable for now.
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Fix parallel rustc not being reproducible due to unstable sorts of items
Currently, A tuple `(DefId, SymbolName)` is used to determine the order of items in the final binary. However `DefId` is expected as non-deterministic, which leads to some not reproducible issues under parallel compilation. (See https://github.com/rust-lang/rust/issues/140425#issuecomment-3111802148)
Theoretically, we don't need the sorting because the order of these items is already deterministic.
However, codegen tests reply on the same order of items between in binary and source.
So here we added a new option `codegen-source-order` to indicate whether sorting based on the order in source. For codegen tests, items are sorted according to the order in the source code, whereas in the normal path, no sorting is performed.
Specially, for codegen tests, in preparation for parallel compilation potentially being enabled by default in the future, we use `Span` replacing `DefId` to make the order deterministic.
This PR is purposed to fix rust-lang/rust#140425, but seemly works on rust-lang/rust#140413 too.
This behavior hasn't added into any test until we have a test suit for the parallel frontend. (See https://github.com/rust-lang/rust/pull/143953)
Related discussion: [Zulip](https://rust-lang.zulipchat.com/#narrow/channel/187679-t-compiler.2Fparallel-rustc/topic/Async.20closures.20not.20reproducible.28.23140425.29) https://github.com/rust-lang/rust/pull/144576
Update rust-lang/rust#113349
r? `@oli-obk`
cc `@lqd` `@cramertj` `@matthiaskrgr` `@Zoxc` `@SparrowLii` `@bjorn3` `@cjgillot` `@joshtriplett`
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Rollup of 11 pull requests
Successful merges:
- rust-lang/rust#143467 (Add ASCII-related methods from `u8` and `MIN`/`MAX` to `core::ascii::Char`)
- rust-lang/rust#144519 (Constify `SystemTime` methods)
- rust-lang/rust#144642 (editorconfig: don't trim trailing whitespace in tests)
- rust-lang/rust#144870 (Stabilize `path_file_prefix` feature)
- rust-lang/rust#145269 (Deprecate RUST_TEST_* env variables)
- rust-lang/rust#145274 (Remove unused `#[must_use]`)
- rust-lang/rust#145289 (chore(ci): upgrade checkout to v5)
- rust-lang/rust#145303 (Docs: Link to payload_as_str() from payload().)
- rust-lang/rust#145308 (Adjust documentation of `dangling`)
- rust-lang/rust#145320 (Allow cross-compiling the Cranelift dist component)
- rust-lang/rust#145325 (Add `cast_init` and `cast_uninit` methods for pointers)
r? `@ghost`
`@rustbot` modify labels: rollup
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Remove unused `#[must_use]`
Self-explanatory
Fixes https://github.com/rust-lang/rust/issues/145257
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Set dead_on_return attribute for indirect arguments
Set the dead_on_return attribute (added in LLVM 21) for arguments that are passed indirectly, but not byval.
This indicates that the value of the argument on return does not matter, enabling additional dead store elimination.
From LangRef:
> This attribute indicates that the memory pointed to by the argument is dead upon function return, both upon normal return and if the calls unwinds, meaning that the caller will not depend on its contents. Stores that would be observable either on the return path or on the unwind path may be elided.
>
> Specifically, the behavior is as-if any memory written through the pointer during the execution of the function is overwritten with a poison value upon function return. The caller may access the memory, but any load not preceded by a store will return poison.
>
> This attribute does not imply aliasing properties. For pointer arguments that do not alias other memory locations, noalias attribute may be used in conjunction. Conversely, this attribute always implies dead_on_unwind.
>
> This attribute cannot be applied to return values.
This fixes parts of https://github.com/rust-lang/rust/issues/96497.
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The use of `Not` to describe the `!` in `macro_rules!` reads
confusingly, and also results in search collisions with the diagnostic
structure `MacroRulesNot` elsewhere in the compiler. Rename it to use
the more conventional `Bang` for `!`.
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This eliminates the case in `failed_to_match_macro` to check for a
function-like invocation of a macro with no function-like rules.
Instead, macro kind mismatches now result in an unresolved macro, and we
detect this case in `unresolved_macro_suggestions`, which now carefully
distinguishes between a kind mismatch and other errors.
This also handles cases of forward-referenced attributes and cyclic
attributes.
Expand test coverage to include all of these cases.
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I discovered this via research through the git log, and I want to leave
additional guidance for future macro spelunkers.
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Review everything that uses `MacroKind`, and switch anything that could
refer to more than one kind to use `MacroKinds`.
Add a new `SyntaxExtensionKind::MacroRules` for `macro_rules!` macros,
using the concrete `MacroRulesMacroExpander` type, and have it track
which kinds it can handle. Eliminate the separate optional `attr_ext`,
now that a `SyntaxExtension` can handle multiple macro kinds.
This also avoids the need to downcast when calling methods on
`MacroRulesMacroExpander`, such as `get_unused_rule`.
Integrate macro kind checking into name resolution's
`sub_namespace_match`, so that we only find a macro if it's the right
type, and eliminate the special-case hack for attributes.
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Make no_mangle on foreign items explicit instead of implicit
for a followup PR I'm working on I need some foreign items to mangle. I could add a new attribute: `no_no_mangle` or something silly like that but by explicitly putting `no_mangle` in the codegen fn attrs of foreign items we can default it to `no_mangle` and then easily remove it when we don't want it.
I guess you'd know about this r? `@bjorn3.` Shouldn't be too hard to review :)
Builds on rust-lang/rust#144655 which should merge first.
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Support using #[unstable_feature_bound] on trait
This is needed to unblock https://github.com/rust-lang/rust/pull/145095
r? ```````@BoxyUwU```````
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Rename entered trace span variables from `_span` to `_trace`
This PR just changes the name of `EnteredTraceSpan` variables used to automatically close tracing spans when going out of scope. This renaming was needed because `_span` could possibly be confused with the `Span` type in rustc, so I used `_trace` as suggested in https://github.com/rust-lang/rust/pull/144727#discussion_r2247267670.
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Tweak invalid builtin attribute output
- Add link to reference/docs when possible
- More accurate suggestions by supporting multiple alternative suggestions
```
error: malformed `crate_type` attribute input
--> $DIR/crate-type-macro-call.rs:1:1
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LL | #![crate_type = foo!()]
| ^^^^^^^^^^^^^^^^^^^^^^^
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= note: for more information, visit <https://doc.rust-lang.org/reference/linkage.html>
help: the following are the possible correct uses
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LL - #![crate_type = foo!()]
LL + #![crate_type = "bin"]
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LL - #![crate_type = foo!()]
LL + #![crate_type = "cdylib"]
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LL - #![crate_type = foo!()]
LL + #![crate_type = "dylib"]
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LL - #![crate_type = foo!()]
LL + #![crate_type = "lib"]
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= and 4 other candidates
```
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fix: re-enable self-assignment
## Description
Re-enables the self-assignment detection that was previously disabled due to unrelated regressions. The fix detects useless assignments like `x = x` and `foo.field = foo.field`.
## History
The original regressions (rust-lang/rust#81626, rust-lang/rust#81658) were specifically about false positives in write-only field detection, not self-assignment detection. Belows are brief history for the rule that I understand.
- Self-assignment detection was originally implemented in rust-lang/rust#87129 to address rust-lang/rust#75356
- The implementation was disabled alongside the revert of rust-lang/rust#81473's "write-only fields" detection
- rust-lang/rust#81473 was reverted via rust-lang/rust#86212 and rust-lang/rust#83171 due to false positives in write-only field detection (rust-lang/rust#81626, rust-lang/rust#81658)
- The self-assignment detection feature got removed, even though it wasn't the reason for the problems
This PR only re-enables the self-assignment checks, which are orthogonal to the problematic write-only field analysis.
## Changes
- Removed `#[allow(dead_code)]` from `compiler/rustc_passes/src/dead.rs` file
- `handle_assign` and
- `check_for_self_assign`
- Added `ExprKind::Assign` handling in `visit_expr` to call both methods
- Updated test expectations in `tests/ui/lint/dead-code/self-assign.rs`
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Port `#[allow_internal_unsafe]` to the new attribute system (attempt 2)
This is a slightly modified version of ae1487aa9922de7642c448cc0908584026699e1c, which caused a performance regression (reverted in https://github.com/rust-lang/rust/pull/145086#issue-3303428759). The diff between this PR and the previous one can be seen in 027a1def.
r? ```````@jdonszelmann``````` :sparkling_heart:
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Extract TraitImplHeader in AST/HIR
Several fields of `Impl` are only applicable when it's a trait impl. This moves those fields into a new struct that is only present for trait impls.
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Apple: Always pass SDK root when linking with `cc`, and pass it via `SDKROOT` env var
Fixes https://github.com/rust-lang/rust/issues/80817, fixes https://github.com/rust-lang/rust/issues/96943, and generally simplifies our linker invocation on Apple platforms.
Part of https://github.com/rust-lang/rust/issues/129432.
### Necessary background on trampoline binaries
The developer binaries such as `/usr/bin/cc` and `/usr/bin/clang` are actually trampolines (similar in spirit to the Rust binaries in `~/.cargo/bin`) which effectively invokes `xcrun` to get the current Xcode developer directory, which allows it to find the actual binary under `/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/*`.
This binary is then launched with the following environment variables set (but none of them are set if `SDKROOT` is set explicitly):
- `SDKROOT=/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk`
- `LIBRARY_PATH=/usr/local/lib` (appended)
- `CPATH=/usr/local/include` (appended)
- `MANPATH=/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/share/man:/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/usr/share/man:/Applications/Xcode.app/Contents/Developer/usr/share/man:/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/share/man:` (prepended)
This allows the user to type e.g. `clang foo.c` in their terminal on macOS, and have it automatically pick up a suitable Clang binary and SDK from either an installed Xcode.app or the Xcode Command Line Tools.
(It acts roughly as-if you typed `xcrun -sdk macosx clang foo.c`).
### Finding a suitable SDK
All compilation on macOS is cross-compilation using SDKs, there are no system headers any more (`/usr/include` is gone), and the system libraries are elsewhere in the file system (`/usr/lib` is basically empty). Instead, the logic for finding the SDK is handled by the `/usr/bin/cc` trampoline (see above).
But relying on the `cc` trampoline doesn't work when:
- Cross-compiling, since a different SDK is needed there.
- Invoking the linker directly, since the linker doesn't understand `SDKROOT`.
- Linking build scripts inside Xcode (see https://github.com/rust-lang/rust/issues/80817), since Xcode prepends `/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin` to `PATH`, which means `cc` refers to the _actual_ Clang binary, and we end up with the wrong SDK root specified.
Basically, we cannot rely on the trampoline at all, so the last commit removes the special-casing that was done when linking with `cc` for macOS (i.e. the most common path), so that **we now always invoke `xcrun` (if `SDKROOT` is not explicitly specified) to find the SDK root**.
Making sure this is non-breaking has a few difficulties though, namely that the user might not have Xcode installed, and that the compiler driver may not understand the `-isysroot` flag. These difficulties are explored below.
#### No Xcode
There are several compiler drivers which work without Xcode by bundling their own SDK, including `zig cc`, Nixpkgs' `clang` and Homebrew's `llvm` package. Additionally, `xcrun` is rarely available when cross-compiling from non-macOS and instead the user might provide a downloaded SDK manually with `-Clink-args=...`.
We do still want to _try_ to invoke `xcrun` if possible, since it is usually the SDK that the user wants (and if not, the environment should override `xcrun`, such as is done by Nixpkgs). But we do not want failure to invoke `xcrun` to stop the linking process. This is changed in the second-to-last commit.
#### `SDKROOT` vs. `-isysroot`
The exact reasoning why we do not always pass the SDK root when linking on macOS eludes me (the git history dead ends in rust-lang/rust#100286), but I suspect it's because we want to support compiler drivers which do not support the `-isysroot` option.
To make sure that such use-cases continue to work, we now pass the SDK root via the `SDKROOT` environment variable. This way, compiler drivers that support setting the SDK root (such as Clang and GCC) can use it, while compiler drivers that don't (presumably because they figure out the SDK in some other way) can just ignore it.
One small danger here would be if there's some compiler driver out there which works with the `-isysroot` flag, but not with the `SDKROOT` environment variable. I am not aware of any?
In a sense, this also shifts the blame; if a compiler driver does not understand `SDKROOT`, it won't work with e.g. `xcrun -sdk macosx15.0 $tool` either, so it can more clearly be argued that this is incorrect behaviour on the part of the tool.
Note also that this overrides the behaviour discussed above (`/usr/bin/cc` sets some extra environment variables), I will argue that is fine since `MANPATH` and `CPATH` is useless when linking, and `/usr/local/lib` is empty on a default system at least since macOS 10.14 (it might be filled by extra libraries installed by the user, but I'll argue that if we want it to be part of the default library search path, we should set it explicitly so that it's also set when linking with `-Clinker=ld`).
### Considered alternatives
- Invoke `/usr/bin/cc` instead of `cc`.
- This breaks many other use-cases though where overriding `cc` in the PATH is desired.
- Look up `which cc`, and do special logic if in Xcode toolchain.
- Seems brittle, and besides, it's not the `cc` in the Xcode toolchain that's wrong, it's the `/usr/bin/cc` behaviour that is a bit too magical.
- Invoke `xcrun --sdk macosx cc`.
- This completely ignores `SDKROOT`, so we'd still have to parse that first to figure out if it's suitable or not, but would probably be workable.
- Maybe somehow configure the linker with extra flags such that it'll be able to link regardless of linking for macOS or e.g. iOS? Though I doubt this is possible.
- Bundle the SDK, similar to `zig-cc`.
- Comes with it's own host of problems.
### Testing
Tested that this works with the following `-Clinker=...`:
- [x] Default (`cc`)
- [x] `/usr/bin/ld`
- [x] Actual Clang from Xcode (`/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/clang`)
- [x] `/usr/bin/clang` (invoked via `clang` instead of `cc`)
- [x] Homebrew's `llvm` package (ignores `SDKROOT`, uses their own SDK)
- [x] Homebrew's `gcc` package (`SDKROOT` is preferred over their own SDK)
- [x] ~Macports `clang`~ Couldn't get it to build
- [x] Macports `gcc` (`SDKROOT` is preferred over their own SDK)
- [x] Zig CC installed via. homebrew (ignores both `-isysroot` and `SDKROOT`, uses their own SDK)
- [x] Nixpkgs `clang` (ignores `SDKROOT`, uses their own SDK)
- [x] Nixpkgs `gcc` (ignores `SDKROOT`, uses their own SDK)
- [x] ~[`cosmocc`](https://github.com/jart/cosmopolitan)?~ Doesn't accept common flags (like `-arch`)
CC ```````@BlackHoleFox``````` ```````@thomcc```````
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search graph: improve rebasing and add forced ambiguity support
Based on rust-lang/rust#142774
This slightly strengthens rebasing and actually checks for the property we want to maintain. There are two additional optimizations we can and should do here:
- we should be able to just always rebase if cycle heads already have a provisional result from a previous iteration
- we currently only apply provisional cache entries if the `path_to_entry` matches exactly. We should be able to extend this e.g. if you have an entry for `B` in `ABA` where the path `BA` is coinductive, then we can use this entry even if the current path from `A` to `B` is inductive.
---
I've also added support for `PathKind::ForcedAmbiguity` which always forced the initial provisional result to be ambiguous. A am using this for cycles involving negative reasons, which is currently only used by the fuzzer in https://github.com/lcnr/search_graph_fuzz. Consider the following setup: A goal `A` which only holds if `B` does not hold, and `B` which only holds if `A` does not hold.
- A only holds if B does not hold, results in X
- B only holds if A does not hold, results in !X
- A cycle, provisional result X
- B only holds if A does not hold, results in X
- A only holds if B does not hold, results in !X
- B cycle, provisional result X
With negative reasoning, the result of cycle participants depends on their position in the cycle. This means using cache entries while other entries are on the stack/have been popped is wrong. It's also generally just kinda iffy. By always forcing the initial provisional result of such cycles to be ambiguity, we can avoid this, as "not maybe" is just "maybe" again.
Rust kind of has negative reasoning due to incompleteness, consider the following setup:
- `T::Foo eq u32`
- normalize `T::Foo`
- via impl -> `u32`
- via param_env -> `T`
- nested goals...
`T::Foo eq u32` holds exactly if the nested goals of the `param_env` candidate do not hold, as preferring that candidate over the impl causes the alias-relate to fail. This means the current provisional cache may cause us to ignore `param_env` preference in rare cases. This is not unsound and I don't care about it, as we already have this behavior when rerunning on changed fixpoint results:
- `T: Trait`
- via impl ok
- via env
- `T: Trait` non-productive cycle
- result OK, rerun changed provisional result
- `T: Trait`
- via impl ok
- via env
- `T: Trait` using the provisional result, can be thought of as recursively expanding the proof tree
- via impl ok
- via env <don't care>
- prefer the env candidate, reached fixpoint
---
One could imaging changing `ParamEnv` candidates or the impl shadowing check to use `PathKind::ForcedAmbiguity` to make the search graph less observable instead of only using it for fuzzing. However, incomplete candidate preference isn't really negative reasoning and doing this is a breaking change https://github.com/rust-lang/trait-system-refactor-initiative/issues/114
r? `@compiler-errors`
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This is a technically a breaking change for what can be parsed in
`#[cfg(false)]`.
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The exact reasoning why we do not always pass the SDK root when linking
on macOS eludes me, but I suspect it's because we want to support
compiler drivers which do not support the `-isysroot` option.
Since we now pass the SDK root via the environment variable SDKROOT,
compiler drivers that don't support it can just ignore it.
Similarly, since we only warn when xcrun fails, users that expect their
compiler driver to provide the SDK location can do so now.
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To allow using zig-cc or similar as the compiler driver.
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This is more in-line with what Apple's tooling expects, and allows us to
better support custom compiler drivers (such as certain Homebrew and
Nixpkgs compilers) that prefer their own `-isysroot` flag.
Effectively, we now invoke the compiler driver as-if it was invoked as
`xcrun -sdk $sdk_name $tool`.
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Reduce indentation and avoid needless checks (checking the target OS and
vendor is unnecessary).
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`NamedValueStr`
Modify `AttributeTemplate` to support list of alternatives for list and name value attribute styles.
Suggestions now provide more correct suggested code:
```
error[E0805]: malformed `used` attribute input
--> $DIR/used_with_multi_args.rs:3:1
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LL | #[used(compiler, linker)]
| ^^^^^^------------------^
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| expected a single argument here
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help: try changing it to one of the following valid forms of the attribute
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LL - #[used(compiler, linker)]
LL + #[used(compiler)]
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LL - #[used(compiler, linker)]
LL + #[used(linker)]
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LL - #[used(compiler, linker)]
LL + #[used]
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```
instead of the prior "masking" of the lack of this feature by suggesting pipe-separated lists:
```
error[E0805]: malformed `used` attribute input
--> $DIR/used_with_multi_args.rs:3:1
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LL | #[used(compiler, linker)]
| ^^^^^^------------------^
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| expected a single argument here
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help: try changing it to one of the following valid forms of the attribute
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LL - #[used(compiler, linker)]
LL + #[used(compiler|linker)]
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LL - #[used(compiler, linker)]
LL + #[used]
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```
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remove some unused private trait impls
they're neither required for completeness nor used
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Improve suggestion for "missing function argument" on multiline call
`rustc` has a very neat suggestion when the argument count does not match, with a nice placeholder that shows where an argument may be missing. Unfortunately the suggestion is always single-line, even when the function call spans across multiple lines. With this PR, `rustc` tries to guess if the function call is multiline or not, and emits a multiline suggestion when required.
r? `@jdonszelmann`
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