Eliminate print_expr_maybe_paren function from pretty printers
This PR is part of backporting Syn's expression precedence design into rustc. (See #133603 for other work on this.)
In Syn, our version of `print_expr_cond_paren` is called `print_subexpression` and it is called from 19 places. Of those calls, 12 of them need a "custom" behavior for the `needs_paren` argument, whereas only 7 use a "standard" behavior resembling `print_subexpression($e, $e.precedence() < Precedence::$Variant, ...)`. In other words the behavior that rustc_ast_pretty's `print_expr_maybe_paren` implements is actually not what you want most of the time. The current usage you see in rustc is overuse.
<details>
<summary>Aside: am I confident about the correctness of Syn's parenthesization? Yes. Click for details.</summary>
---
The behavior is constrained by the following pair of tests which both run over every Rust source file of rustc and the standard library and tools and test suites:
- To rule out **false positives**: for every expression in every source file, print the expression, parse it back, and verify that not a single new parenthesis got added. Since these are expressions parsed from source code, not macro-generated syntax trees, we know they must never need automatic parenthesis insertion. Rustc's pretty printer does not pass this.
Pseudocode: `assert(expr == parse(print(expr)))`
- To rule out **false negatives**: for every expression in every source file, replace every Expr::Paren node in the syntax tree with just its contents, i.e. stripping the parentheses but otherwise preserving the syntax tree structure. Then print the stripped expression performing parenthesis insertion wherever needed, and reparse it. Verify that the reparsed expression has identical structure to the original, despite there being no parentheses in the original prior to printing, i.e. all the right parentheses got re-inserted by the printer to preserve the expression's structure. Rustc's pretty printer does not pass this. See https://github.com/dtolnay/syn/pull/1788 which reveals multiple rustc_ast_pretty bugs.
Pseudocode: `assert(unparenthesize(expr) == unparenthesize(parse(print(unparenthesize(expr)))))`
---
</details>
If `print_expr_maybe_paren` is usually not correct, is there harm in keeping it for the minority of cases where it is correct? I think the answer is yes and Syn doesn't use any equivalent of this helper function. The problems with it are:
- Having both `print_expr_maybe_paren` and `print_expr_cond_paren` applies counterproductive inertia against moving from the first to the second. When looking at a call site like `print_expr_maybe_paren(e, Precedence::$Variant, ...)` with parentheses not being inserted where they should be, anyone's first inclination would be to solve the bug by tweaking $Variant because that is the only knob that visibly appears in the function call. For example to pass "prec + 1", like tweaking the code to conditionally pass `Precedence::Prefix` instead of `Precedence::Cast`.
Experience in Syn shows this is (almost?) never what you want the person to do. In a call `print_expr_cond_paren(e, e.precedence() < ExprPrecedence::$Variant, ...)` almost always the best fix involves one of:
- Changing `e.precedence()`, e.g. to `fixup.leading_precedence(e)` and `fixup.trailing_precedence(e)` in cases of asymmetrical precedence (`(return 1) + 1` vs `1 + return 1`).
- Changing `<` to `<=`, to handle associativity and other grammar restrictions like chained comparisons (which rustc gets wrong today).
- Adding `||` and/or `&&` clauses to the condition.
By using these 3 better knobs instead of $Variant, it upholds the property that any time we talk about precedence, it is always the precedence of some actual expression that our code is actively manipulating, instead of a value standing in for some imaginary precedence level that would exist between two consecutive [real levels](https://doc.rust-lang.org/1.83.0/reference/expressions.html#expression-precedence). For example consider that "`Cast` + 1" might be `Prefix` today, but only until some new Rust syntax ends up adding a level between those.
- The `print_expr_maybe_paren` call sites look shorter, but they are not clearer. For myself, a function argument that says "does this subexpression need parenthesization" is a concrete thing that is easy to think about, while a function argument that is "what is the effective precedence level associated with this subexpression's placement inside its parent expression" is abstract and tricky to even state a precise meaning for. I expect that for someone less familiar with the pretty printer working on adding a new expression kind (like postfix match, recently), having every subexpression consistently printed using `print_expr_cond_paren` will be more beneficial, for the same reason, than having `print_expr_maybe_paren` available.
r? ``@lcnr``
Mark visionOS as supporting `std`
Cargo's -Zbuild-std has recently started checking this field, which causes it to fail to compile even though we have full support for the standard library on these targets.
[Example of failed build](https://github.com/rust-random/getrandom/actions/runs/12069033154/job/33655430622).
Affected targets: `aarch64-apple-visionos` and `aarch64-apple-visionos-sim`.
r? Noratrieb (because you've worked with `rustc` target metadata IIRC)
``@rustbot`` label O-visionos
use stores of the correct size to set discriminants
Resolves an old HACK /FIXME.
Note that I haven't worked much with codegen so I'm not sure if I'm using the functions correctly and I was surprised seeing out-of-range values being fed into `const_uint_big` but apparently they're wrapped implicitly? By making it explicit we can pass in-range values instead.
This reverts commit 76f3ff6059, reversing
changes made to 1fc691e6dd.
The new pgo_works test fails when rust is built without profiling
support, including in CI on x86_64-gnu-aux.
Improve span handling in `parse_expr_bottom`.
`parse_expr_bottom` stores `this.token.span` in `lo`, but then fails to use it in many places where it could. This commit fixes that, and likewise (to a smaller extent) in `parse_ty_common`.
r? ``@spastorino``
Simplify hir_typeck_pass_to_variadic_function
r? ``@compiler-errors``
This reworks a bit how the diagnostic is generated so that it does the same as #133538
The `help` is useless now so I removed it
Add `+forced-atomics` feature to esp32s2 no_std target
Similar to https://github.com/rust-lang/rust/pull/114499 but for the Xtensa backend. The ESP32-S2 doesn't have native atomic support, but can have atomic load/stores as part of the ISA with this LLVM codegen feature.
Note: The current rev of LLVM that rustc is using doesn't contain the `+forced-atomics` feature for Xtensa, but I'm pushing this now to remove the patch from our fork in `esp-rs/rust`.
r? ``@Amanieu`` because you reviewed the related RISC-V PR
Fix target_feature handling in freg of LoongArch inline assembly
In LoongArch inline assembly, freg currently always accepts f32/f64 as input/output.
9b4d7c6a40/compiler/rustc_target/src/asm/loongarch.rs (L41)
However, these types actually require f/d target features as in RISC-V.
Otherwise, an (ugly) compile error will occur: https://godbolt.org/z/K61Gq1E9E
f32/f64 without f:
```
error: couldn't allocate output register for constraint '{$f1}'
--> <source>:12:11
|
12 | asm!("", in("$f1") x, lateout("$f1") y);
| ^
```
f64 with f but without d:
```
error: scalar-to-vector conversion failed, possible invalid constraint for vector type
--> <source>:19:11
|
19 | asm!("", in("$f1") x, lateout("$f1") y);
| ^
```
cc ``@heiher``
r? ``@Amanieu``
``@rustbot`` label +O-LoongArch +A-inline-assembly
Do not call `extern_crate` on current trait on crate mismatch errors
When we encounter an error caused by traits/types of different versions of the same crate, filter out the current crate when collecting spans to add to the context so we don't call `extern_crate` on the `DefId` of the current crate, which is meaningless and ICEs.
Produced output with this filter:
```
error[E0277]: the trait bound `foo::Struct: Trait` is not satisfied
--> y.rs:13:19
|
13 | check_trait::<foo::Struct>();
| ^^^^^^^^^^^ the trait `Trait` is not implemented for `foo::Struct`
|
note: there are multiple different versions of crate `foo` in the dependency graph
--> y.rs:7:1
|
4 | extern crate foo;
| ----------------- one version of crate `foo` is used here, as a direct dependency of the current crate
5 |
6 | pub struct Struct;
| ----------------- this type implements the required trait
7 | pub trait Trait {}
| ^^^^^^^^^^^^^^^ this is the required trait
|
::: x.rs:4:1
|
4 | pub struct Struct;
| ----------------- this type doesn't implement the required trait
5 | pub trait Trait {}
| --------------- this is the found trait
= note: two types coming from two different versions of the same crate are different types even if they look the same
= help: you can use `cargo tree` to explore your dependency tree
note: required by a bound in `check_trait`
--> y.rs:10:19
|
10 | fn check_trait<T: Trait>() {}
| ^^^^^ required by this bound in `check_trait`
```
Fix#133563.
tests: Add regression test for self referential structs with cow as last field
Making compilation pass for this code was retroactively stabilized via FCP in 1.79. The code does not compile in 1.78.
See https://github.com/rust-lang/rust/issues/129541 for details.
Closes#107481
[AIX] handle libunwind native_libs
AIX should follow a similar path here to other libunwind platforms, with regards to system vs in-tree libunwind and the native lib search directories.
Having the right native lib search directories here is also required to get the correct default library search paths, due to some quirks of the AIX linker.
Stabilize `extended_varargs_abi_support`
I think that is everything? If there is any documentation regarding `extern` and/or varargs to correct, let me know, some quick greps suggest that there might be none.
Tracking issue: https://github.com/rust-lang/rust/issues/100189
Bump boostrap compiler to new beta
Currently failing due to something about the const stability checks and `panic!`. I'm not sure why though since I wasn't able to see any PRs merged in the past few days that would result in a `cfg(bootstrap)` that shouldn't be removed. cc `@RalfJung` #131349
Support `clobber_abi` in AVR inline assembly
This PR implements the `clobber_abi` part necessary to eventually stabilize the inline assembly for AVR. This is tracked in #93335.
This is heavily inspired by the sibling-PR #131310 for the MSP430. I've explained my reasoning in the first commit message in detail, which is reproduced below for easier reviewing:
This follows the [ABI documentation] of AVR-GCC:
> The [...] call-clobbered general purpose registers (GPRs) are registers that might be destroyed (clobbered) by a function call.
>
> - **R18–R27, R30, R31**
>
> These GPRs are call clobbered. An ordinary function may use them without restoring the contents. [...]
>
> - **R0, T-Flag**
>
> The temporary register and the T-flag in SREG are also call-clobbered, but this knowledge is not exposed explicitly to the compiler (R0 is a fixed register).
Therefore this commit lists the aforementioned registers `r18–r27`, `r30` and `r31` as clobbered registers. Since the `r0` register (listed above as well) is not available in inline assembly at all (potentially because the AVR-GCC considers it a fixed register causing the register to never be used in register allocation and LLVM adopting this), there is no need to list it in the clobber list (the `r0`-variant is not even available). A comment was added to ensure, that the `r0` gets added to the clobber-list once the register gets usable in inline ASM.
Since the SREG is normally considered clobbered anyways (unless the user supplies the `preserve_flags`-option), there is no need to explicitly list a bit in this register (which is not possible to list anyways).
Note, that this commit completely ignores the case of interrupts (that are described in the ABI-specification), since every register touched in an ISR need to be saved anyways.
[ABI documentation]: https://gcc.gnu.org/wiki/avr-gcc#Call-Used_Registers
r? ``@Amanieu``
``@rustbot`` label +O-AVR
Rollup of 7 pull requests
Successful merges:
- #132782 (improvements on initial sysroot and libdir finding logics)
- #133466 (Fix typos in pin.rs)
- #133492 (bootstrap: allow skipping steps with start of path)
- #133501 (support revealing defined opaque post borrowck)
- #133530 (Use consistent wording in docs, use is zero instead of is 0)
- #133538 (Better diagnostic for fn items in variadic functions)
- #133590 (Rename `-Zparse-only`)
r? `@ghost`
`@rustbot` modify labels: rollup
Use consistent wording in docs, use is zero instead of is 0
In documentation, wording of _"`rhs` is zero"_ and _"`rhs` is 0"_ is intermixed. This is especially visible [here](https://doc.rust-lang.org/std/primitive.usize.html#method.div_ceil).
This changes all occurrences to _"`rhs` is zero"_ for better readability.
support revealing defined opaque post borrowck
By adding a new `TypingMode::PostBorrowckAnalysis`. Currently only supported with the new solver and I didn't look into the way we replace `ReErased`. ``@compiler-errors`` mentioned that always using existentials may be unsound.
r? ``@compiler-errors``
