New const traits syntax

[oli-obk]

This PR only affects the AST and doesn't actually change anything semantically.

All occurrences of ~const outside of libcore have been replaced by [const]. Within libcore we have to wait for rustfmt to be bumped in the bootstrap compiler. This will happen "automatically" (when rustfmt is run) during the bootstrap bump, as rustfmt converts ~const into [const]. After this we can remove the ~const support from the parser

Caveat discovered during impl: there is no legacy bare trait object recovery for [const] Trait as that snippet in type position goes down the slice /array parsing code and will error

r? @fee1-dead

cc @nikomatsakis @traviscross @compiler-errors

[rustbot]

Some changes occurred in src/tools/rustfmt

cc @rust-lang/rustfmt

Some changes occurred in src/tools/clippy

cc @rust-lang/clippy

[bors]

☔ The latest upstream changes (presumably #140695) made this pull request unmergeable. Please resolve the merge conflicts.

[compiler-errors]

Have we actually settled on a syntax here? Sorry for punting it back over, but would like to get an update here if it's actually ready to review :> ping me when it's ready, sorry for the delays!

@rustbot author

[rustbot]

Reminder, once the PR becomes ready for a review, use @rustbot ready.

[traviscross]

Have we actually settled on a syntax here?

No. Discussion is ongoing.

[oli-obk]

Afaict the syntax with which to move forward was settled as much as it could be in the last lang team design meeting. The lang team wants to get hands-on experience with the feature to see how it feels, so this PR is ready to be merged now.

[fee1-dead]

not necessary for this PR; but would be nice if we renamed the "tilde-const" in the file names to either something syntax agnostic ("maybe-const") or matches the latest syntax

[oli-obk]

done in a follow-up commit

[oli-obk]

@rustbot ready

[rustbot]

There are changes to the tidy tool.

cc @jieyouxu

[rust-log-analyzer]

The job aarch64-gnu-llvm-19-1 failed! Check out the build log: (web) (plain)

Click to see the possible cause of the failure (guessed by this bot)

---- [run-make] tests/run-make/const-trait-stable-toolchain stdout ----

error: rmake recipe failed to complete
status: exit status: 101
command: cd "/checkout/obj/build/aarch64-unknown-linux-gnu/test/run-make/const-trait-stable-toolchain/rmake_out" && env -u RUSTFLAGS AR="ar" BUILD_ROOT="/checkout/obj/build/aarch64-unknown-linux-gnu" CARGO="/checkout/obj/build/aarch64-unknown-linux-gnu/stage1-tools-bin/cargo" CC="cc" CC_DEFAULT_FLAGS="-ffunction-sections -fdata-sections -fPIC" CXX="c++" CXX_DEFAULT_FLAGS="-ffunction-sections -fdata-sections -fPIC" HOST_RUSTC_DYLIB_PATH="/checkout/obj/build/aarch64-unknown-linux-gnu/stage2/lib" LD_LIBRARY_PATH="/checkout/obj/build/aarch64-unknown-linux-gnu/bootstrap-tools/aarch64-unknown-linux-gnu/release/deps:/checkout/obj/build/aarch64-unknown-linux-gnu/stage0/lib/rustlib/aarch64-unknown-linux-gnu/lib" LD_LIB_PATH_ENVVAR="LD_LIBRARY_PATH" LLVM_BIN_DIR="/usr/lib/llvm-19/bin" LLVM_COMPONENTS="aarch64 aarch64asmparser aarch64codegen aarch64desc aarch64disassembler aarch64info aarch64utils aggressiveinstcombine all all-targets amdgpu amdgpuasmparser amdgpucodegen amdgpudesc amdgpudisassembler amdgpuinfo amdgputargetmca amdgpuutils analysis arm armasmparser armcodegen armdesc armdisassembler arminfo armutils asmparser asmprinter avr avrasmparser avrcodegen avrdesc avrdisassembler avrinfo binaryformat bitreader bitstreamreader bitwriter bpf bpfasmparser bpfcodegen bpfdesc bpfdisassembler bpfinfo cfguard codegen codegendata codegentypes core coroutines coverage debuginfobtf debuginfocodeview debuginfodwarf debuginfogsym debuginfologicalview debuginfomsf debuginfopdb demangle dlltooldriver dwarflinker dwarflinkerclassic dwarflinkerparallel dwp engine executionengine extensions filecheck frontenddriver frontendhlsl frontendoffloading frontendopenacc frontendopenmp fuzzercli fuzzmutate globalisel hexagon hexagonasmparser hexagoncodegen hexagondesc hexagondisassembler hexagoninfo hipstdpar instcombine instrumentation interfacestub interpreter ipo irprinter irreader jitlink lanai lanaiasmparser lanaicodegen lanaidesc lanaidisassembler lanaiinfo libdriver lineeditor linker loongarch loongarchasmparser loongarchcodegen loongarchdesc loongarchdisassembler loongarchinfo lto m68k m68kasmparser m68kcodegen m68kdesc m68kdisassembler m68kinfo mc mca mcdisassembler mcjit mcparser mips mipsasmparser mipscodegen mipsdesc mipsdisassembler mipsinfo mirparser msp430 msp430asmparser msp430codegen msp430desc msp430disassembler msp430info native nativecodegen nvptx nvptxcodegen nvptxdesc nvptxinfo objcarcopts objcopy object objectyaml option orcdebugging orcjit orcshared orctargetprocess passes perfjitevents powerpc powerpcasmparser powerpccodegen powerpcdesc powerpcdisassembler powerpcinfo profiledata remarks riscv riscvasmparser riscvcodegen riscvdesc riscvdisassembler riscvinfo riscvtargetmca runtimedyld sandboxir scalaropts selectiondag sparc sparcasmparser sparccodegen sparcdesc sparcdisassembler sparcinfo support symbolize systemz systemzasmparser systemzcodegen systemzdesc systemzdisassembler systemzinfo tablegen target targetparser textapi textapibinaryreader transformutils ve veasmparser vecodegen vectorize vedesc vedisassembler veinfo webassembly webassemblyasmparser webassemblycodegen webassemblydesc webassemblydisassembler webassemblyinfo webassemblyutils windowsdriver windowsmanifest x86 x86asmparser x86codegen x86desc x86disassembler x86info x86targetmca xcore xcorecodegen xcoredesc xcoredisassembler xcoreinfo xray xtensa xtensaasmparser xtensacodegen xtensadesc xtensadisassembler xtensainfo" LLVM_FILECHECK="/usr/lib/llvm-19/bin/FileCheck" NODE="/usr/bin/node" PYTHON="/usr/bin/python3" RUSTC="/checkout/obj/build/aarch64-unknown-linux-gnu/stage2/bin/rustc" RUSTDOC="/checkout/obj/build/aarch64-unknown-linux-gnu/stage2/bin/rustdoc" SOURCE_ROOT="/checkout" TARGET="aarch64-unknown-linux-gnu" TARGET_EXE_DYLIB_PATH="/checkout/obj/build/aarch64-unknown-linux-gnu/stage2/lib/rustlib/aarch64-unknown-linux-gnu/lib" "/checkout/obj/build/aarch64-unknown-linux-gnu/test/run-make/const-trait-stable-toolchain/rmake"
stdout: none
--- stderr -------------------------------

thread 'main' panicked at /checkout/tests/run-make/const-trait-stable-toolchain/rmake.rs:25:10:
test failed: `const-super-trait-stable-enabled.stderr` is different from `(rustc)`

--- const-super-trait-stable-enabled.stderr
+++ (rustc)
@@ -1,10 +1,10 @@
-error: `~const` is not allowed here
+error: `[const]` is not allowed here
  --> const-super-trait.rs:7:12
   |
 7 | trait Bar: ~const Foo {}
   |            ^^^^^^
   |
-note: this trait is not a `#[const_trait]`, so it cannot have `~const` trait bounds
+note: this trait is not a `#[const_trait]`, so it cannot have `[const]` trait bounds
  --> const-super-trait.rs:7:1
   |
 7 | trait Bar: ~const Foo {}
@@ -16,25 +16,25 @@
 1 | #![cfg_attr(feature_enabled, feature(const_trait_impl))]
   |                              ^^^^^^^^^^^^^^^^^^^^^^^^^
 
-error: `~const` can only be applied to `#[const_trait]` traits
+error: `[const]` can only be applied to `#[const_trait]` traits
  --> const-super-trait.rs:7:12
   |
 7 | trait Bar: ~const Foo {}
   |            ^^^^^^ can't be applied to `Foo`
   |
-note: `Foo` can't be used with `~const` because it isn't annotated with `#[const_trait]`
+note: `Foo` can't be used with `[const]` because it isn't annotated with `#[const_trait]`
  --> const-super-trait.rs:3:1
   |
 3 | trait Foo {
   | ^^^^^^^^^
 
-error: `~const` can only be applied to `#[const_trait]` traits
+error: `[const]` can only be applied to `#[const_trait]` traits
  --> const-super-trait.rs:9:17
   |
 9 | const fn foo<T: ~const Bar>(x: &T) {
   |                 ^^^^^^ can't be applied to `Bar`
   |
-note: `Bar` can't be used with `~const` because it isn't annotated with `#[const_trait]`
+note: `Bar` can't be used with `[const]` because it isn't annotated with `#[const_trait]`
  --> const-super-trait.rs:7:1
   |
 7 | trait Bar: ~const Foo {}

note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace