Stability oddity with const intrinsics

[oli-obk]

cc @RalfJung

In #80699 (comment)@usbalbin realized we accepted some intrinsics as const without a #[rustc_const_(un)stable] attribute. I did some digging, and that example works because intrinsics inherit their stability from their parents... including #[rustc_const_(un)stable] attributes. While we may want to fix that (not sure, wasn't there just a MCPed PR that caused this on purpose?), we definitely want tests for it, thus this PR adding tests and some fun tracing statements.

[rust-highfive]

r? @petrochenkov

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[petrochenkov]

r? @RalfJung

[rust-log-analyzer]

The job x86_64-gnu-llvm-9 failed! Check out the build log: (web)(plain)

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

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failures:
---- [ui] ui/consts/intrinsic_without_const_stab_fail.rs stdout ----
1 error[E0015]: calls in constant functions are limited to constant functions, tuple structs and tuple variants
- --> $DIR/intrinsic_without_const_stab_fail.rs:15:14
+ --> $DIR/intrinsic_without_const_stab_fail.rs:12:14
3 |
4 LL | unsafe { copy(src, dst, count) }
The actual stderr differed from the expected stderr.
The actual stderr differed from the expected stderr.
Actual stderr saved to /checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/consts/intrinsic_without_const_stab_fail/intrinsic_without_const_stab_fail.stderr
To update references, rerun the tests and pass the `--bless` flag
To only update this specific test, also pass `--test-args consts/intrinsic_without_const_stab_fail.rs`
error: 1 errors occurred comparing output.
status: exit code: 1
status: exit code: 1
command: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/bin/rustc" "/checkout/src/test/ui/consts/intrinsic_without_const_stab_fail.rs" "-Zthreads=1" "--target=x86_64-unknown-linux-gnu" "--error-format" "json" "-Zui-testing" "-Zdeduplicate-diagnostics=no" "-Zemit-future-incompat-report" "--emit" "metadata" "-C" "prefer-dynamic" "--out-dir" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/consts/intrinsic_without_const_stab_fail" "-A" "unused" "-Crpath" "-O" "-Cdebuginfo=0" "-Zunstable-options" "-Lnative=/checkout/obj/build/x86_64-unknown-linux-gnu/native/rust-test-helpers" "-L" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/consts/intrinsic_without_const_stab_fail/auxiliary"
------------------------------------------
------------------------------------------
stderr:
stderr:
------------------------------------------
error[E0015]: calls in constant functions are limited to constant functions, tuple structs and tuple variants
--> /checkout/src/test/ui/consts/intrinsic_without_const_stab_fail.rs:12:14
|
LL | unsafe { copy(src, dst, count) } //~ ERROR calls in constant functions are limited
error: aborting due to previous error
For more information about this error, try `rustc --explain E0015`.
---
Some tests failed in compiletest suite=ui mode=ui host=x86_64-unknown-linux-gnu target=x86_64-unknown-linux-gnu
command did not execute successfully: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0-tools-bin/compiletest" "--compile-lib-path" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/lib" "--run-lib-path" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/lib/rustlib/x86_64-unknown-linux-gnu/lib" "--rustc-path" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/bin/rustc" "--src-base" "/checkout/src/test/ui" "--build-base" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui" "--stage-id" "stage2-x86_64-unknown-linux-gnu" "--suite" "ui" "--mode" "ui" "--target" "x86_64-unknown-linux-gnu" "--host" "x86_64-unknown-linux-gnu" "--llvm-filecheck" "/usr/lib/llvm-9/bin/FileCheck" "--nodejs" "/usr/bin/node" "--host-rustcflags" "-Crpath -O -Cdebuginfo=0 -Zunstable-options -Lnative=/checkout/obj/build/x86_64-unknown-linux-gnu/native/rust-test-helpers" "--target-rustcflags" "-Crpath -O -Cdebuginfo=0 -Zunstable-options -Lnative=/checkout/obj/build/x86_64-unknown-linux-gnu/native/rust-test-helpers" "--docck-python" "/usr/bin/python2.7" "--lldb-python" "/usr/bin/python2.7" "--gdb" "/usr/bin/gdb" "--quiet" "--llvm-version" "9.0.0" "--llvm-components" "aarch64 aarch64asmparser aarch64codegen aarch64desc aarch64disassembler aarch64info aarch64utils aggressiveinstcombine all all-targets amdgpu amdgpuasmparser amdgpucodegen amdgpudesc amdgpudisassembler amdgpuinfo 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 codegen core coroutines coverage debuginfocodeview debuginfodwarf debuginfogsym debuginfomsf debuginfopdb demangle dlltooldriver engine executionengine fuzzmutate globalisel hexagon hexagonasmparser hexagoncodegen hexagondesc hexagondisassembler hexagoninfo instcombine instrumentation interpreter ipo irreader jitlink lanai lanaiasmparser lanaicodegen lanaidesc lanaidisassembler lanaiinfo libdriver lineeditor linker lto 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 object objectyaml option orcjit passes perfjitevents powerpc powerpcasmparser powerpccodegen powerpcdesc powerpcdisassembler powerpcinfo profiledata remarks riscv riscvasmparser riscvcodegen riscvdesc riscvdisassembler riscvinfo riscvutils runtimedyld scalaropts selectiondag sparc sparcasmparser sparccodegen sparcdesc sparcdisassembler sparcinfo support symbolize systemz systemzasmparser systemzcodegen systemzdesc systemzdisassembler systemzinfo tablegen target textapi transformutils vectorize webassembly webassemblyasmparser webassemblycodegen webassemblydesc webassemblydisassembler webassemblyinfo windowsmanifest x86 x86asmparser x86codegen x86desc x86disassembler x86info x86utils xcore xcorecodegen xcoredesc xcoredisassembler xcoreinfo xray" "--system-llvm" "--cc" "" "--cxx" "" "--cflags" "" "--adb-path" "adb" "--adb-test-dir" "/data/tmp/work" "--android-cross-path" "" "--color" "always"
failed to run: /checkout/obj/build/bootstrap/debug/bootstrap --stage 2 test --exclude src/tools/tidy
Build completed unsuccessfully in 0:16:03

[RalfJung]

hat example works because intrinsics inherit their stability from their parents

Oh, that's interesting. For normal intrinsics this makes sense (when declared inside a fn they anyway cannot be used from the outside), but since const stability has this extra property of being recursive (stable things may not call unstable things), IMO this makes less sense.

[oli-obk]

since const stability has this extra property of being recursive (stable things may not call unstable things), IMO this makes less sense.

So... should I try to fix it in this PR?

[RalfJung]

I think it should be fixed... and that makes the tests added in this PR a bit odd since they test behavior that I consider buggy. But I'd also be okay with opening an issue and having a comment in the test saying that this is testing buggy behavior and should be adjusted once there's a fix.

[RalfJung]

Looks like we have another case of this a few lines down, around line 1940, according to CI.

[oli-obk]

yea, I had to rebase first ^^

[RalfJung]

r=me with CI fixed and the commits squashed a bit.

[oli-obk]

@bors r=RalfJung

[bors]

📌 Commit 5bac1c9 has been approved by RalfJung

[bors]

⌛ Testing commit 5bac1c9 with merge d98d2f5...

[bors]

☀️ Test successful - checks-actions
Approved by: RalfJung
Pushing d98d2f5 to master...