There isn't a reliable way to determine if a given target tuple supports std or not #142296

jieyouxu · 2025-06-10T13:58:29Z

Related to #141863. I'd like to implement a reliable //@ needs-target-std compiletest directive, but after some experimentation I found out that we don't really have a reliable way to determine if a given target tuple supports std.

Bootstrap, for this reason, has to resort to the hack for determining target std support that is

rust/src/bootstrap/src/core/config/toml/target.rs

Lines 87 to 89 in 100199c

    
           if triple.contains("-none") || triple.contains("nvptx") || triple.contains("switch") { 
        
               target.no_std = true; 
        
           }

Noratrieb suggested a proper long-term solution (on community discord)

the std build script should probably read it from the metadata field [..]
and then the metadata is actually reliable

which seems way more principled to me.

rustc similarly does not have any way to convey this information. For instance, the closest thing is the target spec metadata.std field, but not all built-in target specs actually populate this field¹. Built-in target specs currently without std support field (2025-06-10)²:

aarch64-unknown-redox
aarch64-unknown-teeos
aarch64-unknown-uefi
aarch64-uwp-windows-msvc
arm64ec-pc-windows-msvc
armv6k-nintendo-3ds
armv7-wrs-vxworks-eabihf
avr-none
i586-unknown-redox
i686-unknown-uefi
i686-uwp-windows-gnu
i686-uwp-windows-msvc
mips-mti-none-elf
mipsel-mti-none-elf
powerpc-wrs-vxworks-spe
powerpc64-ibm-aix
riscv32im-risc0-zkvm-elf
riscv32imac-unknown-xous-elf
thumbv7a-pc-windows-msvc
wasm32-wali-linux-musl
wasm64-unknown-unknown
x86_64-unknown-l4re-uclibc
x86_64-unknown-uefi
xtensa-esp32-espidf
xtensa-esp32s2-espidf
xtensa-esp32s3-espidf

Putting aside that metadata is really only intended for doc generation purposes and is by no means guaranteed to be reliable ↩
Just for expository purposes. ↩

The text was updated successfully, but these errors were encountered:

Implement `//@ needs-target-std` compiletest directive Closes #141863. Needed to unblock #139244 and #141856. ### Summary This PR implements a `//@ needs-target-std` compiletest directive that gates test execution based on whether the target supports std or not. For some cases, this should be preferred over e.g. some combination of `//@ ignore-none`, `//@ ignore-nvptx` and more[^none-limit]. ### Implementation limitation Unfortunately, since there is currently [no reliable way to determine from metadata whether a given target supports std or not](#142296), we have to resort to a hack. Bootstrap currently determines whether or not a target supports std by a naive target tuple substring comparison: a target supports std if its target tuple does *not* contain one of `["-none", "nvptx", "switch"]` substrings. This PR simply pulls that hack out into `build_helpers` to avoid reimplementing the same hack in compiletest, and uses that logic to inform `//@ needs-target-std`. ### Auxiliary changes This PR additionally changes a few run-make tests to use `//@ needs-target-std` over an inconsistent combination of target-based `ignore`s. This should help with #139244. --- r? bootstrap [^none-limit]: Notably, `target_os = "none"` is **not** a sufficient condition for "target does not support std" try-job: test-various try-job: armhf-gnu

adamgemmell · 2025-06-10T17:33:01Z

Also discussed in github.com/rust-lang/rfcs/pull/3693

Implement `//@ needs-target-std` compiletest directive Closes rust-lang#141863. Needed to unblock rust-lang#139244 and rust-lang#141856. ### Summary This PR implements a `//@ needs-target-std` compiletest directive that gates test execution based on whether the target supports std or not. For some cases, this should be preferred over e.g. some combination of `//@ ignore-none`, `//@ ignore-nvptx` and more[^none-limit]. ### Implementation limitation Unfortunately, since there is currently [no reliable way to determine from metadata whether a given target supports std or not](rust-lang#142296), we have to resort to a hack. Bootstrap currently determines whether or not a target supports std by a naive target tuple substring comparison: a target supports std if its target tuple does *not* contain one of `["-none", "nvptx", "switch"]` substrings. This PR simply pulls that hack out into `build_helpers` to avoid reimplementing the same hack in compiletest, and uses that logic to inform `//@ needs-target-std`. ### Auxiliary changes This PR additionally changes a few run-make tests to use `//@ needs-target-std` over an inconsistent combination of target-based `ignore`s. This should help with rust-lang#139244. --- r? bootstrap [^none-limit]: Notably, `target_os = "none"` is **not** a sufficient condition for "target does not support std"

Rollup merge of #142297 - jieyouxu:needs-target-std, r=Kobzol Implement `//@ needs-target-std` compiletest directive Closes #141863. Needed to unblock #139244 and #141856. ### Summary This PR implements a `//@ needs-target-std` compiletest directive that gates test execution based on whether the target supports std or not. For some cases, this should be preferred over e.g. some combination of `//@ ignore-none`, `//@ ignore-nvptx` and more[^none-limit]. ### Implementation limitation Unfortunately, since there is currently [no reliable way to determine from metadata whether a given target supports std or not](#142296), we have to resort to a hack. Bootstrap currently determines whether or not a target supports std by a naive target tuple substring comparison: a target supports std if its target tuple does *not* contain one of `["-none", "nvptx", "switch"]` substrings. This PR simply pulls that hack out into `build_helpers` to avoid reimplementing the same hack in compiletest, and uses that logic to inform `//@ needs-target-std`. ### Auxiliary changes This PR additionally changes a few run-make tests to use `//@ needs-target-std` over an inconsistent combination of target-based `ignore`s. This should help with #139244. --- r? bootstrap [^none-limit]: Notably, `target_os = "none"` is **not** a sufficient condition for "target does not support std"

Implement `//@ needs-target-std` compiletest directive Closes rust-lang/rust#141863. Needed to unblock rust-lang/rust#139244 and rust-lang/rust#141856. ### Summary This PR implements a `//@ needs-target-std` compiletest directive that gates test execution based on whether the target supports std or not. For some cases, this should be preferred over e.g. some combination of `//@ ignore-none`, `//@ ignore-nvptx` and more[^none-limit]. ### Implementation limitation Unfortunately, since there is currently [no reliable way to determine from metadata whether a given target supports std or not](rust-lang/rust#142296), we have to resort to a hack. Bootstrap currently determines whether or not a target supports std by a naive target tuple substring comparison: a target supports std if its target tuple does *not* contain one of `["-none", "nvptx", "switch"]` substrings. This PR simply pulls that hack out into `build_helpers` to avoid reimplementing the same hack in compiletest, and uses that logic to inform `//@ needs-target-std`. ### Auxiliary changes This PR additionally changes a few run-make tests to use `//@ needs-target-std` over an inconsistent combination of target-based `ignore`s. This should help with rust-lang/rust#139244. --- r? bootstrap [^none-limit]: Notably, `target_os = "none"` is **not** a sufficient condition for "target does not support std"

rustbot added the needs-triage This issue may need triage. Remove it if it has been sufficiently triaged. label Jun 10, 2025

jieyouxu removed the needs-triage This issue may need triage. Remove it if it has been sufficiently triaged. label Jun 10, 2025

rustbot mentioned this issue Jun 10, 2025

Implement //@ needs-target-std compiletest directive #142297

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There isn't a reliable way to determine if a given target tuple supports std or not #142296

There isn't a reliable way to determine if a given target tuple supports std or not #142296

jieyouxu commented Jun 10, 2025 •

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adamgemmell commented Jun 10, 2025 •

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There isn't a reliable way to determine if a given target tuple supports std or not #142296

There isn't a reliable way to determine if a given target tuple supports std or not #142296

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