Add `-Zimplicit-sysroot-deps` by adamgemmell · Pull Request #159717 · rust-lang/rust

adamgemmell · 2026-07-22T13:08:39Z

This PR, originally authored by @CrooseGit, adds support for a new flag proposed in the build-std=always RFC. It unblocks work by @Bryanskiy around handling panic strategies in build-std, for which rustc must look for them in -Ldependency locations and not the sysroot.

-Zimplicit-sysroot-deps is true by default. When false, rustc will not look in the sysroot when attempting to resolve direct dependencies. It is intended to be used by Cargo when using build-std to improve error messages, avoiding the common "duplicate lang item in crate core" error that occurs when not all required standard library crates have been built.

Not included in this PR is the behaviour around dependencies injected by rustc in rustc_metadata, such as panic runtimes and compiler-builtins, which will be addressed in the future.

When `-Z implicit-sysroot-deps=false`, the sysroot is not added to the list of search paths for resolving top level dependencies.

One UI test that fails to find crate `std` as it does not look in the sysroot. One UI test that which only transitively depends on std, and thus it is searched for in the sysroot.

1) Depending transitively on a lib in the sysroot resolves fine with `-Zimplicit-sysroot-deps=false` 2) Depending directly on a lib in the sysroot does not resolve implicitly with `-Zimplicit-sysroot-deps=false`

rustbot · 2026-07-22T13:08:45Z

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adamgemmell · 2026-07-22T13:08:59Z

r? compiler reroll

nnethercote · 2026-07-23T03:58:50Z

@rustbot author

rustbot · 2026-07-23T03:58:54Z

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

adamgemmell · 2026-07-28T19:59:42Z

@rustbot ready

nnethercote · 2026-07-29T09:26:32Z

@bors r+ rollup

rust-bors · 2026-07-29T09:26:35Z

📌 Commit b2ed4e8 has been approved by nnethercote

It is now in the queue for this repository.

@CrooseGit

…it-sysroot-deps, r=nnethercote Add `-Zimplicit-sysroot-deps` This PR, originally authored by @CrooseGit, adds support for a new flag [proposed in the `build-std=always` RFC](https://rust-lang.github.io/rfcs/3874-build-std-always.html#preventing-implicit-sysroot-dependencies). It unblocks work by @Bryanskiy around handling panic strategies in build-std, for which rustc must look for them in `-Ldependency` locations and not the sysroot. `-Zimplicit-sysroot-deps` is true by default. When false, rustc will not look in the sysroot when attempting to resolve direct dependencies. It is intended to be used by Cargo when using build-std to improve error messages, avoiding the common "duplicate lang item in crate `core`" error that occurs when not all required standard library crates have been built. Not included in this PR is the behaviour around dependencies injected by rustc in `rustc_metadata`, such as panic runtimes and compiler-builtins, which will be addressed in the future.

Rollup of 6 pull requests Successful merges: - #158460 (Remove llvm_enzyme feature outside of bootstrap) - #159671 (Add semver check test command for checking API compatibility of stdlib) - #159717 (Add `-Zimplicit-sysroot-deps`) - #159994 (Show jobs where a given test was executed in `test-dashboard`) - #160085 (Remove various superfluous lint attributes) - #160123 (add additional license option for third-party dependencies)

@CrooseGit

…it-sysroot-deps, r=nnethercote Add `-Zimplicit-sysroot-deps` This PR, originally authored by @CrooseGit, adds support for a new flag [proposed in the `build-std=always` RFC](https://rust-lang.github.io/rfcs/3874-build-std-always.html#preventing-implicit-sysroot-dependencies). It unblocks work by @Bryanskiy around handling panic strategies in build-std, for which rustc must look for them in `-Ldependency` locations and not the sysroot. `-Zimplicit-sysroot-deps` is true by default. When false, rustc will not look in the sysroot when attempting to resolve direct dependencies. It is intended to be used by Cargo when using build-std to improve error messages, avoiding the common "duplicate lang item in crate `core`" error that occurs when not all required standard library crates have been built. Not included in this PR is the behaviour around dependencies injected by rustc in `rustc_metadata`, such as panic runtimes and compiler-builtins, which will be addressed in the future.

…uwer Rollup of 11 pull requests Successful merges: - #158460 (Remove llvm_enzyme feature outside of bootstrap) - #159509 (Generate `valid_range`s for enums sign-agnostically) - #159632 (CFI: Add support for the adt_const_params feature) - #159671 (Add semver check test command for checking API compatibility of stdlib) - #157058 (Rustdoc label badge for notable traits) - #159717 (Add `-Zimplicit-sysroot-deps`) - #159850 (Add regression test for closure in array-length const generic) - #159994 (Show jobs where a given test was executed in `test-dashboard`) - #160110 (convert rustc_hir::Target inherent methods to From impls) - #160123 (add additional license option for third-party dependencies) - #160131 (bootstrap: remove temporary bors email lookup)

@CrooseGit

Rollup merge of #159717 - adamgemmell:dev/reucru01/no-implicit-sysroot-deps, r=nnethercote Add `-Zimplicit-sysroot-deps` This PR, originally authored by @CrooseGit, adds support for a new flag [proposed in the `build-std=always` RFC](https://rust-lang.github.io/rfcs/3874-build-std-always.html#preventing-implicit-sysroot-dependencies). It unblocks work by @Bryanskiy around handling panic strategies in build-std, for which rustc must look for them in `-Ldependency` locations and not the sysroot. `-Zimplicit-sysroot-deps` is true by default. When false, rustc will not look in the sysroot when attempting to resolve direct dependencies. It is intended to be used by Cargo when using build-std to improve error messages, avoiding the common "duplicate lang item in crate `core`" error that occurs when not all required standard library crates have been built. Not included in this PR is the behaviour around dependencies injected by rustc in `rustc_metadata`, such as panic runtimes and compiler-builtins, which will be addressed in the future.

CrooseGit added 4 commits July 22, 2026 11:37

Adds -Z implicit-sysroot-deps boolean flag

0195461

Implements implicit-sysroot-deps=false

7b0ecd3

When `-Z implicit-sysroot-deps=false`, the sysroot is not added to the list of search paths for resolving top level dependencies.

Adds tests for `implicit-sysroot-deps=false

56c4f45

One UI test that fails to find crate `std` as it does not look in the sysroot. One UI test that which only transitively depends on std, and thus it is searched for in the sysroot.

Adds more tests for -Z implicit-syroot-deps=false

fd9a014

1) Depending transitively on a lib in the sysroot resolves fine with `-Zimplicit-sysroot-deps=false` 2) Depending directly on a lib in the sysroot does not resolve implicitly with `-Zimplicit-sysroot-deps=false`

rustbot assigned davidtwco Jul 22, 2026

rustbot added A-run-make Area: port run-make Makefiles to rmake.rs S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels Jul 22, 2026

rustbot assigned nnethercote and unassigned davidtwco Jul 22, 2026

nnethercote reviewed Jul 23, 2026

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rustbot removed the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Jul 23, 2026

rustbot added the S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. label Jul 23, 2026

Bryanskiy reviewed Jul 23, 2026

View reviewed changes

Comment thread tests/run-make/implicit-sysroot-deps/rmake.rs Outdated

Comment thread tests/run-make/implicit-sysroot-deps/rmake.rs Outdated

Bryanskiy mentioned this pull request Jul 27, 2026

allow -Ldependency search paths for panic runtimes #160007

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Review updates

b2ed4e8

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Jul 28, 2026

nnethercote approved these changes Jul 29, 2026

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rust-bors Bot added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Jul 29, 2026

jhpratt mentioned this pull request Jul 29, 2026

Rollup of 6 pull requests #160135

Closed

This was referenced Jul 29, 2026

Rollup of 6 pull requests #160138

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Rollup of 11 pull requests #160146

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rust-bors Bot merged commit 9ad1558 into rust-lang:main Jul 29, 2026
13 checks passed

rustbot added this to the 1.99.0 milestone Jul 29, 2026

adamgemmell deleted the dev/reucru01/no-implicit-sysroot-deps branch July 29, 2026 18:03

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Add `-Zimplicit-sysroot-deps` - #159717

Add `-Zimplicit-sysroot-deps`#159717
rust-bors[bot] merged 5 commits into
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