feat: Extra build dependencies by HARSHVARANDANI · Pull Request #5746 · prefix-dev/pixi

HARSHVARANDANI · 2026-03-21T16:57:29Z

Description

This PR adds support for specifying extra build dependencies for PyPI packages via pixi.toml.

Some PyPI packages rely on build-time dependencies that are not properly declared in their build-system.requires. This can cause builds to fail when using build isolation, making environments non-reproducible without manual intervention.

This change allows users to explicitly declare missing build dependencies directly in pixi.toml, enabling reproducible environments using a single configuration file.

Example:

[extra-build-dependencies]
fused-ssim = ["torch"]

Pixi will ensure that the specified dependencies are available in the PEP 517 build environment when building the package.

Motivation

Certain PyPI packages import or require dependencies during build time but fail to declare them in their metadata.

Examples include packages that:

import torch during setup
require numpy headers to compile extensions
dynamically configure build extensions
rely on build-time tooling such as ninja, packaging, etc.

Without this feature, users must:

disable build isolation
manually preinstall dependencies
maintain separate environment setup steps

This reduces reproducibility and complicates workflows.

This feature brings Pixi in line with similar functionality already available in uv.

Fixes #5614

Behavior

When building a PyPI package from source:

build dependencies = build-system.requires + extra-build-dependencies

Extra dependencies are only available during the build phase and are not installed in the runtime environment unless explicitly declared in [pypi-dependencies].

How Has This Been Tested?

Integration tests confirm:

manifest parsing accepts [extra-build-dependencies]
build dependencies are injected correctly
build succeeds when missing build dependency is provided
runtime environment is unaffected
works with no-build-isolation
lockfile generation unchanged

A custom test package requiring numpy during build phase was used to validate the full pipeline.

AI Disclosure

This PR contains AI-generated content.
- I have tested any AI-generated content in my PR.
- I take responsibility for any AI-generated content in my PR.

Checklist:

I have performed a self-review of my own code
I have commented my code, particularly in hard-to-understand areas
I have made corresponding changes to the documentation
I have added sufficient tests to cover my changes.

Signed-off-by: HARSHVARANDANI <hpvarandani@gmail.com>

… CI since the function is no longer unused Signed-off-by: HARSHVARANDANI <hpvarandani@gmail.com>

…accepted in a real pypi lock/update Signed-off-by: HARSHVARANDANI <hpvarandani@gmail.com>

… requires/config/variables instead of local defaults Signed-off-by: HARSHVARANDANI <hpvarandani@gmail.com>

…rams Signed-off-by: HARSHVARANDANI <hpvarandani@gmail.com>

…est during both lock update context initialization paths Signed-off-by: HARSHVARANDANI <hpvarandani@gmail.com>

… the conversion behavior Signed-off-by: HARSHVARANDANI <hpvarandani@gmail.com>

…OML conversion Signed-off-by: HARSHVARANDANI <hpvarandani@gmail.com>

…EP508 build requirements Signed-off-by: HARSHVARANDANI <hpvarandani@gmail.com>

Signed-off-by: HARSHVARANDANI <hpvarandani@gmail.com>

…te dependencies Signed-off-by: HARSHVARANDANI <hpvarandani@gmail.com>

HARSHVARANDANI · 2026-03-30T16:14:50Z

@baszalmstra Could you take a look at this when you've got time? Some feedback would be really helpful.
Thank you! 🙂

tdejager

Some small changes

tdejager · 2026-03-31T07:30:09Z

+/// Convert manifest-defined extra build dependencies into uv's
+/// [`ExtraBuildRequires`] structure.
+///
+/// Each manifest requirement is converted to a uv requirement and wrapped in an
+/// [`ExtraBuildRequirement`] with `match_runtime = false` for v1 behavior.
+///
+/// The `workspace_root` parameter is currently unused but kept in the API to
+/// preserve call-site intent and future conversion support for path-based
+/// requirement forms.
+pub fn convert_extra_build_dependencies(
+    deps: &Option<IndexMap<PypiPackageName, Vec<pep508_rs::Requirement>>>,
+    _workspace_root: &Path,
+) -> Result<ExtraBuildRequires, pixi_uv_conversions::ConversionError> {
+    let mut extra_build_requires = ExtraBuildRequires::default();
+
+    for (package, specs) in deps.iter().flatten() {
+        let requirements = specs
+            .iter()
+            .map(|spec| {
+                pep508_requirement_to_uv_requirement(spec.clone()).map(|requirement| {
+                    ExtraBuildRequirement {
+                        requirement,
+                        match_runtime: false,
+                    }
+                })
+            })
+            .collect::<Result<Vec<_>, _>>()?;
+
+        if requirements.is_empty() {
+            continue;
+        }
+
+        let package_name = uv_normalize::PackageName::from_str(package.as_normalized().as_ref())
+            .expect("pypi package names in manifest should always be valid");
+        extra_build_requires.insert(package_name, requirements);
+    }
+
+    Ok(extra_build_requires)
+}


I think this can go into the pixi_uv_conversions crate.

tdejager · 2026-03-31T07:30:29Z

+mod tests {
+    use std::str::FromStr;
+
+    use indexmap::IndexMap;
+    use pixi_pypi_spec::PypiPackageName;
+
+    use super::convert_extra_build_dependencies;
+
+    #[test]
+    fn converts_extra_build_dependencies() {
+        let mut deps: IndexMap<PypiPackageName, Vec<pep508_rs::Requirement>> = IndexMap::new();
+        deps.insert(
+            PypiPackageName::from_str("fused-ssim").unwrap(),
+            vec![pep508_rs::Requirement::from_str("torch>=2").unwrap()],
+        );
+
+        let converted = convert_extra_build_dependencies(&Some(deps), std::path::Path::new("."))
+            .expect("conversion should succeed");
+
+        let pkg_name = uv_normalize::PackageName::from_str("fused-ssim").unwrap();
+        let requirements = converted.get(&pkg_name).expect("package should be present");
+        assert_eq!(requirements.len(), 1);
+        assert_eq!(requirements[0].requirement.name.as_ref(), "torch");
+        assert!(!requirements[0].match_runtime);
+    }
+
+    #[test]
+    fn empty_extra_build_dependencies_is_noop() {
+        let converted = convert_extra_build_dependencies(&None, std::path::Path::new(".")).unwrap();
+        assert!(converted.is_empty());
+    }
+}


Same for this.

tdejager

Also we @ruben-arts pointed me to this but we should make the extra-build-dependencies avialable under the dependency types, merge these across feature somehow and re-construct the map before doing the environment installation and solve.

…se tests

… test cases

…ments

HARSHVARANDANI · 2026-04-04T20:14:25Z

@tdejager I have made requested changes. If you could please check for any more changes needed?

tdejager · 2026-04-07T07:06:24Z

Hey, this did not make the changes we requested its still a top-level table.

HARSHVARANDANI changed the title ~~feat:extra build dependencies~~ feat: Extra build dependencies Mar 21, 2026

HARSHVARANDANI force-pushed the feat/extra-build-dependencies branch 2 times, most recently from e714a86 to a6604de Compare March 22, 2026 19:18

HARSHVARANDANI added 13 commits March 23, 2026 00:57

added extra-build-dependencies as expected key in the snapshots

e4f13ab

Signed-off-by: HARSHVARANDANI <hpvarandani@gmail.com>

added missing toml snippet close fence

57e02c8

Signed-off-by: HARSHVARANDANI <hpvarandani@gmail.com>

added some comments

830e615

Signed-off-by: HARSHVARANDANI <hpvarandani@gmail.com>

commented [expect(unused)] for with_extra_build_requires fucntion for…

9b81b30

… CI since the function is no longer unused Signed-off-by: HARSHVARANDANI <hpvarandani@gmail.com>

added integration smoke test to verify [extra-build-dependencies] is …

708d9cd

…accepted in a real pypi lock/update Signed-off-by: HARSHVARANDANI <hpvarandani@gmail.com>

switched install planning indexes to use context-provided extra build…

88632d0

… requires/config/variables instead of local defaults Signed-off-by: HARSHVARANDANI <hpvarandani@gmail.com>

passed context.extra_build_requires into solve-time UvBuildDispatchPa…

ff1d2b4

…rams Signed-off-by: HARSHVARANDANI <hpvarandani@gmail.com>

add UvResolutionContext.extra_build_dependencies from workspace manif…

ebe1979

…est during both lock update context initialization paths Signed-off-by: HARSHVARANDANI <hpvarandani@gmail.com>

added conversion from manifest to uv ExtraBuildRequires and tests for…

fcc7eab

… the conversion behavior Signed-off-by: HARSHVARANDANI <hpvarandani@gmail.com>

initialized Workspace.extra_build_dependencies to None on workspave T…

879b824

…OML conversion Signed-off-by: HARSHVARANDANI <hpvarandani@gmail.com>

added Workspace.extra_build_dependencies to store per-package extra P…

9bca7c2

…EP508 build requirements Signed-off-by: HARSHVARANDANI <hpvarandani@gmail.com>

added parsing for [extra-build-dependencies] and a test for the same

846ce59

Signed-off-by: HARSHVARANDANI <hpvarandani@gmail.com>

recorded lockfile dependency updates from the new pixi_uv_context cra…

896a854

…te dependencies Signed-off-by: HARSHVARANDANI <hpvarandani@gmail.com>

HARSHVARANDANI force-pushed the feat/extra-build-dependencies branch from a6604de to 896a854 Compare March 22, 2026 19:35

HARSHVARANDANI and others added 3 commits March 23, 2026 01:08

merge conflicts resolved

428f84f

Merge branch 'main' into feat/extra-build-dependencies

70651eb

Merge branch 'main' into feat/extra-build-dependencies

066c778

tdejager requested changes Mar 31, 2026

View reviewed changes

HARSHVARANDANI and others added 7 commits April 1, 2026 01:44

Merge branch 'main' into feat/extra-build-dependencies

126cde6

moved helpers from pixi_uv_context crate to pixi_uv_conversions crate

e4b9422

lint fixes

61f99b6

removed workspace level extra-build-dependencies fields

9b32f55

removed workspace level extra-build-dependencies fields from toml wiring

066915f

added parsng of feature scoped extra-build-dependencies

c1a1529

routing extra-build-dependencies to default feature and added edge ca…

14d1217

…se tests

HARSHVARANDANI added 9 commits April 1, 2026 12:25

added merging if extra-build-dependencies per environment

a9b99c0

using the merged extra-build-dependencies in lock update

3344720

added environment-level tests for scoped merge semantics and EDE edge…

03bf367

… test cases

added EDE conversion tests for empty-map and multi-package scenarios

7c40020

integration of feature-scoped extra-build-dependencies across environ…

887412d

…ments

added parsing of feature scoped extra-build-dependenies from toml

ee85682

test script for merged and scoped extra-build-dependencies

798192c

ran linters

86e6814

changed snapshots for updated extra-build-dependencies

2f32c72

HARSHVARANDANI requested a review from tdejager April 1, 2026 16:45

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HARSHVARANDANI commented Mar 21, 2026 •

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Description

Motivation

Behavior

How Has This Been Tested?

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HARSHVARANDANI commented Mar 21, 2026 •

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