Add tool.uv.build-constraint-dependencies to pyproject.toml (#11585)

## Summary

Resolves #6913. 

Add `tool.uv.build-constraint-dependencies` to pyproject.toml.
The changes are analogous to the constraint-dependencies feature
implemented in #5248.

Add documentation for `build-constraint-dependencies`

## Test Plan

Add tests for `uv lock`, `uv add`, `uv pip install` and `uv pip
compile`.

---------

Co-authored-by: Charlie Marsh <charlie.r.marsh@gmail.com>

crates/uv-scripts/src/lib.rs

@@ -331,6 +331,7 @@ pub struct ToolUv {
     pub top_level: ResolverInstallerOptions,
     pub override_dependencies: Option<Vec<uv_pep508::Requirement<VerbatimParsedUrl>>>,
     pub constraint_dependencies: Option<Vec<uv_pep508::Requirement<VerbatimParsedUrl>>>,
+    pub build_constraint_dependencies: Option<Vec<uv_pep508::Requirement<VerbatimParsedUrl>>>,
     pub sources: Option<BTreeMap<PackageName, Sources>>,
 }
 

crates/uv-settings/src/settings.rs

@@ -107,6 +107,9 @@ pub struct Options {
     #[cfg_attr(feature = "schemars", schemars(skip))]
     pub constraint_dependencies: Option<Vec<Requirement<VerbatimParsedUrl>>>,
 
+    #[cfg_attr(feature = "schemars", schemars(skip))]
+    pub build_constraint_dependencies: Option<Vec<Requirement<VerbatimParsedUrl>>>,
+
     #[cfg_attr(feature = "schemars", schemars(skip))]
     pub environments: Option<SupportedEnvironments>,
 
@@ -1792,6 +1795,7 @@ pub struct OptionsWire {
     // They're respected in both `pyproject.toml` and `uv.toml` files.
     override_dependencies: Option<Vec<Requirement<VerbatimParsedUrl>>>,
     constraint_dependencies: Option<Vec<Requirement<VerbatimParsedUrl>>>,
+    build_constraint_dependencies: Option<Vec<Requirement<VerbatimParsedUrl>>>,
     environments: Option<SupportedEnvironments>,
     required_environments: Option<SupportedEnvironments>,
 
@@ -1858,6 +1862,7 @@ impl From<OptionsWire> for Options {
             cache_keys,
             override_dependencies,
             constraint_dependencies,
+            build_constraint_dependencies,
             environments,
             required_environments,
             conflicts,
@@ -1922,6 +1927,7 @@ impl From<OptionsWire> for Options {
             cache_keys,
             override_dependencies,
             constraint_dependencies,
+            build_constraint_dependencies,
             environments,
             required_environments,
             install_mirrors: PythonInstallMirrors::resolve(

crates/uv-workspace/src/pyproject.rs

@@ -479,6 +479,37 @@ pub struct ToolUv {
     )]
     pub constraint_dependencies: Option<Vec<uv_pep508::Requirement<VerbatimParsedUrl>>>,
 
+    /// Constraints to apply when solving build dependencies.
+    ///
+    /// Build constraints are used to restrict the versions of build dependencies that are selected
+    /// when building a package during resolution or installation.
+    ///
+    /// Including a package as a constraint will _not_ trigger installation of the package during
+    /// a build; instead, the package must be requested elsewhere in the project's build dependency
+    /// graph.
+    ///
+    /// !!! note
+    ///     In `uv lock`, `uv sync`, and `uv run`, uv will only read `build-constraint-dependencies` from
+    ///     the `pyproject.toml` at the workspace root, and will ignore any declarations in other
+    ///     workspace members or `uv.toml` files.
+    #[cfg_attr(
+        feature = "schemars",
+        schemars(
+            with = "Option<Vec<String>>",
+            description = "PEP 508-style requirements, e.g., `ruff==0.5.0`, or `ruff @ https://...`."
+        )
+    )]
+    #[option(
+        default = "[]",
+        value_type = "list[str]",
+        example = r#"
+            # Ensure that the setuptools v60.0.0 is used whenever a package has a build dependency
+            # on setuptools.
+            build-constraint-dependencies = ["setuptools==60.0.0"]
+        "#
+    )]
+    pub build_constraint_dependencies: Option<Vec<uv_pep508::Requirement<VerbatimParsedUrl>>>,
+
     /// A list of supported environments against which to resolve dependencies.
     ///
     /// By default, uv will resolve for all possible environments during a `uv lock` operation.

crates/uv-workspace/src/workspace.rs

@@ -496,6 +496,20 @@ impl Workspace {
         constraints.clone()
     }
 
+    /// Returns the set of build constraints for the workspace.
+    pub fn build_constraints(&self) -> Vec<uv_pep508::Requirement<VerbatimParsedUrl>> {
+        let Some(build_constraints) = self
+            .pyproject_toml
+            .tool
+            .as_ref()
+            .and_then(|tool| tool.uv.as_ref())
+            .and_then(|uv| uv.build_constraint_dependencies.as_ref())
+        else {
+            return vec![];
+        };
+        build_constraints.clone()
+    }
+
     /// The path to the workspace root, the directory containing the top level `pyproject.toml` with
     /// the `uv.tool.workspace`, or the `pyproject.toml` in an implicit single workspace project.
     pub fn install_path(&self) -> &PathBuf {
@@ -1725,6 +1739,7 @@ mod tests {
                       "dev-dependencies": null,
                       "override-dependencies": null,
                       "constraint-dependencies": null,
+                      "build-constraint-dependencies": null,
                       "environments": null,
                       "required-environments": null,
                       "conflicts": null
@@ -1818,6 +1833,7 @@ mod tests {
                       "dev-dependencies": null,
                       "override-dependencies": null,
                       "constraint-dependencies": null,
+                      "build-constraint-dependencies": null,
                       "environments": null,
                       "required-environments": null,
                       "conflicts": null
@@ -2025,6 +2041,7 @@ mod tests {
                       "dev-dependencies": null,
                       "override-dependencies": null,
                       "constraint-dependencies": null,
+                      "build-constraint-dependencies": null,
                       "environments": null,
                       "required-environments": null,
                       "conflicts": null
@@ -2130,6 +2147,7 @@ mod tests {
                       "dev-dependencies": null,
                       "override-dependencies": null,
                       "constraint-dependencies": null,
+                      "build-constraint-dependencies": null,
                       "environments": null,
                       "required-environments": null,
                       "conflicts": null
@@ -2248,6 +2266,7 @@ mod tests {
                       "dev-dependencies": null,
                       "override-dependencies": null,
                       "constraint-dependencies": null,
+                      "build-constraint-dependencies": null,
                       "environments": null,
                       "required-environments": null,
                       "conflicts": null
@@ -2340,6 +2359,7 @@ mod tests {
                       "dev-dependencies": null,
                       "override-dependencies": null,
                       "constraint-dependencies": null,
+                      "build-constraint-dependencies": null,
                       "environments": null,
                       "required-environments": null,
                       "conflicts": null

crates/uv/src/commands/pip/compile.rs

@@ -56,6 +56,7 @@ pub(crate) async fn pip_compile(
     build_constraints: &[RequirementsSource],
     constraints_from_workspace: Vec<Requirement>,
     overrides_from_workspace: Vec<Requirement>,
+    build_constraints_from_workspace: Vec<Requirement>,
     environments: SupportedEnvironments,
     extras: ExtrasSpecification,
     groups: DevGroupsSpecification,
@@ -184,8 +185,17 @@ pub(crate) async fn pip_compile(
         .collect();
 
     // Read build constraints.
-    let build_constraints =
+    let build_constraints: Vec<NameRequirementSpecification> =
-        operations::read_constraints(build_constraints, &client_builder).await?;
+        operations::read_constraints(build_constraints, &client_builder)
+            .await?
+            .iter()
+            .cloned()
+            .chain(
+                build_constraints_from_workspace
+                    .into_iter()
+                    .map(NameRequirementSpecification::from),
+            )
+            .collect();
 
     // If all the metadata could be statically resolved, validate that every extra was used. If we
     // need to resolve metadata via PEP 517, we don't know which extras are used until much later.

crates/uv/src/commands/pip/install.rs

@@ -51,6 +51,7 @@ pub(crate) async fn pip_install(
     build_constraints: &[RequirementsSource],
     constraints_from_workspace: Vec<Requirement>,
     overrides_from_workspace: Vec<Requirement>,
+    build_constraints_from_workspace: Vec<Requirement>,
     extras: &ExtrasSpecification,
     groups: &DevGroupsSpecification,
     resolution_mode: ResolutionMode,
@@ -123,10 +124,6 @@ pub(crate) async fn pip_install(
     )
     .await?;
 
-    // Read build constraints.
-    let build_constraints =
-        operations::read_constraints(build_constraints, &client_builder).await?;
-
     let constraints: Vec<NameRequirementSpecification> = constraints
         .iter()
         .cloned()
@@ -147,6 +144,20 @@ pub(crate) async fn pip_install(
         )
         .collect();
 
+    // Read build constraints.
+    let build_constraints: Vec<NameRequirementSpecification> =
+        operations::read_constraints(build_constraints, &client_builder)
+            .await?
+            .iter()
+            .cloned()
+            .chain(
+                build_constraints_from_workspace
+                    .iter()
+                    .cloned()
+                    .map(NameRequirementSpecification::from),
+            )
+            .collect();
+
     // Detect the current Python interpreter.
     let environment = if target.is_some() || prefix.is_some() {
         let installation = PythonInstallation::find(

crates/uv/src/commands/project/lock.rs

@@ -366,6 +366,7 @@ async fn do_lock(
     let requirements = target.requirements();
     let overrides = target.overrides();
     let constraints = target.constraints();
+    let build_constraints = target.build_constraints();
     let dependency_groups = target.dependency_groups()?;
     let source_trees = vec![];
 
@@ -373,6 +374,7 @@ async fn do_lock(
     let requirements = target.lower(requirements, index_locations, sources)?;
     let overrides = target.lower(overrides, index_locations, sources)?;
     let constraints = target.lower(constraints, index_locations, sources)?;
+    let build_constraints = target.lower(build_constraints, index_locations, sources)?;
     let dependency_groups = dependency_groups
         .into_iter()
         .map(|(name, requirements)| {
@@ -556,9 +558,10 @@ async fn do_lock(
         .build();
     let hasher = HashStrategy::Generate(HashGeneration::Url);
 
+    let build_constraints = Constraints::from_requirements(build_constraints.iter().cloned());
+
     // TODO(charlie): These are all default values. We should consider whether we want to make them
     // optional on the downstream APIs.
-    let build_constraints = Constraints::default();
     let build_hasher = HashStrategy::default();
     let extras = ExtrasSpecification::default();
     let groups = DevGroupsSpecification::default();

crates/uv/src/commands/project/lock_target.rs

@@ -79,6 +79,23 @@ impl<'lock> LockTarget<'lock> {
         }
     }
 
+    /// Returns the set of build constraints for the [`LockTarget`].
+    pub(crate) fn build_constraints(self) -> Vec<uv_pep508::Requirement<VerbatimParsedUrl>> {
+        match self {
+            Self::Workspace(workspace) => workspace.build_constraints(),
+            Self::Script(script) => script
+                .metadata
+                .tool
+                .as_ref()
+                .and_then(|tool| tool.uv.as_ref())
+                .and_then(|uv| uv.build_constraint_dependencies.as_ref())
+                .into_iter()
+                .flatten()
+                .cloned()
+                .collect(),
+        }
+    }
+
     /// Return the dependency groups that are attached to the target directly, as opposed to being
     /// attached to any members within the target.
     pub(crate) fn dependency_groups(

crates/uv/src/lib.rs

@@ -389,6 +389,7 @@ async fn run(mut cli: Cli) -> Result<ExitStatus> {
                 &build_constraints,
                 args.constraints_from_workspace,
                 args.overrides_from_workspace,
+                args.build_constraints_from_workspace,
                 args.environments,
                 args.settings.extras,
                 args.settings.groups,
@@ -561,6 +562,7 @@ async fn run(mut cli: Cli) -> Result<ExitStatus> {
                 &build_constraints,
                 args.constraints_from_workspace,
                 args.overrides_from_workspace,
+                args.build_constraints_from_workspace,
                 &args.settings.extras,
                 &args.settings.groups,
                 args.settings.resolution,

crates/uv/src/settings.rs

@@ -1540,6 +1540,7 @@ pub(crate) struct PipCompileSettings {
     pub(crate) build_constraints: Vec<PathBuf>,
     pub(crate) constraints_from_workspace: Vec<Requirement>,
     pub(crate) overrides_from_workspace: Vec<Requirement>,
+    pub(crate) build_constraints_from_workspace: Vec<Requirement>,
     pub(crate) environments: SupportedEnvironments,
     pub(crate) refresh: Refresh,
     pub(crate) settings: PipSettings,
@@ -1626,6 +1627,20 @@ impl PipCompileSettings {
             Vec::new()
         };
 
+        let build_constraints_from_workspace = if let Some(configuration) = &filesystem {
+            configuration
+                .build_constraint_dependencies
+                .clone()
+                .unwrap_or_default()
+                .into_iter()
+                .map(|requirement| {
+                    Requirement::from(requirement.with_origin(RequirementOrigin::Workspace))
+                })
+                .collect()
+        } else {
+            Vec::new()
+        };
+
         let environments = if let Some(configuration) = &filesystem {
             configuration.environments.clone().unwrap_or_default()
         } else {
@@ -1648,6 +1663,7 @@ impl PipCompileSettings {
                 .collect(),
             constraints_from_workspace,
             overrides_from_workspace,
+            build_constraints_from_workspace,
             environments,
             refresh: Refresh::from(refresh),
             settings: PipSettings::combine(
@@ -1783,6 +1799,7 @@ pub(crate) struct PipInstallSettings {
     pub(crate) dry_run: DryRun,
     pub(crate) constraints_from_workspace: Vec<Requirement>,
     pub(crate) overrides_from_workspace: Vec<Requirement>,
+    pub(crate) build_constraints_from_workspace: Vec<Requirement>,
     pub(crate) modifications: Modifications,
     pub(crate) refresh: Refresh,
     pub(crate) settings: PipSettings,
@@ -1858,6 +1875,20 @@ impl PipInstallSettings {
             Vec::new()
         };
 
+        let build_constraints_from_workspace = if let Some(configuration) = &filesystem {
+            configuration
+                .build_constraint_dependencies
+                .clone()
+                .unwrap_or_default()
+                .into_iter()
+                .map(|requirement| {
+                    Requirement::from(requirement.with_origin(RequirementOrigin::Workspace))
+                })
+                .collect()
+        } else {
+            Vec::new()
+        };
+
         Self {
             package,
             requirements,
@@ -1877,6 +1908,7 @@ impl PipInstallSettings {
             dry_run: DryRun::from_args(dry_run),
             constraints_from_workspace,
             overrides_from_workspace,
+            build_constraints_from_workspace,
             modifications: if flag(exact, inexact).unwrap_or(false) {
                 Modifications::Exact
             } else {

crates/uv/tests/it/edit.rs

@@ -9714,3 +9714,59 @@ fn repeated_index_cli_reversed() -> Result<()> {
 
     Ok(())
 }
+
+#[test]
+fn add_with_build_constraints() -> Result<()> {
+    let context = TestContext::new("3.8");
+
+    let pyproject_toml = context.temp_dir.child("pyproject.toml");
+    pyproject_toml.write_str(indoc! {r#"
+    [project]
+    name = "project"
+    version = "0.1.0"
+    requires-python = ">=3.8"
+    dependencies = []
+
+    [tool.uv]
+    build-constraint-dependencies = ["setuptools==1"]
+    "#})?;
+
+    uv_snapshot!(context.filters(), context.add().arg("requests==1.2"), @r"
+    success: false
+    exit_code: 1
+    ----- stdout -----
+
+    ----- stderr -----
+      × Failed to download and build `requests==1.2.0`
+      ├─▶ Failed to resolve requirements from `setup.py` build
+      ├─▶ No solution found when resolving: `setuptools>=40.8.0`
+      ╰─▶ Because you require setuptools>=40.8.0 and setuptools==1, we can conclude that your requirements are unsatisfiable.
+      help: `requests` (v1.2.0) was included because `project` (v0.1.0) depends on `requests==1.2`
+    ");
+
+    let pyproject_toml = context.temp_dir.child("pyproject.toml");
+    pyproject_toml.write_str(indoc! {r#"
+    [project]
+    name = "project"
+    version = "0.1.0"
+    requires-python = ">=3.8"
+    dependencies = []
+
+    [tool.uv]
+    build-constraint-dependencies = ["setuptools>=40"]
+    "#})?;
+
+    uv_snapshot!(context.filters(), context.add().arg("requests==1.2"), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+
+    ----- stderr -----
+    Resolved 2 packages in [TIME]
+    Prepared 1 package in [TIME]
+    Installed 1 package in [TIME]
+     + requests==1.2.0
+    "###);
+
+    Ok(())
+}

crates/uv/tests/it/lock.rs

@@ -1883,6 +1883,146 @@ fn lock_project_with_constraint_sources() -> Result<()> {
     Ok(())
 }
 
+/// Lock a project with `uv.tool.build-constraint-dependencies`.
+#[test]
+fn lock_project_with_build_constraints() -> Result<()> {
+    let context = TestContext::new("3.12");
+
+    let pyproject_toml = context.temp_dir.child("pyproject.toml");
+    pyproject_toml.write_str(
+        r#"
+        [project]
+        name = "project"
+        version = "0.1.0"
+        requires-python = ">=3.12"
+        dependencies = ["anyio==3.7.0"]
+
+        # This should be ignored because none of the dependencies requires `setuptools`
+        [tool.uv]
+        build-constraint-dependencies = ["setuptools==1"]
+        "#,
+    )?;
+
+    uv_snapshot!(context.filters(), context.lock(), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+
+    ----- stderr -----
+    Resolved 4 packages in [TIME]
+    "###);
+
+    // Re-run with `--locked`.
+    uv_snapshot!(context.filters(), context.lock().arg("--locked"), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+
+    ----- stderr -----
+    Resolved 4 packages in [TIME]
+    "###);
+
+    // Install the base dependencies from the lockfile.
+    uv_snapshot!(context.filters(), context.sync().arg("--frozen"), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+
+    ----- stderr -----
+    Prepared 3 packages in [TIME]
+    Installed 3 packages in [TIME]
+     + anyio==3.7.0
+     + idna==3.6
+     + sniffio==1.3.1
+    "###);
+
+    let pyproject_toml = context.temp_dir.child("pyproject.toml");
+    pyproject_toml.write_str(
+        r#"
+        [project]
+        name = "project"
+        version = "0.1.0"
+        requires-python = ">=3.8"
+        dependencies = ["requests==1.2"]
+
+        # This should fail the operation, since `requests` depends on `setuptools` at build time.
+        [tool.uv]
+        build-constraint-dependencies = ["setuptools==1"]
+        "#,
+    )?;
+
+    uv_snapshot!(context.filters(), context.lock(), @r"
+    success: false
+    exit_code: 1
+    ----- stdout -----
+
+    ----- stderr -----
+      × Failed to download and build `requests==1.2.0`
+      ├─▶ Failed to resolve requirements from `setup.py` build
+      ├─▶ No solution found when resolving: `setuptools>=40.8.0`
+      ╰─▶ Because you require setuptools>=40.8.0 and setuptools==1, we can conclude that your requirements are unsatisfiable.
+      help: `requests` (v1.2.0) was included because `project` (v0.1.0) depends on `requests==1.2`
+    ");
+
+    Ok(())
+}
+
+/// Lock a project with `uv.tool.build-constraint-dependencies` that reference `tool.uv.sources`.
+#[test]
+fn lock_project_with_build_constraint_sources() -> Result<()> {
+    let context = TestContext::new("3.9");
+
+    let pyproject_toml = context.temp_dir.child("pyproject.toml");
+    pyproject_toml.write_str(
+        r#"
+        [project]
+        name = "project"
+        version = "0.1.0"
+        requires-python = ">=3.8"
+        dependencies = ["requests==1.2"]
+
+        [tool.uv]
+        build-constraint-dependencies = ["setuptools==75.8.0"]
+
+        [tool.uv.sources]
+        setuptools = { url = "https://files.pythonhosted.org/packages/69/8a/b9dc7678803429e4a3bc9ba462fa3dd9066824d3c607490235c6a796be5a/setuptools-75.8.0-py3-none-any.whl" }
+        "#,
+    )?;
+
+    uv_snapshot!(context.filters(), context.lock(), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+
+    ----- stderr -----
+    Resolved 2 packages in [TIME]
+    "###);
+
+    // Re-run with `--locked`.
+    uv_snapshot!(context.filters(), context.lock().arg("--locked"), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+
+    ----- stderr -----
+    Resolved 2 packages in [TIME]
+    "###);
+
+    // Install the base dependencies from the lockfile.
+    uv_snapshot!(context.filters(), context.sync().arg("--frozen"), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+
+    ----- stderr -----
+    Prepared 1 package in [TIME]
+    Installed 1 package in [TIME]
+     + requests==1.2.0
+    "###);
+
+    Ok(())
+}
+
 /// Lock a project with a dependency that has an extra.
 #[test]
 fn lock_dependency_extra() -> Result<()> {

crates/uv/tests/it/pip_compile.rs

@@ -13572,6 +13572,259 @@ fn compatible_build_constraint() -> Result<()> {
     Ok(())
 }
 
+/// Include `build-constraint-dependencies` in pyproject.toml with an incompatible constraint.
+#[test]
+fn incompatible_build_constraint_in_pyproject_toml() -> Result<()> {
+    let context = TestContext::new("3.8");
+    let pyproject_toml = context.temp_dir.child("pyproject.toml");
+    pyproject_toml.write_str(
+        r#"[build-system]
+requires = ["setuptools"]
+
+[project]
+name = "project"
+version = "0.1.0"
+dependencies = [
+    "requests==1.2",
+]
+
+[tool.uv]
+build-constraint-dependencies = [
+    "setuptools==1",
+]
+"#,
+    )?;
+
+    uv_snapshot!(context.pip_compile()
+        .arg("pyproject.toml"), @r###"
+    success: false
+    exit_code: 1
+    ----- stdout -----
+
+    ----- stderr -----
+      × Failed to download and build `requests==1.2.0`
+      ├─▶ Failed to resolve requirements from `setup.py` build
+      ├─▶ No solution found when resolving: `setuptools>=40.8.0`
+      ╰─▶ Because you require setuptools>=40.8.0 and setuptools==1, we can conclude that your requirements are unsatisfiable.
+    "###
+    );
+
+    Ok(())
+}
+
+/// Include `build-constraint-dependencies` in pyproject.toml with a compatible constraint.
+#[test]
+fn compatible_build_constraint_in_pyproject_toml() -> Result<()> {
+    let context = TestContext::new("3.8");
+    let pyproject_toml = context.temp_dir.child("pyproject.toml");
+    pyproject_toml.write_str(
+        r#"[build-system]
+requires = ["setuptools"]
+
+[project]
+name = "project"
+version = "0.1.0"
+dependencies = [
+    "requests==1.2",
+]
+
+[tool.uv]
+build-constraint-dependencies = [
+    "setuptools>=40",
+]
+"#,
+    )?;
+
+    uv_snapshot!(context.pip_compile()
+        .arg("pyproject.toml"), @r"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+    # This file was autogenerated by uv via the following command:
+    #    uv pip compile --cache-dir [CACHE_DIR] pyproject.toml
+    requests==1.2.0
+        # via project (pyproject.toml)
+
+    ----- stderr -----
+    Resolved 1 package in [TIME]
+    "
+    );
+
+    Ok(())
+}
+
+/// Merge `build_constraints.txt` with `build-constraint-dependencies` in pyproject.toml with an incompatible constraint.
+#[test]
+fn incompatible_build_constraint_merged_with_pyproject_toml() -> Result<()> {
+    let context = TestContext::new("3.8");
+
+    // incompatible setuptools version in pyproject.toml, compatible in build_constraints.txt
+    let constraints_txt = context.temp_dir.child("build_constraints.txt");
+    constraints_txt.write_str("setuptools>=40")?;
+    let pyproject_toml = context.temp_dir.child("pyproject.toml");
+    pyproject_toml.write_str(
+        r#"[build-system]
+requires = ["setuptools"]
+
+[project]
+name = "project"
+version = "0.1.0"
+dependencies = [
+    "requests==1.2",
+]
+
+[tool.uv]
+build-constraint-dependencies = [
+    "setuptools==1",
+]
+"#,
+    )?;
+
+    uv_snapshot!(context.pip_compile()
+        .arg("pyproject.toml")
+        .arg("--build-constraint")
+        .arg("build_constraints.txt"), @r###"
+    success: false
+    exit_code: 1
+    ----- stdout -----
+
+    ----- stderr -----
+      × Failed to download and build `requests==1.2.0`
+      ├─▶ Failed to resolve requirements from `setup.py` build
+      ├─▶ No solution found when resolving: `setuptools>=40.8.0`
+      ╰─▶ Because you require setuptools>=40 and setuptools==1, we can conclude that your requirements are unsatisfiable.
+    "###
+    );
+
+    // compatible setuptools version in pyproject.toml, incompatible in build_constraints.txt
+    let constraints_txt = context.temp_dir.child("build_constraints.txt");
+    constraints_txt.write_str("setuptools==1")?;
+
+    let pyproject_toml = context.temp_dir.child("pyproject.toml");
+    pyproject_toml.write_str(
+        r#"[build-system]
+requires = ["setuptools"]
+
+[project]
+name = "project"
+version = "0.1.0"
+dependencies = [
+    "requests==1.2",
+]
+
+[tool.uv]
+build-constraint-dependencies = [
+    "setuptools>=40",
+]
+"#,
+    )?;
+
+    uv_snapshot!(context.pip_compile()
+        .arg("pyproject.toml")
+        .arg("--build-constraint")
+        .arg("build_constraints.txt"), @r###"
+    success: false
+    exit_code: 1
+    ----- stdout -----
+
+    ----- stderr -----
+      × Failed to download and build `requests==1.2.0`
+      ├─▶ Failed to resolve requirements from `setup.py` build
+      ├─▶ No solution found when resolving: `setuptools>=40.8.0`
+      ╰─▶ Because you require setuptools==1 and setuptools>=40, we can conclude that your requirements are unsatisfiable.
+    "###
+    );
+
+    Ok(())
+}
+
+/// Merge CLI args `build_constraints.txt` with `build-constraint-dependencies` in pyproject.toml with a compatible constraint.
+#[test]
+fn compatible_build_constraint_merged_with_pyproject_toml() -> Result<()> {
+    let context = TestContext::new("3.8");
+
+    // incompatible setuptools version in pyproject.toml, compatible in build_constraints.txt
+    let constraints_txt = context.temp_dir.child("build_constraints.txt");
+    constraints_txt.write_str("setuptools>=40")?;
+    let pyproject_toml = context.temp_dir.child("pyproject.toml");
+    pyproject_toml.write_str(
+        r#"[build-system]
+requires = ["setuptools"]
+
+[project]
+name = "project"
+version = "0.1.0"
+dependencies = [
+    "requests==1.2",
+]
+
+[tool.uv]
+build-constraint-dependencies = [
+    "setuptools>=1",
+]
+"#,
+    )?;
+
+    uv_snapshot!(context.pip_compile()
+        .arg("pyproject.toml")
+        .arg("--build-constraint")
+        .arg("build_constraints.txt"), @r"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+    # This file was autogenerated by uv via the following command:
+    #    uv pip compile --cache-dir [CACHE_DIR] pyproject.toml --build-constraint build_constraints.txt
+    requests==1.2.0
+        # via project (pyproject.toml)
+
+    ----- stderr -----
+    Resolved 1 package in [TIME]
+    "
+    );
+
+    // compatible setuptools version in pyproject.toml, incompatible in build_constraints.txt
+    let constraints_txt = context.temp_dir.child("build_constraints.txt");
+    constraints_txt.write_str("setuptools>=1")?;
+
+    let pyproject_toml = context.temp_dir.child("pyproject.toml");
+    pyproject_toml.write_str(
+        r#"[build-system]
+requires = ["setuptools"]
+
+[project]
+name = "project"
+version = "0.1.0"
+dependencies = [
+    "requests==1.2",
+]
+
+[tool.uv]
+build-constraint-dependencies = [
+    "setuptools>=40",
+]
+"#,
+    )?;
+
+    uv_snapshot!(context.pip_compile()
+        .arg("pyproject.toml")
+        .arg("--build-constraint")
+        .arg("build_constraints.txt"), @r"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+    # This file was autogenerated by uv via the following command:
+    #    uv pip compile --cache-dir [CACHE_DIR] pyproject.toml --build-constraint build_constraints.txt
+    requests==1.2.0
+        # via project (pyproject.toml)
+
+    ----- stderr -----
+    Resolved 1 package in [TIME]
+    "
+    );
+
+    Ok(())
+}
+
 /// Ensure that we treat invalid extra markers as `false`, i.e., in projects that define
 /// non-spec-compliant extras.
 #[test]

crates/uv/tests/it/pip_install.rs

@@ -7797,6 +7797,166 @@ fn compatible_build_constraint() -> Result<()> {
     Ok(())
 }
 
+/// Include `build-constraint-dependencies` in pyproject.toml with an incompatible constraint.
+#[test]
+fn incompatible_build_constraint_in_pyproject_toml() -> Result<()> {
+    let context = TestContext::new("3.8");
+
+    let pyproject_toml = context.temp_dir.child("pyproject.toml");
+    pyproject_toml.write_str(
+        r#"[tool.uv]
+build-constraint-dependencies = [
+    "setuptools==1",
+]
+"#,
+    )?;
+
+    uv_snapshot!(context.pip_install()
+        .arg("requests==1.2"), @r###"
+    success: false
+    exit_code: 1
+    ----- stdout -----
+
+    ----- stderr -----
+      × Failed to download and build `requests==1.2.0`
+      ├─▶ Failed to resolve requirements from `setup.py` build
+      ├─▶ No solution found when resolving: `setuptools>=40.8.0`
+      ╰─▶ Because you require setuptools>=40.8.0 and setuptools==1, we can conclude that your requirements are unsatisfiable.
+    "###
+    );
+
+    Ok(())
+}
+
+/// Include a `build_constraints.txt` file with a compatible constraint.
+#[test]
+fn compatible_build_constraint_in_pyproject_toml() -> Result<()> {
+    let context = TestContext::new("3.8");
+
+    let pyproject_toml = context.temp_dir.child("pyproject.toml");
+    pyproject_toml.write_str(
+        r#"[tool.uv]
+build-constraint-dependencies = [
+    "setuptools==40.8.0",
+]
+"#,
+    )?;
+
+    uv_snapshot!(context.pip_install()
+        .arg("requests==1.2"), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+
+    ----- stderr -----
+    Resolved 1 package in [TIME]
+    Prepared 1 package in [TIME]
+    Installed 1 package in [TIME]
+     + requests==1.2.0
+    "###
+    );
+
+    Ok(())
+}
+
+/// Merge `build_constraints.txt` with `build-constraint-dependencies` in pyproject.toml with an incompatible constraint.
+#[test]
+fn incompatible_build_constraint_merged_with_pyproject_toml() -> Result<()> {
+    let context = TestContext::new("3.8");
+
+    // Incompatible setuptools version in pyproject.toml, compatible in build_constraints.txt.
+    let constraints_txt = context.temp_dir.child("build_constraints.txt");
+    constraints_txt.write_str("setuptools>=40")?;
+    let pyproject_toml = context.temp_dir.child("pyproject.toml");
+    pyproject_toml.write_str(
+        r#"[tool.uv]
+build-constraint-dependencies = [
+    "setuptools==1",
+]
+"#,
+    )?;
+
+    uv_snapshot!(context.pip_install()
+        .arg("requests==1.2")
+        .arg("--build-constraint")
+        .arg("build_constraints.txt"), @r###"
+    success: false
+    exit_code: 1
+    ----- stdout -----
+
+    ----- stderr -----
+      × Failed to download and build `requests==1.2.0`
+      ├─▶ Failed to resolve requirements from `setup.py` build
+      ├─▶ No solution found when resolving: `setuptools>=40.8.0`
+      ╰─▶ Because you require setuptools>=40 and setuptools==1, we can conclude that your requirements are unsatisfiable.
+    "###
+    );
+
+    // Compatible setuptools version in pyproject.toml, incompatible in build_constraints.txt.
+    let constraints_txt = context.temp_dir.child("build_constraints.txt");
+    constraints_txt.write_str("setuptools==1")?;
+    let pyproject_toml = context.temp_dir.child("pyproject.toml");
+    pyproject_toml.write_str(
+        r#"[tool.uv]
+build-constraint-dependencies = [
+    "setuptools>=40",
+]
+"#,
+    )?;
+
+    uv_snapshot!(context.pip_install()
+        .arg("requests==1.2")
+        .arg("--build-constraint")
+        .arg("build_constraints.txt"), @r###"
+    success: false
+    exit_code: 1
+    ----- stdout -----
+
+    ----- stderr -----
+      × Failed to download and build `requests==1.2.0`
+      ├─▶ Failed to resolve requirements from `setup.py` build
+      ├─▶ No solution found when resolving: `setuptools>=40.8.0`
+      ╰─▶ Because you require setuptools==1 and setuptools>=40, we can conclude that your requirements are unsatisfiable.
+    "###
+    );
+
+    Ok(())
+}
+
+/// Merge `build_constraints.txt` with `build-constraint-dependencies` in pyproject.toml with a compatible constraint.
+#[test]
+fn compatible_build_constraint_merged_with_pyproject_toml() -> Result<()> {
+    let context = TestContext::new("3.8");
+
+    let constraints_txt = context.temp_dir.child("build_constraints.txt");
+    constraints_txt.write_str("setuptools>=40")?;
+    let pyproject_toml = context.temp_dir.child("pyproject.toml");
+    pyproject_toml.write_str(
+        r#"[tool.uv]
+build-constraint-dependencies = [
+    "setuptools>=1",
+]
+"#,
+    )?;
+
+    uv_snapshot!(context.pip_install()
+        .arg("requests==1.2")
+        .arg("--build-constraint")
+        .arg("build_constraints.txt"), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+
+    ----- stderr -----
+    Resolved 1 package in [TIME]
+    Prepared 1 package in [TIME]
+    Installed 1 package in [TIME]
+     + requests==1.2.0
+    "###
+    );
+    Ok(())
+}
+
 #[test]
 fn install_build_isolation_package() -> Result<()> {
     let context = TestContext::new("3.12");

crates/uv/tests/it/show_settings.rs

@@ -90,6 +90,7 @@ fn resolve_uv_toml() -> anyhow::Result<()> {
         build_constraints: [],
         constraints_from_workspace: [],
         overrides_from_workspace: [],
+        build_constraints_from_workspace: [],
         environments: SupportedEnvironments(
             [],
         ),
@@ -261,6 +262,7 @@ fn resolve_uv_toml() -> anyhow::Result<()> {
         build_constraints: [],
         constraints_from_workspace: [],
         overrides_from_workspace: [],
+        build_constraints_from_workspace: [],
         environments: SupportedEnvironments(
             [],
         ),
@@ -433,6 +435,7 @@ fn resolve_uv_toml() -> anyhow::Result<()> {
         build_constraints: [],
         constraints_from_workspace: [],
         overrides_from_workspace: [],
+        build_constraints_from_workspace: [],
         environments: SupportedEnvironments(
             [],
         ),
@@ -637,6 +640,7 @@ fn resolve_pyproject_toml() -> anyhow::Result<()> {
         build_constraints: [],
         constraints_from_workspace: [],
         overrides_from_workspace: [],
+        build_constraints_from_workspace: [],
         environments: SupportedEnvironments(
             [],
         ),
@@ -810,6 +814,7 @@ fn resolve_pyproject_toml() -> anyhow::Result<()> {
         build_constraints: [],
         constraints_from_workspace: [],
         overrides_from_workspace: [],
+        build_constraints_from_workspace: [],
         environments: SupportedEnvironments(
             [],
         ),
@@ -962,6 +967,7 @@ fn resolve_pyproject_toml() -> anyhow::Result<()> {
         build_constraints: [],
         constraints_from_workspace: [],
         overrides_from_workspace: [],
+        build_constraints_from_workspace: [],
         environments: SupportedEnvironments(
             [],
         ),
@@ -1158,6 +1164,7 @@ fn resolve_index_url() -> anyhow::Result<()> {
         build_constraints: [],
         constraints_from_workspace: [],
         overrides_from_workspace: [],
+        build_constraints_from_workspace: [],
         environments: SupportedEnvironments(
             [],
         ),
@@ -1360,6 +1367,7 @@ fn resolve_index_url() -> anyhow::Result<()> {
         build_constraints: [],
         constraints_from_workspace: [],
         overrides_from_workspace: [],
+        build_constraints_from_workspace: [],
         environments: SupportedEnvironments(
             [],
         ),
@@ -1616,6 +1624,7 @@ fn resolve_find_links() -> anyhow::Result<()> {
         build_constraints: [],
         constraints_from_workspace: [],
         overrides_from_workspace: [],
+        build_constraints_from_workspace: [],
         environments: SupportedEnvironments(
             [],
         ),
@@ -1811,6 +1820,7 @@ fn resolve_top_level() -> anyhow::Result<()> {
         build_constraints: [],
         constraints_from_workspace: [],
         overrides_from_workspace: [],
+        build_constraints_from_workspace: [],
         environments: SupportedEnvironments(
             [],
         ),
@@ -1969,6 +1979,7 @@ fn resolve_top_level() -> anyhow::Result<()> {
         build_constraints: [],
         constraints_from_workspace: [],
         overrides_from_workspace: [],
+        build_constraints_from_workspace: [],
         environments: SupportedEnvironments(
             [],
         ),
@@ -2169,6 +2180,7 @@ fn resolve_top_level() -> anyhow::Result<()> {
         build_constraints: [],
         constraints_from_workspace: [],
         overrides_from_workspace: [],
+        build_constraints_from_workspace: [],
         environments: SupportedEnvironments(
             [],
         ),
@@ -2393,6 +2405,7 @@ fn resolve_user_configuration() -> anyhow::Result<()> {
         build_constraints: [],
         constraints_from_workspace: [],
         overrides_from_workspace: [],
+        build_constraints_from_workspace: [],
         environments: SupportedEnvironments(
             [],
         ),
@@ -2541,6 +2554,7 @@ fn resolve_user_configuration() -> anyhow::Result<()> {
         build_constraints: [],
         constraints_from_workspace: [],
         overrides_from_workspace: [],
+        build_constraints_from_workspace: [],
         environments: SupportedEnvironments(
             [],
         ),
@@ -2689,6 +2703,7 @@ fn resolve_user_configuration() -> anyhow::Result<()> {
         build_constraints: [],
         constraints_from_workspace: [],
         overrides_from_workspace: [],
+        build_constraints_from_workspace: [],
         environments: SupportedEnvironments(
             [],
         ),
@@ -2839,6 +2854,7 @@ fn resolve_user_configuration() -> anyhow::Result<()> {
         build_constraints: [],
         constraints_from_workspace: [],
         overrides_from_workspace: [],
+        build_constraints_from_workspace: [],
         environments: SupportedEnvironments(
             [],
         ),
@@ -3167,6 +3183,7 @@ fn resolve_poetry_toml() -> anyhow::Result<()> {
         build_constraints: [],
         constraints_from_workspace: [],
         overrides_from_workspace: [],
+        build_constraints_from_workspace: [],
         environments: SupportedEnvironments(
             [],
         ),
@@ -3343,6 +3360,7 @@ fn resolve_both() -> anyhow::Result<()> {
         build_constraints: [],
         constraints_from_workspace: [],
         overrides_from_workspace: [],
+        build_constraints_from_workspace: [],
         environments: SupportedEnvironments(
             [],
         ),
@@ -3637,6 +3655,7 @@ fn resolve_config_file() -> anyhow::Result<()> {
         build_constraints: [],
         constraints_from_workspace: [],
         overrides_from_workspace: [],
+        build_constraints_from_workspace: [],
         environments: SupportedEnvironments(
             [],
         ),
@@ -3793,7 +3812,7 @@ fn resolve_config_file() -> anyhow::Result<()> {
       |
     1 | [project]
       |  ^^^^^^^
-    unknown field `project`, expected one of `required-version`, `native-tls`, `offline`, `no-cache`, `cache-dir`, `preview`, `python-preference`, `python-downloads`, `concurrent-downloads`, `concurrent-builds`, `concurrent-installs`, `index`, `index-url`, `extra-index-url`, `no-index`, `find-links`, `index-strategy`, `keyring-provider`, `allow-insecure-host`, `resolution`, `prerelease`, `fork-strategy`, `dependency-metadata`, `config-settings`, `no-build-isolation`, `no-build-isolation-package`, `exclude-newer`, `link-mode`, `compile-bytecode`, `no-sources`, `upgrade`, `upgrade-package`, `reinstall`, `reinstall-package`, `no-build`, `no-build-package`, `no-binary`, `no-binary-package`, `python-install-mirror`, `pypy-install-mirror`, `publish-url`, `trusted-publishing`, `check-url`, `pip`, `cache-keys`, `override-dependencies`, `constraint-dependencies`, `environments`, `required-environments`, `conflicts`, `workspace`, `sources`, `managed`, `package`, `default-groups`, `dev-dependencies`, `build-backend`
+    unknown field `project`, expected one of `required-version`, `native-tls`, `offline`, `no-cache`, `cache-dir`, `preview`, `python-preference`, `python-downloads`, `concurrent-downloads`, `concurrent-builds`, `concurrent-installs`, `index`, `index-url`, `extra-index-url`, `no-index`, `find-links`, `index-strategy`, `keyring-provider`, `allow-insecure-host`, `resolution`, `prerelease`, `fork-strategy`, `dependency-metadata`, `config-settings`, `no-build-isolation`, `no-build-isolation-package`, `exclude-newer`, `link-mode`, `compile-bytecode`, `no-sources`, `upgrade`, `upgrade-package`, `reinstall`, `reinstall-package`, `no-build`, `no-build-package`, `no-binary`, `no-binary-package`, `python-install-mirror`, `pypy-install-mirror`, `publish-url`, `trusted-publishing`, `check-url`, `pip`, `cache-keys`, `override-dependencies`, `constraint-dependencies`, `build-constraint-dependencies`, `environments`, `required-environments`, `conflicts`, `workspace`, `sources`, `managed`, `package`, `default-groups`, `dev-dependencies`, `build-backend`
     "###
     );
 
@@ -3909,6 +3928,7 @@ fn resolve_skip_empty() -> anyhow::Result<()> {
         build_constraints: [],
         constraints_from_workspace: [],
         overrides_from_workspace: [],
+        build_constraints_from_workspace: [],
         environments: SupportedEnvironments(
             [],
         ),
@@ -4060,6 +4080,7 @@ fn resolve_skip_empty() -> anyhow::Result<()> {
         build_constraints: [],
         constraints_from_workspace: [],
         overrides_from_workspace: [],
+        build_constraints_from_workspace: [],
         environments: SupportedEnvironments(
             [],
         ),
@@ -4230,6 +4251,7 @@ fn allow_insecure_host() -> anyhow::Result<()> {
         build_constraints: [],
         constraints_from_workspace: [],
         overrides_from_workspace: [],
+        build_constraints_from_workspace: [],
         environments: SupportedEnvironments(
             [],
         ),
@@ -4392,6 +4414,7 @@ fn index_priority() -> anyhow::Result<()> {
         build_constraints: [],
         constraints_from_workspace: [],
         overrides_from_workspace: [],
+        build_constraints_from_workspace: [],
         environments: SupportedEnvironments(
             [],
         ),
@@ -4594,6 +4617,7 @@ fn index_priority() -> anyhow::Result<()> {
         build_constraints: [],
         constraints_from_workspace: [],
         overrides_from_workspace: [],
+        build_constraints_from_workspace: [],
         environments: SupportedEnvironments(
             [],
         ),
@@ -4802,6 +4826,7 @@ fn index_priority() -> anyhow::Result<()> {
         build_constraints: [],
         constraints_from_workspace: [],
         overrides_from_workspace: [],
+        build_constraints_from_workspace: [],
         environments: SupportedEnvironments(
             [],
         ),
@@ -5005,6 +5030,7 @@ fn index_priority() -> anyhow::Result<()> {
         build_constraints: [],
         constraints_from_workspace: [],
         overrides_from_workspace: [],
+        build_constraints_from_workspace: [],
         environments: SupportedEnvironments(
             [],
         ),
@@ -5215,6 +5241,7 @@ fn index_priority() -> anyhow::Result<()> {
         build_constraints: [],
         constraints_from_workspace: [],
         overrides_from_workspace: [],
+        build_constraints_from_workspace: [],
         environments: SupportedEnvironments(
             [],
         ),
@@ -5418,6 +5445,7 @@ fn index_priority() -> anyhow::Result<()> {
         build_constraints: [],
         constraints_from_workspace: [],
         overrides_from_workspace: [],
+        build_constraints_from_workspace: [],
         environments: SupportedEnvironments(
             [],
         ),
@@ -5637,6 +5665,7 @@ fn verify_hashes() -> anyhow::Result<()> {
         dry_run: Disabled,
         constraints_from_workspace: [],
         overrides_from_workspace: [],
+        build_constraints_from_workspace: [],
         modifications: Sufficient,
         refresh: None(
             Timestamp(
@@ -5779,6 +5808,7 @@ fn verify_hashes() -> anyhow::Result<()> {
         dry_run: Disabled,
         constraints_from_workspace: [],
         overrides_from_workspace: [],
+        build_constraints_from_workspace: [],
         modifications: Sufficient,
         refresh: None(
             Timestamp(
@@ -5919,6 +5949,7 @@ fn verify_hashes() -> anyhow::Result<()> {
         dry_run: Disabled,
         constraints_from_workspace: [],
         overrides_from_workspace: [],
+        build_constraints_from_workspace: [],
         modifications: Sufficient,
         refresh: None(
             Timestamp(
@@ -6061,6 +6092,7 @@ fn verify_hashes() -> anyhow::Result<()> {
         dry_run: Disabled,
         constraints_from_workspace: [],
         overrides_from_workspace: [],
+        build_constraints_from_workspace: [],
         modifications: Sufficient,
         refresh: None(
             Timestamp(
@@ -6201,6 +6233,7 @@ fn verify_hashes() -> anyhow::Result<()> {
         dry_run: Disabled,
         constraints_from_workspace: [],
         overrides_from_workspace: [],
+        build_constraints_from_workspace: [],
         modifications: Sufficient,
         refresh: None(
             Timestamp(
@@ -6342,6 +6375,7 @@ fn verify_hashes() -> anyhow::Result<()> {
         dry_run: Disabled,
         constraints_from_workspace: [],
         overrides_from_workspace: [],
+        build_constraints_from_workspace: [],
         modifications: Sufficient,
         refresh: None(
             Timestamp(

docs/pip/compile.md

@@ -125,6 +125,38 @@ $ uv pip compile requirements.in --constraint constraints.txt
 
 Note that multiple constraints can be defined in each file and multiple files can be used.
 
+uv will also read `constraint-dependencies` from the `pyproject.toml` at the workspace root, and
+append them to those specified in the constraints file.
+
+## Adding build constraints
+
+Similar to `constraints`, but specifically for build-time dependencies, including those required
+when building runtime dependencies.
+
+Build constraint files are `requirements.txt`-like files that only control the _version_ of a
+build-time requirement. However, including a package in a build constraints file will _not_ trigger
+its installation at build time; instead, constraints apply only when the package is required as a
+direct or transitive build-time dependency. Build constraints can be used to add bounds to
+dependencies that are not explicitly declared as build-time dependencies of the current project.
+
+For example, if a package defines its build dependencies as follows:
+
+```toml title="pyproject.toml"
+[build-system]
+requires = ["setuptools"]
+build-backend = "setuptools.build_meta"
+```
+
+Build constraints could be used to ensure that a specific version of `setuptools` is used for every
+package in the workspace:
+
+```python title="build-constraints.txt"
+setuptools==75.0.0
+```
+
+uv will also read `build-constraint-dependencies` from the `pyproject.toml` at the workspace root,
+and append them to those specified in the build constraints file.
+
 ## Overriding dependency versions
 
 Overrides files are `requirements.txt`-like files that force a specific version of a requirement to

docs/reference/settings.md

@@ -1,4 +1,35 @@
 ## Project metadata
+### [`build-constraint-dependencies`](#build-constraint-dependencies) {: #build-constraint-dependencies }
+
+Constraints to apply when solving build dependencies.
+
+Build constraints are used to restrict the versions of build dependencies that are selected
+when building a package during resolution or installation.
+
+Including a package as a constraint will _not_ trigger installation of the package during
+a build; instead, the package must be requested elsewhere in the project's build dependency
+graph.
+
+!!! note
+    In `uv lock`, `uv sync`, and `uv run`, uv will only read `build-constraint-dependencies` from
+    the `pyproject.toml` at the workspace root, and will ignore any declarations in other
+    workspace members or `uv.toml` files.
+
+**Default value**: `[]`
+
+**Type**: `list[str]`
+
+**Example usage**:
+
+```toml title="pyproject.toml"
+[tool.uv]
+# Ensure that the setuptools v60.0.0 is used whenever a package has a build dependency
+# on setuptools.
+build-constraint-dependencies = ["setuptools==60.0.0"]
+```
+
+---
+
 ### [`conflicts`](#conflicts) {: #conflicts }
 
 Declare collections of extras or dependency groups that are conflicting

docs/reference/troubleshooting/build-failures.md

@@ -288,6 +288,28 @@ uv will avoid using an old version of `apache-beam`.
 Constraints can also be defined for indirect dependencies using `constraints.txt` files or the
 [`constraint-dependencies`](../settings.md#constraint-dependencies) setting.
 
+### Old Version of a build dependency is used
+
+If a package fails to build because `uv` selects an incompatible or outdated version of a build-time
+dependency, you can enforce constraints specifically for build dependencies. The
+[`build-constraint-dependencies`](../settings.md#build-constraint-dependencies) setting (or an
+analogous `build-constraints.txt` file) can be used to ensure that `uv` selects an appropriate
+version of a given build requirements.
+
+For example, the issue described in
+[#5551](https://github.com/astral-sh/uv/issues/5551#issuecomment-2256055975) could be addressed by
+specifying a build constraint that excludes `setuptools` version `72.0.0`:
+
+```toml title="pyproject.toml"
+[tool.uv]
+# Prevent setuptools version 72.0.0 from being used as a build dependency.
+build-constraint-dependencies = ["setuptools!=72.0.0"]
+```
+
+The build constraint will thus ensure that any package requiring `setuptools` during the build
+process will avoid using the problematic version, preventing build failures caused by incompatible
+build dependencies.
+
 ### Package is only needed for an unused platform
 
 If locking fails due to building a package from a platform you do not need to support, consider

uv.schema.json

@@ -14,6 +14,16 @@
         "$ref": "#/definitions/TrustedHost"
       }
     },
+    "build-constraint-dependencies": {
+      "description": "PEP 508-style requirements, e.g., `ruff==0.5.0`, or `ruff @ https://...`.",
+      "type": [
+        "array",
+        "null"
+      ],
+      "items": {
+        "type": "string"
+      }
+    },
     "cache-dir": {
       "description": "Path to the cache directory.\n\nDefaults to `$HOME/Library/Caches/uv` on macOS, `$XDG_CACHE_HOME/uv` or `$HOME/.cache/uv` on Linux, and `%LOCALAPPDATA%\\uv\\cache` on Windows.",
       "type": [