Add constraint key

pyodide_build/recipe/builder.py

@@ -22,6 +22,7 @@
     RUST_BUILD_PRELUDE,
     BuildArgs,
     get_build_environment_vars,
+    get_build_flag,
     get_pyodide_root,
     pyodide_tags,
     replace_so_abi_tags,
@@ -335,7 +336,34 @@ def _download_and_extract(self) -> None:
             extract_dir_name = trim_archive_extension(tarballname)
 
         shutil.move(self.build_dir / extract_dir_name, self.src_extract_dir)
-        self.src_dist_dir.mkdir(parents=True, exist_ok=True)
+        self.src_dist_dir.mkdir(parents=True, exist_ok=True)\
+
+    def _override_constraints(self) -> str:
+        """
+        Override global constraints (PIP_CONSTRAINT) with constraints specific to this package.
+
+        returns the path to the new constraints file.
+        """
+        try:
+            host_constraints = get_build_flag("PIP_CONSTRAINT")
+        except ValueError:
+            host_constraints = ""
+
+        constraints = self.recipe.requirements.constraint
+        if not constraints:
+            # nothing to override
+            return host_constraints
+
+        host_constraints_file = Path(host_constraints)
+        new_constraints_file = self.build_dir / "constraints.txt"
+        if host_constraints_file.is_file():
+            shutil.copy(host_constraints_file, new_constraints_file)
+
+        with new_constraints_file.open("a") as f:
+            for constraint in constraints:
+                f.write(constraint + "\n")
+
+        return str(new_constraints_file)
 
     def _compile(
         self,
@@ -383,6 +411,8 @@ def _compile(
                     )
                     build_env = runner.env
 
+            build_env["PIP_CONSTRAINT"] = str(self._override_constraints())
+
             pypabuild.build(
                 self.src_extract_dir, self.src_dist_dir, build_env, config_settings
             )

pyodide_build/recipe/spec.py

@@ -124,6 +124,7 @@ class _RequirementsSpec(BaseModel):
     run: list[str] = []
     host: list[str] = []
     executable: list[str] = []
+    constraint: list[str] = []
     model_config = ConfigDict(extra="forbid")
 
 

pyodide_build/tests/recipe/_test_recipes/pkg_test_constraint/meta.yaml

@@ -0,0 +1,10 @@
+package:
+  name: pkg_test_constraint
+  version: "1.0.0"
+requirements:
+  constraint:
+    - numpy < 2.0
+    - scipy > 1.0
+    - pytest == 7.0
+source:
+  path: src

pyodide_build/tests/recipe/_test_recipes/pkg_test_constraint/src/pyproject.toml

@@ -0,0 +1,8 @@
+[build-system]
+requires = ["setuptools>=42", "wheel"]
+build-backend = "setuptools.build_meta"
+
+[project]
+name = "pkg_test_constraint"
+version = "1.0.0"
+authors = []

pyodide_build/tests/recipe/test_builder.py

@@ -8,7 +8,7 @@
 import pytest
 
 from pyodide_build import common
-from pyodide_build.build_env import BuildArgs
+from pyodide_build.build_env import BuildArgs, get_build_flag
 from pyodide_build.recipe import builder as _builder
 from pyodide_build.recipe.builder import (
     RecipeBuilder,
@@ -216,6 +216,35 @@ def rlist(input_dir):
     assert n_moved == 3
 
 
+def test_override_constraints_no_override(tmp_path, dummy_xbuildenv):
+    builder = RecipeBuilder.get_builder(
+        recipe=RECIPE_DIR / "pkg_test_executable",  # constraints not set, so no override
+        build_args=BuildArgs(),
+        build_dir=tmp_path,
+    )
+
+    path = builder._override_constraints()
+    assert path == get_build_flag("PIP_CONSTRAINT")
+
+
+def test_override_constraints_override(tmp_path, dummy_xbuildenv):
+    builder = RecipeBuilder.get_builder(
+        recipe=RECIPE_DIR / "pkg_test_constraint",
+        build_args=BuildArgs(),
+        build_dir=tmp_path,
+    )
+
+    path = builder._override_constraints()
+    assert path == str(tmp_path / "constraints.txt")
+
+    data = Path(path).read_text().strip().split("\n")
+    assert data[-3:] == [
+        "numpy < 2.0",
+        "scipy > 1.0",
+        "pytest == 7.0"
+    ], data
+
+
 class MockSourceSpec(_SourceSpec):
     @pydantic.model_validator(mode="after")
     def _check_patches_extra(self) -> Self: