Refactor get_build_backend_hook_caller() API

src/fromager/build_environment.py

@@ -203,7 +203,7 @@ def prepare_build_environment(
     ctx: context.WorkContext,
     req: Requirement,
     sdist_root_dir: pathlib.Path,
-) -> pathlib.Path:
+) -> BuildEnvironment:
     logger.info(f"{req.name}: preparing build environment")
 
     next_req_type = RequirementType.BUILD_SYSTEM
@@ -300,7 +300,7 @@ def prepare_build_environment(
                 | build_sdist_dependencies,
             ) from err
         raise
-    return build_env.path
+    return build_env
 
 
 def maybe_install(

src/fromager/commands/build.py

@@ -370,10 +370,9 @@ def _build(
     )
 
     # Build environment
-    build_environment.prepare_build_environment(
+    build_env = build_environment.prepare_build_environment(
         ctx=wkctx, req=req, sdist_root_dir=source_root_dir
     )
-    build_env = build_environment.BuildEnvironment(wkctx, source_root_dir.parent, None)
 
     # Make a new source distribution, in case we patched the code.
     sdist_filename = sources.build_sdist(

src/fromager/dependencies.py

@@ -140,9 +140,11 @@ def default_get_build_backend_dependencies(
     Defaults to result of hook call
     :meth:`~pyproject_hooks.BuildBackendHookCaller.get_requires_for_build_wheel`
     """
-    pyproject_toml = get_pyproject_contents(build_dir)
     hook_caller = get_build_backend_hook_caller(
-        build_dir, pyproject_toml, override_environ=extra_environ
+        ctx=ctx,
+        req=req,
+        build_dir=build_dir,
+        override_environ=extra_environ,
     )
     return hook_caller.get_requires_for_build_wheel()
 
@@ -197,9 +199,11 @@ def default_get_build_sdist_dependencies(
     Defaults to result of hook call
     :meth:`~pyproject_hooks.BuildBackendHookCaller.get_requires_for_build_wheel`
     """
-    pyproject_toml = get_pyproject_contents(build_dir)
     hook_caller = get_build_backend_hook_caller(
-        build_dir, pyproject_toml, override_environ=extra_environ
+        ctx=ctx,
+        req=req,
+        build_dir=build_dir,
+        override_environ=extra_environ,
     )
     return hook_caller.get_requires_for_build_wheel()
 
@@ -220,13 +224,12 @@ def get_install_dependencies_of_sdist(
     logger.info(
         f"{req.name}: getting install requirements for {req} from sdist in {build_dir}"
     )
-    pyproject_toml = get_pyproject_contents(build_dir)
     extra_environ = pbi.get_extra_environ()
     hook_caller = get_build_backend_hook_caller(
-        build_dir,
-        pyproject_toml,
+        ctx=ctx,
+        req=req,
+        build_dir=build_dir,
         override_environ=extra_environ,
-        network_isolation=ctx.network_isolation,
         build_env=build_env,
     )
     with tempfile.TemporaryDirectory() as tmp_dir:
@@ -296,39 +299,44 @@ def get_build_backend(pyproject_toml: dict[str, typing.Any]) -> dict[str, typing
 
 
 def get_build_backend_hook_caller(
-    sdist_root_dir: pathlib.Path,
-    pyproject_toml: dict[str, typing.Any],
-    override_environ: dict[str, typing.Any],
     *,
-    network_isolation: bool = False,
+    ctx: context.WorkContext,
+    req: Requirement,
+    build_dir: pathlib.Path,
+    override_environ: dict[str, typing.Any],
     build_env: build_environment.BuildEnvironment | None = None,
 ) -> pyproject_hooks.BuildBackendHookCaller:
-    backend = get_build_backend(pyproject_toml)
+    """Create pyproject_hooks build backend caller"""
 
     def _run_hook_with_extra_environ(
         cmd: typing.Sequence[str],
         cwd: str | None = None,
         extra_environ: typing.Mapping[str, str] | None = None,
     ) -> None:
         """The BuildBackendHookCaller is going to pass extra_environ
-        and our build system may want to set some values, too. Merge
-        the 2 sets of values before calling the actual runner function.
+        and our build system may want to set some values, too. The hook
+        also needs env vars from the build environment's virtualenv. Merge
+        the 3 sets of values before calling the actual runner function.
         """
-        full_environ: dict[str, typing.Any] = {}
-        if extra_environ is not None:
-            full_environ.update(extra_environ)
-        full_environ.update(override_environ)
+        if typing.TYPE_CHECKING:
+            assert build_env is not None
+        extra_environ = dict(extra_environ) if extra_environ else {}
+        extra_environ.update(override_environ)
+        if build_env is not None:
+            extra_environ.update(build_env.get_venv_environ(template_env=extra_environ))
         external_commands.run(
             cmd,
             cwd=cwd,
-            extra_environ=full_environ,
-            network_isolation=network_isolation,
+            extra_environ=extra_environ,
+            network_isolation=ctx.network_isolation,
         )
 
+    pyproject_toml = get_pyproject_contents(build_dir)
+    backend = get_build_backend(pyproject_toml)
     python_executable = str(build_env.python) if build_env is not None else None
 
     return pyproject_hooks.BuildBackendHookCaller(
-        source_dir=str(sdist_root_dir),
+        source_dir=str(build_dir),
         build_backend=backend["build-backend"],
         backend_path=backend["backend-path"],
         runner=_run_hook_with_extra_environ,

src/fromager/sources.py

@@ -255,13 +255,15 @@ def _get_version_from_package_metadata(
     req: Requirement,
     source_dir: str,
 ) -> Version:
+    pbi = ctx.package_build_info(req)
+    build_dir = pbi.build_dir(source_dir)
     logger.info(f"{req.name}: generating metadata to get version")
-    pyproject_toml = dependencies.get_pyproject_contents(source_dir)
+
     hook_caller = dependencies.get_build_backend_hook_caller(
-        source_dir,
-        pyproject_toml,
-        {},
-        network_isolation=ctx.network_isolation,
+        ctx=ctx,
+        req=req,
+        build_dir=build_dir,
+        override_environ={},
     )
     metadata_dir_base = hook_caller.prepare_metadata_for_build_wheel(
         metadata_directory=source_dir.parent,
@@ -672,12 +674,13 @@ def pep517_build_sdist(
     version: Version,
 ) -> pathlib.Path:
     """Use the PEP 517 API to build a source distribution from a modified source tree."""
-    pyproject_toml = dependencies.get_pyproject_contents(sdist_root_dir)
+    pbi = ctx.package_build_info(req)
+    build_dir = pbi.build_dir(sdist_root_dir)
     hook_caller = dependencies.get_build_backend_hook_caller(
-        sdist_root_dir,
-        pyproject_toml,
-        extra_environ,
-        network_isolation=ctx.network_isolation,
+        ctx=ctx,
+        req=req,
+        build_dir=build_dir,
+        override_environ=extra_environ,
     )
     sdist_filename = hook_caller.build_sdist(ctx.sdists_builds)
     return ctx.sdists_builds / sdist_filename