_should_build is never called for constraints

The only call sites are in pip install in pip wheel,
after resolution, so there are never constraint requirements there.

Author: sbidoul

src/pip/_internal/wheel_builder.py

@@ -46,9 +46,8 @@ def _should_build(
     need_wheel: bool,
 ) -> bool:
     """Return whether an InstallRequirement should be built into a wheel."""
-    if req.constraint:
-        # never build requirements that are merely constraints
-        return False
+    assert not req.constraint
+
     if req.is_wheel:
         if need_wheel:
             logger.info(

tests/unit/test_wheel_builder.py

@@ -51,8 +51,6 @@ class ReqMock:
         # We build, whether pep 517 is enabled or not.
         (ReqMock(use_pep517=True), True),
         (ReqMock(use_pep517=False), True),
-        # We don't build constraints.
-        (ReqMock(constraint=True), False),
         # We don't build reqs that are already wheels.
         (ReqMock(is_wheel=True), False),
         # We build editables if the backend supports PEP 660.
@@ -90,7 +88,6 @@ def test_should_build_for_install_command(req: ReqMock, expected: bool) -> None:
     "req, expected",
     [
         (ReqMock(), True),
-        (ReqMock(constraint=True), False),
         (ReqMock(is_wheel=True), False),
         (ReqMock(editable=True, use_pep517=False), True),
         (ReqMock(editable=True, use_pep517=True), True),