Extend should_build scope wrt legacy requirements

We don't build legacy requirements
when wheel is not installed because
we'll fallback to a legacy install in such case.

1 files changed, 8 insertions, 1 deletions

diff --git a/src/pip/_internal/wheel_builder.py b/src/pip/_internal/wheel_builder.py
index d80f982fc..423d3b726 100644
--- a/src/pip/_internal/wheel_builder.py
+++ b/src/pip/_internal/wheel_builder.py
@@ -13,7 +13,7 @@ from pip._internal.models.link import Link
 from pip._internal.operations.build.wheel import build_wheel_pep517
 from pip._internal.operations.build.wheel_legacy import build_wheel_legacy
 from pip._internal.utils.logging import indent_log
-from pip._internal.utils.misc import ensure_dir, hash_file
+from pip._internal.utils.misc import ensure_dir, hash_file, is_wheel_installed
 from pip._internal.utils.setuptools_build import make_setuptools_clean_args
 from pip._internal.utils.subprocess import call_subprocess
 from pip._internal.utils.temp_dir import TempDirectory
@@ -69,6 +69,13 @@ def should_build(
         # i.e. pip wheel, not pip install
         return True
 
+    # From this point, this concerns the pip install command only
+    # (need_wheel=False).
+
+    if not req.use_pep517 and not is_wheel_installed():
+        # we don't build legacy requirements if wheel is not installed
+        return False
+
     if req.editable or not req.source_dir:
         return False