Improve deprecation message for issue 8368

news/8752.feature

@@ -0,0 +1,3 @@
+Make the ``setup.py install`` deprecation warning less noisy. We warn only
+when ``setup.py install`` succeeded and ``setup.py bdist_wheel`` failed, as
+situations where both fails are most probably irrelevant to this deprecation.

src/pip/_internal/commands/install.py

@@ -21,7 +21,6 @@
 from pip._internal.operations.check import check_install_conflicts
 from pip._internal.req import install_given_reqs
 from pip._internal.req.req_tracker import get_requirement_tracker
-from pip._internal.utils.deprecation import deprecated
 from pip._internal.utils.distutils_args import parse_distutils_args
 from pip._internal.utils.filesystem import test_writable_dir
 from pip._internal.utils.misc import (
@@ -371,23 +370,9 @@ def run(self, options, args):
             # For now, we just warn about failures building legacy
             # requirements, as we'll fall through to a direct
             # install for those.
-            legacy_build_failure_names = [
-                r.name  # type: ignore
-                for r in build_failures if not r.use_pep517
-            ]  # type: List[str]
-            if legacy_build_failure_names:
-                deprecated(
-                    reason=(
-                        "Could not build wheels for {} which do not use "
-                        "PEP 517. pip will fall back to legacy 'setup.py "
-                        "install' for these.".format(
-                            ", ".join(legacy_build_failure_names)
-                        )
-                    ),
-                    replacement="to fix the wheel build issue reported above",
-                    gone_in="21.0",
-                    issue=8368,
-                )
+            for r in build_failures:
+                if not r.use_pep517:
+                    r.legacy_install_reason = 8368
 
             to_install = resolver.get_installation_order(
                 requirement_set

src/pip/_internal/req/req_install.py

@@ -121,6 +121,7 @@ def __init__(
         self.comes_from = comes_from
         self.constraint = constraint
         self.editable = editable
+        self.legacy_install_reason = None  # type: Optional[int]
 
         # source_dir is the local directory where the linked requirement is
         # located, or unpacked. In case unpacking is needed, creating and
@@ -862,6 +863,18 @@ def install(
 
         self.install_succeeded = success
 
+        if success and self.legacy_install_reason == 8368:
+            deprecated(
+                reason=(
+                    "{} was installed using the legacy 'setup.py install' "
+                    "method, because a wheel could not be built for it.".
+                    format(self.name)
+                ),
+                replacement="to fix the wheel build issue reported above",
+                gone_in="21.0",
+                issue=8368,
+            )
+
 
 def check_invalid_constraint_type(req):
     # type: (InstallRequirement) -> str