From 1983ef0edc61fb71960d6b2caf2d0a6baa83ae0e Mon Sep 17 00:00:00 2001
From: Tzu-ping Chung <uranusjr@gmail.com>
Date: Tue, 4 May 2021 16:50:52 +0800
Subject: [PATCH 1/2] Better diagnose when setup.py/cfg cannot be found

This adds a check before invoking 'egg_info' to make sure either setup.py or
setup.cfg actually exists, and emit a clearer error message when neither can
be found and the egg_info command can never succeed.
---
 news/9944.bugfix.rst                 |  2 ++
 src/pip/_internal/req/req_install.py | 19 +++++++++++++++++++
 2 files changed, 21 insertions(+)
 create mode 100644 news/9944.bugfix.rst

diff --git a/news/9944.bugfix.rst b/news/9944.bugfix.rst
new file mode 100644
index 00000000000..58bb70b78f3
--- /dev/null
+++ b/news/9944.bugfix.rst
@@ -0,0 +1,2 @@
+Emit clearer error message when a project root does not contain either
+``pyproject.toml``, ``setup.py`` or ``setup.cfg``.
diff --git a/src/pip/_internal/req/req_install.py b/src/pip/_internal/req/req_install.py
index 55c17ac8b45..c2eea37123e 100644
--- a/src/pip/_internal/req/req_install.py
+++ b/src/pip/_internal/req/req_install.py
@@ -509,6 +509,19 @@ def load_pyproject_toml(self):
             self.unpacked_source_directory, backend, backend_path=backend_path,
         )
 
+    def _check_setup_py_or_cfg_exists(self) -> bool:
+        """Check if the requirement actually has a setuptools build file.
+
+        If setup.py does not exist, we also check setup.cfg in the same
+        directory and allow the directory if that exists.
+        """
+        if os.path.exists(self.setup_py_path):
+            return True
+        stem, ext = os.path.splitext(self.setup_py_path)
+        if ext == ".py" and os.path.exists(f"{stem}.cfg"):
+            return True
+        return False
+
     def _generate_metadata(self):
         # type: () -> str
         """Invokes metadata generator functions, with the required arguments.
@@ -516,6 +529,12 @@ def _generate_metadata(self):
         if not self.use_pep517:
             assert self.unpacked_source_directory
 
+            if not self._check_setup_py_or_cfg_exists():
+                raise InstallationError(
+                    f'File "setup.py" or "setup.cfg" not found for legacy '
+                    f'project {self}.'
+                )
+
             return generate_metadata_legacy(
                 build_env=self.build_env,
                 setup_py_path=self.setup_py_path,

From 1904e4d66da3cdc0f853dc9c9c99efffe3ca243b Mon Sep 17 00:00:00 2001
From: Tzu-ping Chung <uranusjr@gmail.com>
Date: Tue, 11 May 2021 21:48:22 +0800
Subject: [PATCH 2/2] Relax installable dir check to allow cfg-only

---
 src/pip/_internal/utils/misc.py | 16 ++++++----------
 1 file changed, 6 insertions(+), 10 deletions(-)

diff --git a/src/pip/_internal/utils/misc.py b/src/pip/_internal/utils/misc.py
index 26037dbdcbb..a4ad35be61c 100644
--- a/src/pip/_internal/utils/misc.py
+++ b/src/pip/_internal/utils/misc.py
@@ -269,18 +269,14 @@ def tabulate(rows):
     return table, sizes
 
 
-def is_installable_dir(path):
-    # type: (str) -> bool
-    """Is path is a directory containing setup.py or pyproject.toml?"""
+def is_installable_dir(path: str) -> bool:
+    """Is path is a directory containing pyproject.toml, setup.cfg or setup.py?"""
     if not os.path.isdir(path):
         return False
-    setup_py = os.path.join(path, "setup.py")
-    if os.path.isfile(setup_py):
-        return True
-    pyproject_toml = os.path.join(path, "pyproject.toml")
-    if os.path.isfile(pyproject_toml):
-        return True
-    return False
+    return any(
+        os.path.isfile(os.path.join(path, signifier))
+        for signifier in ("pyproject.toml", "setup.cfg", "setup.py")
+    )
 
 
 def read_chunks(file, size=io.DEFAULT_BUFFER_SIZE):