From 0534aeb89129718e44e34d67f50dc2072bc6a144 Mon Sep 17 00:00:00 2001
From: Pradyun Gedam <pradyunsg@gmail.com>
Date: Mon, 18 Jun 2018 17:05:45 +0530
Subject: [PATCH 1/6] Start refusing non PEP 518 pyproject.toml files

---
 src/pip/_internal/req/req_install.py | 26 ++++++++++++++++++++++++--
 1 file changed, 24 insertions(+), 2 deletions(-)

diff --git a/src/pip/_internal/req/req_install.py b/src/pip/_internal/req/req_install.py
index 7846f3c169f..a3b6f820b08 100644
--- a/src/pip/_internal/req/req_install.py
+++ b/src/pip/_internal/req/req_install.py
@@ -571,8 +571,30 @@ def get_pep_518_info(self):
         if os.path.isfile(self.pyproject_toml):
             with io.open(self.pyproject_toml, encoding="utf-8") as f:
                 pp_toml = pytoml.load(f)
-            build_sys = pp_toml.get('build-system', {})
-            return (build_sys.get('requires', ['setuptools', 'wheel']), True)
+
+            build_system = pp_toml.get('build-system', {})
+            if "requires" not in build_system:
+                raise InstallationError(
+                    "{} does not comply with PEP 518 as it since it's "
+                    "pyproject.toml file does not have a '[build-system]' "
+                    "table with a 'requires' key."
+                    .format(self)
+                )
+
+            requires = build_system["requires"]
+            is_list_of_str = isinstance(requires, list) and all(
+                isinstance(req, str) for req in requires
+            )
+            if not is_list_of_str:
+                raise InstallationError(
+                    "{} does not comply with PEP 518 as it since it's "
+                    "pyproject.toml file contains [build-system].requires "
+                    "which is not a list of strings."
+                    .format(self)
+                )
+
+            return requires, True
+
         return (['setuptools', 'wheel'], False)
 
     def run_egg_info(self):

From a25cb53d025ad5e3c546e27f11a9c7afd3a9ffd6 Mon Sep 17 00:00:00 2001
From: Pradyun Gedam <pradyunsg@gmail.com>
Date: Mon, 18 Jun 2018 17:06:28 +0530
Subject: [PATCH 2/6] Add tests to verify refusal of non PEP 518 compliant
 pyproject.toml

---
 .../src/pep518_invalid_requires/MANIFEST.in   |  1 +
 .../src/pep518_invalid_requires/pep518.py     |  1 +
 .../pep518_invalid_requires/pyproject.toml    |  2 ++
 .../src/pep518_invalid_requires/setup.cfg     |  0
 .../data/src/pep518_invalid_requires/setup.py |  9 +++++++
 .../src/pep518_missing_requires/MANIFEST.in   |  1 +
 .../src/pep518_missing_requires/pep518.py     |  1 +
 .../pep518_missing_requires/pyproject.toml    |  0
 .../src/pep518_missing_requires/setup.cfg     |  0
 .../data/src/pep518_missing_requires/setup.py |  9 +++++++
 tests/functional/test_install.py              | 24 +++++++++++++++++++
 11 files changed, 48 insertions(+)
 create mode 100644 tests/data/src/pep518_invalid_requires/MANIFEST.in
 create mode 100644 tests/data/src/pep518_invalid_requires/pep518.py
 create mode 100644 tests/data/src/pep518_invalid_requires/pyproject.toml
 create mode 100644 tests/data/src/pep518_invalid_requires/setup.cfg
 create mode 100644 tests/data/src/pep518_invalid_requires/setup.py
 create mode 100644 tests/data/src/pep518_missing_requires/MANIFEST.in
 create mode 100644 tests/data/src/pep518_missing_requires/pep518.py
 create mode 100644 tests/data/src/pep518_missing_requires/pyproject.toml
 create mode 100644 tests/data/src/pep518_missing_requires/setup.cfg
 create mode 100644 tests/data/src/pep518_missing_requires/setup.py

diff --git a/tests/data/src/pep518_invalid_requires/MANIFEST.in b/tests/data/src/pep518_invalid_requires/MANIFEST.in
new file mode 100644
index 00000000000..bec201fc83b
--- /dev/null
+++ b/tests/data/src/pep518_invalid_requires/MANIFEST.in
@@ -0,0 +1 @@
+include pyproject.toml
diff --git a/tests/data/src/pep518_invalid_requires/pep518.py b/tests/data/src/pep518_invalid_requires/pep518.py
new file mode 100644
index 00000000000..7986d11379a
--- /dev/null
+++ b/tests/data/src/pep518_invalid_requires/pep518.py
@@ -0,0 +1 @@
+#dummy
diff --git a/tests/data/src/pep518_invalid_requires/pyproject.toml b/tests/data/src/pep518_invalid_requires/pyproject.toml
new file mode 100644
index 00000000000..17bc681d654
--- /dev/null
+++ b/tests/data/src/pep518_invalid_requires/pyproject.toml
@@ -0,0 +1,2 @@
+[build-system]
+requires = [1, 2, 3]  # not a list of strings
diff --git a/tests/data/src/pep518_invalid_requires/setup.cfg b/tests/data/src/pep518_invalid_requires/setup.cfg
new file mode 100644
index 00000000000..e69de29bb2d
diff --git a/tests/data/src/pep518_invalid_requires/setup.py b/tests/data/src/pep518_invalid_requires/setup.py
new file mode 100644
index 00000000000..b63f59926f7
--- /dev/null
+++ b/tests/data/src/pep518_invalid_requires/setup.py
@@ -0,0 +1,9 @@
+#!/usr/bin/env python
+from setuptools import setup
+
+import simplewheel  # ensure dependency is installed
+
+setup(name='pep518',
+      version='3.0',
+      py_modules=['pep518'],
+      )
diff --git a/tests/data/src/pep518_missing_requires/MANIFEST.in b/tests/data/src/pep518_missing_requires/MANIFEST.in
new file mode 100644
index 00000000000..bec201fc83b
--- /dev/null
+++ b/tests/data/src/pep518_missing_requires/MANIFEST.in
@@ -0,0 +1 @@
+include pyproject.toml
diff --git a/tests/data/src/pep518_missing_requires/pep518.py b/tests/data/src/pep518_missing_requires/pep518.py
new file mode 100644
index 00000000000..7986d11379a
--- /dev/null
+++ b/tests/data/src/pep518_missing_requires/pep518.py
@@ -0,0 +1 @@
+#dummy
diff --git a/tests/data/src/pep518_missing_requires/pyproject.toml b/tests/data/src/pep518_missing_requires/pyproject.toml
new file mode 100644
index 00000000000..e69de29bb2d
diff --git a/tests/data/src/pep518_missing_requires/setup.cfg b/tests/data/src/pep518_missing_requires/setup.cfg
new file mode 100644
index 00000000000..e69de29bb2d
diff --git a/tests/data/src/pep518_missing_requires/setup.py b/tests/data/src/pep518_missing_requires/setup.py
new file mode 100644
index 00000000000..b63f59926f7
--- /dev/null
+++ b/tests/data/src/pep518_missing_requires/setup.py
@@ -0,0 +1,9 @@
+#!/usr/bin/env python
+from setuptools import setup
+
+import simplewheel  # ensure dependency is installed
+
+setup(name='pep518',
+      version='3.0',
+      py_modules=['pep518'],
+      )
diff --git a/tests/functional/test_install.py b/tests/functional/test_install.py
index 385db77ae34..b1944cb71ef 100644
--- a/tests/functional/test_install.py
+++ b/tests/functional/test_install.py
@@ -37,6 +37,30 @@ def test_pep518_uses_build_env(script, data, common_wheels, command, variant):
     )
 
 
+def test_pep518_refuses_missing_requires(script, data, common_wheels):
+    result = script.pip(
+        'install',
+        '-f', common_wheels,
+        '-f', data.find_links,
+        data.src.join("pep518_missing_requires"),
+        expect_error=True
+    )
+    assert result.returncode == 1
+    assert "does not comply with PEP 518" in result.stderr
+
+
+def test_pep518_refuses_invalid_requires(script, data, common_wheels):
+    result = script.pip(
+        'install',
+        '-f', common_wheels,
+        '-f', data.find_links,
+        data.src.join("pep518_invalid_requires"),
+        expect_error=True
+    )
+    assert result.returncode == 1
+    assert "does not comply with PEP 518" in result.stderr
+
+
 def test_pep518_with_user_pip(script, virtualenv, pip_src,
                               data, common_wheels):
     virtualenv.system_site_packages = True

From 0eb566fa8236d340a1a9e52c41ff9d96493e762d Mon Sep 17 00:00:00 2001
From: Pradyun Gedam <pradyunsg@gmail.com>
Date: Tue, 19 Jun 2018 01:00:10 +0530
Subject: [PATCH 3/6] Rework PEP 518 requirement logic

---
 src/pip/_internal/operations/prepare.py | 42 ++++++++++---------
 src/pip/_internal/req/req_install.py    | 56 ++++++++++++-------------
 2 files changed, 49 insertions(+), 49 deletions(-)

diff --git a/src/pip/_internal/operations/prepare.py b/src/pip/_internal/operations/prepare.py
index ff9b1e6a1df..3ad721f019a 100644
--- a/src/pip/_internal/operations/prepare.py
+++ b/src/pip/_internal/operations/prepare.py
@@ -95,31 +95,33 @@ def dist(self, finder):
     def prep_for_dist(self, finder, build_isolation):
         # Before calling "setup.py egg_info", we need to set-up the build
         # environment.
-        build_requirements, isolate = self.req.get_pep_518_info()
-        should_isolate = build_isolation and isolate
-
-        minimum_requirements = ('setuptools', 'wheel')
-        missing_requirements = set(minimum_requirements) - set(
-            pkg_resources.Requirement(r).key
-            for r in build_requirements
-        )
-        if missing_requirements:
-            def format_reqs(rs):
-                return ' and '.join(map(repr, sorted(rs)))
-            logger.warning(
-                "Missing build time requirements in pyproject.toml for %s: "
-                "%s.", self.req, format_reqs(missing_requirements)
-            )
-            logger.warning(
-                "This version of pip does not implement PEP 517 so it cannot "
-                "build a wheel without %s.", format_reqs(minimum_requirements)
-            )
+        build_requirements = self.req.get_pep_518_info()
+        should_isolate = build_isolation and build_requirements is not None
 
         if should_isolate:
+            # Haven't implemented PEP 517 yet, so spew a warning about it if
+            # build-requirements don't include setuptools and wheel.
+            missing_requirements = {'setuptools', 'wheel'} - {
+                pkg_resources.Requirement(r).key for r in build_requirements
+            }
+            if missing_requirements:
+                logger.warning(
+                    "Missing build requirements in pyproject.toml for %s.",
+                    self.req,
+                )
+                logger.warning(
+                    "This version of pip does not implement PEP 517 so it "
+                    "cannot build a wheel without %s.",
+                    " and ".join(map(repr, sorted(missing_requirements)))
+                )
+
+            # Isolate in a BuildEnvironment and install the build-time
+            # requirements.
             self.req.build_env = BuildEnvironment()
             self.req.build_env.install_requirements(
                 finder, build_requirements,
-                "Installing build dependencies")
+                "Installing build dependencies"
+            )
 
         self.req.run_egg_info()
         self.req.assert_source_matches_version()
diff --git a/src/pip/_internal/req/req_install.py b/src/pip/_internal/req/req_install.py
index a3b6f820b08..7a24af16c0e 100644
--- a/src/pip/_internal/req/req_install.py
+++ b/src/pip/_internal/req/req_install.py
@@ -560,42 +560,40 @@ def pyproject_toml(self):
         return pp_toml
 
     def get_pep_518_info(self):
-        """Get a list of the packages required to build the project, if any,
-        and a flag indicating whether pyproject.toml is present, indicating
-        that the build should be isolated.
+        """Get PEP 518 build-time requirements.
 
-        Build requirements can be specified in a pyproject.toml, as described
-        in PEP 518. If this file exists but doesn't specify build
-        requirements, pip will default to installing setuptools and wheel.
+        Returns the list of the packages required to build the project,
+        specified as per PEP 518 within the package. If `pyproject.toml` is not
+        present, returns None to signify not using the same.
         """
-        if os.path.isfile(self.pyproject_toml):
-            with io.open(self.pyproject_toml, encoding="utf-8") as f:
-                pp_toml = pytoml.load(f)
+        if not os.path.isfile(self.pyproject_toml):
+            return None
 
-            build_system = pp_toml.get('build-system', {})
-            if "requires" not in build_system:
-                raise InstallationError(
-                    "{} does not comply with PEP 518 as it since it's "
-                    "pyproject.toml file does not have a '[build-system]' "
-                    "table with a 'requires' key."
-                    .format(self)
-                )
+        with io.open(self.pyproject_toml, encoding="utf-8") as f:
+            pp_toml = pytoml.load(f)
 
-            requires = build_system["requires"]
+        # Extract the build requirements
+        requires = pp_toml.get("build-system", {}).get("requires", None)
+
+        # Error out if it's not valid
+        error_reason = None
+        if requires is None:
+            error_reason = "is missing."
+        else:
             is_list_of_str = isinstance(requires, list) and all(
-                isinstance(req, str) for req in requires
+                isinstance(req, six.string_types) for req in requires
             )
             if not is_list_of_str:
-                raise InstallationError(
-                    "{} does not comply with PEP 518 as it since it's "
-                    "pyproject.toml file contains [build-system].requires "
-                    "which is not a list of strings."
-                    .format(self)
-                )
-
-            return requires, True
-
-        return (['setuptools', 'wheel'], False)
+                error_reason = "not a list of strings."
+        if error_reason is not None:
+            msg = (
+                "{} does not comply with PEP 518 since pyproject.toml does "
+                "not contain a valid '[build-system].requires' key: {}"
+            ).format(self, error_reason)
+            raise InstallationError(msg)
+
+        # If control flow reaches here, we're good to go.
+        return requires
 
     def run_egg_info(self):
         assert self.source_dir

From fdd51011288312757c618039e632b40d4df56d23 Mon Sep 17 00:00:00 2001
From: Pradyun Gedam <pradyunsg@gmail.com>
Date: Tue, 19 Jun 2018 01:00:25 +0530
Subject: [PATCH 4/6] Cleanup Tests

---
 .../src/pep518_invalid_requires/setup.cfg     |  0
 .../data/src/pep518_invalid_requires/setup.py | 11 +++++-----
 .../src/pep518_missing_requires/setup.cfg     |  0
 .../data/src/pep518_missing_requires/setup.py | 11 +++++-----
 tests/functional/test_install.py              | 22 +++++--------------
 5 files changed, 15 insertions(+), 29 deletions(-)
 delete mode 100644 tests/data/src/pep518_invalid_requires/setup.cfg
 delete mode 100644 tests/data/src/pep518_missing_requires/setup.cfg

diff --git a/tests/data/src/pep518_invalid_requires/setup.cfg b/tests/data/src/pep518_invalid_requires/setup.cfg
deleted file mode 100644
index e69de29bb2d..00000000000
diff --git a/tests/data/src/pep518_invalid_requires/setup.py b/tests/data/src/pep518_invalid_requires/setup.py
index b63f59926f7..e8a92da312a 100644
--- a/tests/data/src/pep518_invalid_requires/setup.py
+++ b/tests/data/src/pep518_invalid_requires/setup.py
@@ -1,9 +1,8 @@
 #!/usr/bin/env python
 from setuptools import setup
 
-import simplewheel  # ensure dependency is installed
-
-setup(name='pep518',
-      version='3.0',
-      py_modules=['pep518'],
-      )
+setup(
+    name='pep518_invalid_requires',
+    version='1.0.0',
+    py_modules=['pep518'],
+)
diff --git a/tests/data/src/pep518_missing_requires/setup.cfg b/tests/data/src/pep518_missing_requires/setup.cfg
deleted file mode 100644
index e69de29bb2d..00000000000
diff --git a/tests/data/src/pep518_missing_requires/setup.py b/tests/data/src/pep518_missing_requires/setup.py
index b63f59926f7..cbc5d28af04 100644
--- a/tests/data/src/pep518_missing_requires/setup.py
+++ b/tests/data/src/pep518_missing_requires/setup.py
@@ -1,9 +1,8 @@
 #!/usr/bin/env python
 from setuptools import setup
 
-import simplewheel  # ensure dependency is installed
-
-setup(name='pep518',
-      version='3.0',
-      py_modules=['pep518'],
-      )
+setup(
+    name='pep518_missing_requires',
+    version='1.0.0',
+    py_modules=['pep518'],
+)
diff --git a/tests/functional/test_install.py b/tests/functional/test_install.py
index b1944cb71ef..2a97f92164b 100644
--- a/tests/functional/test_install.py
+++ b/tests/functional/test_install.py
@@ -37,24 +37,12 @@ def test_pep518_uses_build_env(script, data, common_wheels, command, variant):
     )
 
 
-def test_pep518_refuses_missing_requires(script, data, common_wheels):
-    result = script.pip(
-        'install',
-        '-f', common_wheels,
-        '-f', data.find_links,
-        data.src.join("pep518_missing_requires"),
-        expect_error=True
-    )
-    assert result.returncode == 1
-    assert "does not comply with PEP 518" in result.stderr
-
-
-def test_pep518_refuses_invalid_requires(script, data, common_wheels):
+@pytest.mark.parametrize(
+    "package", ["pep518_invalid_requires", "pep518_missing_requires"]
+)
+def test_pep518_refuses_invalid_requires(script, data, common_wheels, package):
     result = script.pip(
-        'install',
-        '-f', common_wheels,
-        '-f', data.find_links,
-        data.src.join("pep518_invalid_requires"),
+        'install', '-f', common_wheels, data.src.join(package),
         expect_error=True
     )
     assert result.returncode == 1

From 8f1cd5fa40ea7842c6e2d82a28537256d8015cc4 Mon Sep 17 00:00:00 2001
From: Pradyun Gedam <pradyunsg@gmail.com>
Date: Tue, 19 Jun 2018 01:07:40 +0530
Subject: [PATCH 5/6] :newspaper:

---
 news/5416.bugfix | 1 +
 news/5512.bugfix | 1 +
 2 files changed, 2 insertions(+)
 create mode 100644 news/5416.bugfix
 create mode 100644 news/5512.bugfix

diff --git a/news/5416.bugfix b/news/5416.bugfix
new file mode 100644
index 00000000000..2f7707e0ce6
--- /dev/null
+++ b/news/5416.bugfix
@@ -0,0 +1 @@
+Start refusing to install packages with non PEP-518 compliant pyproject.toml
diff --git a/news/5512.bugfix b/news/5512.bugfix
new file mode 100644
index 00000000000..2f7707e0ce6
--- /dev/null
+++ b/news/5512.bugfix
@@ -0,0 +1 @@
+Start refusing to install packages with non PEP-518 compliant pyproject.toml

From 2b68c7983e1a71efe8cf638a34d515d909c26932 Mon Sep 17 00:00:00 2001
From: Pradyun Gedam <pradyunsg@gmail.com>
Date: Tue, 19 Jun 2018 15:28:32 +0530
Subject: [PATCH 6/6] Only disable isolation when build-system.requires is
 skipped

---
 src/pip/_internal/req/req_install.py | 35 +++++++++++++++++++---------
 tests/functional/test_install.py     | 20 ++++++++++++----
 2 files changed, 39 insertions(+), 16 deletions(-)

diff --git a/src/pip/_internal/req/req_install.py b/src/pip/_internal/req/req_install.py
index 7a24af16c0e..bd6d4e9fe95 100644
--- a/src/pip/_internal/req/req_install.py
+++ b/src/pip/_internal/req/req_install.py
@@ -33,7 +33,9 @@
     PIP_DELETE_MARKER_FILENAME, running_under_virtualenv,
 )
 from pip._internal.req.req_uninstall import UninstallPathSet
-from pip._internal.utils.deprecation import RemovedInPip11Warning
+from pip._internal.utils.deprecation import (
+    RemovedInPip11Warning, RemovedInPip12Warning,
+)
 from pip._internal.utils.hashes import Hashes
 from pip._internal.utils.logging import indent_log
 from pip._internal.utils.misc import (
@@ -575,22 +577,33 @@ def get_pep_518_info(self):
         # Extract the build requirements
         requires = pp_toml.get("build-system", {}).get("requires", None)
 
-        # Error out if it's not valid
-        error_reason = None
+        template = (
+            "%s does not comply with PEP 518 since pyproject.toml "
+            "does not contain a valid '[build-system].requires' key: %s"
+        )
+
         if requires is None:
-            error_reason = "is missing."
+            logging.warn(template, self, "it is missing.")
+            warnings.warn(
+                "Future versions of pip will reject packages with "
+                "pyproject.toml files that do not comply with PEP 518.",
+                RemovedInPip12Warning,
+            )
+
+            # NOTE: Currently allowing projects to skip this key so that they
+            #       can transition to a PEP 518 compliant pyproject.toml or
+            #       push to update the PEP.
+            # Come pip 19.0, bring this to compliance with PEP 518.
+            return None
         else:
+            # Error out if it's not a list of strings
             is_list_of_str = isinstance(requires, list) and all(
                 isinstance(req, six.string_types) for req in requires
             )
             if not is_list_of_str:
-                error_reason = "not a list of strings."
-        if error_reason is not None:
-            msg = (
-                "{} does not comply with PEP 518 since pyproject.toml does "
-                "not contain a valid '[build-system].requires' key: {}"
-            ).format(self, error_reason)
-            raise InstallationError(msg)
+                raise InstallationError(
+                    template % (self, "it is not a list of strings.")
+                )
 
         # If control flow reaches here, we're good to go.
         return requires
diff --git a/tests/functional/test_install.py b/tests/functional/test_install.py
index 2a97f92164b..b1025190706 100644
--- a/tests/functional/test_install.py
+++ b/tests/functional/test_install.py
@@ -37,18 +37,28 @@ def test_pep518_uses_build_env(script, data, common_wheels, command, variant):
     )
 
 
-@pytest.mark.parametrize(
-    "package", ["pep518_invalid_requires", "pep518_missing_requires"]
-)
-def test_pep518_refuses_invalid_requires(script, data, common_wheels, package):
+def test_pep518_refuses_invalid_requires(script, data, common_wheels):
     result = script.pip(
-        'install', '-f', common_wheels, data.src.join(package),
+        'install', '-f', common_wheels,
+        data.src.join("pep518_invalid_requires"),
         expect_error=True
     )
     assert result.returncode == 1
     assert "does not comply with PEP 518" in result.stderr
 
 
+def test_pep518_allows_but_warns_missing_requires(script, data, common_wheels):
+    result = script.pip(
+        'install', '-f', common_wheels,
+        data.src.join("pep518_missing_requires"),
+        expect_stderr=True
+    )
+    assert "does not comply with PEP 518" in result.stderr
+    assert "DEPRECATION" in result.stderr
+    assert result.returncode == 0
+    assert result.files_created
+
+
 def test_pep518_with_user_pip(script, virtualenv, pip_src,
                               data, common_wheels):
     virtualenv.system_site_packages = True