Fix invalid header path when --root is set

When we invoke setuptools with a `--root`, the header directory we take
from the Scheme object already contains the root as a prefix. Passing
both `--root` and `--install-headers` will result in setuptools adding
the root prefix twice in the header path.

As the Scheme object already has all directories relative to `--root`,
we can pass these separately with the `--install-*` setuptools
arguments and drop the `--root` argument.

As the specific locations differ across interpreters and platforms, the
included test only checks that scripts, headers and library contents are
installed under the specified package root. This is not the case without
the fix, as some files will be installed under the duplicated root path,
outside the test `venv`.

news/8477.bugfix

@@ -0,0 +1,2 @@
+Install libs, headers and data files in the correct location when
+``--root`` is specified.

src/pip/_internal/operations/install/legacy.py

@@ -48,8 +48,6 @@ def install(
 ):
     # type: (...) -> bool
 
-    header_dir = scheme.headers
-
     with TempDirectory(kind="record") as temp_dir:
         try:
             record_filename = os.path.join(temp_dir.path, 'install-record.txt')
@@ -60,11 +58,11 @@ def install(
                 record_filename=record_filename,
                 root=root,
                 prefix=prefix,
-                header_dir=header_dir,
                 home=home,
                 use_user_site=use_user_site,
                 no_user_config=isolated,
                 pycompile=pycompile,
+                scheme=scheme,
             )
 
             runner = runner_with_spinner_message(
@@ -103,7 +101,7 @@ def prepend_root(path):
     for line in record_lines:
         directory = os.path.dirname(line)
         if directory.endswith('.egg-info'):
-            egg_info_dir = prepend_root(directory)
+            egg_info_dir = directory
             break
     else:
         message = (

src/pip/_internal/utils/setuptools_build.py

@@ -1,5 +1,6 @@
 import sys
 
+from pip._internal.models.scheme import Scheme
 from pip._internal.utils.typing import MYPY_CHECK_RUNNING
 
 if MYPY_CHECK_RUNNING:
@@ -140,11 +141,11 @@ def make_setuptools_install_args(
     record_filename,  # type: str
     root,  # type: Optional[str]
     prefix,  # type: Optional[str]
-    header_dir,  # type: Optional[str]
     home,  # type: Optional[str]
     use_user_site,  # type: bool
     no_user_config,  # type: bool
-    pycompile  # type: bool
+    pycompile,  # type: bool
+    scheme,  # type: Scheme
 ):
     # type: (...) -> List[str]
     assert not (use_user_site and prefix)
@@ -159,8 +160,12 @@ def make_setuptools_install_args(
     args += ["install", "--record", record_filename]
     args += ["--single-version-externally-managed"]
 
-    if root is not None:
-        args += ["--root", root]
+    args += ["--install-purelib", scheme.purelib,
+             "--install-platlib", scheme.platlib,
+             "--install-headers", scheme.headers,
+             "--install-scripts", scheme.scripts,
+             "--install-data", scheme.data]
+
     if prefix is not None:
         args += ["--prefix", prefix]
     if home is not None:
@@ -173,9 +178,6 @@ def make_setuptools_install_args(
     else:
         args += ["--no-compile"]
 
-    if header_dir:
-        args += ["--install-headers", header_dir]
-
     args += install_options
 
     return args

tests/functional/test_install.py

@@ -1,4 +1,5 @@
 import distutils
+import fnmatch
 import glob
 import os
 import re
@@ -14,6 +15,7 @@
 from pip._internal.cli.status_codes import ERROR, SUCCESS
 from pip._internal.models.index import PyPI, TestPyPI
 from pip._internal.utils.misc import rmtree
+from pip._internal.utils.temp_dir import TempDirectory
 from tests.lib import (
     _create_svn_repo,
     _create_test_package,
@@ -1027,6 +1029,58 @@ def test_install_package_with_root(script, data, with_wheel):
     assert "Looking in links: " in result.stdout
 
 
+def test_install_package_with_root_check_dirs(script):
+    """
+    Test that specifying --root works correctly and headers, scripts
+    and data files are installed in the correct location.
+    """
+
+    def find_in_path(path, pattern):
+        for root, dirnames, filenames in os.walk(path):
+            for dirname in fnmatch.filter(dirnames, pattern):
+                return os.path.join(root, dirname)
+            for filename in fnmatch.filter(filenames, pattern):
+                return os.path.join(root, filename)
+
+        return None
+
+    header_path = script.scratch_path / "header.h"
+    header_path.write_text('/* hello world */\n')
+    data_path = script.scratch_path / "data_file"
+    data_path.write_text("bletch")
+    pkga_path = script.scratch_path / "pkga"
+    pkga_path.mkdir()
+    setup_py = textwrap.dedent("""
+            from setuptools import setup
+            setup(name='pkga',
+                  version='0.1',
+                  py_modules=["pkga"],
+                  entry_points={{
+                      'console_scripts': ['pkga_script=pkga:main']
+                  }},
+                  headers=[{header_path!r}],
+                  data_files=[('data_files', [{data_path!r}])]
+            )
+        """).format(header_path=str(header_path), data_path=str(data_path))
+
+    pkga_path.joinpath("setup.py").write_text(setup_py)
+    pkga_path.joinpath("pkga.py").write_text(textwrap.dedent("""
+            def main(): pass
+        """))
+    with TempDirectory() as temp_dir:
+        script.pip('install', '--root', temp_dir.path, pkga_path)
+        # Find the installation prefix. If we are running in a virtual
+        # environment, we will find the entire path leading up to the
+        # venv replicated under the root, so we might not find the
+        # root installation where we expect.
+        venv_base = find_in_path(temp_dir.path, "venv")
+        assert find_in_path(venv_base, "header.h")
+        assert find_in_path(venv_base, "pkga-0.1*.egg-info")
+        assert (find_in_path(venv_base, "pkga_script") or
+                find_in_path(venv_base, "pkga_script.exe"))
+        assert find_in_path(venv_base, "data_file")
+
+
 def test_install_package_with_prefix(script, data):
     """
     Test installing a package using pip install --prefix