[Python-checkins] bpo-46028: Calculate base_executable by resolving symlinks in a venv (GH-30144)

[zooba]

https://github.com/python/cpython/commit/7407fe4c25ba0308d49e3e88e4a107ef32251cdc
commit: 7407fe4c25ba0308d49e3e88e4a107ef32251cdc
branch: main
author: Steve Dower <steve.dower at python.org>
committer: zooba <steve.dower at microsoft.com>
date: 2022-01-18T15:46:26Z
summary:

bpo-46028: Calculate base_executable by resolving symlinks in a venv (GH-30144)

files:
A Misc/NEWS.d/next/Core and Builtins/2021-12-16-15-04-58.bpo-46028.zfWacB.rst
M Lib/test/test_getpath.py
M Modules/getpath.py

diff --git a/Lib/test/test_getpath.py b/Lib/test/test_getpath.py
index 1a336a4abcafd..eaf4a99279663 100644
--- a/Lib/test/test_getpath.py
+++ b/Lib/test/test_getpath.py
@@ -328,6 +328,38 @@ def test_venv_posix(self):
         actual = getpath(ns, expected)
         self.assertEqual(expected, actual)
 
+    def test_venv_changed_name_posix(self):
+        "Test a venv layout on *nix."
+        ns = MockPosixNamespace(
+            argv0="python",
+            PREFIX="/usr",
+            ENV_PATH="/venv/bin:/usr/bin",
+        )
+        ns.add_known_xfile("/usr/bin/python3")
+        ns.add_known_xfile("/venv/bin/python")
+        ns.add_known_link("/venv/bin/python", "/usr/bin/python3")
+        ns.add_known_file("/usr/lib/python9.8/os.py")
+        ns.add_known_dir("/usr/lib/python9.8/lib-dynload")
+        ns.add_known_file("/venv/pyvenv.cfg", [
+            r"home = /usr/bin"
+        ])
+        expected = dict(
+            executable="/venv/bin/python",
+            prefix="/usr",
+            exec_prefix="/usr",
+            base_executable="/usr/bin/python3",
+            base_prefix="/usr",
+            base_exec_prefix="/usr",
+            module_search_paths_set=1,
+            module_search_paths=[
+                "/usr/lib/python98.zip",
+                "/usr/lib/python9.8",
+                "/usr/lib/python9.8/lib-dynload",
+            ],
+        )
+        actual = getpath(ns, expected)
+        self.assertEqual(expected, actual)
+
     def test_symlink_normal_posix(self):
         "Test a 'standard' install layout via symlink on *nix"
         ns = MockPosixNamespace(
diff --git a/Misc/NEWS.d/next/Core and Builtins/2021-12-16-15-04-58.bpo-46028.zfWacB.rst b/Misc/NEWS.d/next/Core and Builtins/2021-12-16-15-04-58.bpo-46028.zfWacB.rst
new file mode 100644
index 0000000000000..cc34c0fa2405b
--- /dev/null
+++ b/Misc/NEWS.d/next/Core and Builtins/2021-12-16-15-04-58.bpo-46028.zfWacB.rst	
@@ -0,0 +1,3 @@
+Fixes calculation of :data:`sys._base_executable` when inside a virtual
+environment that uses symlinks with different binary names than the base
+environment provides.
diff --git a/Modules/getpath.py b/Modules/getpath.py
index 6f2e038557722..f84e6e8afaf62 100644
--- a/Modules/getpath.py
+++ b/Modules/getpath.py
@@ -351,7 +351,18 @@ def search_up(prefix, *landmarks, test=isfile):
         key, had_equ, value = line.partition('=')
         if had_equ and key.strip().lower() == 'home':
             executable_dir = real_executable_dir = value.strip()
-            base_executable = joinpath(executable_dir, basename(executable))
+            if not base_executable:
+                # First try to resolve symlinked executables, since that may be
+                # more accurate than assuming the executable in 'home'.
+                try:
+                    base_executable = realpath(executable)
+                    if base_executable == executable:
+                        # No change, so probably not a link. Clear it and fall back
+                        base_executable = ''
+                except OSError:
+                    pass
+                if not base_executable:
+                    base_executable = joinpath(executable_dir, basename(executable))
             break
     else:
         venv_prefix = None