gh-109615: Fix support test_copy_python_src_ignore() (#109958)

Fix the test when run on an installed Python: use "abs_srcdir" of
sysconfig, and skip the test if the Python source code cannot be
found.

* Tools/patchcheck/patchcheck.py, Tools/freeze/test/freeze.py and
  Lib/test/libregrtest/utils.py now first try to get "abs_srcdir"
  from sysconfig, before getting "srcdir" from sysconfig.
* test.pythoninfo logs sysconfig "abs_srcdir".

3 files changed, 14 insertions, 6 deletions

diff --git a/Lib/test/libregrtest/utils.py b/Lib/test/libregrtest/utils.py
index 7692217..bedf9a5 100644
--- a/Lib/test/libregrtest/utils.py
+++ b/Lib/test/libregrtest/utils.py
@@ -355,11 +355,13 @@ def get_temp_dir(tmp_dir: StrPath | None = None) -> StrPath:
             if not support.is_wasi:
                 tmp_dir = sysconfig.get_config_var('abs_builddir')
                 if tmp_dir is None:
-                    # gh-74470: On Windows, only srcdir is available. Using
-                    # abs_builddir mostly matters on UNIX when building Python
-                    # out of the source tree, especially when the source tree
-                    # is read only.
-                    tmp_dir = sysconfig.get_config_var('srcdir')
+                    tmp_dir = sysconfig.get_config_var('abs_srcdir')
+                    if not tmp_dir:
+                        # gh-74470: On Windows, only srcdir is available. Using
+                        # abs_builddir mostly matters on UNIX when building
+                        # Python out of the source tree, especially when the
+                        # source tree is read only.
+                        tmp_dir = sysconfig.get_config_var('srcdir')
                 tmp_dir = os.path.join(tmp_dir, 'build')
             else:
                 # WASI platform
diff --git a/Lib/test/pythoninfo.py b/Lib/test/pythoninfo.py
index c372efa..0e7528e 100644
--- a/Lib/test/pythoninfo.py
+++ b/Lib/test/pythoninfo.py
@@ -520,6 +520,7 @@ def collect_sysconfig(info_add):
         'SHELL',
         'SOABI',
         'abs_builddir',
+        'abs_srcdir',
         'prefix',
         'srcdir',
     ):
diff --git a/Lib/test/test_support.py b/Lib/test/test_support.py
index af38db5..134ce24 100644
--- a/Lib/test/test_support.py
+++ b/Lib/test/test_support.py
@@ -802,8 +802,13 @@ class TestSupport(unittest.TestCase):
             support.real_max_memuse = old_real_max_memuse
 
     def test_copy_python_src_ignore(self):
-        src_dir = sysconfig.get_config_var('srcdir')
+        src_dir = sysconfig.get_config_var('abs_srcdir')
+        if not src_dir:
+            src_dir = sysconfig.get_config_var('srcdir')
         src_dir = os.path.abspath(src_dir)
+        if not os.path.exists(src_dir):
+            self.skipTest(f"cannot access Python source code directory:"
+                          f" {src_dir!r}")
 
         ignored = {'.git', '__pycache__'}