python@3.9: move tkinter into separate formula

Formula/python@3.9.rb

@@ -1,10 +1,11 @@
 class PythonAT39 < Formula
   desc "Interpreted, interactive, object-oriented programming language"
   homepage "https://www.python.org/"
+  # Keep in sync with python-tk@3.9.
   url "https://www.python.org/ftp/python/3.9.2/Python-3.9.2.tar.xz"
   sha256 "3c2034c54f811448f516668dce09d24008a0716c3a794dd8639b5388cbde247d"
   license "Python-2.0"
-  revision 2
+  revision 3
 
   livecheck do
     url "https://www.python.org/ftp/python/"
@@ -37,7 +38,6 @@ class PythonAT39 < Formula
   depends_on "openssl@1.1"
   depends_on "readline"
   depends_on "sqlite"
-  depends_on "tcl-tk"
   depends_on "xz"
 
   uses_from_macos "bzip2"
@@ -168,8 +168,8 @@ class PythonAT39 < Formula
     # Avoid linking to libgcc https://mail.python.org/pipermail/python-dev/2012-February/116205.html
     args << "MACOSX_DEPLOYMENT_TARGET=#{MacOS.version}"
 
-    args << "--with-tcltk-includes=-I#{Formula["tcl-tk"].opt_include}"
-    args << "--with-tcltk-libs=-L#{Formula["tcl-tk"].opt_lib} -ltcl8.6 -ltk8.6"
+    # Disable _tkinter - this is built in a separate formula python-tk
+    inreplace "setup.py", "DISABLED_MODULE_LIST = []", "DISABLED_MODULE_LIST = ['_tkinter']"
 
     # We want our readline! This is just to outsmart the detection code,
     # superenv makes cc always find includes/libs!
@@ -380,9 +380,9 @@ class PythonAT39 < Formula
 
     # Help distutils find brewed stuff when building extensions
     include_dirs = [HOMEBREW_PREFIX/"include", Formula["openssl@1.1"].opt_include,
-                    Formula["sqlite"].opt_include, Formula["tcl-tk"].opt_include]
+                    Formula["sqlite"].opt_include]
     library_dirs = [HOMEBREW_PREFIX/"lib", Formula["openssl@1.1"].opt_lib,
-                    Formula["sqlite"].opt_lib, Formula["tcl-tk"].opt_lib]
+                    Formula["sqlite"].opt_lib]
 
     cfg = lib_cellar/"distutils/distutils.cfg"
 
@@ -457,6 +457,9 @@ class PythonAT39 < Formula
       They will install into the site-package directory
         #{HOMEBREW_PREFIX/"lib/python#{version.major_minor}/site-packages"}
 
+      tkinter is no longer included with this formula, but it is available separately:
+        brew install python-tk@#{version.major_minor}
+
       See: https://docs.brew.sh/Homebrew-and-Python
     EOS
   end
@@ -475,9 +478,10 @@ class PythonAT39 < Formula
     system "#{bin}/python#{version.major_minor}", "-c", "import _gdbm"
     system "#{bin}/python#{version.major_minor}", "-c", "import pyexpat"
     system "#{bin}/python#{version.major_minor}", "-c", "import zlib"
-    on_macos do
-      system "#{bin}/python#{version.major_minor}", "-c", "import tkinter; root = tkinter.Tk()"
-    end
+
+    # tkinter is provided in a separate formula
+    assert_match "ModuleNotFoundError: No module named '_tkinter'",
+                 shell_output("#{bin}/python#{version.major_minor} -c 'import tkinter' 2>&1", 1)
 
     # Verify that the selected DBM interface works
     (testpath/"dbm_test.py").write <<~EOS