patch 9.0.1776: No support for stable Python 3 ABIv9.0.1776

Problem:  No support for stable Python 3 ABI
Solution: Support Python 3 stable ABI

Commits:
1) Support Python 3 stable ABI to allow mixed version interoperatbility

Vim currently supports embedding Python for use with plugins, and the
"dynamic" linking option allows the user to specify a locally installed
version of Python by setting `pythonthreedll`. However, one caveat is
that the Python 3 libs are not binary compatible across minor versions,
and mixing versions can potentially be dangerous (e.g. let's say Vim was
linked against the Python 3.10 SDK, but the user sets `pythonthreedll`
to a 3.11 lib). Usually, nothing bad happens, but in theory this could
lead to crashes, memory corruption, and other unpredictable behaviors.
It's also difficult for the user to tell something is wrong because Vim
has no way of reporting what Python 3 version Vim was linked with.

For Vim installed via a package manager, this usually isn't an issue
because all the dependencies would already be figured out. For prebuilt
Vim binaries like MacVim (my motivation for working on this), AppImage,
and Win32 installer this could potentially be an issue as usually a
single binary is distributed. This is more tricky when a new Python
version is released, as there's a chicken-and-egg issue with deciding
what Python version to build against and hard to keep in sync when a new
Python version just drops and we have a mix of users of different Python
versions, and a user just blindly upgrading to a new Python could lead to
bad interactions with Vim.

Python 3 does have a solution for this problem: stable ABI / limited API
(see https://docs.python.org/3/c-api/stable.html). The C SDK limits the
API to a set of functions that are promised to be stable across
versions. This pull request adds an ifdef config that allows us to turn
it on when building Vim. Vim binaries built with this option should be
safe to freely link with any Python 3 libraies without having the
constraint of having to use the same minor version.

Note: Python 2 has no such concept and this doesn't change how Python 2
integration works (not that there is going to be a new version of Python
2 that would cause compatibility issues in the future anyway).

---

Technical details:
======

The stable ABI can be accessed when we compile with the Python 3 limited
API (by defining `Py_LIMITED_API`). The Python 3 code (in `if_python3.c`
and `if_py_both.h`) would now handle this and switch to limited API
mode. Without it set, Vim will still use the full API as before so this
is an opt-in change.

The main difference is that `PyType_Object` is now an opaque struct that
we can't directly create "static types" out of, and we have to create
type objects as "heap types" instead. This is because the struct is not
stable and changes from version to version (e.g. 3.8 added a
`tp_vectorcall` field to it). I had to change all the types to be
allocated on the heap instead with just a pointer to them.

Other functions are also simply missing in limited API, or they are
introduced too late (e.g. `PyUnicode_AsUTF8AndSize` in 3.10) to it that
we need some other ways to do the same thing, so I had to abstract a few
things into macros, and sometimes re-implement functions like
`PyObject_NEW`.

One caveat is that in limited API, `OutputType` (used for replacing
`sys.stdout`) no longer inherits from `PyStdPrinter_Type` which I don't
think has any real issue other than minor differences in how they
convert to a string and missing a couple functions like `mode()` and
`fileno()`.

Also fixed an existing bug where `tp_basicsize` was set incorrectly for
`BufferObject`, `TabListObject, `WinListObject`.

Technically, there could be a small performance drop, there is a little
more indirection with accessing type objects, and some APIs like
`PyUnicode_AsUTF8AndSize` are missing, but in practice I didn't see any
difference, and any well-written Python plugin should try to avoid
excessing callbacks to the `vim` module in Python anyway.

I only tested limited API mode down to Python 3.7, which seemes to
compile and work fine. I haven't tried earlier Python versions.

2) Fix PyIter_Check on older Python vers / type##Ptr unused warning

For PyIter_Check, older versions exposed them as either macros (used in
full API), or a function (for use in limited API). A previous change
exposed PyIter_Check to the dynamic build because Python just moved it
to function-only in 3.10 anyway. Because of that, just make sure we
always grab the function in dynamic builds in earlier versions since
that's what Python eventually did anyway.

3) Move Py_LIMITED_API define to configure script

Can now use --with-python-stable-abi flag to customize what stable ABI
version to target. Can also use an env var to do so as well.

4) Show +python/dyn-stable in :version, and allow has() feature query

Not sure if the "/dyn-stable" suffix would break things, or whether we
should do it another way. Or just don't show it in version and rely on
has() feature checking.

5) Documentation first draft. Still need to implement v:python3_version

6) Fix PyIter_Check build breaks when compiling against Python 3.8

7) Add CI coverage stable ABI on Linux/Windows / make configurable on Windows

This adds configurable options for Windows make files (both MinGW and
MSVC). CI will also now exercise both traditional full API and stable
ABI for Linux and Windows in the matrix for coverage.

Also added a "dynamic" option to Linux matrix as a drive-by change to
make other scripting languages like Ruby / Perl testable under both
static and dynamic builds.

8) Fix inaccuracy in Windows docs

Python's own docs are confusing but you don't actually want to use
`python3.dll` for the dynamic linkage.

9) Add generated autoconf file

10) Add v:python3_version support

This variable indicates the version of Python3 that Vim was built
against (PY_VERSION_HEX), and will be useful to check whether the Python
library you are loading in dynamically actually fits it. When built with
stable ABI, it will be the limited ABI version instead
(`Py_LIMITED_API`), which indicates the minimum version of Python 3 the
user should have, rather than the exact match. When stable ABI is used,
we won't be exposing PY_VERSION_HEX in this var because it just doesn't
seem necessary to do so (the whole point of stable ABI is the promise
that it will work across versions), and I don't want to confuse the user
with too many variables.

Also, cleaned up some documentation, and added help tags.

11) Fix Python 3.7 compat issues

Fix a couple issues when using limited API < 3.8

- Crash on exit: In Python 3.7, if a heap-allocated type is destroyed
  before all instances are, it would cause a crash later. This happens
  when we destroyed `OptionsType` before calling `Py_Finalize` when
  using the limited API. To make it worse, later versions changed the
  semantics and now each instance has a strong reference to its own type
  and the recommendation has changed to have each instance de-ref its
  own type and have its type in GC traversal. To avoid dealing with
  these cross-version variations, we just don't free the heap type. They
  are static types in non-limited-API anyway and are designed to last
  through the entirety of the app, and we also don't restart the Python
  runtime and therefore do not need it to have absolutely 0 leaks.

  See:
  - https://docs.python.org/3/whatsnew/3.8.html#changes-in-the-c-api
  - https://docs.python.org/3/whatsnew/3.9.html#changes-in-the-c-api

- PyIter_Check: This function is not provided in limited APIs older than
  3.8. Previously I was trying to mock it out using manual
  PyType_GetSlot() but it was brittle and also does not actually work
  properly for static types (it will generate a Python error). Just
  return false. It does mean using limited API < 3.8 is not recommended
  as you lose the functionality to handle iterators, but from playing
  with plugins I couldn't find it to be an issue.

- Fix loading of PyIter_Check so it will be done when limited API < 3.8.
  Otherwise loading a 3.7 Python lib will fail even if limited API was
  specified to use it.

12) Make sure to only load `PyUnicode_AsUTF8AndSize` in needed in limited API

We don't use this function unless limited API >= 3.10, but we were
loading it regardless. Usually it's ok in Unix-like systems where Python
just has a single lib that we load from, but in Windows where there is a
separate python3.dll this would not work as the symbol would not have
been exposed in this more limited DLL file. This makes it much clearer
under what condition is this function needed.

closes: #12032

Signed-off-by: Christian Brabandt <cb@256bit.org>
Co-authored-by: Yee Cheng Chin <ychin.git@gmail.com>

18 files changed, 769 insertions, 153 deletions

diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 273dedf3be..98bff17d42 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -51,8 +51,14 @@ jobs:
           - features: huge
             coverage: true
           - features: huge
+            compiler: clang
+            extra: none
+            interface: dynamic
+            python3: stable-abi
+          - features: huge
             compiler: gcc
             coverage: true
+            interface: dynamic
             extra: testgui
             uchar: true
             luaver: lua5.4
@@ -141,7 +147,16 @@ jobs:
             ;;
           huge)
             echo "TEST=scripttests test_libvterm"
-            echo "CONFOPT=--enable-perlinterp --enable-pythoninterp --enable-python3interp --enable-rubyinterp --enable-luainterp --enable-tclinterp"
+            if ${{ matrix.interface == 'dynamic' }}; then
+              if ${{ matrix.python3 == 'stable-abi' }}; then
+                PYTHON3_FLAGS="--with-python3-stable-abi=3.8"
+              else
+                PYTHON3_FLAGS=""
+              fi
+              echo "CONFOPT=--enable-perlinterp=dynamic --enable-pythoninterp=dynamic --enable-python3interp=dynamic --enable-rubyinterp=dynamic --enable-luainterp=dynamic --enable-tclinterp=dynamic ${PYTHON3_FLAGS}"
+            else
+              echo "CONFOPT=--enable-perlinterp --enable-pythoninterp --enable-python3interp --enable-rubyinterp --enable-luainterp --enable-tclinterp"
+            fi
             ;;
           esac
 
@@ -369,8 +384,8 @@ jobs:
       fail-fast: false
       matrix:
         include:
-          - { features: HUGE,   toolchain: msvc,  VIMDLL: no,  GUI: no,  arch: x64 }
-          - { features: HUGE,   toolchain: mingw, VIMDLL: yes, GUI: yes, arch: x86, coverage: yes }
+          - { features: HUGE,   toolchain: msvc,  VIMDLL: no,  GUI: no,  arch: x64, python3: stable }
+          - { features: HUGE,   toolchain: mingw, VIMDLL: yes, GUI: yes, arch: x86, python3: stable, coverage: yes }
           - { features: HUGE,   toolchain: msvc,  VIMDLL: no,  GUI: yes, arch: x86 }
           - { features: HUGE,   toolchain: mingw, VIMDLL: yes, GUI: no,  arch: x64, coverage: yes }
           - { features: NORMAL, toolchain: msvc,  VIMDLL: yes, GUI: no,  arch: x86 }
@@ -501,6 +516,11 @@ jobs:
           ) else (
             set GUI=${{ matrix.GUI }}
           )
+          if "${{ matrix.python3 }}"=="stable" (
+            set PYTHON3_STABLE=yes
+          ) else (
+            set PYTHON3_STABLE=no
+          )
           if "${{ matrix.features }}"=="HUGE" (
             nmake -nologo -f Make_mvc.mak ^
               FEATURES=${{ matrix.features }} ^
@@ -508,6 +528,7 @@ jobs:
               DYNAMIC_LUA=yes LUA=%LUA_DIR% ^
               DYNAMIC_PYTHON=yes PYTHON=%PYTHON_DIR% ^
               DYNAMIC_PYTHON3=yes PYTHON3=%PYTHON3_DIR% ^
+              DYNAMIC_PYTHON3_STABLE_ABI=%PYTHON3_STABLE% ^
               DYNAMIC_SODIUM=yes SODIUM=%SODIUM_DIR%
           ) else (
             nmake -nologo -f Make_mvc.mak ^
@@ -525,6 +546,11 @@ jobs:
           else
             GUI=${{ matrix.GUI }}
           fi
+          if [ "${{ matrix.python3 }}" = "stable" ]; then
+            PYTHON3_STABLE=yes
+          else
+            PYTHON3_STABLE=no
+          fi
           if [ "${{ matrix.features }}" = "HUGE" ]; then
             mingw32-make -f Make_ming.mak -j2 \
               FEATURES=${{ matrix.features }} \
@@ -532,6 +558,7 @@ jobs:
               DYNAMIC_LUA=yes LUA=${LUA_DIR_SLASH} \
               DYNAMIC_PYTHON=yes PYTHON=${PYTHON_DIR} \
               DYNAMIC_PYTHON3=yes PYTHON3=${PYTHON3_DIR} \
+              DYNAMIC_PYTHON3_STABLE_ABI=${PYTHON3_STABLE} \
               DYNAMIC_SODIUM=yes SODIUM=${SODIUM_DIR} \
               STATIC_STDCPLUS=yes COVERAGE=${{ matrix.coverage }}
           else
diff --git a/runtime/doc/builtin.txt b/runtime/doc/builtin.txt
index e9bdad2edf..99bc9e2be7 100644
--- a/runtime/doc/builtin.txt
+++ b/runtime/doc/builtin.txt
@@ -10986,6 +10986,7 @@ python_dynamic		Python 2.x interface is dynamically loaded. |has-python|
 python3			Python 3.x interface available. |has-python|
 python3_compiled	Compiled with Python 3.x interface. |has-python|
 python3_dynamic		Python 3.x interface is dynamically loaded. |has-python|
+python3_stable		Python 3.x interface is using Python Stable ABI. |has-python|
 pythonx			Python 2.x and/or 3.x interface available. |python_x|
 qnx			QNX version of Vim.
 quickfix		Compiled with |quickfix| support.
diff --git a/runtime/doc/eval.txt b/runtime/doc/eval.txt
index 7e26605f84..4f9a3c99f5 100644
--- a/runtime/doc/eval.txt
+++ b/runtime/doc/eval.txt
@@ -2424,6 +2424,25 @@ v:progpath	Contains the command with which Vim was invoked, in a form
 		".exe" is not added to v:progpath.
 		Read-only.
 
+				    *v:python3_version* *python3-version-variable*
+v:python3_version
+		Version of Python 3 that Vim was built against.  When
+		Python is loaded dynamically (|python-dynamic|), this version
+		should exactly match the Python library up to the minor
+		version (e.g.  3.10.2 and 3.10.3 are compatible as the minor
+		version is "10", whereas 3.9.4 and 3.10.3 are not compatible).
+		When |python-stable-abi| is used, this will be the minimum Python
+		version that you can use instead. (e.g. if v:python3_version
+		indicates 3.9, you can use 3.9, 3.10, or anything above).
+
+		This number is encoded as a hex number following Python ABI
+		versioning conventions.  Do the following to have a
+		human-readable full version in hex: >
+			echo printf("%08X", v:python3_version)
+<		You can obtain only the minor version by doing: >
+			echo and(v:python3_version>>16,0xff)
+<		Read-only.
+
 					*v:register* *register-variable*
 v:register	The name of the register in effect for the current normal mode
 		command (regardless of whether that command actually used a
diff --git a/runtime/doc/if_pyth.txt b/runtime/doc/if_pyth.txt
index c2a0094b63..3d3b92a662 100644
--- a/runtime/doc/if_pyth.txt
+++ b/runtime/doc/if_pyth.txt
@@ -769,7 +769,19 @@ Unix ~
 The 'pythondll' or 'pythonthreedll' option can be used to specify the Python
 shared library file instead of DYNAMIC_PYTHON_DLL or DYNAMIC_PYTHON3_DLL file
 what were specified at compile time.  The version of the shared library must
-match the Python 2.x or Python 3 version Vim was compiled with.
+match the Python 2.x or Python 3 version (|v:python3_version|) Vim was
+compiled with unless using |python3-stable-abi|.
+
+
+Stable ABI and mixing Python versions ~
+			*python-stable* *python-stable-abi* *python3-stable-abi*
+If Vim was not compiled with Stable ABI (only available for Python 3), the
+version of the Python shared library must match the version that Vim was
+compiled with.  Otherwise, mixing versions could result in unexpected crashes
+and failures.  With Stable ABI, this restriction is relaxed, and any Python 3
+library with version of at least |v:python3_version| will work.  See
+|has-python| for how to check if Stable ABI is supported, or see if version
+output includes |+python3/dyn-stable|.
 
 ==============================================================================
 10. Python 3						*python3*
@@ -881,6 +893,18 @@ python support: >
 	  endif
 	endif
 
+When loading the library dynamically, Vim can be compiled to support Python 3
+Stable ABI (|python3-stable-abi|) which allows you to load a different version
+of Python 3 library than the one Vim was compiled with.  To check it: >
+	if has('python3_dynamic')
+	  if has('python3_stable')
+	    echo 'support Python 3 Stable ABI.'
+	  else
+	    echo 'does not support Python 3 Stable ABI.'
+	    echo 'only use Python 3 version ' .. v:python3_version
+	  endif
+	endif
+
 This also tells you whether Python is dynamically loaded, which will fail if
 the runtime library cannot be found.
 
diff --git a/runtime/doc/tags b/runtime/doc/tags
index ce1918f26a..673c0db654 100644
--- a/runtime/doc/tags
+++ b/runtime/doc/tags
@@ -1434,6 +1434,7 @@ $quote	eval.txt	/*$quote*
 +python/dyn	various.txt	/*+python\/dyn*
 +python3	various.txt	/*+python3*
 +python3/dyn	various.txt	/*+python3\/dyn*
++python3/dyn-stable	various.txt	/*+python3\/dyn-stable*
 +quickfix	various.txt	/*+quickfix*
 +reltime	various.txt	/*+reltime*
 +rightleft	various.txt	/*+rightleft*
@@ -9294,6 +9295,8 @@ python-path_hook	if_pyth.txt	/*python-path_hook*
 python-pyeval	if_pyth.txt	/*python-pyeval*
 python-range	if_pyth.txt	/*python-range*
 python-special-path	if_pyth.txt	/*python-special-path*
+python-stable	if_pyth.txt	/*python-stable*
+python-stable-abi	if_pyth.txt	/*python-stable-abi*
 python-strwidth	if_pyth.txt	/*python-strwidth*
 python-tabpage	if_pyth.txt	/*python-tabpage*
 python-tabpages	if_pyth.txt	/*python-tabpages*
@@ -9306,6 +9309,8 @@ python.vim	syntax.txt	/*python.vim*
 python2-directory	if_pyth.txt	/*python2-directory*
 python3	if_pyth.txt	/*python3*
 python3-directory	if_pyth.txt	/*python3-directory*
+python3-stable-abi	if_pyth.txt	/*python3-stable-abi*
+python3-version-variable	eval.txt	/*python3-version-variable*
 python_x	if_pyth.txt	/*python_x*
 python_x-special-comments	if_pyth.txt	/*python_x-special-comments*
 pythonx	if_pyth.txt	/*pythonx*
@@ -10632,6 +10637,7 @@ v:prevcount	eval.txt	/*v:prevcount*
 v:profiling	eval.txt	/*v:profiling*
 v:progname	eval.txt	/*v:progname*
 v:progpath	eval.txt	/*v:progpath*
+v:python3_version	eval.txt	/*v:python3_version*
 v:register	eval.txt	/*v:register*
 v:scrollstart	eval.txt	/*v:scrollstart*
 v:searchforward	eval.txt	/*v:searchforward*
diff --git a/runtime/doc/various.txt b/runtime/doc/various.txt
index a11e166c38..e478c8266e 100644
--- a/runtime/doc/various.txt
+++ b/runtime/doc/various.txt
@@ -450,6 +450,8 @@ m  *+python*		Python 2 interface |python|
 m  *+python/dyn*	Python 2 interface |python-dynamic| |/dyn|
 m  *+python3*		Python 3 interface |python|
 m  *+python3/dyn*	Python 3 interface |python-dynamic| |/dyn|
+m  *+python3/dyn-stable*
+			Python 3 interface |python-dynamic| |python-stable| |/dyn|
 N  *+quickfix*		|:make| and |quickfix| commands
 N  *+reltime*		|reltime()| function, 'hlsearch'/'incsearch' timeout,
 			'redrawtime' option
diff --git a/src/Make_cyg_ming.mak b/src/Make_cyg_ming.mak
index 426125663c..e4fe0be8fb 100644
--- a/src/Make_cyg_ming.mak
+++ b/src/Make_cyg_ming.mak
@@ -412,6 +412,9 @@ PYTHON3INC=-I $(PYTHON3)/include
   else
 PYTHON3INC=-I $(PYTHON3)/win32inc
   endif
+  ifeq ($(DYNAMIC_PYTHON3_STABLE_ABI),yes)
+PYTHON3INC += -DPy_LIMITED_API=0x3080000
+  endif
  endif
 endif
 
@@ -594,6 +597,9 @@ ifdef PYTHON3
 CFLAGS += -DFEAT_PYTHON3
  ifeq (yes, $(DYNAMIC_PYTHON3))
 CFLAGS += -DDYNAMIC_PYTHON3 -DDYNAMIC_PYTHON3_DLL=\"$(DYNAMIC_PYTHON3_DLL)\"
+  ifeq (yes, $(DYNAMIC_PYTHON3_STABLE_ABI))
+CFLAGS += -DDYNAMIC_PYTHON3_STABLE_ABI
+  endif
  else
 CFLAGS += -DPYTHON3_DLL=\"$(DYNAMIC_PYTHON3_DLL)\"
  endif
diff --git a/src/Make_mvc.mak b/src/Make_mvc.mak
index f98d905042..e1d42fdcb9 100644
--- a/src/Make_mvc.mak
+++ b/src/Make_mvc.mak
@@ -950,7 +950,13 @@ PYTHON3_INC = /I "$(PYTHON3)\Include" /I "$(PYTHON3)\PC"
 ! if "$(DYNAMIC_PYTHON3)" == "yes"
 CFLAGS = $(CFLAGS) -DDYNAMIC_PYTHON3 \
 		-DDYNAMIC_PYTHON3_DLL=\"$(DYNAMIC_PYTHON3_DLL)\"
+!  if "$(DYNAMIC_PYTHON3_STABLE_ABI)" == "yes"
+CFLAGS = $(CFLAGS) -DDYNAMIC_PYTHON3_STABLE_ABI
+PYTHON3_INC = $(PYTHON3_INC) -DPy_LIMITED_API=0x3080000
+PYTHON3_LIB = /nodefaultlib:python3.lib
+!  else
 PYTHON3_LIB = /nodefaultlib:python$(PYTHON3_VER).lib
+!  endif
 ! else
 CFLAGS = $(CFLAGS) -DPYTHON3_DLL=\"$(DYNAMIC_PYTHON3_DLL)\"
 PYTHON3_LIB = "$(PYTHON3)\libs\python$(PYTHON3_VER).lib"
diff --git a/src/auto/configure b/src/auto/configure
index b914aec84c..9fd6888191 100755
--- a/src/auto/configure
+++ b/src/auto/configure
@@ -680,6 +680,7 @@ PYTHON3_SRC
 PYTHON3_CFLAGS_EXTRA
 PYTHON3_CFLAGS
 PYTHON3_LIBS
+vi_cv_var_python3_stable_abi
 vi_cv_path_python3
 PYTHON_OBJ
 PYTHON_SRC
@@ -811,6 +812,7 @@ with_python_command
 with_python_config_dir
 enable_python3interp
 with_python3_command
+with_python3_stable_abi
 with_python3_config_dir
 enable_tclinterp
 with_tclsh
@@ -1531,6 +1533,7 @@ Optional Packages:
   --with-python-command=NAME  name of the Python 2 command (default: python2 or python)
   --with-python-config-dir=PATH  Python's config directory (deprecated)
   --with-python3-command=NAME  name of the Python 3 command (default: python3 or python)
+  --with-python3-stable-abi=VERSION  stable ABI version to target (e.g. 3.8)
   --with-python3-config-dir=PATH  Python's config directory (deprecated)
   --with-tclsh=PATH       which tclsh to use (default: tclsh8.0)
   --with-ruby-command=RUBY  name of the Ruby command (default: ruby)
@@ -6753,6 +6756,34 @@ $as_echo_n "checking Python is 3.0 or better... " >&6; }
       { $as_echo "$as_me:${as_lineno-$LINENO}: result: yep" >&5
 $as_echo "yep" >&6; }
 
+            { $as_echo "$as_me:${as_lineno-$LINENO}: checking --with-python3-stable-abi argument" >&5
+$as_echo_n "checking --with-python3-stable-abi argument... " >&6; }
+
+
+# Check whether --with-python3-stable-abi was given.
+if test "${with_python3_stable_abi+set}" = set; then :
+  withval=$with_python3_stable_abi; vi_cv_var_python3_stable_abi="$withval"; { $as_echo "$as_me:${as_lineno-$LINENO}: result: $vi_cv_var_python3_stable_abi" >&5
+$as_echo "$vi_cv_var_python3_stable_abi" >&6; }
+else
+  { $as_echo "$as_me:${as_lineno-$LINENO}: result: no" >&5
+$as_echo "no" >&6; }
+fi
+
+      if test "X$vi_cv_var_python3_stable_abi" != "X"; then
+        if ${vi_cv_var_python3_stable_abi_hex+:} false; then :
+  $as_echo_n "(cached) " >&6
+else
+
+         vi_cv_var_python3_stable_abi_hex=`
+         ${vi_cv_path_python3} -c \
+         "major_minor='${vi_cv_var_python3_stable_abi}'.split('.'); print('0x{0:X}'.format( (int(major_minor.__getitem__(0))<<24) + (int(major_minor.__getitem__(1))<<16) ))"`
+fi
+
+        if test "X$vi_cv_var_python3_stable_abi_hex" == "X"; then
+          as_fn_error $? "can't parse Python 3 stable ABI version. It should be \"<major>.<minor>\"" "$LINENO" 5
+        fi
+      fi
+
             { $as_echo "$as_me:${as_lineno-$LINENO}: checking Python's abiflags" >&5
 $as_echo_n "checking Python's abiflags... " >&6; }
 if ${vi_cv_var_python3_abiflags+:} false; then :
@@ -6897,9 +6928,12 @@ $as_echo "$vi_cv_dll_name_python3" >&6; }
         else
           PYTHON3_CFLAGS="-I${vi_cv_path_python3_pfx}/include/python${vi_cv_var_python3_version}${vi_cv_var_python3_abiflags} -I${vi_cv_path_python3_epfx}/include/python${vi_cv_var_python3_version}${vi_cv_var_python3_abiflags}"
         fi
-	if test "X$have_python3_config_dir" = "X1" -a "$enable_python3interp" = "dynamic"; then
-	  	  PYTHON3_CFLAGS="${PYTHON3_CFLAGS}  -DPYTHON3_HOME='L\"${vi_cv_path_python3_pfx}\"'"
-	fi
+        if test "X$have_python3_config_dir" = "X1" -a "$enable_python3interp" = "dynamic"; then
+                    PYTHON3_CFLAGS="${PYTHON3_CFLAGS}  -DPYTHON3_HOME='L\"${vi_cv_path_python3_pfx}\"'"
+        fi
+        if test "X$vi_cv_var_python3_stable_abi_hex" != "X"; then
+          PYTHON3_CFLAGS="${PYTHON3_CFLAGS} -DPy_LIMITED_API=${vi_cv_var_python3_stable_abi_hex}"
+        fi
         PYTHON3_SRC="if_python3.c"
         PYTHON3_OBJ="objects/if_python3.o"
 
@@ -7009,6 +7043,10 @@ if test "$python_ok" = yes && test "$python3_ok" = yes; then
 
   $as_echo "#define DYNAMIC_PYTHON3 1" >>confdefs.h
 
+  if test "X$vi_cv_var_python3_stable_abi_hex" != "X"; then
+    $as_echo "#define DYNAMIC_PYTHON3_STABLE_ABI 1" >>confdefs.h
+
+  fi
   { $as_echo "$as_me:${as_lineno-$LINENO}: checking whether we can do without RTLD_GLOBAL for Python" >&5
 $as_echo_n "checking whether we can do without RTLD_GLOBAL for Python... " >&6; }
   cflags_save=$CFLAGS
@@ -7190,6 +7228,10 @@ rm -f core conftest.err conftest.$ac_objext \
 elif test "$python3_ok" = yes && test "$enable_python3interp" = "dynamic"; then
   $as_echo "#define DYNAMIC_PYTHON3 1" >>confdefs.h
 
+  if test "X$vi_cv_var_python3_stable_abi_hex" != "X"; then
+    $as_echo "#define DYNAMIC_PYTHON3_STABLE_ABI 1" >>confdefs.h
+
+  fi
   PYTHON3_SRC="if_python3.c"
   PYTHON3_OBJ="objects/if_python3.o"
   PYTHON3_CFLAGS="$PYTHON3_CFLAGS -DDYNAMIC_PYTHON3_DLL=\\\"${vi_cv_dll_name_python3}\\\""
diff --git a/src/config.h.in b/src/config.h.in
index d0257ccabe..93972ca0cc 100644
--- a/src/config.h.in
+++ b/src/config.h.in
@@ -354,6 +354,9 @@
 /* Define for linking via dlopen() or LoadLibrary() */
 #undef DYNAMIC_PYTHON3
 
+/* Define if compiled against Python 3 stable ABI / limited API */
+#undef DYNAMIC_PYTHON3_STABLE_ABI
+
 /* Define if dynamic python does not require RTLD_GLOBAL */
 #undef PY_NO_RTLD_GLOBAL
 
diff --git a/src/configure.ac b/src/configure.ac
index a3c5f8da8c..cefd0c3b31 100644
--- a/src/configure.ac
+++ b/src/configure.ac
@@ -1503,6 +1503,23 @@ if test "$enable_python3interp" = "yes" -o "$enable_python3interp" = "dynamic";
     then
       AC_MSG_RESULT(yep)
 
+      dnl -- get the stable ABI version if passed in
+      AC_MSG_CHECKING(--with-python3-stable-abi argument)
+      AC_SUBST(vi_cv_var_python3_stable_abi)
+      AC_ARG_WITH(python3-stable-abi, [  --with-python3-stable-abi=VERSION  stable ABI version to target (e.g. 3.8)],
+        vi_cv_var_python3_stable_abi="$withval"; AC_MSG_RESULT($vi_cv_var_python3_stable_abi),
+        AC_MSG_RESULT(no))
+      if test "X$vi_cv_var_python3_stable_abi" != "X"; then
+        AC_CACHE_VAL(vi_cv_var_python3_stable_abi_hex,
+        [
+         vi_cv_var_python3_stable_abi_hex=`
+         ${vi_cv_path_python3} -c \
+         "major_minor='${vi_cv_var_python3_stable_abi}'.split('.'); print('0x{0:X}'.format( (int(major_minor.__getitem__(0))<<24) + (int(major_minor.__getitem__(1))<<16) ))"` ])
+        if test "X$vi_cv_var_python3_stable_abi_hex" == "X"; then
+          AC_MSG_ERROR([can't parse Python 3 stable ABI version. It should be "<major>.<minor>"])
+        fi
+      fi
+
       dnl -- get abiflags for python 3.2 or higher (PEP 3149)
       AC_CACHE_CHECK(Python's abiflags,vi_cv_var_python3_abiflags,
       [
@@ -1609,10 +1626,13 @@ eof
         else
           PYTHON3_CFLAGS="-I${vi_cv_path_python3_pfx}/include/python${vi_cv_var_python3_version}${vi_cv_var_python3_abiflags} -I${vi_cv_path_python3_epfx}/include/python${vi_cv_var_python3_version}${vi_cv_var_python3_abiflags}"
         fi
-	if test "X$have_python3_config_dir" = "X1" -a "$enable_python3interp" = "dynamic"; then
-	  dnl Define PYTHON3_HOME if --with-python-config-dir was used
-	  PYTHON3_CFLAGS="${PYTHON3_CFLAGS}  -DPYTHON3_HOME='L\"${vi_cv_path_python3_pfx}\"'"
-	fi
+        if test "X$have_python3_config_dir" = "X1" -a "$enable_python3interp" = "dynamic"; then
+          dnl Define PYTHON3_HOME if --with-python-config-dir was used
+          PYTHON3_CFLAGS="${PYTHON3_CFLAGS}  -DPYTHON3_HOME='L\"${vi_cv_path_python3_pfx}\"'"
+        fi
+        if test "X$vi_cv_var_python3_stable_abi_hex" != "X"; then
+          PYTHON3_CFLAGS="${PYTHON3_CFLAGS} -DPy_LIMITED_API=${vi_cv_var_python3_stable_abi_hex}"
+        fi
         PYTHON3_SRC="if_python3.c"
         PYTHON3_OBJ="objects/if_python3.o"
 
@@ -1693,6 +1713,9 @@ dnl with dlopen(), dlsym(), dlclose()
 if test "$python_ok" = yes && test "$python3_ok" = yes; then
   AC_DEFINE(DYNAMIC_PYTHON)
   AC_DEFINE(DYNAMIC_PYTHON3)
+  if test "X$vi_cv_var_python3_stable_abi_hex" != "X"; then
+    AC_DEFINE(DYNAMIC_PYTHON3_STABLE_ABI)
+  fi
   AC_MSG_CHECKING(whether we can do without RTLD_GLOBAL for Python)
   cflags_save=$CFLAGS
   CFLAGS="$CFLAGS $PYTHON_CFLAGS"
@@ -1816,6 +1839,9 @@ elif test "$python_ok" = yes; then
   fi
 elif test "$python3_ok" = yes && test "$enable_python3interp" = "dynamic"; then
   AC_DEFINE(DYNAMIC_PYTHON3)
+  if test "X$vi_cv_var_python3_stable_abi_hex" != "X"; then
+    AC_DEFINE(DYNAMIC_PYTHON3_STABLE_ABI)
+  fi
   PYTHON3_SRC="if_python3.c"
   PYTHON3_OBJ="objects/if_python3.o"
   PYTHON3_CFLAGS="$PYTHON3_CFLAGS -DDYNAMIC_PYTHON3_DLL=\\\"${vi_cv_dll_name_python3}\\\""
diff --git a/src/evalfunc.c b/src/evalfunc.c
index 8561e94d22..3e020bcde0 100644
--- a/src/evalfunc.c
+++ b/src/evalfunc.c
@@ -6167,6 +6167,13 @@ f_has(typval_T *argvars, typval_T *rettv)
 		0
 #endif
 		},
+	{"python3_stable",
+#if defined(FEAT_PYTHON3) && defined(DYNAMIC_PYTHON3_STABLE_ABI)
+		1
+#else
+		0
+#endif
+		},
 	{"python3",
 #if defined(FEAT_PYTHON3) && !defined(DYNAMIC_PYTHON3)
 		1
diff --git a/src/evalvars.c b/src/evalvars.c
index cb31966bd2..bd096dfd7b 100644
--- a/src/evalvars.c
+++ b/src/evalvars.c
@@ -157,6 +157,7 @@ static struct vimvar
     {VV_NAME("sizeoflong",	 VAR_NUMBER), NULL, VV_RO},
     {VV_NAME("sizeofpointer",	 VAR_NUMBER), NULL, VV_RO},
     {VV_NAME("maxcol",		 VAR_NUMBER), NULL, VV_RO},
+    {VV_NAME("python3_version",	 VAR_NUMBER), NULL, VV_RO},
 };
 
 // shorthand
@@ -264,6 +265,10 @@ evalvars_init(void)
 
     set_vim_var_dict(VV_COLORNAMES, dict_alloc());
 
+#ifdef FEAT_PYTHON3
+    set_vim_var_nr(VV_PYTHON3_VERSION, python3_version());
+#endif
+
     // Default for v:register is not 0 but '"'.  This is adjusted once the
     // clipboard has been setup by calling reset_reg_var().
     set_reg_var(0);
diff --git a/src/if_py_both.h b/src/if_py_both.h
index 110de234fd..ff18098605 100644
--- a/src/if_py_both.h
+++ b/src/if_py_both.h
@@ -30,9 +30,285 @@ static const char *vim_special_path = "_vim_path_";
 #define PyErr_FORMAT2(exc, str, arg1, arg2) PyErr_Format(exc, _(str), arg1,arg2)
 #define PyErr_VIM_FORMAT(str, arg) PyErr_FORMAT(VimError, str, arg)
 
-#define Py_TYPE_NAME(obj) ((obj)->ob_type->tp_name == NULL \
+#ifdef USE_LIMITED_API
+// Limited Python API. Need to call only exposed functions and remap macros.
+// PyTypeObject is an opaque struct.
+
+typedef struct {
+    lenfunc sq_length;
+    binaryfunc sq_concat;
+    ssizeargfunc sq_repeat;
+    ssizeargfunc sq_item;
+    void *was_sq_slice;
+    ssizeobjargproc sq_ass_item;
+    void *was_sq_ass_slice;
+    objobjproc sq_contains;
+
+    binaryfunc sq_inplace_concat;
+    ssizeargfunc sq_inplace_repeat;
+} PySequenceMethods;
+
+typedef struct {
+    lenfunc mp_length;
+    binaryfunc mp_subscript;
+    objobjargproc mp_ass_subscript;
+} PyMappingMethods;
+
+// This struct emulates the concrete _typeobject struct to allow the code to
+// work the same way in both limited and full Python APIs.
+struct typeobject_wrapper {
+    const char *tp_name;
+    Py_ssize_t tp_basicsize;
+    unsigned long tp_flags;
+
+    // When adding new slots below, also need to make sure we add ADD_TP_SLOT
+    // call in AddHeapType for it.
+
+    destructor tp_dealloc;
+    reprfunc tp_repr;
+
+    PySequenceMethods *tp_as_sequence;
+    PyMappingMethods *tp_as_mapping;
+
+    ternaryfunc tp_call;
+    getattrofunc tp_getattro;
+    setattrofunc tp_setattro;
+
+    const char *tp_doc;
+
+    traverseproc tp_traverse;
+
+    inquiry tp_clear;
+
+    getiterfunc tp_iter;
+    iternextfunc tp_iternext;
+
+    struct PyMethodDef *tp_methods;
+    struct _typeobject *tp_base;
+    allocfunc tp_alloc;
+    newfunc tp_new;
+    freefunc tp_free;
+};
+
+# define DEFINE_PY_TYPE_OBJECT(type) \
+    static struct typeobject_wrapper type; \
+    static PyTypeObject* type##Ptr = NULL
+
+// PyObject_HEAD_INIT_TYPE and PyObject_FINISH_INIT_TYPE need to come in pairs
+// We first initialize with NULL because the type is not allocated until
+// init_types() is called later. It's in FINISH_INIT_TYPE where we fill the
+// type in with the newly allocated type.
+# define PyObject_HEAD_INIT_TYPE(type) PyObject_HEAD_INIT(NULL)
+# define PyObject_FINISH_INIT_TYPE(obj, type) obj.ob_base.ob_type = type##Ptr
+
+# define Py_TYPE_GET_TP_ALLOC(type) ((allocfunc)PyType_GetSlot(type, Py_tp_alloc))
+# define Py_TYPE_GET_TP_METHODS(type) ((PyMethodDef *)PyType_GetSlot(type, Py_tp_methods))
+
+// PyObject_NEW is not part of stable ABI, but PyObject_Malloc/Init are.
+PyObject* Vim_PyObject_New(PyTypeObject *type, size_t objsize)
+{
+    PyObject *obj = (PyObject *)PyObject_Malloc(objsize);
+    if (obj == NULL)
+        return PyErr_NoMemory();
+    return PyObject_Init(obj, type);
+}
+# undef PyObject_NEW
+# define PyObject_NEW(type, typeobj) ((type *)Vim_PyObject_New(typeobj, sizeof(type)))
+
+// This is a somewhat convoluted because limited API doesn't expose an easy way
+// to get the tp_name field, and so we have to manually reconstruct it as
+// "__module__.__name__" (with __module__ omitted for builtins to emulate
+// Python behavior). Also, some of the more convenient functions like
+// PyUnicode_AsUTF8AndSize and PyType_GetQualName() are not available until
+// late Python 3 versions, and won't be available if you set Py_LIMITED_API too
+// low.
+# define PyErr_FORMAT_TYPE(msg, obj) \
+    do { \
+	PyObject* qualname = PyObject_GetAttrString((PyObject*)(obj)->ob_type, "__qualname__"); \
+	if (qualname == NULL) \
+	{ \
+	    PyErr_FORMAT(PyExc_TypeError, msg, "(NULL)"); \
+	    break; \
+	} \
+	PyObject* module = PyObject_GetAttrString((PyObject*)(obj)->ob_type, "__module__"); \
+	PyObject* full; \
+	if (module == NULL || PyUnicode_CompareWithASCIIString(module, "builtins") == 0 \
+		|| PyUnicode_CompareWithASCIIString(module, "__main__") == 0) \
+	{ \
+	    full = qualname; \
+	    Py_INCREF(full); \
+	} \
+	else \
+	    full = PyUnicode_FromFormat("%U.%U", module, qualname); \
+	PyObject* full_bytes = PyUnicode_AsUTF8String(full); \
+	const char* full_str = PyBytes_AsString(full_bytes); \
+	full_str = full_str == NULL ? "(NULL)" : full_str; \
+	PyErr_FORMAT(PyExc_TypeError, msg, full_str); \
+	Py_DECREF(qualname); \
+	Py_XDECREF(module); \
+	Py_XDECREF(full); \
+	Py_XDECREF(full_bytes); \
+    } while(0)
+
+# define PyList_GET_ITEM(list, i) PyList_GetItem(list, i)
+# define PyList_GET_SIZE(o) PyList_Size(o)
+# define PyTuple_GET_ITEM(o, pos) PyTuple_GetItem(o, pos)
+# define PyTuple_GET_SIZE(o) PyTuple_Size(o)
+
+// PyList_SET_ITEM and PyList_SetItem have slightly different behaviors. The
+// former will leave the old item dangling, and the latter will decref on it.
+// Since we only use this on new lists, this difference doesn't matter.
+# define PyList_SET_ITEM(list, i, item) PyList_SetItem(list, i, item)
+
+# if Py_LIMITED_API < 0x03080000
+// PyIter_check only became part of stable ABI in 3.8, and there is no easy way
+// to check for it in the API. We simply return false as a compromise. This
+// does mean we should avoid compiling with stable ABI < 3.8.
+#  undef PyIter_Check
+#  define PyIter_Check(obj) (FALSE)
+# endif
+
+PyTypeObject* AddHeapType(struct typeobject_wrapper* type_object)
+{
+    PyType_Spec type_spec;
+    type_spec.name = type_object->tp_name;
+    type_spec.basicsize = type_object->tp_basicsize;
+    type_spec.itemsize = 0;
+    type_spec.flags = type_object->tp_flags;
+
+    // We just need to statically allocate a large enough buffer that can hold
+    // all slots. We need to leave a null-terminated slot at the end.
+    PyType_Slot slots[40] = { {0, NULL} };
+    size_t slot_i = 0;
+
+# define ADD_TP_SLOT(slot_name) \
+    if (slot_i >= 40) return NULL; /* this shoul