* src/w32term.c (w32_initialize):
* src/w32console.c (initialize_w32_display):
* src/w32fns.c (globals_of_w32fns): Don't record the main thread
ID independently for each type of session (GUI, TTY, batch).
* src/w32term.c (w32_init_main_thread): New function, records the
main thread's thread ID.
* src/w32term.h: Add prototype for w32_init_main_thread.
* src/emacs.c (main) [WINDOWSNT]: Call w32_init_main_thread.

* src/emacs-module.c [WINDOWSNT]: Rename main_thread_id to
main_thread, for consistency with other threading libraries.  All
users changed.  Include w32term.h.
(check_main_thread) [WINDOWSNT]: Simplify the test: no need to
make sure the main thread is alive, as we hold a handle on it
opened by w32_init_main_thread.
(module_init) [WINDOWSNT]: Reuse the thread ID recorded by
w32_init_main_thread, instead of calling the requisite APIs once
more.

* src/window.c (grow_mini_window, shrink_mini_window): Set the
frame's 'window_sizes_changed' flag.
* src/xdisp.c (redisplay_internal): Call the hooks on
'window-size-change-functions' if the call to 'echo_area_display'
sets the frame's 'window_sizes_changed' flag.
(syms_of_xdisp) <window-size-change-functions>:
Update doc string to indicate the mini-window resizes trigger a
call to the hooks, and don't promise that will happen "before
redisplay".  (Bug#19576, Bug#21333)

* doc/lispref/windows.texi (Window Hooks): Update the description
of 'window-size-change-functions'.

* src/fns.c (Frequire): Doc fix to include the dynamic module
support.
* src/lread.c (Fload, Vload_suffixes): Doc fixes to include the
dynamic module support.
(Fload): Treat the module suffix the same as '*.el' and '*.elc'
wrt the MUST-SUFFIX argument.

* etc/NEWS: Expand documentation of dynamically loaded modules.

* src/emacs-module.c (module_free_global_ref): Add a FIXME
comment about error reporting.  Fix a recently-introduced typo
that double-decremented the refcount.

* src/emacs-module.h (emacs_module_init): New decl.
Without it, GCC might complain about a module that defines
emacs_module_init without using it.  This also checks the
API better.

* src/emacs-module.c (MODULE_SETJMP_1): Fix typo that I
introduced while reindenting the code earlier, and add a
comment explaining the unusual use of do-while here.

* src/emacs-module.c (struct module_fun_env)
(module_make_function, module_funcall, Fmodule_call):
* src/emacs-module.h (struct emacs_runtime, struct emacs_env_25):
Use ptrdiff_t, not int, for arg counts.
* src/emacs-module.c (module_make_function): Don’t bother
checking arity against MOST_POSITIVE_FIXNUM, as that’s
unnecessary here.  Make the checking clearer by negating it.
(module_make_function, Fmodule_call): No need to use xzalloc
since the storage doesn’t need to be cleared.
(module_funcall): Don’t use VLA, since C11 doesn’t guarantee support
for it, and many implementations are buggy with large VLAs anyway.
Use SAFE_ALLOCA_LISP instead.
(module_vec_set): Don’t crash if i < 0.
(module_vec_get): Don’t crash if i < MOST_NEGATIVE_FIXNUM.
(module_vec_set, module_vec_get): Do fixnum checks only when
i is out of array bounds, for efficiency in the usual case.
(Fmodule_load): Simplify fixnum range check.
(Fmodule_call): Simplify arity check.  Use xnmalloc to detect
integer overflow in array allocation size.

* src/dynlib.c [WINDOWSNT]: Include errno.h, lisp.h, and w32.h.
No need to include windows.h, as w32.h already does that.
<dynlib_last_err>: New static variable.
(dynlib_reset_last_error): New function.
(dynlib_open): Convert forward slashes to backslashes.  Convert
file names from UTF-8 to either UTF-16 or the current ANSI
codepage, and call either LoadLibraryW or LoadLibraryA.  If the
argument is NULL, return a handle to the main module, like
'dlopen' does.  Record the error, if any, for use by dynlib_error.
(dynlib_sym): Check the handle for validity. Record the error, if
any, for use by dynlib_error.
(dynlib_error): Call w32_strerror to produce the error string, and
zero out the last error code, like dlerror does.
(dynlib_close): Check the handle for validity.  Record the error,
if any, for use by dynlib_error.  Don't call FreeLibrary with a
handle for the main module.
* src/w32.c (globals_of_w32): Call dynlib_reset_last_error.

* src/dynlib.c, src/emacs-module.c: Include <config.h> first.
* src/dynlib.h: Do not include config.h.
It’s every .c file’s responsibility to include config.h first.
* src/emacs-module.c: Include emacs-module.h immediately after
config.h, to test that emacs-module.h doesn’t depend on
include files other than config.h.