* lisp/kmacro.el (kmacro-step-edit-active): Initialize to nil to
avoid 'void-variable' errors.  (Bug#28818)
* test/lisp/kmacro-tests.el
(kmacro-tests-step-edit-cleans-up-hook): Now succeeds.  (Bug#18708)

Don't start the check immediately if the buffer is not being
displayed.  Wait until it is, using window-configuration-change-hook.

This enables the user to batch-enable flymake-mode on many buffers and
not have that operation exhaust system resources for checking each
one.  Likewise, an editing or save operation in a currently
non-displayed buffer does not immediately start a check.

* lisp/progmodes/flymake.el (flymake-start-on-flymake-mode):
Rename from flymake-start-syntax-check-on-find-file.
(flymake-start-syntax-check-on-find-file): Obsolete alias for
flymake-start-on-flymake-mode.
(flymake-start): Redesign.  Affect the global post-command-hook
and local window-configuraiton-change-hook.
(flymake--schedule-timer-maybe)
(flymake-after-change-function, flymake-after-save-hook): Pass
t to flymake-start.

* test/lisp/progmodes/flymake-tests.el (flymake-tests--call-with-fixture)
(dummy-backends, recurrent-backend): Start flymake check
explicitly and immediately.

* lisp/net/tramp-adb.el (tramp-adb-handle-make-directory):
* lisp/net/tramp-gvfs.el (tramp-gvfs-handle-make-directory):
Handle PARENTS properly.

* test/lisp/net/tramp-tests.el (tramp-test13-make-directory):
Extend test.

* lisp/emacs-lisp/generator.el (cps--make-dynamic-binding-wrapper):
Remove extra evaluation of form.
* test/lisp/emacs-lisp/generator-tests.el
(cps-iter-lambda-with-dynamic-binding): New test.

* lisp/net/tramp.el (tramp-file-name-for-operation):
Add `file-system-info'.

* lisp/net/tramp-adb.el (tramp-adb-handle-file-system-info): New defun.
(tramp-adb-file-name-handler-alist): Use it.

* lisp/net/tramp-gvfs.el (tramp-gvfs-file-system-attributes)
(tramp-gvfs-file-system-attributes-regexp): New defconst.
(tramp-gvfs-handle-file-system-info): New defun.
(tramp-gvfs-file-name-handler-alist): Use it.
(tramp-gvfs-get-directory-attributes): Fix property name.
(tramp-gvfs-get-root-attributes): Support also file system attributes.

* lisp/net/tramp-sh.el (tramp-sh-handle-file-system-info): New defun.
(tramp-sh-file-name-handler-alist): Use it.
(tramp-sh-handle-insert-directory): Insert size information.
(tramp-get-remote-df): New defun.

* lisp/net/tramp-smb.el (tramp-smb-handle-file-system-info): New defun.
(tramp-smb-file-name-handler-alist): Use it.
(tramp-smb-handle-insert-directory): Insert size information.

* test/lisp/net/tramp-tests.el (tramp-test37-file-system-info):
New test.
(tramp-test38-asynchronous-requests)
(tramp-test39-recursive-load, tramp-test40-remote-load-path)
(tramp-test41-unload): Rename.

Rewrote a significant part of the Flymake backend API.  Flymake now
ignores the return value of backend functions: a function can either
returns or errors.  If it doesn't error, a backend is no longer
constrained to call REPORT-FN exactly once.  It may do so any number
of times, cumulatively reporting diagnostics.  Flymake keeps track of
outdated REPORT-FN instances and disconsiders obsolete reports.
Backends should avoid reporting obsolete data by cancelling any
ongoing processing at every renewed call to the backend function.

Consolidated flymake.el internal data structures to require less
buffer-local variables.  Adjusted Flymake's mode-line indicator to the
new semantics.

Adapted and simplified the implementation of elisp and legacy
backends, fixing potential race conditions when calling backends in
rapid succession.

Added a new test for a backend that calls REPORT-FN multiple
times.  Simplify test infrastructure.

* lisp/progmodes/flymake-elisp.el (flymake-elisp-checkdoc)
(flymake-elisp-byte-compile): Error instead of returning nil
if not in emacs-lisp-mode.
(flymake-elisp--byte-compile-process): New buffer-local variable.
(flymake-elisp-byte-compile): Mark (and kill) previous process
obsolete process before starting a new one.  Don't report if
obsolete process.

* lisp/progmodes/flymake-proc.el
(flymake-proc--current-process): New buffer-local variable.
(flymake-proc--processes): Remove.
(flymake-proc--process-filter): Don't bind
flymake-proc--report-fn.
(flymake-proc--process-sentinel): Rewrite.  Don't report if
obsolete process.
(flymake-proc-legacy-flymake): Rewrite.  Mark (and kill)
previous process obsolete process before starting a new
one.  Integrate flymake-proc--start-syntax-check-process
helper.
(flymake-proc--start-syntax-check-process): Delete.
(flymake-proc-stop-all-syntax-checks): Don't use
flymake-proc--processes, iterate buffers.
(flymake-proc-compile):

* lisp/progmodes/flymake.el (subr-x): Require it
explicitly.
(flymake-diagnostic-functions): Reword docstring.
(flymake--running-backends, flymake--disabled-backends)
(flymake--diagnostics-table): Delete.
(flymake--backend-state): New buffer-local variable and new defstruct.
(flymake--with-backend-state, flymake--collect)
(flymake-running-backends, flymake-disabled-backends)
(flymake-reporting-backends): New helpers.
(flymake-is-running): Use flymake-running-backends.
(flymake--handle-report): Rewrite.
(flymake-make-report-fn): Ensure REPORT-FN runs in the correct
buffer or not at all.
(flymake--disable-backend, flymake--run-backend): Rewrite.
(flymake-start): Rewrite.
(flymake-mode): Set flymake--backend-state.
(flymake--mode-line-format): Rewrite.

* test/lisp/progmodes/flymake-tests.el
(flymake-tests--wait-for-backends): New helper.
(flymake-tests--call-with-fixture): Use it.
(included-c-header-files): Fix whitespace.
(flymake-tests--diagnose-words): New helper.
(dummy-backends): Rewrite for new semantics.  Use cl-letf.
(flymake-tests--assert-set): Use quote.
(recurrent-backend): New test.

The first of these problems is longstanding: if an error-less B.h is
included from error-ridden A.h, flymake's legacy parser will panic
(and disable itself) since it sees a non-zero exit for a clean file.
To fix this, recommend returning 'true' in the documentation for the
check-syntax target.

Another problem was introduced by the parser rewrite.  For error
patterns spanning more than one line, point may be left in the middle
of a line and thus render other patterns useless.  Those patterns were
written for the old line-by-line parser.  To make them useful again,
move to the beginning of line in those situations.

The third problem was also longstanding and happened on newer GCC's:
The "In file included from" prefix confused
flymake-proc-get-real-file-name.  Fix this.

Also updated flymake--diag-region to fallback to highlighting a full
line less often.

Add automatic tests to check this.

* lisp/progmodes/flymake-proc.el
(flymake-proc--diagnostics-for-pattern): Fix bug when patterns
accidentally spans more than one line.  Don't create
diagnostics without error messages.
(flymake-proc-real-file-name-considering-includes): New
helper.
(flymake-proc-allowed-file-name-masks): Use it.

* lisp/progmodes/flymake.el (flymake-diag-region): Make COL
argument explicitly optional.  Only fall back to full line in extreme
cases.

* test/lisp/progmodes/flymake-tests.el
(included-c-header-files): New test.
(different-diagnostic-types): Update.

* test/lisp/progmodes/flymake-resources/Makefile
(check-syntax): Always return success (0) error code.
(CC_OPTS): Add -Wextra

* test/lisp/progmodes/flymake-resources/errors-and-warnings.c
(main): Rewrite comments.

* test/lisp/progmodes/flymake-resources/errors-and-warnings.c:
Include some dummy header files.

* test/lisp/progmodes/flymake-resources/no-problems.h: New file.

* test/lisp/progmodes/flymake-resources/some-problems.h: New file.

* doc/misc/flymake.texi (Example---Configuring a tool called
via make): Recommend adding "|| true" to the check-syntax target.