New Flymake API variable flymake-diagnostic-functions

New Flymake API variable flymake-diagnostic-functions

Lay groundwork for multiple active backends in the same buffer.

Backends are lisp functions called when flymake-mode sees fit.  They
are responsible for examining the current buffer and telling
flymake.el, via return value, if they can syntax check it.
Backends should return quickly and inexpensively, but they are also
passed a REPORT-FN argument which they may or may not call
asynchronously after performing more expensive work.

REPORT-FN's calling convention stipulates that a backend calls it with
a list of diagnostics as argument, or, alternatively, with a symbol
denoting an exceptional situation, usually some panic resulting from a
misconfigured backend.  In keeping with legacy behaviour,
flymake.el's response to a panic is to disable the issuing backend.

The flymake--diag object representing a diagnostic now also keeps
information about its source backend.  Among other uses, this allows
flymake to selectively cleanup overlays based on which backend is
updating its diagnostics.

* lisp/progmodes/flymake-proc.el (flymake-proc--report-fn):
New dynamic variable.
(flymake-proc--process): New variable.
(flymake-can-syntax-check-buffer): Remove.
(flymake-proc--process-sentinel): Simplify.  Use
unwind-protect.  Affect flymake-proc--processes here.
Bind flymake-proc--report-fn.
(flymake-proc--process-filter): Bind flymake-proc--report-fn.
(flymake-proc--post-syntax-check): Delete
(flymake-proc-start-syntax-check): Take mandatory
report-fn.  Rewrite.  Bind flymake-proc--report-fn.
(flymake-proc--process-sentinel): Rewrite and simplify.
(flymake-proc--panic): New helper.
(flymake-proc--start-syntax-check-process): Record report-fn
in process.  Use flymake-proc--panic.
(flymake-proc-stop-all-syntax-checks): Use mapc.  Don't affect
flymake-proc--processes here.  Record interruption reason.
(flymake-proc--init-find-buildfile-dir)
(flymake-proc--init-create-temp-source-and-master-buffer-copy):
Use flymake-proc--panic.
(flymake-diagnostic-functions): Add
flymake-proc-start-syntax-check.
(flymake-proc-compile): Call
flymake-proc-stop-all-syntax-checks with a reason.

* lisp/progmodes/flymake.el (flymake-backends): Delete.
(flymake-check-was-interrupted): Delete.
(flymake--diag): Add backend slot.
(flymake-delete-own-overlays): Take optional filter arg.
(flymake-diagnostic-functions): New user-visible variable.
(flymake--running-backends, flymake--disabled-backends): New
buffer-local variables.
(flymake-is-running): Now a function, not a variable.
(flymake-mode-line, flymake-mode-line-e-w)
(flymake-mode-line-status): Delete.
(flymake-lighter):  flymake's minor-mode "lighter".
(flymake-report): Delete.
(flymake--backend): Delete.
(flymake--can-syntax-check-buffer): Delete.
(flymake--handle-report, flymake--disable-backend)
(flymake--run-backend, flymake--run-backend):  New helpers.
(flymake-make-report-fn): Make a lambda.
(flymake--start-syntax-check): Iterate
flymake-diagnostic-functions.
(flymake-mode): Use flymake-lighter.  Simplify.  Initialize
flymake--running-backends and flymake--disabled-backends.
(flymake-find-file-hook): Simplify.

* test/lisp/progmodes/flymake-tests.el
(flymake-tests--call-with-fixture): Use flymake-is-running the
function.  Check if flymake-mode already active before activating it.
Add a thorough test for flymake multiple backends

* lisp/progmodes/flymake.el (flymake--start-syntax-check):
Don't use condition-case-unless-debug, use condition-case

* test/lisp/progmodes/flymake-tests.el
(flymake-tests--assert-set): New helper macro.
(dummy-backends): New test.