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.