lint: s/illegal/invalid/g

Lint does not provide legal advice.

lint: mention the assignment operator in 'illegal combination'

In source lines that contain both a 'return' statement as well as a
function-like macro, such as the C11 atomics, seeing the word 'init' in
the diagnostic helps to see that the type conflict is not in the
'return' statement but instead in some initializer.

Seen in userspace-rcu/wfcqueue.h:147.

branches: 1.16.2;
tests/lint: group tests by topic

lint: warn about extern declarations outside headers

https://mail-index.netbsd.org/tech-userlevel/2023/03/15/msg013727.html

tests/lint: remove obsolete comments

The handling of initializers was completely rewritten in init.c 1.228
from 2021-12-21.

lint: add quotes around placeholders for the remaining messages

Reword some of the messages slightly, exchanging brevity for clarity.

Message 138 is kept as-is, as it is not yet covered by any tests.

Message 240 is kep as-is, as it is unreachable.

tests/lint: add quotes around placeholders in a few messages

lint: add quotes around a few more placeholders in messages

lint: fix handling of initializations

The implementation from March 2021 added proper support for designators
but didn't model the brace levels correctly. In particular, it could
not handle additional braces or omitted braces. In such a case, lint
skipped the remaining initializers from the initialization. Due to
this, type errors in the remaining initializers went unnoticed. Another
effect was that arrays of unknown size were wrongly reported as having
size 0.

Both GCC and Clang recommend placing braces around each sub-type that is
initialized, such as a struct, union or array. Postfix does not follow
these recommendations, therefore lint had to be disabled in
external/ibm-public/postfix/Makefile.inc. This commit fixes the bugs
mentioned there.

lint: treat incomplete union in the same way as incomplete struct

The newly added tests triggered the assertion in begin_designation since
for incomplete types the initialization is stopped before handling the
first brace.

tests/lint: test initialization of incomplete union

The function initialization_lbrace only mentions STRUCT, which looks
suspicious.

lint: fix initialization with few braces from function

Seen in Postfix, smtp_proto.c.

tests/lint: demonstrate another initialization with few braces

Seen in Postfix, smtp_proto.c.

lint: fix initialization of array with fewer braces

Seen in Postfix, cleanup_strerror.c.

tests/lint: demonstrate another initialization that lint cannot handle

Seen in external/ibm-public/postfix/dist/src/global/cleanup_strerror.c.

lint: work around lint bug in initialization with few braces

Needs a proper fix later, but for now, this workaround allows to run
lint on Postfix again.

lint: demonstrate wrong error message in initialization

History of the new test fragment:

libexec/2021.09.14.19.44.40-plain/lint1
| (14): error: cannot initialize 'struct typedef histogram_entry'
| from 'pointer to char' [185]
| exit status 1
libexec/2021.04.01.14.20.30-plain/lint1

libexec/2021.03.30.20.23.30-plain/lint1
| (14): error: cannot initialize 'struct typedef histogram_entry'
| from 'pointer to char' [185]
| (14): error: cannot initialize 'struct typedef histogram_entry'
| from 'int' [185]
| (15): error: cannot initialize 'struct typedef histogram_entry'
| from 'pointer to char' [185]
| (15): error: cannot initialize 'struct typedef histogram_entry'
| from 'int' [185]
| exit status 1
libexec/2021.03.30.14.25.28-plain/lint1

libexec/2021.03.29.21.34.17-plain/lint1
| (15): error: too many struct/union initializers [172]
| exit status 1
libexec/2021.03.28.15.36.37-plain/lint1

libexec/2021.03.28.14.13.18-plain/lint1
| (18): error: too many struct/union initializers [172]
| exit status 1
libexec/2021.03.21.20.44.59-plain/lint1

libexec/2021.03.21.20.30.19-plain/lint1
| (18): too many struct/union initializers [172]
| exit status 1
libexec/2014.11.20.20.49.06-plain/lint1

libexec/2014.11.20.20.48.33-plain/lint1
| exit status 0

tests/lint: add more tests for covering the grammar