sh: Fix heredoc at certain places in case and for

[jilles]

Summary

After an unescaped newline, there may be a here-document. Some places in
case and for did not check for one.

Test Plan

Testsuite, including three new tests

[bdrewery]

The here-document shall be treated as a single word that begins after the next <newline>

https://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_07_04

Huh interesting. I did not know this. dash (git) fails on heredoc14.0 but the rest of the shells, and other scripts, pass outside of sh.
I was surprised about this but there is a clear example at that doc showing ; is allowed.

An example of a here-document follows:

cat <<eof1; cat <<eof2
Hi,
eof1
Helene.
eof2

bin/sh/parser.c

483–485

dash also has CHKKWD | CHKALIAS here but I don't see how a keyword or alias is valid here.

531–532

And dash checks for CHKKWD here too but seems wrong.

[jilles]

bin/sh/parser.c

483–485

Like most shells, dash recognizes in as a keyword, resulting in a syntax error if it occurs unquoted as the first word of a command. zsh and FreeBSD sh only recognize in in the appropriate location in a case or for command, allowing it unquoted as a utility or function name.

Recognizing aliases here is an extension shared by a few other shells. In older shells, this happened because keyword and alias recognition were tied together. For example,

sh -c 'alias DO=do; eval "$1"' arg0 'for i in a b c; DO echo ".$i"; done'

works with a variety of shells, and

sh -c 'alias IN=in; eval "$1"' arg0 'for i IN a b c; do echo ".$i"; done'

works a bit less commonly. Per POSIX, this is allowed because the syntax is otherwise invalid. Expanding an alias in in a for command would not be allowed, however.