sh: also auto-complete built-ins

[pstef]

Summary

Inspired by a question asked in PR 261728.

[pstef]

This doesn't follow the Don't Repeat Yourself principle, but currently I don't have a better idea how to express this code.

[pstef]

builtincmd doesn't hold C strings, use memcmp().

[bapt]

bin/sh/histedit.c

662

verify if the allocation fails?

[pstef]

bin/sh/histedit.c

662

This part is a copy-paste from the while loop above. In each case, if strdup/strndup fails, it returns a null pointer which is assigned to matches[++i]. The next consumer of that is libedit which handles this as nice as I can imagine.

We could perhaps break the loop on allocation failure, but it's a potential microoptimization in a corner case, I think.

[jilles]

This doesn't follow the Don't Repeat Yourself principle, but currently I don't have a better idea how to express this code.

The code doesn't really repeat itself since there was nothing before that returned a list of builtins.

bin/sh/histedit.c

660

The MIN seems incorrect. Instead, if curpos > bp[0], it's not a match.

[pstef]

Address reviews.

[pstef]

bin/sh/histedit.c

660

That's a good point, thank you.

662

I added the check both here and in the original part.

[pstef]

Reduce code duplication.
I was worried about some repetitive code here when adding the second source of commands (built-ins, after files from $PATH), but it became visibly worse when I started working on adding a third source (aliases). So the sooner I factor this out, the cleaner the future commits will be.