Re: [PATCH v4 2/5] am: improve author-script error reporting

Eric Sunshine [off-list ref] writes:

Junio labeled the "-2" trick "cute", and while it is optimal in that
it only traverses the key/value list once, it also increases cognitive
load since the reader has to spend a good deal more brain cycles
understanding what is going on than would be the case with simpler
(and less noisily repetitive) code.

... and update three copies of very similar looking code that have
to stay similar.  If this were parsing unbounded and customizable
set of variables, I think the approach you suggest to use a helper
that iterates over the whole array for each key makes sense, but for
now I think what was queued would be OK.

An alternative would be to make the code trivially easy to understand,
though a bit more costly, but that expense should be negligible since
this file should always be tiny, containing very few key/value pairs,
and it's not timing critical code anyhow. For instance:

static char *find(struct string_list *kv, const char *key)
{
    const char *val = NULL;
    int i;
    for (i = 0; i < kv.nr; i++) {
        if (!strcmp(kv.items[i].string, key)) {
            if (val) {
                error(_("duplicate %s"), key);
                return NULL;
            }
            val = kv.items[i].util;
        }
    }
    if (!val)
        error(_("missing %s"), key);
    return val;
}

static int read_author_script(struct am_state *state)
{
    ...
    char *name, *email, *date;
    ...
    name = find(&kv, "GIT_AUTHOR_NAME");
    email = find(&kv, "GIT_AUTHOR_EMAIL");
    date = find(&kv, "GIT_AUTHOR_DATE");
    if (name && email && date) {
        state->author_name = name;
        state->author_email = email;
        state->author_date = date;
        retval = 0;
    }
    string_list_clear&kv, !!retval);
    ...