Re: Inconsistent/buggy behaviour of "git config --add"

Tim Landscheidt [off-list ref] writes:

| # git config section.key value0
| # git config --add section.key value1

The action verb --add comes immediately after "git config" (and
possibly file-option and type option), so this is a request to
append "key = value1" in the "[section]" (if there is no existing
section.key, then "[section]" would have to be created at the same
time, but in this case there already is one).

| # cat .git/config
| [core]
|         repositoryformatversion = 0
|         filemode = true
|         bare = false
|         logallrefupdates = true
| [section]
|         key = value0
|         key = value1

So this makes perfect sense.

| # git config section.key --add value2

No action verb immediately after "git config" (possibly after
file-option and type option).  This should be taken as

    git config <name> <value> <value-pattern>

where

    <name> = section.key
    <value> = --add
    <value-pattern> = value2

As we lack --replace-all, the default behaviour is to replace a
single existing entry of "section.key" with existing value "value2",
with the new value "--add", or if there is no such existing entry,
add one such entry.

| # cat .git/config
| [core]
|         repositoryformatversion = 0
|         filemode = true
|         bare = false
|         logallrefupdates = true
| [section]
|         key = value0
|         key = value1
|         key = --add

which seems to be what the code did.

| # git config section.key --add

No action verb immediately after "git config" (possibly after
file-option and type option).  This should be taken as

    git config <name> <value>

where

    <name> = section.key
    <value> = --add

and is an attempt to replace existing section.key with the new value
"--add", but because we have already three such entries, we get 

| warning: section.key has multiple values
| error: cannot overwrite multiple values with a single value
|        Use a regexp, --add or --replace-all to change section.key.
| #

which sounds sensible.

So on one hand, "--add" must be given before the key to add
a line, but if on the other hand one passes the option after
the key and before the value, it is literally taken as the
value and the value does not seem to be interpreted as a
value-pattern, either.  However, if the value is missing,
Git correctly recognizes that this does not make sense.

Not really.  I agree that the "git config" syntax is messy, but I
followed your example with "git config --help" (especially its
SYNOPSIS section) in hand, and reached the above explanation, which
your conjecutre does not quite match.

My expectation of least surprise is that "git config
section.key --add value" should be equivalent to "git config
--add section.key value".

You cannot have "--add" as a value by doing so.

If that is not possible, I would expect "git config
section.key --add value2" to mean "change the values of
section.key to '--add' where they currently match the
value-pattern of 'value2'".

I think your expectation needs to be updated in this particular
case, but there is a discussion to revamp the UI started elsewhere,
which stops the double-dashed action verbs and instead trigger
different actions as subcommands of "git config", which will
hopefully make things easier to understand.