threads / rfc / 41720

RFC patchparse-options.c: make OPTION__COUNTUP consider negative values

Subject: [PATCH/RFC] parse-options.c: make OPTION__COUNTUP consider negative values

## tl;dr

8 messages between Mar 16, 2016 and Mar 20, 2016. Diffs are folded; open one to read it.

replies: 7people: 3as markdown or json

Pranit Bauva· Mar 16, 2016, 23:16 UTC · lore

The reason to make it consider negative values or more specifically "unspecified" values is to differentiate between the option passed once, multiple times or with --no-option. This makes the receiver know what actually happened with the arguments which is particularly required with option have multiple levels of that option.

Eg. : initialize verbose = -1 `git commit` => verbose = -1 `git commit -v` => verbose = 1 `git commit -v -v` => verbose = 1 `git commit --no-verbose` => verbose = 0

Signed-off-by: Pranit Bauva <pranit.bauva@gmail.com>

--- The discussion on the mailing list[1] suggested this approach. I plan to include this with my previous patch regarding "configuration for commonly used command `git commit -v`" as this is a requirement for latter.

[1] : http://thread.gmane.org/gmane.comp.version-control.git/289027
---
 Documentation/technical/api-parse-options.txt | 6 ++++--
 parse-options.c                               | 8 +++++++-
 2 files changed, 11 insertions(+), 3 deletions(-)
Show changes to 2 files +11 −4

Documentation/technical/api-parse-options.txt, parse-options.c

diff --git a/Documentation/technical/api-parse-options.txt b/Documentation/technical/api-parse-options.txt
index 5f0757d..a908d8a 100644
--- a/Documentation/technical/api-parse-options.txt
+++ b/Documentation/technical/api-parse-options.txt
@@ -144,8 +144,10 @@ There are some macros to easily define options:
 
 `OPT_COUNTUP(short, long, &int_var, description)`::
 	Introduce a count-up option.
-	`int_var` is incremented on each use of `--option`, and
-	reset to zero with `--no-option`.
+	If the `int_var` is negative and `--option` is absent,
+	then it will retain its value. Otherwise it will first set
+	`int_var` to 0 and then increment it on each use of `--option`,
+	and reset to zero with `--no-option`.
 
 `OPT_BIT(short, long, &int_var, description, mask)`::
 	Introduce a boolean option.
diff --git a/parse-options.c b/parse-options.c
index 47a9192..86d30bd 100644
--- a/parse-options.c
+++ b/parse-options.c
@@ -110,7 +110,13 @@ static int get_value(struct parse_opt_ctx_t *p,
 		return 0;
 
 	case OPTION_COUNTUP:
-		*(int *)opt->value = unset ? 0 : *(int *)opt->value + 1;
+		if (unset)
+			*(int *)opt->value = 0;
+		else {
+			if (*(int *)opt->value < 0)
+				*(int *)opt->value = 0;
+			*(int *)opt->value += 1;
+		}
 		return 0;
 
 	case OPTION_SET_INT:

--
https://github.com/git/git/pull/212
Jeff King· Mar 17, 2016, 01:50 UTC · re: Pranit Bauva · lore

Re: [PATCH/RFC] parse-options.c: make OPTION__COUNTUP consider negative values

On Wed, Mar 16, 2016 at 11:16:58PM +0000, Pranit Bauva wrote:
Show 12 quoted lines
> The reason to make it consider negative values or more specifically
> "unspecified" values is to differentiate between the option passed
> once, multiple times or with --no-option. This makes the receiver
> know what actually happened with the arguments which is particularly
> required with option have multiple levels of that option.
> 
> Eg. :
> initialize verbose = -1
> `git commit` => verbose = -1
> `git commit -v` => verbose = 1
> `git commit -v -v` => verbose = 1
> `git commit --no-verbose` => verbose = 0
This second to last example would be 2, right?

That aside, this patch does mean that one can no longer use OPT_COUNTUP() for negative values (i.e., the caller must start it at either 0 or 1, and it must always go up from there).

And we would need to verify that all of the existing callers are OK with this. Did you check that that (not rhetorical; I suspect they are all OK, but somebody needs to check)?

We are also changing semantics without changing the interface, which means any topics in flight (that you _cannot_ review, because you have not seen them yet) may be subtly broken. To me that is not an absolute deal-breaker, but something to weigh against the utility of the change.

When looking more carefully at builtin/commit.c for the other thread, it occurred to me that OPT_BOOL might be a better fit for commit's "-v". It really is a boolean "show the diff or not" and thus unlike the other "make me more verbose". And OPT_BOOL already has the behavior you want, I think.

-Peff
Eric Sunshine· Mar 17, 2016, 07:28 UTC · re: Jeff King · lore

Re: [PATCH/RFC] parse-options.c: make OPTION__COUNTUP consider negative values

On Wed, Mar 16, 2016 at 9:50 PM, Jeff King <peff@peff.net> wrote:
> On Wed, Mar 16, 2016 at 11:16:58PM +0000, Pranit Bauva wrote:
>> The reason to make it consider negative values or more specifically
>> "unspecified" values is to differentiate between the option passed
>> once, multiple times or with --no-option. This makes the receiver

This is inaccurate and rather confusing. It's not that an "unspecified" value gives you the ability to "differentiate between once, multiple time or with --no-option", but rather that it allows you to determine wether --option or --no-option was encountered at all.

Show 11 quoted lines
>> know what actually happened with the arguments which is particularly
>> required with option have multiple levels of that option.
>>
>> Eg. :
>> initialize verbose = -1
>> `git commit` => verbose = -1
>> `git commit -v` => verbose = 1
>> `git commit -v -v` => verbose = 1
>> `git commit --no-verbose` => verbose = 0
>
> This second to last example would be 2, right?
Right.

I'm not sure that this example block is helpful, though. A clearer commit message which does a better job of explaining the reason for the change would likely eliminate the need for an example.

Show 12 quoted lines
> That aside, this patch does mean that one can no longer use
> OPT_COUNTUP() for negative values (i.e., the caller must start it at
> either 0 or 1, and it must always go up from there).
>
> And we would need to verify that all of the existing callers are OK with
> this. Did you check that that (not rhetorical; I suspect they are all
> OK, but somebody needs to check)?
>
> We are also changing semantics without changing the interface, which
> means any topics in flight (that you _cannot_ review, because you have
> not seen them yet) may be subtly broken. To me that is not an absolute
> deal-breaker, but something to weigh against the utility of the change.

Indeed, I was envisioning a more conservative approach of having OPT__VERBOSE use a custom callback or perhaps introducing a new 'flags' value or even (probably too ugly) abusing the 'defval' field to specially indicate that it wants the "negative means unspecified" behavior; the other consumers of OPT_COUNTUP would not request this special behavior. But, as you say, changing the behavior of OPT_COUNTUP unconditionally may not be a deal-breaker.

I also realized that Pranit can achieve the desired behavior without modifying OPT__VERBOSE at all. Specifically, rather than initializing his opt_verbose variable to -1, he can instead initialize it to 1. Then:

* if --verbose is seen (one or more times), opt_verbose will be >=2,
and the real verbosity level will be (opt_verbose - 1)
* if --no-verbose is seen, opt_verbose will be 0
* if neither is seen, then opt_verbose will remain 1

However, I think this approach is far too ugly and non-obvious to seriously suggest using it, whereas the change to OPT__VERBOSE is easily understood and could prove useful in the future for other commands with multiple verbosity levels.

Show 5 quoted lines
> When looking more carefully at builtin/commit.c for the other thread, it
> occurred to me that OPT_BOOL might be a better fit for commit's "-v". It
> really is a boolean "show the diff or not" and thus unlike the other
> "make me more verbose". And OPT_BOOL already has the behavior you want,
> I think.

For completeness (for readers of this thread), it was pointed out in the other thread[1] that git-commit does indeed recognize multiple verbosity levels, so changing it to use OPT_BOOL would be undesirable (wrong).

[1]: http://thread.gmane.org/gmane.comp.version-control.git/289027/focus=289074
Eric Sunshine· Mar 17, 2016, 08:14 UTC · re: Eric Sunshine · lore

Re: [PATCH/RFC] parse-options.c: make OPTION__COUNTUP consider negative values

On Thu, Mar 17, 2016 at 3:28 AM, Eric Sunshine <sunshine@sunshineco.com> wrote:
Show 11 quoted lines
> I also realized that Pranit can achieve the desired behavior without
> modifying OPT__VERBOSE at all. Specifically, rather than initializing
> his opt_verbose variable to -1, he can instead initialize it to 1.
> Then:
>
> * if --verbose is seen (one or more times), opt_verbose will be >=2,
> and the real verbosity level will be (opt_verbose - 1)
>
> * if --no-verbose is seen, opt_verbose will be 0
>
> * if neither is seen, then opt_verbose will remain 1

Eh, this is bogus. "git commit --no-verbose --verbose" would leave opt_verbose at 1, which would fool it into thinking neither had been seen.

Thus, a further +1 for an OPT__VERBOSE which understands "unspecified".
> However, I think this approach is far too ugly and non-obvious to
> seriously suggest using it, whereas the change to OPT__VERBOSE is
> easily understood and could prove useful in the future for other
> commands with multiple verbosity levels.
Pranit Bauva· Mar 17, 2016, 20:22 UTC · re: Eric Sunshine · lore

Re: [PATCH/RFC] parse-options.c: make OPTION__COUNTUP consider negative values

On Thu, Mar 17, 2016 at 12:58 PM, Eric Sunshine <sunshine@sunshineco.com> wrote:
Show 11 quoted lines
> On Wed, Mar 16, 2016 at 9:50 PM, Jeff King <peff@peff.net> wrote:
>> On Wed, Mar 16, 2016 at 11:16:58PM +0000, Pranit Bauva wrote:
>>> The reason to make it consider negative values or more specifically
>>> "unspecified" values is to differentiate between the option passed
>>> once, multiple times or with --no-option. This makes the receiver
>
> This is inaccurate and rather confusing. It's not that an
> "unspecified" value gives you the ability to "differentiate between
> once, multiple time or with --no-option", but rather that it allows
> you to determine wether --option or --no-option was encountered at
> all.
I guess the language wasn't very clear. I will change this.
Show 13 quoted lines
>>> know what actually happened with the arguments which is particularly
>>> required with option have multiple levels of that option.
>>>
>>> Eg. :
>>> initialize verbose = -1
>>> `git commit` => verbose = -1
>>> `git commit -v` => verbose = 1
>>> `git commit -v -v` => verbose = 1
>>> `git commit --no-verbose` => verbose = 0
>>
>> This second to last example would be 2, right?
>
> Right.
My bad, it should be 2.
Show 55 quoted lines
>
> I'm not sure that this example block is helpful, though. A clearer
> commit message which does a better job of explaining the reason for
> the change would likely eliminate the need for an example.
>
>> That aside, this patch does mean that one can no longer use
>> OPT_COUNTUP() for negative values (i.e., the caller must start it at
>> either 0 or 1, and it must always go up from there).
>>
>> And we would need to verify that all of the existing callers are OK with
>> this. Did you check that that (not rhetorical; I suspect they are all
>> OK, but somebody needs to check)?
>>
>> We are also changing semantics without changing the interface, which
>> means any topics in flight (that you _cannot_ review, because you have
>> not seen them yet) may be subtly broken. To me that is not an absolute
>> deal-breaker, but something to weigh against the utility of the change.
>
> Indeed, I was envisioning a more conservative approach of having
> OPT__VERBOSE use a custom callback or perhaps introducing a new
> 'flags' value or even (probably too ugly) abusing the 'defval' field
> to specially indicate that it wants the "negative means unspecified"
> behavior; the other consumers of OPT_COUNTUP would not request this
> special behavior. But, as you say, changing the behavior of
> OPT_COUNTUP unconditionally may not be a deal-breaker.
>
> I also realized that Pranit can achieve the desired behavior without
> modifying OPT__VERBOSE at all. Specifically, rather than initializing
> his opt_verbose variable to -1, he can instead initialize it to 1.
> Then:
>
> * if --verbose is seen (one or more times), opt_verbose will be >=2,
> and the real verbosity level will be (opt_verbose - 1)
>
> * if --no-verbose is seen, opt_verbose will be 0
>
> * if neither is seen, then opt_verbose will remain 1
>
> However, I think this approach is far too ugly and non-obvious to
> seriously suggest using it, whereas the change to OPT__VERBOSE is
> easily understood and could prove useful in the future for other
> commands with multiple verbosity levels.
>
>> When looking more carefully at builtin/commit.c for the other thread, it
>> occurred to me that OPT_BOOL might be a better fit for commit's "-v". It
>> really is a boolean "show the diff or not" and thus unlike the other
>> "make me more verbose". And OPT_BOOL already has the behavior you want,
>> I think.
>
> For completeness (for readers of this thread), it was pointed out in
> the other thread[1] that git-commit does indeed recognize multiple
> verbosity levels, so changing it to use OPT_BOOL would be undesirable
> (wrong).
>
> [1]: http://thread.gmane.org/gmane.comp.version-control.git/289027/focus=289074
Pranit Bauva· Mar 18, 2016, 11:23 UTC · re: Jeff King · lore

Re: [PATCH/RFC] parse-options.c: make OPTION__COUNTUP consider negative values

Sorry for a little late reply. I was under the impression that I had replied before.

On Thu, Mar 17, 2016 at 7:20 AM, Jeff King <peff@peff.net> wrote:
Show 8 quoted lines
> That aside, this patch does mean that one can no longer use
> OPT_COUNTUP() for negative values (i.e., the caller must start it at
> either 0 or 1, and it must always go up from there).
>
>
> And we would need to verify that all of the existing callers are OK with
> this. Did you check that that (not rhetorical; I suspect they are all
> OK, but somebody needs to check)?

I did a grep on parse-options.h and saw that only "verbose", "quiet" and "force" use OPT_COUNTUP(). I then did a git grep for "verbose = -1", "quiet = -1" But with "force = -1" showed that "builtin/clean.c" uses it. On a bit careful examination, this patch would not make difference to it.

> We are also changing semantics without changing the interface, which
> means any topics in flight (that you _cannot_ review, because you have
> not seen them yet) may be subtly broken. To me that is not an absolute
> deal-breaker, but something to weigh against the utility of the change.

As I am new here, I don't really know how to go about with this. Could you describe in a little detail so that I can work on it?

Show 7 quoted lines
> When looking more carefully at builtin/commit.c for the other thread, it
> occurred to me that OPT_BOOL might be a better fit for commit's "-v". It
> really is a boolean "show the diff or not" and thus unlike the other
> "make me more verbose". And OPT_BOOL already has the behavior you want,
> I think.
>
> -Peff
Jeff King· Mar 20, 2016, 04:10 UTC · re: Pranit Bauva · lore

Re: [PATCH/RFC] parse-options.c: make OPTION__COUNTUP consider negative values

On Fri, Mar 18, 2016 at 04:53:34PM +0530, Pranit Bauva wrote:
Show 9 quoted lines
> > And we would need to verify that all of the existing callers are OK with
> > this. Did you check that that (not rhetorical; I suspect they are all
> > OK, but somebody needs to check)?
> 
> I did a grep on parse-options.h and saw that only "verbose", "quiet"
> and "force" use OPT_COUNTUP().
> I then did a git grep for "verbose = -1", "quiet = -1"
> But with "force = -1" showed that "builtin/clean.c" uses it. On a bit
> careful examination, this patch would not make difference to it.

Yeah, I see that it handles the config for force separately, and then munges the "-1" into 0 before we get to parse_options.

There are uses of COUNTUP in cmd_hash_object() and test-parse-options.c, but I think they are both fine.

Grepping for "verbose = -1" would miss any cases where we call the argument something else (e.g., apply_verbosely). So I think it would be more thorough to grep for OPT__VERBOSE, etc, and then follow-up on whatever variable they use.

I just did so, and I didn't see any problems.
Show 7 quoted lines
> > We are also changing semantics without changing the interface, which
> > means any topics in flight (that you _cannot_ review, because you have
> > not seen them yet) may be subtly broken. To me that is not an absolute
> > deal-breaker, but something to weigh against the utility of the change.
> 
> As I am new here, I don't really know how to go about with this. Could
> you describe in a little detail so that I can work on it?

A more canonical example is changing a function return value. Imagine I have a function which returns "1" for success and "0" for error, and I want to change it to return "0" for success and "-1" for error. If I do so and update each caller, then merging with a branch that has a new caller will not result in any conflicts (there is no textual link between the callers and the function), but the result will be subtly broken (the new caller will get the error-check wrong).

So we generally try to find some way that the compiler will notice the breakage. E.g., if the function changes name when the return value semantics change, or if it gains a new argument at the same time, then the compiler will notice and complain. We still have to fix it up during the merge, of course, but it's easy to spot.

Likewise here. If you change the semantics of OPT_COUNTUP(), then any branch which introduces a new use of "int foo = -1" and expects the old semantics will be subtly broken.

The obvious fix would be to switch the name (to OPT_COUNTUP_DEFAULT() or something). But that's a bit painful, as almost nobody uses COUNTUP directly, so we'd need OPT__VERBOSE_DEFAULT().

I do think we could also declare that it's sufficiently unlikely for somebody to have been using the old semantics for OPT_COUNTUP() with a negative integer (as it does not really do anything useful), and just accept the risk.

Which in the end is the same as ignoring the problem in the first place, but there is a big difference between not thinking about the problem, and thinking about it and deciding it's not a problem. :)

-Peff
Pranit Bauva· Mar 20, 2016, 09:07 UTC · re: Jeff King · lore

Re: [PATCH/RFC] parse-options.c: make OPTION__COUNTUP consider negative values

On Sun, Mar 20, 2016 at 9:40 AM, Jeff King <peff@peff.net> wrote:
Show 29 quoted lines
>> > We are also changing semantics without changing the interface, which
>> > means any topics in flight (that you _cannot_ review, because you have
>> > not seen them yet) may be subtly broken. To me that is not an absolute
>> > deal-breaker, but something to weigh against the utility of the change.
>>
>> As I am new here, I don't really know how to go about with this. Could
>> you describe in a little detail so that I can work on it?
>
> A more canonical example is changing a function return value. Imagine I
> have a function which returns "1" for success and "0" for error, and I
> want to change it to return "0" for success and "-1" for error. If I do
> so and update each caller, then merging with a branch that has a new
> caller will not result in any conflicts (there is no textual link
> between the callers and the function), but the result will be subtly
> broken (the new caller will get the error-check wrong).
>
> So we generally try to find some way that the compiler will notice the
> breakage. E.g., if the function changes name when the return value
> semantics change, or if it gains a new argument at the same time, then
> the compiler will notice and complain. We still have to fix it up during
> the merge, of course, but it's easy to spot.
>
> Likewise here. If you change the semantics of OPT_COUNTUP(), then any
> branch which introduces a new use of "int foo = -1" and expects the old
> semantics will be subtly broken.
>
> The obvious fix would be to switch the name (to OPT_COUNTUP_DEFAULT() or
> something). But that's a bit painful, as almost nobody uses COUNTUP
> directly, so we'd need OPT__VERBOSE_DEFAULT().
This is quite new to me. It took me some time to digest it.
> Which in the end is the same as ignoring the problem in the first place,
> but there is a big difference between not thinking about the problem,
> and thinking about it and deciding it's not a problem. :)
True That! ;)

Regards, Pranit Bauva

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