Subject: Re: [PATCH 1/4] rev-list: refactor --missing=<missing-action>

From: Junio C Hamano <[email-masked]>
Date: Thu, 18 Apr 2024 14:39:03 -0700

Christian Couder <[email-masked]> writes:

> Both `git rev-list` and `git pack-objects` support a
> `--missing=<missing-action>` feature, but they currently don't share
> any code for that.

So "git pack-objects" will still stay unaware of <missing.h> after
this step, which was a bit unexpected.

> For now, this refactoring is about moving code from
> "builtin/rev-list.c" into new "missing.{c,h}" files. But in a
> following commit, that refactored code will be used in
> `git pack-objects` too.

I think it is easier to grok if you said this in the second
paragraph, before mentioning "another command".  The first paragraph
talks about rev-list and pack-objects logically but not phisically
sharing the feature, so with "For now, this refactoring is about
moving ... into" -> "Refactor the support for --missing in rev-list
into", it is enough to explain how this change is a first step to
make things better, without bringing the third thing into picture.

IOW ...

> In a following commit, we are going to add support for a similar
> 'missing-action' feature to another command. To avoid duplicating
> similar code, let's start refactoring the rev-list code for this
> feature into new "missing.{c,h}" files.

... this paragraph should have much lower weight in explaining this
commit.

> As `enum missing_action` and parse_missing_action_value() are moved to
> "missing.{c,h}", we need to modify the later a bit, so that it stops

"later" -> "latter"?

> updating a global variable, but instead returns either -1 on error or
> the parsed value otherwise.

OK.  As a shared helper function, I agree that assignment to a global
should be outside of its responsibility.  Which means that the caller
is now responsible for making that assignment.

>  static int try_bitmap_count(struct rev_info *revs,
>  			    int filter_provided_objects)
>  {
> @@ -569,10 +536,14 @@ int cmd_rev_list(int argc, const char **argv, const char *prefix)
>  	for (i = 1; i < argc; i++) {
>  		const char *arg = argv[i];
>  		if (skip_prefix(arg, "--missing=", &arg)) {
> +			int res;
>  			if (revs.exclude_promisor_objects)
>  				die(_("options '%s' and '%s' cannot be used together"), "--exclude-promisor-objects", "--missing");
> -			if (parse_missing_action_value(arg))
> +			res = parse_missing_action_value(arg);
> +			if (res >= 0) {
> +				arg_missing_action = res;
>  				break;
> +			}

... which seems to be missing from here.

>  		}
>  	}
>  
> diff --git a/missing.c b/missing.c
> new file mode 100644
> index 0000000000..83e0c5e584
> --- /dev/null
> +++ b/missing.c
> @@ -0,0 +1,26 @@
> +#include "git-compat-util.h"
> +#include "missing.h"
> +#include "object-file.h"
> +
> +int parse_missing_action_value(const char *value)
> +{
> +	if (!strcmp(value, "error"))
> +		return MA_ERROR;
> +
> +	if (!strcmp(value, "allow-any")) {
> +		fetch_if_missing = 0;
> +		return MA_ALLOW_ANY;
> +	}
> +
> +	if (!strcmp(value, "print")) {
> +		fetch_if_missing = 0;
> +		return MA_PRINT;
> +	}
> +
> +	if (!strcmp(value, "allow-promisor")) {
> +		fetch_if_missing = 0;
> +		return MA_ALLOW_PROMISOR;
> +	}

... and this one still touches the global.

> +	return -1;
> +}
> diff --git a/missing.h b/missing.h
> new file mode 100644
> index 0000000000..c8261dfe55
> --- /dev/null
> +++ b/missing.h
> @@ -0,0 +1,18 @@
> +#ifndef MISSING_H
> +#define MISSING_H
> +
> +enum missing_action {
> +	MA_ERROR = 0,    /* fail if any missing objects are encountered */
> +	MA_ALLOW_ANY,    /* silently allow ALL missing objects */
> +	MA_PRINT,        /* print ALL missing objects in special section */
> +	MA_ALLOW_PROMISOR, /* silently allow all missing PROMISOR objects */
> +};
> +
> +/*
> +  Return an `enum missing_action` in case parsing is successful or -1
> +  if parsing failed. Also sets the fetch_if_missing global variable
> +  from "object-file.h".
> + */

... and this also mentions the global.

> +int parse_missing_action_value(const char *value);
> +
> +#endif /* MISSING_H */