Re: [GSoC PATCH v2] rm: fix sign comparison warnings

[Arnav Bhate <bhatearnav@gmail.com>]

Junio C Hamano <gitster@pobox.com> writes:

> Arnav Bhate <bhatearnav@gmail.com> writes:
> 
>> -static int get_ours_cache_pos(const char *path, int pos)
>> +static int get_ours_cache_pos(const char *path, unsigned int inverted_pos)
> 
> This renaming of parameter is not right.  
> 
> At this point when the value comes to this function, it *IS* the
> position, there is nothing inverted about it.  It points at the
> position in the .cache[] array where an cache_entry at a higher
> stage would appear.
> 
> It is perfectly fine to state that the value that is returned from
> index_name_pos() is potentially inverted.  The function is given a
> path name (without any stage information) and
> 
>  - returns a non-negative number, the position in the .cache[] array,
>    where a cache_entry at stage #0 (i.e. an entry for a path that does
>    not require conflict resolution), or
> 
>  - returns a negative number, when there is no such cache_entry
>    exists.  The caller can "invert" the value to recover a position
>    in the .cache[] array, where a cache_entry for the path at stage
>    #0 _would_ _have_ been found, if existed.  Due to the way the
>    cache entries are sorted in the .cache[] array, when you are
>    interested in finding cache entries for a path at higher stages,
>    like this function is, you can start scanning at this point until
>    you see an entry for a different path.
> 
> Calling the parameter "pos" is the right thing to do.  The value
> used to come here _could_ have been called "inverted", and the
> result of (-inverted_pos-1) can be assigned to "pos".  But because
> the patch moves the inversion to the caller, what the code in the
> while loop sees is no longer "inverted".

My logic was that it was the inversion of the variable pos, but your
logic makes more sense. I'll make the change.
 
>>  {
>> -	int i = -pos - 1;
>> -
>> -	while ((i < the_repository->index->cache_nr) && !strcmp(the_repository->index->cache[i]->name, path)) {
>> -		if (ce_stage(the_repository->index->cache[i]) == 2)
>> -			return i;
>> -		i++;
>> +	while ((inverted_pos < the_repository->index->cache_nr) && !strcmp(the_repository->index->cache[inverted_pos]->name, path)) {
>> +		if (ce_stage(the_repository->index->cache[inverted_pos]) == 2)
>> +			return inverted_pos;
>> +		inverted_pos++;
>>  	}
>>  	return -1;
>>  }
>> @@ -58,7 +55,7 @@ static void print_error_files(struct string_list *files_list,
>>  			      int *errs)
>>  {
>>  	if (files_list->nr) {
>> -		int i;
>> +		unsigned int i;
>>  		struct strbuf err_msg = STRBUF_INIT;
>>  
>>  		strbuf_addstr(&err_msg, main_msg);
>> @@ -83,7 +80,7 @@ static void submodules_absorb_gitdir_if_needed(void)
>>  
>>  		pos = index_name_pos(the_repository->index, name, strlen(name));
>>  		if (pos < 0) {
> 
> Here is where the caller notices that index_name_pos() did not see a
> stage #0 entry.  This caller wants to see "ours" entry at stage #2,
> so it "inverts" the returned value and asks the helper function if
> it sees such an entry in the .cache[] array.
> 
> A handful of prerequisite pieces of knowledge to understand this
> code are:
> 
>  - The index (i.e. the .cache[] array) is sorted by full path name
>    (down from the top level of the working tree).
> 
>  - The index can have at most one stage #0 entry for each path name.
>    When a stage #0 entry exists for a path name, there cannot be
>    higher stage entries (the path is called "resolved").
> 
>  - The cache entries in the .cache[] array for the same path name
>    are sorted by their stage number.
> 
>  - There can be at most one stage #2 entry for each path name, which
>    are called "ours".  Entries at stage #1 are from common ancestor,
>    entries at stage #3 are from "their" tree.  These higher (i.e.
>    more than zero) stage entries appear only for "conflicting"
>    paths in the .cache[] array.
> 
> With the understanding above, you can see why "our" position is
> computed only when index_name_pos() returns negative in this hunk.

Thanks for the explanation, I was not able to get this from the code.

> 
>> -			pos = get_ours_cache_pos(name, pos);
>> +			pos = get_ours_cache_pos(name, -pos - 1);
>>  			if (pos < 0)
>>  				continue;
>>  		}
>> @@ -131,7 +128,7 @@ static int check_local_mod(struct object_id *head, int index_only)
>>  			 * Skip unmerged entries except for populated submodules
>>  			 * that could lose history when removed.
>>  			 */
>> -			pos = get_ours_cache_pos(name, pos);
>> +			pos = get_ours_cache_pos(name, -pos - 1);
>>  			if (pos < 0)
>>  				continue;
> 
> The above hunks are perfectly fine.  
> 
>> @@ -314,7 +311,7 @@ int cmd_rm(int argc,
>>  	if (pathspec_needs_expanded_index(the_repository->index, &pathspec))
>>  		ensure_full_index(the_repository->index);
>>  
>> -	for (i = 0; i < the_repository->index->cache_nr; i++) {
>> +	for (unsigned int i = 0; i < the_repository->index->cache_nr; i++) {
>>  		const struct cache_entry *ce = the_repository->index->cache[i];
>>  
>>  		if (!include_sparse &&
> 
> OK.
> 
> Thanks.

-- 
Regards,
Arnav Bhate
(He/Him)