diff-filter can't identify renaming if not done directly

> quick question about using diff-filter in linux. In the scenario
> that in my repository, I first copy file1 to file2, then move file2 to
> file3 and delete file1, "git diff" returns:
> 
> diff --git a/file1 b/file3
> similarity index 100%
> rename from file1
> rename to file3
> 
>  but running "git diff --diff-filter=r" doesn't return anything. Only
> flag "t" will return the change. Can this be considered as a bug?

> On Fri, Dec 04, 2020 at 03:59:03PM +0100, Sofia Syria wrote:
>
>> quick question about using diff-filter in linux. In the scenario
>> that in my repository, I first copy file1 to file2, then move file2 to
>> file3 and delete file1, "git diff" returns:
>> 
>> diff --git a/file1 b/file3
>> similarity index 100%
>> rename from file1
>> rename to file3
>> 
>>  but running "git diff --diff-filter=r" doesn't return anything. Only
>> flag "t" will return the change. Can this be considered as a bug?
>
> Lowercase filters exclude particular types. From "git help diff":
>
>     --diff-filter=[(A|C|D|M|R|T|U|X|B)...[*]]
> 	   Select only files that are Added (A), Copied (C), Deleted
> 	   (D), Modified (M), Renamed (R), have their type (i.e. regular
> 	   file, symlink, submodule, ...) changed (T), are Unmerged (U),
> 	   are Unknown (X), or have had their pairing Broken (B). Any
> 	   combination of the filter characters (including none) can be
> 	   used. When * (All-or-none) is added to the combination, all
> 	   paths are selected if there is any file that matches other
> 	   criteria in the comparison; if there is no file that matches
> 	   other criteria, nothing is selected.
>
> 	   Also, these upper-case letters can be downcased to exclude.
> 	   E.g. --diff-filter=ad excludes added and deleted paths.
>
> So "--diff-filter=R" asks to see only renames. But "--diff-filter=r"
> asks to exclude them. And "--diff-filter=t" excludes typechanges, which
> means that renames are still OK. Doing "--diff-filter=a", etc, would
> still show it as well.