Re: sizeof(var) vs sizeof(type), was Re: [PATCH] git: use COPY_ARRAY and MOVE_ARRAY in handle_alias()

[Derrick Stolee <stolee@gmail.com>]

On 9/26/2019 9:22 AM, Johannes Schindelin wrote:
> Hi Peff,
> 
> On Mon, 23 Sep 2019, Jeff King wrote:
> 
>> On Thu, Sep 19, 2019 at 10:48:30PM +0200, René Scharfe wrote:
>>
>>> Use the macro COPY_ARRAY to copy array elements and MOVE_ARRAY to do the
>>> same for moving them backwards in an array with potential overlap.  The
>>> result is shorter and safer, as it infers the element type automatically
>>> and does a (very) basic type compatibility check for its first two
>>> arguments.
>>>
>>> These cases were missed by Coccinelle and contrib/coccinelle/array.cocci
>>> because the type of the elements is "const char *", not "char *", and
>>> the rules in the semantic patch cautiously insist on the sizeof operator
>>> being used on exactly the same type to avoid generating transformations
>>> that introduce subtle bugs into tricky code.
>>
>> Another good reason to use "sizeof(var)" instead of sizeof(type)". :)
> 
> That is indeed a very good reason, in addition to getting the type right
> automatically (by virtue of letting the compiler pick it).
> 
> Should we make this an explicit guideline in our documentation?

Better yet: can we create a Coccinelle script to fix it automatically?

-Stolee