patchmore meaningful error message in gitk when git binary is not available

> Hi. I ran across what is a decidedly trivial little issue in gitk. The
> TCL/Tk looked simple enough so I am giving you a patch anyhow in case
> you want to fix it.
> 
> When for whatever reason the git binary is unavailable, gitk would
> complain about missing git repository instead, so this patch adds a
> check for git binary availability.
> 
> In case anyone is curious, I found this issue here:
> 
> http://stackoverflow.com/q/11967110/53936
> 
> 
> 
> Signed-off-by: Josef Assad <josef@josefassad.com>
> ---
> gitk-git/gitk |    6 ++++++
> 1 files changed, 6 insertions(+), 0 deletions(-)
> 
> diff --git a/gitk-git/gitk b/gitk-git/gitk
> index d93bd99..7e2e0a7 100755
> --- a/gitk-git/gitk
> +++ b/gitk-git/gitk
> @@ -11680,6 +11680,12 @@ setui $uicolor
> 
> setoptions
> 
> +# check that the git executables are available for use
> +if [catch {set gitexists [exec which git]}] {

> +    show_error {} . [mc "Cannot find a suitable git executable."]
> +    exit 1
> +}
> +
> # check that we can find a .git directory somewhere...
> if {[catch {set gitdir [exec git rev-parse --git-dir]}]} {
>     show_error {} . [mc "Cannot find a git repository here."]

> diff --git a/gitk-git/gitk b/gitk-git/gitk
> index d93bd99..7e2e0a7 100755
> --- a/gitk-git/gitk
> +++ b/gitk-git/gitk
> @@ -11680,6 +11680,12 @@ setui $uicolor
>
>  setoptions
>
> +# check that the git executables are available for use
> +if [catch {set gitexists [exec which git]}] {
> +    show_error {} . [mc "Cannot find a suitable git executable."]
> +    exit 1
> +}
> +
>  # check that we can find a .git directory somewhere...
>  if {[catch {set gitdir [exec git rev-parse --git-dir]}]} {
>      show_error {} . [mc "Cannot find a git repository here."]

> On 10/01/2012 07:11 PM, Junio C Hamano wrote:
>> Josef Assad <josef@josefassad.com> writes:
>>
>>> Signed-off-by: Josef Assad <josef@josefassad.com>
>>> ---
>>>  gitk-git/gitk |    6 ++++++
>>>  1 files changed, 6 insertions(+), 0 deletions(-)
>>
>> Thanks.
>>
>>> diff --git a/gitk-git/gitk b/gitk-git/gitk
>>> index d93bd99..7e2e0a7 100755
>>> --- a/gitk-git/gitk
>>> +++ b/gitk-git/gitk
>>> @@ -11680,6 +11680,12 @@ setui $uicolor
>>>
>>>  setoptions
>>>
>>> +# check that the git executables are available for use
>>> +if [catch {set gitexists [exec which git]}] {
>>> +    show_error {} . [mc "Cannot find a suitable git executable."]
>>> +    exit 1
>>> +}
>>> +
>>>  # check that we can find a .git directory somewhere...
>>>  if {[catch {set gitdir [exec git rev-parse --git-dir]}]} {
>>>      show_error {} . [mc "Cannot find a git repository here."]
>>
>> It is somewhat a stupid solution to add an extra fork that will only
>> waste cycles in the normal non-error case, especially when we
>> already have an error codepath that acts on lack of the "git"
>> command anyway, isn't it?
> 
> I don't think it's actually _stupid_, but I also think your solution
> works better if you're trying to avoid one more exec call.
> 
> Mine has one less level of indentation though, and it has clearer
> delineation between checking for and handling two distinct error
> conditions. :)
> 
>> The "rev-parse" you see in the post-context will fail when we are
>> not in a git repository, but it will also fail when we do not have
>> git.
>>
>> You can add the new check to if {[catch {... git rev-parse }]} block;
>> before unconditionally saying "cannot find a git repo", you check if
>> "git" even exists, and give an appropriate error message.  That way,
>> you do not punish normal use case with an extra useless fork.
>>
>> Something like this, I presume.
>>
>>
>>  gitk | 7 ++++++-
>>  1 file changed, 6 insertions(+), 1 deletion(-)
>>
>> diff --git a/gitk b/gitk
>> index d93bd99..60794a7 100755
>> --- a/gitk
>> +++ b/gitk
>> @@ -11682,7 +11682,12 @@ setoptions
>>  
>>  # check that we can find a .git directory somewhere...
>>  if {[catch {set gitdir [exec git rev-parse --git-dir]}]} {
>> -    show_error {} . [mc "Cannot find a git repository here."]
>> +    # we could have failed because there is no git to begin with
>> +    if {[catch {exec git version}]} {
>> +        show_error {} . [mc "You do not seem to have 'git' command."]
>> +    } else {
>> +        show_error {} . [mc "Cannot find a git repository here."]
>> +    }
>>      exit 1
>>  }
> 
> I'm neutral though and not married to my patch in any way, just trying
> to be helpful. In my opinon, yours is cleaner, mine is a tiny bit more
> readable in a file already closing on 12k lines.
>