[PATCH v1] devtools: allow variable declaration inside for loop

[PATCH v1] devtools: allow variable declaration inside for loop

[Ferruh Yigit]

Declaring variable inside for loop is not supported via C89 and it was
checked in checkpatch.sh via commit [1].
But as DPDK supported C standard is becoming C99 [2], declaring variable
inside loop can be allowed.

[1]
Commit 43e73483a4b8 ("devtools: forbid variable declaration inside for")

[2]
https://dpdk.org/patch/121912

Signed-off-by: Ferruh Yigit <ferruh.yigit@amd.com>
---
Cc: Bruce Richardson <bruce.richardson@intel.com>
Cc: David Marchand <david.marchand@redhat.com>
---
 devtools/checkpatches.sh | 8 --------
 1 file changed, 8 deletions(-)

diff --git a/devtools/checkpatches.sh b/devtools/checkpatches.sh
index 15d5d6709445..b5baf6f2b161 100755
--- a/devtools/checkpatches.sh
+++ b/devtools/checkpatches.sh
@@ -78,14 +78,6 @@ check_forbidden_additions() { # <patch>
 		-f $(dirname $(readlink -f $0))/check-forbidden-tokens.awk \
 		"$1" || res=1
 
-	# forbid variable declaration inside "for" loop
-	awk -v FOLDERS='.' \
-		-v EXPRESSIONS='for[[:space:]]*\\((char|u?int|unsigned|s?size_t)' \
-		-v RET_ON_FAIL=1 \
-		-v MESSAGE='Declaring a variable inside for()' \
-		-f $(dirname $(readlink -f $0))/check-forbidden-tokens.awk \
-		"$1" || res=1
-
 	# refrain from new additions of 16/32/64 bits rte_atomicNN_xxx()
 	awk -v FOLDERS="lib drivers app examples" \
 		-v EXPRESSIONS="rte_atomic[0-9][0-9]_.*\\\(" \
-- 
2.34.1

Re: [PATCH v1] devtools: allow variable declaration inside for loop

[Bruce Richardson]

On Wed, May 03, 2023 at 10:50:18AM +0100, Ferruh Yigit wrote:
> Declaring variable inside for loop is not supported via C89 and it was
> checked in checkpatch.sh via commit [1].  But as DPDK supported C
> standard is becoming C99 [2], declaring variable inside loop can be
> allowed.
> 
> [1] Commit 43e73483a4b8 ("devtools: forbid variable declaration inside
> for")
> 
> [2] https://dpdk.org/patch/121912
> 
> Signed-off-by: Ferruh Yigit <ferruh.yigit@amd.com> --- Cc: Bruce
> Richardson <bruce.richardson@intel.com> Cc: David Marchand
> <david.marchand@redhat.com> --- devtools/checkpatches.sh | 8 -------- 1
> file changed, 8 deletions(-)
> 

Definite +1 from me for allowing this. However, is the plan still to move
to C99 in this release. I thought we were just going to jump to C11 in
23.11 release? However, I can't see any compilers refusing this if we do
relax things a bit now.

I was thinking that our coding standards doc might need an update for this,
but I don't see the restriction on not doing this documented there, so it
seems no doc change is necessary.

/Bruce

Re: [PATCH v1] devtools: allow variable declaration inside for loop

[Ferruh Yigit]

On 5/3/2023 11:02 AM, Bruce Richardson wrote:
> On Wed, May 03, 2023 at 10:50:18AM +0100, Ferruh Yigit wrote:
>> Declaring variable inside for loop is not supported via C89 and it was
>> checked in checkpatch.sh via commit [1].  But as DPDK supported C
>> standard is becoming C99 [2], declaring variable inside loop can be
>> allowed.
>>
>> [1] Commit 43e73483a4b8 ("devtools: forbid variable declaration inside
>> for")
>>
>> [2] https://dpdk.org/patch/121912
>>
>> Signed-off-by: Ferruh Yigit <ferruh.yigit@amd.com> --- Cc: Bruce
>> Richardson <bruce.richardson@intel.com> Cc: David Marchand
>> <david.marchand@redhat.com> --- devtools/checkpatches.sh | 8 -------- 1
>> file changed, 8 deletions(-)
>>
> 
> Definite +1 from me for allowing this. However, is the plan still to move
> to C99 in this release. I thought we were just going to jump to C11 in
> 23.11 release? However, I can't see any compilers refusing this if we do
> relax things a bit now.

I will update the commit log for target as C99/C11 .

> 
> I was thinking that our coding standards doc might need an update for this,
> but I don't see the restriction on not doing this documented there, so it
> seems no doc change is necessary.
> 

Commit 43e73483a4b8 refers to following document:

http://doc.dpdk.org/guides/contributing/coding_style.html#local-variables

Which has: "Variables should be declared at the start of a block of code
rather than in the middle."

Although it is comparing between declaring start of a block and middle
of the code, maybe we can update the document to explicitly state that
declaring variable inside for loop is allowed to prevent confusion.

Let me send a new version with documentation update.

[PATCH v2] devtools: allow variable declaration inside for loop

[Ferruh Yigit]

Declaring variable inside for loop is not supported via C89 and it was
checked in checkpatch.sh via commit [1].
But as DPDK supported C standard is becoming C99/C11 [2], declaring
variable inside loop can be allowed.

[1]
Commit 43e73483a4b8 ("devtools: forbid variable declaration inside for")

[2]
https://dpdk.org/patch/121912

Signed-off-by: Ferruh Yigit <ferruh.yigit@amd.com>
---
Cc: Bruce Richardson <bruce.richardson@intel.com>
Cc: David Marchand <david.marchand@redhat.com>

v2:
 * Update coding convention too
---
 devtools/checkpatches.sh                 | 8 --------
 doc/guides/contributing/coding_style.rst | 1 +
 2 files changed, 1 insertion(+), 8 deletions(-)

diff --git a/devtools/checkpatches.sh b/devtools/checkpatches.sh
index 15d5d6709445..b5baf6f2b161 100755
--- a/devtools/checkpatches.sh
+++ b/devtools/checkpatches.sh
@@ -78,14 +78,6 @@ check_forbidden_additions() { # <patch>
 		-f $(dirname $(readlink -f $0))/check-forbidden-tokens.awk \
 		"$1" || res=1
 
-	# forbid variable declaration inside "for" loop
-	awk -v FOLDERS='.' \
-		-v EXPRESSIONS='for[[:space:]]*\\((char|u?int|unsigned|s?size_t)' \
-		-v RET_ON_FAIL=1 \
-		-v MESSAGE='Declaring a variable inside for()' \
-		-f $(dirname $(readlink -f $0))/check-forbidden-tokens.awk \
-		"$1" || res=1
-
 	# refrain from new additions of 16/32/64 bits rte_atomicNN_xxx()
 	awk -v FOLDERS="lib drivers app examples" \
 		-v EXPRESSIONS="rte_atomic[0-9][0-9]_.*\\\(" \
diff --git a/doc/guides/contributing/coding_style.rst b/doc/guides/contributing/coding_style.rst
index 89db6260cfbf..e18b8d4439ea 100644
--- a/doc/guides/contributing/coding_style.rst
+++ b/doc/guides/contributing/coding_style.rst
@@ -558,6 +558,7 @@ Local Variables
 
 * Variables should be declared at the start of a block of code rather than in the middle.
   The exception to this is when the variable is ``const`` in which case the declaration must be at the point of first use/assignment.
+  Declaring variable inside a for loop is OK.
 * When declaring variables in functions, multiple variables per line are OK.
   However, if multiple declarations would cause the line to exceed a reasonable line length, begin a new set of declarations on the next line rather than using a line continuation.
 * Be careful to not obfuscate the code by initializing variables in the declarations, only the last variable on a line should be initialized.
-- 
2.34.1

Re: [PATCH v2] devtools: allow variable declaration inside for loop

[Bruce Richardson]

On Wed, May 03, 2023 at 11:30:53AM +0100, Ferruh Yigit wrote:
> Declaring variable inside for loop is not supported via C89 and it was
> checked in checkpatch.sh via commit [1].
> But as DPDK supported C standard is becoming C99/C11 [2], declaring
> variable inside loop can be allowed.
> 
> [1]
> Commit 43e73483a4b8 ("devtools: forbid variable declaration inside for")
> 
> [2]
> https://dpdk.org/patch/121912
> 
> Signed-off-by: Ferruh Yigit <ferruh.yigit@amd.com>
> ---
> Cc: Bruce Richardson <bruce.richardson@intel.com>
> Cc: David Marchand <david.marchand@redhat.com>
> 
> v2:
>  * Update coding convention too
> ---

Acked-by: Bruce Richardson <bruce.richardson@intel.com>

>  devtools/checkpatches.sh                 | 8 --------
>  doc/guides/contributing/coding_style.rst | 1 +
>  2 files changed, 1 insertion(+), 8 deletions(-)
> 
> diff --git a/devtools/checkpatches.sh b/devtools/checkpatches.sh
> index 15d5d6709445..b5baf6f2b161 100755
> --- a/devtools/checkpatches.sh
> +++ b/devtools/checkpatches.sh
> @@ -78,14 +78,6 @@ check_forbidden_additions() { # <patch>
>  		-f $(dirname $(readlink -f $0))/check-forbidden-tokens.awk \
>  		"$1" || res=1
>  
> -	# forbid variable declaration inside "for" loop
> -	awk -v FOLDERS='.' \
> -		-v EXPRESSIONS='for[[:space:]]*\\((char|u?int|unsigned|s?size_t)' \
> -		-v RET_ON_FAIL=1 \
> -		-v MESSAGE='Declaring a variable inside for()' \
> -		-f $(dirname $(readlink -f $0))/check-forbidden-tokens.awk \
> -		"$1" || res=1
> -
>  	# refrain from new additions of 16/32/64 bits rte_atomicNN_xxx()
>  	awk -v FOLDERS="lib drivers app examples" \
>  		-v EXPRESSIONS="rte_atomic[0-9][0-9]_.*\\\(" \
> diff --git a/doc/guides/contributing/coding_style.rst b/doc/guides/contributing/coding_style.rst
> index 89db6260cfbf..e18b8d4439ea 100644
> --- a/doc/guides/contributing/coding_style.rst
> +++ b/doc/guides/contributing/coding_style.rst
> @@ -558,6 +558,7 @@ Local Variables
>  
>  * Variables should be declared at the start of a block of code rather than in the middle.

I'd love to see this restriction removed in future too. Having a variable
declared on first use in the middle of block I find a far easier way of
working as a) it saves scrolling to look for variable definitions and b) it
makes it far easier when adding/removing blocks of code e.g. commenting out
for testing,  to have all the code together rather than having variables at
the top to add/remove also.

>    The exception to this is when the variable is ``const`` in which case the declaration must be at the point of first use/assignment.
> +  Declaring variable inside a for loop is OK.
>  * When declaring variables in functions, multiple variables per line are OK.
>    However, if multiple declarations would cause the line to exceed a reasonable line length, begin a new set of declarations on the next line rather than using a line continuation.
>  * Be careful to not obfuscate the code by initializing variables in the declarations, only the last variable on a line should be initialized.
> -- 
> 2.34.1
> 

RE: [PATCH v2] devtools: allow variable declaration inside for loop

[Morten Brørup]

> From: Bruce Richardson [mailto:bruce.richardson@intel.com]
> Sent: Wednesday, 3 May 2023 12.57
> 
> On Wed, May 03, 2023 at 11:30:53AM +0100, Ferruh Yigit wrote:
> > Declaring variable inside for loop is not supported via C89 and it was
> > checked in checkpatch.sh via commit [1].
> > But as DPDK supported C standard is becoming C99/C11 [2], declaring
> > variable inside loop can be allowed.
> >
> > [1]
> > Commit 43e73483a4b8 ("devtools: forbid variable declaration inside
> for")
> >
> > [2]
> > https://dpdk.org/patch/121912
> >
> > Signed-off-by: Ferruh Yigit <ferruh.yigit@amd.com>
> > ---
> > Cc: Bruce Richardson <bruce.richardson@intel.com>
> > Cc: David Marchand <david.marchand@redhat.com>
> >
> > v2:
> >  * Update coding convention too
> > ---
> 
> Acked-by: Bruce Richardson <bruce.richardson@intel.com>

Acked-by: Morten Brørup <mb@smartsharesystems.com>

[...]

> > @@ -558,6 +558,7 @@ Local Variables
> >
> >  * Variables should be declared at the start of a block of code rather
> than in the middle.
> 
> I'd love to see this restriction removed in future too. Having a
> variable
> declared on first use in the middle of block I find a far easier way of
> working as a) it saves scrolling to look for variable definitions and b)
> it
> makes it far easier when adding/removing blocks of code e.g. commenting
> out
> for testing,  to have all the code together rather than having variables
> at
> the top to add/remove also.

And c) Initializing the variables close to where they are used the first time reduces the risk of initializing them incorrectly. Especially when modifying a block of code, initialization of its variables might be missed if out of sight. (Although this is probably a consequence of "a)".)

I consider it old style to only declare variables at the start of a block of code, and this style of coding should be considered obsolete.

If you are really old (like me?), you might remember when function parameters were provided like this:

int main(argc, argv)
int argc;
char *argv[];
{
	return(0);
}

We have moved on from that to a more modern coding style a long time ago. We should also move on to a more modern coding style regarding variable declarations.

> 
> >    The exception to this is when the variable is ``const`` in which
> case the declaration must be at the point of first use/assignment.
> > +  Declaring variable inside a for loop is OK.
> >  * When declaring variables in functions, multiple variables per line
> are OK.
> >    However, if multiple declarations would cause the line to exceed a
> reasonable line length, begin a new set of declarations on the next line
> rather than using a line continuation.
> >  * Be careful to not obfuscate the code by initializing variables in
> the declarations, only the last variable on a line should be
> initialized.
> > --
> > 2.34.1
> >

Re: [PATCH v2] devtools: allow variable declaration inside for loop

[Thomas Monjalon]

03/05/2023 14:19, Morten Brørup:
> > From: Bruce Richardson [mailto:bruce.richardson@intel.com]
> > Sent: Wednesday, 3 May 2023 12.57
> > 
> > On Wed, May 03, 2023 at 11:30:53AM +0100, Ferruh Yigit wrote:
> > > Declaring variable inside for loop is not supported via C89 and it was
> > > checked in checkpatch.sh via commit [1].
> > > But as DPDK supported C standard is becoming C99/C11 [2], declaring
> > > variable inside loop can be allowed.
> > >
> > > [1]
> > > Commit 43e73483a4b8 ("devtools: forbid variable declaration inside
> > for")
> > >
> > > [2]
> > > https://dpdk.org/patch/121912
> > >
> > > Signed-off-by: Ferruh Yigit <ferruh.yigit@amd.com>
> > > ---
> > > Cc: Bruce Richardson <bruce.richardson@intel.com>
> > > Cc: David Marchand <david.marchand@redhat.com>
> > >
> > > v2:
> > >  * Update coding convention too
> > > ---
> > 
> > Acked-by: Bruce Richardson <bruce.richardson@intel.com>
> 
> Acked-by: Morten Brørup <mb@smartsharesystems.com>
> 
> [...]
> 
> > > @@ -558,6 +558,7 @@ Local Variables
> > >
> > >  * Variables should be declared at the start of a block of code rather
> > than in the middle.
> > 
> > I'd love to see this restriction removed in future too. Having a
> > variable
> > declared on first use in the middle of block I find a far easier way of
> > working as a) it saves scrolling to look for variable definitions and b)
> > it
> > makes it far easier when adding/removing blocks of code e.g. commenting
> > out
> > for testing,  to have all the code together rather than having variables
> > at
> > the top to add/remove also.
> 
> And c) Initializing the variables close to where they are used the first time reduces the risk of initializing them incorrectly. Especially when modifying a block of code, initialization of its variables might be missed if out of sight. (Although this is probably a consequence of "a)".)
> 
> I consider it old style to only declare variables at the start of a block of code, and this style of coding should be considered obsolete.
> 
> If you are really old (like me?), you might remember when function parameters were provided like this:
> 
> int main(argc, argv)
> int argc;
> char *argv[];
> {
> 	return(0);
> }
> 
> We have moved on from that to a more modern coding style a long time ago. We should also move on to a more modern coding style regarding variable declarations.

Old men are used to look for variable types at the beginning of functions.
Having only new code adopting a different style may be confusing a little.
Note I'm not against it, just asking for more feedbacks.

Re: [PATCH v2] devtools: allow variable declaration inside for loop

[Tyler Retzlaff]

On Wed, May 03, 2023 at 05:01:01PM +0200, Thomas Monjalon wrote:
> 03/05/2023 14:19, Morten Brørup:
> > > From: Bruce Richardson [mailto:bruce.richardson@intel.com]
> > > Sent: Wednesday, 3 May 2023 12.57
> > > 
> > > On Wed, May 03, 2023 at 11:30:53AM +0100, Ferruh Yigit wrote:
> > > > Declaring variable inside for loop is not supported via C89 and it was
> > > > checked in checkpatch.sh via commit [1].
> > > > But as DPDK supported C standard is becoming C99/C11 [2], declaring
> > > > variable inside loop can be allowed.
> > > >
> > > > [1]
> > > > Commit 43e73483a4b8 ("devtools: forbid variable declaration inside
> > > for")
> > > >
> > > > [2]
> > > > https://dpdk.org/patch/121912
> > > >
> > > > Signed-off-by: Ferruh Yigit <ferruh.yigit@amd.com>
> > > > ---
> > > > Cc: Bruce Richardson <bruce.richardson@intel.com>
> > > > Cc: David Marchand <david.marchand@redhat.com>
> > > >
> > > > v2:
> > > >  * Update coding convention too
> > > > ---
> > > 
> > > Acked-by: Bruce Richardson <bruce.richardson@intel.com>
> > 
> > Acked-by: Morten Brørup <mb@smartsharesystems.com>
> > 
> > [...]
> > 
> > > > @@ -558,6 +558,7 @@ Local Variables
> > > >
> > > >  * Variables should be declared at the start of a block of code rather
> > > than in the middle.
> > > 
> > > I'd love to see this restriction removed in future too. Having a
> > > variable
> > > declared on first use in the middle of block I find a far easier way of
> > > working as a) it saves scrolling to look for variable definitions and b)
> > > it
> > > makes it far easier when adding/removing blocks of code e.g. commenting
> > > out
> > > for testing,  to have all the code together rather than having variables
> > > at
> > > the top to add/remove also.
> > 
> > And c) Initializing the variables close to where they are used the first time reduces the risk of initializing them incorrectly. Especially when modifying a block of code, initialization of its variables might be missed if out of sight. (Although this is probably a consequence of "a)".)
> > 
> > I consider it old style to only declare variables at the start of a block of code, and this style of coding should be considered obsolete.
> > 
> > If you are really old (like me?), you might remember when function parameters were provided like this:
> > 
> > int main(argc, argv)
> > int argc;
> > char *argv[];
> > {
> > 	return(0);
> > }

heh, k&r C

> > 
> > We have moved on from that to a more modern coding style a long time ago. We should also move on to a more modern coding style regarding variable declarations.
> 
> Old men are used to look for variable types at the beginning of functions.
> Having only new code adopting a different style may be confusing a little.
> Note I'm not against it, just asking for more feedbacks.

Acked-by: Tyler Retzlaff <roretzla@linux.microsoft.com>

+1 for declare in minimum necessary scope
+1 for declare at first use (enables more use of const)

thank you!

Re: [PATCH v2] devtools: allow variable declaration inside for loop

[Thomas Monjalon]

> > > > > Declaring variable inside for loop is not supported via C89 and it was
> > > > > checked in checkpatch.sh via commit [1].
> > > > > But as DPDK supported C standard is becoming C99/C11 [2], declaring
> > > > > variable inside loop can be allowed.
> > > > >
> > > > > [1]
> > > > > Commit 43e73483a4b8 ("devtools: forbid variable declaration inside
> > > > for")
> > > > >
> > > > > [2]
> > > > > https://dpdk.org/patch/121912
> > > > >
> > > > > Signed-off-by: Ferruh Yigit <ferruh.yigit@amd.com>
> > > > > ---
> > > > > Cc: Bruce Richardson <bruce.richardson@intel.com>
> > > > > Cc: David Marchand <david.marchand@redhat.com>
> > > > >
> > > > > v2:
> > > > >  * Update coding convention too
> > > > > ---
> > > > 
> > > > Acked-by: Bruce Richardson <bruce.richardson@intel.com>
> > > 
> > > Acked-by: Morten Brørup <mb@smartsharesystems.com>
> 
> Acked-by: Tyler Retzlaff <roretzla@linux.microsoft.com>

Applied, thanks.