linux-kernel - Re: [PATCH] checkpatch: prefer = {} initializations to = {0}

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Date:   Thu, 05 Aug 2021 05:27:27 -0700
From:   Joe Perches <joe@...ches.com>
To:     Dan Carpenter <dan.carpenter@...cle.com>,
        Andy Whitcroft <apw@...onical.com>
Cc:     Dwaipayan Ray <dwaipayanray1@...il.com>,
        Lukas Bulwahn <lukas.bulwahn@...il.com>,
        linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org
Subject: Re: [PATCH] checkpatch: prefer = {} initializations to = {0}

On Thu, 2021-08-05 at 13:43 +0300, Dan Carpenter wrote:
> The "= {};" style empty struct initializer is preferred over = {0}.
> It avoids the situation where the first struct member is a pointer and
> that generates a Sparse warning about assigning using zero instead of
> NULL.  Also it's just nicer to look at.
> 
> Some people complain that {} is less portable but the kernel has
> different portability requirements from userspace so this is not a
> issue that we care about.
[]
> diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
[]
> @@ -4029,6 +4029,12 @@ sub process {
>  			     "Using $1 is unnecessary\n" . $herecurr);
>  		}
> 
> +# prefer = {}; to = {0};
> +		if ($line =~ /= \{ *0 *\}/) {

Have you done a grep and looked at this pattern's actual use in the kernel?
I rather doubt it.

> +			WARN("ZERO_INITIALIZER",
> +			     "= {} is preferred over = {0}\n" . $herecurr);
> +		}
> +

To be much more specific to the actual desired match as stated in
the possible commit log, this should probably be something like:

	if (defined($stat) &&
	    $stat =~ /^\+\s+$Declare\s*$Ident\s*=\s*\{\s*0\s*\}\s*;/) {

and maybe it should be a --strict CHK and not WARN.

And I generally avoid using "we" in a commit message.

Maybe something like:
---
 scripts/checkpatch.pl | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index 461d4221e4a4a..e3d4aa5f86c46 100755
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -6911,6 +6911,21 @@ sub process {
 			     "externs should be avoided in .c files\n" .  $herecurr);
 		}
 
+# check for non-global single initializers with '= {0};', prefer '= {};'
+# there is already a GLOBAL_INITIALIZERS test so avoid those too with /^\+\s+/
+		if (defined($stat) &&
+		    $stat =~ /^\+\s+$Declare\s*$Ident\s*(=\s*\{\s*0\s*\}\s*);/) {
+			my $match = $1;
+			my $cnt = statement_rawlines($stat);
+			my $herectx = get_stat_here($linenr, $cnt, $here);
+			if (WARN("ZERO_INITIALIZER",
+				 "Prefer '= {}' over '$match'\n" . $herectx) &&
+			    $fix &&
+			    $cnt == 1) {	# can only --fix single line statements
+				$fixed[$fixlinenr] =~ s/\s*=\s*\{\s*0\s*\}\s*;/ = {};/;
+			}
+		}
+
 # check for function declarations that have arguments without identifier names
 		if (defined $stat &&
 		    $stat =~ /^.\s*(?:extern\s+)?$Type\s*(?:$Ident|\(\s*\*\s*$Ident\s*\))\s*\(\s*([^{]+)\s*\)\s*;/s &&