[PATCH v3] checkpatch: add support to check 'Fixes:' tag format

[Wang YanQing <udknight@gmail.com>]

According to submitting-patches.rst, 'Fixes:' tag has a little
stricter condition about the one line summary than normal git
commit description:
“...
Do not split the tag across multiple lines, tags are exempt from
the "wrap at 75 columns" rule in order to simplify parsing scripts
...”

And there is no sanity check for 'Fixes:' tag format in checkpatch
the same as GIT_COMMIT_ID for git commit description, so let's expand
the GIT_COMMIT_ID to add 'Fixes:' tag format check support.

The check supports below formats:
Fixes: 54a4f0239f2e ("KVM: MMU: make kvm_mmu_zap_page() return the number of pages it actually freed")
Fixes: 85f7cd3a2aad ("Revert "media: Kconfig: better support hybrid TV devices"")
Fixes: 878520ac45f9 ("ext4: save the error code which triggered...")
Fixes: 878520ac45f9 ("ext4: save the error code which triggered")
Fixes: 277f27e2f277 ("SUNRPC/cache: Allow garbage collection ... ")

The check doesn't support below formats:
Fixes: f2c2e717642c ("usb: gadget: add raw-gadget interface"
Fixes: 6c73698904aa pinctrl: qcom: Introduce readl/writel accessors
Fixes: 3fd6e7d9a146 (ASoC: tas571x: New driver for TI TAS571x power amplifiers)
Fixes: 55697cbb44e4 ("arm64: dts: renesas: r8a779{65,80,90}: Add IPMMU devices nodes)
Fixes: ba35f8588f47 (“ipvlan: Defer multicast / broadcast processing to a work-queue”)
Fixes: cd758a9b57ee "KVM: PPC: Book3S HV: Use __gfn_to_pfn_memslot in HPT page fault handler"
Fixes:      9b1640686470 ("scsi: lpfc: Fix use-after-free mailbox cmd completion")
Fixes: 03f6fc6de919 ('ASoC: rt5682: Add the soundwire support')

Note: this patch also fixes double quotation mark issue for normal git
      commit description, and now it supports double quotation mark in
      title line, for example:
      Commit e33e2241e272 ("Revert "cfg80211: Use 5MHz bandwidth by default
      when checking usable channels"")

Based on original patch by Joe Perches <joe@perches.com>

Link: https://lore.kernel.org/lkml/40bfc40958fca6e2cc9b86101153aa0715fac4f7.camel@perches.com/
Signed-off-by: Wang YanQing <udknight@gmail.com>
---
 v3:
 1: Fix a bug in short title line support.

 v2:
 1: Add support for double quotation mark in title line, suggested by Markus Elfring.
 2: Add support for short title line with/without ellipsis.
 3: Add supported format examples and unsupported format examples in changelog.
 4: Fix a little wording issue in changelog , suggested by Markus Elfring.

 scripts/checkpatch.pl | 68 +++++++++++++++++++++++++++++++------------
 1 file changed, 49 insertions(+), 19 deletions(-)

diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index 23a001a66006..a649b9f711b6 100755
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -2818,57 +2818,87 @@ sub process {
 		    $line !~ /^\s*(?:Link|Patchwork|http|https|BugLink|base-commit):/i &&
 		    $line !~ /^This reverts commit [0-9a-f]{7,40}/ &&
 		    ($line =~ /\bcommit\s+[0-9a-f]{5,}\b/i ||
+		     $line =~ /\bfixes:\s+[0-9a-f]{5,}\b/i ||
 		     ($line =~ /(?:\s|^)[0-9a-f]{12,40}(?:[\s"'\(\[]|$)/i &&
-		      $line !~ /[\<\[][0-9a-f]{12,40}[\>\]]/i &&
-		      $line !~ /\bfixes:\s*[0-9a-f]{12,40}/i))) {
+		      $line !~ /[\<\[][0-9a-f]{12,40}[\>\]]/i))) {
 			my $init_char = "c";
 			my $orig_commit = "";
+			my $prefix = "commit";
+			my $prefix_case = "[Cc]ommit";
 			my $short = 1;
 			my $long = 0;
 			my $case = 1;
 			my $space = 1;
 			my $hasdesc = 0;
-			my $hasparens = 0;
+			my $has_parens_and_dqm = 0; # Double quotation mark
 			my $id = '0123456789ab';
 			my $orig_desc = "commit description";
 			my $description = "";
+			my $acrosslines = 0;
+			my $title = "title line";
+			my $desc_mismatch = 0;
 
-			if ($line =~ /\b(c)ommit\s+([0-9a-f]{5,})\b/i) {
+			if ($line =~ /\b(f)ixes:\s+([0-9a-f]{5,})\b/i) {
+				$init_char = $1;
+				$orig_commit = lc($2);
+				$prefix = "Fixes:";
+				$prefix_case = "Fixes:";
+				$init_char = "F";
+				$title = "a single line title (without line breaks but ellipsis is fine!)";
+			} elsif ($line =~ /\b(c)ommit\s+([0-9a-f]{5,})\b/i) {
 				$init_char = $1;
 				$orig_commit = lc($2);
 			} elsif ($line =~ /\b([0-9a-f]{12,40})\b/i) {
 				$orig_commit = lc($1);
 			}
 
-			$short = 0 if ($line =~ /\bcommit\s+[0-9a-f]{12,40}/i);
-			$long = 1 if ($line =~ /\bcommit\s+[0-9a-f]{41,}/i);
-			$space = 0 if ($line =~ /\bcommit [0-9a-f]/i);
-			$case = 0 if ($line =~ /\b[Cc]ommit\s+[0-9a-f]{5,40}[^A-F]/);
-			if ($line =~ /\bcommit\s+[0-9a-f]{5,}\s+\("([^"]+)"\)/i) {
+			$short = 0 if ($line =~ /\b$prefix\s+[0-9a-f]{12,40}/i);
+			$long = 1 if ($line =~ /\b$prefix\s+[0-9a-f]{41,}/i);
+			$space = 0 if ($line =~ /\b$prefix [0-9a-f]/i);
+			$case = 0 if ($line =~ /\b$prefix_case\s+[0-9a-f]{5,40}[^A-F]/);
+			if ($line =~ /\b$prefix\s+[0-9a-f]{5,}\s+\("(.+)"\)/i) {
 				$orig_desc = $1;
-				$hasparens = 1;
+				$has_parens_and_dqm = 1;
+				# Drop the ellipsis
+				if ($prefix eq "Fixes:" && $orig_desc =~ /(\s*\.{3}\s*$)/) {
+				    $orig_desc = substr($orig_desc, 0, length($orig_desc) - length($1));
+				}
 			} elsif ($line =~ /\bcommit\s+[0-9a-f]{5,}\s*$/i &&
 				 defined $rawlines[$linenr] &&
-				 $rawlines[$linenr] =~ /^\s*\("([^"]+)"\)/) {
+				 $rawlines[$linenr] =~ /^\s*\("(.+)"\)/) {
 				$orig_desc = $1;
-				$hasparens = 1;
-			} elsif ($line =~ /\bcommit\s+[0-9a-f]{5,}\s+\("[^"]+$/i &&
+				$has_parens_and_dqm = 1;
+			} elsif ($line =~ /\b$prefix\s+[0-9a-f]{5,}\s+\(".+$/i &&
 				 defined $rawlines[$linenr] &&
-				 $rawlines[$linenr] =~ /^\s*[^"]+"\)/) {
-				$line =~ /\bcommit\s+[0-9a-f]{5,}\s+\("([^"]+)$/i;
+				 $rawlines[$linenr] =~ /^\s*.+"\)/) {
+				$line =~ /\b$prefix\s+[0-9a-f]{5,}\s+\("(.+)$/i;
 				$orig_desc = $1;
-				$rawlines[$linenr] =~ /^\s*([^"]+)"\)/;
+				$rawlines[$linenr] =~ /^\s*(.+)"\)/;
 				$orig_desc .= " " . $1;
-				$hasparens = 1;
+				$has_parens_and_dqm = 1;
+				$acrosslines = 1 if ($prefix eq "Fixes:");
 			}
 
 			($id, $description) = git_commit_info($orig_commit,
 							      $id, $orig_desc);
 
+			if (defined($id) && ($orig_desc ne $description)) {
+			    # Allow short description without too short!
+			    if ($prefix eq "Fixes:" && $has_parens_and_dqm  && length($orig_desc) >= length($description)/2) {
+				my $desc = substr($description, 0, length($orig_desc));
+
+				if ($orig_desc ne $desc) {
+				    $desc_mismatch = 1;
+				}
+			    } else {
+				$desc_mismatch = 1;
+			    }
+			}
+
 			if (defined($id) &&
-			   ($short || $long || $space || $case || ($orig_desc ne $description) || !$hasparens)) {
+			   ($short || $long || $space || $case || $desc_mismatch || !$has_parens_and_dqm || $acrosslines)) {
 				ERROR("GIT_COMMIT_ID",
-				      "Please use git commit description style 'commit <12+ chars of sha1> (\"<title line>\")' - ie: '${init_char}ommit $id (\"$description\")'\n" . $herecurr);
+				      "Please use git commit description style '$prefix <12+ chars of sha1> (\"<$title>\")' - ie: '${init_char}" . substr($prefix, 1) . " $id (\"$description\")'\n" . $herecurr);
 			}
 		}
 
-- 
2.17.1