From 9364d710205903ac387e3991b742ddfec842d142 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?John=20Ankarstr=C3=B6m?= <john@ankarstrom.se>
Date: Mon, 19 Jul 2021 19:33:39 +0200
Subject: vipatch: Check for lines incorrectly added/removed

---
 vipatch | 60 +++++++++++++++++++++++++++---------------------------------
 1 file changed, 27 insertions(+), 33 deletions(-)

diff --git a/vipatch b/vipatch
index 0a8f54d..4711388 100755
--- a/vipatch
+++ b/vipatch
@@ -4,39 +4,32 @@
 
 # This is a simple awk script that re-adjusts headers in
 # a patch generated by diff -u, depending on the actual
-# number of added/removed lines. As the script performs no
-# error checks, it is up to the user to edit (and verify)
-# the patch correctly.
-
-ep | awk '
-/^@@ / {
-	head = $0 "\n"
-	next
-}
-
-head && /^---/ {
-	end()
-	print
-	next
-}
-
-head && /^\+/ { plus++ }
-head && /^-/ { minus++ }
-
-head {
-	body = body $0 "\n"
-	next
-}
-
-{ print }
-
-END { end() }
-
-function end() {
+# number of added/removed lines.
+
+ep | awk -vname=${0##*/} '
+/^@@ /		{ head = $0 "\n"; next }
+head && /^---/	{ printpatch(); print; next }
+head && /^\+/	{ plus++ }
+head && /^-/	{ minus++ }
+head && /^ /	{ same++ }
+head		{ body = body $0 "\n"; next }
+		{ print }
+END		{ if (head) printpatch() }
+
+function printpatch() {
 	match(head, /,[0-9]+/)
 	old = substr(head, RSTART+1, RLENGTH-1)
 	new = old + plus - minus
 
+	diff = old - same - minus
+	if (diff != 0) {
+		printf "%s: %d %s incorrectly %s\n", name, abs(diff),
+			(abs(diff) > 1) ? "lines" : "line",
+			(diff > 0) ? "removed" : "added" > "/dev/stderr"
+		head = ""
+		exit 1
+	}
+
 	match(head, /^@@ -[0-9]+,[0-9]+ \+[0-9]+,/)
 	prefix = substr(head, RSTART, RLENGTH)
 
@@ -46,9 +39,10 @@ function end() {
 	printf "%s%d%s", prefix, new, suffix
 	printf "%s", body
 
-	head = ""
-	body = ""
-	plus = 0
-	minus = 0
+	head = ""; body = ""; plus = 0; minus = 0; same = 0
+}
+
+function abs(n) {
+	return (n > 0) ? n : -n;
 }
 '
-- 
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