commit 7b6fb155cadd5e5ee70b55c2770e1bdd2f5d2a38
Author: Paul Eggert <eggert@cs.ucla.edu>
Date:   Thu Sep 5 14:38:35 2024 -0700

    Improve style checks for months
    
    * checktab.awk: Check style of STDOFF and month names.

diff --git a/checktab.awk b/checktab.awk
index 9a26e465..15a3a697 100644
--- a/checktab.awk
+++ b/checktab.awk
@@ -9,6 +9,19 @@ BEGIN {
 	if (!zone_table) zone_table = "zone1970.tab"
 	if (!want_warnings) want_warnings = -1
 
+	monthabbr["Jan"] = 1
+	monthabbr["Feb"] = 1
+	monthabbr["Mar"] = 1
+	monthabbr["Apr"] = 1
+	monthabbr["May"] = 1
+	monthabbr["Jun"] = 1
+	monthabbr["Jul"] = 1
+	monthabbr["Aug"] = 1
+	monthabbr["Sep"] = 1
+	monthabbr["Oct"] = 1
+	monthabbr["Nov"] = 1
+	monthabbr["Dec"] = 1
+
 	while (getline <iso_table) {
 		iso_NR++
 		if ($0 ~ /^#/) continue
@@ -128,12 +141,14 @@ BEGIN {
 $1 ~ /^#/ { next }
 
 {
-	tz = rules = ""
+	tz = rules = stdoff = ""
 	if ($1 == "Zone") {
 		tz = $2
+		stdoff = $3
 		ruleUsed[$4] = 1
 		if ($5 ~ /%/) rulePercentUsed[$4] = 1
-	} else if ($1 == "Link" && zone_table == "zone.tab") {
+	} else if ($1 == "Link") {
+	    if (zone_table == "zone.tab") {
 		# Ignore Link commands if source and destination basenames
 		# are identical, e.g. Europe/Istanbul versus Asia/Istanbul.
 		src = $2
@@ -141,13 +156,27 @@ $1 ~ /^#/ { next }
 		while ((i = index(src, "/"))) src = substr(src, i+1)
 		while ((i = index(dst, "/"))) dst = substr(dst, i+1)
 		if (src != dst) tz = $3
+	    }
 	} else if ($1 == "Rule") {
 		ruleDefined[$2] = 1
 		if ($10 != "-") ruleLetters[$2] = 1
+		if (!monthabbr[$6]) {
+		  printf "%s:%d: tricky month: %s\n", FILENAME, FNR, $6 \
+			  >>"/dev/stderr"
+		  status = 1
+		}
 	} else {
+		stdoff = $1
 		ruleUsed[$2] = 1
 		if ($3 ~ /%/) rulePercentUsed[$2] = 1
 	}
+
+	if (stdoff && stdoff !~ /^\-?1?[0-9](:[0-5][0-9](:[0-5][0-9])?)?$/) {
+		printf "%s:%d: unlikely STDOFF: %s\n", FILENAME, FNR, stdoff \
+			>>"/dev/stderr"
+		status = 1
+	}
+
 	if (tz && tz ~ /\// && tz !~ /^Etc\//) {
 		if (!tztab[tz] && FILENAME != "backward" \
 		    && zone_table != "zonenow.tab") {