[tz] [PROPOSED] Assume zic 2017c or later when shrinking

[Paul Eggert]

The tzdata.zi file was first released in 2017c, and deliberately
avoided zic features that were also new to that release, to avoid
problems with people mistakenly running older zic when generating
this new file.  After a year’s wait it is reasonable to assume
that anybody using this new file is also using a new-enough zic.
This saves about 900 bytes in tzdata.zi.
* NEWS: Mention this.
* zishrink.awk (gen_rule_name, prehash_rule_names)
(process_input_line, output_saved_lines):
For clarity, use the convention that parameters are on the first
line of function definition, and local vars are on later lines.
(process_input_line): Assume zic 2017c or later.
Make line types more explicit.
---
 NEWS         |  5 +++++
 zishrink.awk | 44 +++++++++++++++++++++++---------------------
 2 files changed, 28 insertions(+), 21 deletions(-)

diff --git a/NEWS b/NEWS
index c939b8f..be6dd26 100644
--- a/NEWS
+++ b/NEWS
@@ -25,6 +25,11 @@ Unreleased, experimental changes
     Europe/Rome between those dates.  (Thanks to Stephen Trainor and
     Luigi Rosa.)
 
+  Changes to build procedure
+
+    tzdata.zi now assumes zic 2017c or later.  This shrinks tzdata.zi
+    by a percent or so.
+
 
 Release 2019a - 2019-03-25 22:01:33 -0700
 
diff --git a/zishrink.awk b/zishrink.awk
index 8876b68..4e187ac 100644
--- a/zishrink.awk
+++ b/zishrink.awk
@@ -20,7 +20,8 @@ function record_hash(n, name)
 # Return a shortened rule name representing NAME,
 # and record this relationship to the hash table.
 
-function gen_rule_name(name, n)
+function gen_rule_name(name, \
+		       n)
 {
   # Use a simple memonic: the first two letters.
   n = substr(name, 1, 2)
@@ -29,7 +30,8 @@ function gen_rule_name(name, n)
   return n
 }
 
-function prehash_rule_names(name)
+function prehash_rule_names( \
+			    name)
 {
   # Rule names are not part of the tzdb API, so substitute shorter
   # ones.  Shortening them consistently from one release to the next
@@ -148,20 +150,21 @@ function prehash_rule_names(name)
   }
 }
 
-# Process an input line and save it for later output.
+# Process the input line LINE and save it for later output.
 
-function process_input_line(line, field, end, i, n, startdef)
+function process_input_line(line, \
+			    field, end, i, n, startdef, \
+			    linkline, ruleline, zoneline)
 {
   # Remove comments, normalize spaces, and append a space to each line.
   sub(/#.*/, "", line)
   line = line " "
   gsub(/[\t ]+/, " ", line)
 
-  # Abbreviate keywords.  Do not abbreviate "Link" to just "L",
-  # as pre-2017c zic erroneously diagnoses "Li" as ambiguous.
-  sub(/^Link /, "Li ", line)
-  sub(/^Rule /, "R ", line)
-  sub(/^Zone /, "Z ", line)
+  # Abbreviate keywords and determine line type.
+  linkline = sub(/^Link /, "L ", line)
+  ruleline = sub(/^Rule /, "R ", line)
+  zoneline = sub(/^Zone /, "Z ", line)
 
   # SystemV rules are not needed.
   if (line ~ /^R SystemV /) return
@@ -169,7 +172,7 @@ function process_input_line(line, field, end, i, n, startdef)
   # Replace FooAsia rules with the same rules without "Asia", as they
   # are duplicates.
   if (match(line, /[^ ]Asia /)) {
-    if (line ~ /^R /) return
+    if (ruleline) return
     line = substr(line, 1, RSTART) substr(line, RSTART + 5)
   }
 
@@ -179,21 +182,19 @@ function process_input_line(line, field, end, i, n, startdef)
   while (match(line, /:0[^:]/))
     line = substr(line, 1, RSTART - 1) substr(line, RSTART + 2)
 
-  # Abbreviate weekday names.  Do not abbreviate "Sun" and "Sat", as
-  # pre-2017c zic erroneously diagnoses "Su" and "Sa" as ambiguous.
+  # Abbreviate weekday names.
   while (match(line, / (last)?(Mon|Wed|Fri)[ <>]/)) {
     end = RSTART + RLENGTH
     line = substr(line, 1, end - 4) substr(line, end - 1)
   }
-  while (match(line, / (last)?(Tue|Thu)[ <>]/)) {
+  while (match(line, / (last)?(Sun|Tue|Thu|Sat)[ <>]/)) {
     end = RSTART + RLENGTH
     line = substr(line, 1, end - 3) substr(line, end - 1)
   }
 
-  # Abbreviate "max", "only" and month names.
-  # Do not abbreviate "min", as pre-2017c zic erroneously diagnoses "mi"
-  # as ambiguous.
+  # Abbreviate "max", "min", "only" and month names.
   gsub(/ max /, " ma ", line)
+  gsub(/ min /, " mi ", line)
   gsub(/ only /, " o ", line)
   gsub(/ Jan /, " Ja ", line)
   gsub(/ Feb /, " F ", line)
@@ -221,7 +222,7 @@ function process_input_line(line, field, end, i, n, startdef)
   n = split(line, field)
 
   # Abbreviate rule names.
-  i = field[1] == "Z" ? 4 : field[1] == "Li" ? 0 : 2
+  i = zoneline ? 4 : linkline ? 0 : 2
   if (i && field[i] ~ /^[^-+0-9]/) {
     if (!rule[field[i]])
       rule[field[i]] = gen_rule_name(field[i])
@@ -231,11 +232,11 @@ function process_input_line(line, field, end, i, n, startdef)
   # If this zone supersedes an earlier one, delete the earlier one
   # from the saved output lines.
   startdef = ""
-  if (field[1] == "Z")
+  if (zoneline)
     zonename = startdef = field[2]
-  else if (field[1] == "Li")
+  else if (linkline)
     zonename = startdef = field[3]
-  else if (field[1] == "R")
+  else if (ruleline)
     zonename = ""
   if (startdef) {
     i = zonedef[startdef]
@@ -254,7 +255,8 @@ function process_input_line(line, field, end, i, n, startdef)
   output_line[nout++] = line
 }
 
-function output_saved_lines(i)
+function output_saved_lines( \
+			    i)
 {
   for (i = 0; i < nout; i++)
     if (output_line[i])
-- 
2.21.0