scripts: Add sort-makefile-lines.py to sort Makefile variables.

The scripts/sort-makefile-lines.py script sorts Makefile variables
according to project expected order.

The script can be used like this:

$ scripts/sort-makefile-lines.py < elf/Makefile > elf/Makefile.tmp
$ mv elf/Makefile.tmp elf/Makefile

Reviewed-by: Siddhesh Poyarekar <siddhesh@sourceware.org>

scripts/sort-makefile-lines.py

@@ -0,0 +1,160 @@
+#!/usr/bin/python3
+# Sort Makefile lines as expected by project policy.
+# Copyright (C) 2023 Free Software Foundation, Inc.
+# This file is part of the GNU C Library.
+#
+# The GNU C Library is free software; you can redistribute it and/or
+# modify it under the terms of the GNU Lesser General Public
+# License as published by the Free Software Foundation; either
+# version 2.1 of the License, or (at your option) any later version.
+#
+# The GNU C Library is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+# Lesser General Public License for more details.
+#
+# You should have received a copy of the GNU Lesser General Public
+# License along with the GNU C Library; if not, see
+# <https://www.gnu.org/licenses/>.
+
+# The project consensus is to split Makefile variable assignment
+# across multiple lines with one value per line.  The values are
+# then sorted as described below, and terminated with a special
+# list termination marker.  This splitting makes it much easier
+# to add new tests to the list since they become just a single
+# line insertion.  It also makes backports and merges easier
+# since the new test may not conflict due to the ordering.
+#
+# Consensus discussion:
+# https://inbox.sourceware.org/libc-alpha/f6406204-84f5-adb1-d00e-979ebeebbbde@redhat.com/
+#
+# To support cleaning up Makefiles we created this program to
+# help sort existing lists converted to the new format.
+#
+# The program takes as input the Makefile to sort correctly,
+# and the output file to write the correctly sorted output
+# (it can be the same file).
+#
+# Sorting is only carried out between two special markers:
+# (a) Marker start is '<variable> += \' (or '= \', or ':= \')
+# (b) Marker end is '  # <variable>' (whitespace matters)
+# With everthing between (a) and (b) being sorted accordingly.
+#
+# You can use it like this:
+# $ scripts/sort-makefile-lines.py < elf/Makefile > elf/Makefile.tmp
+# $ mv elf/Makefile.tmp elf/Makefile
+#
+# The Makefile lines in the project are sorted using the
+# following rules:
+# - All lines are sorted as-if `LC_COLLATE=C sort`
+# - Lines that have a numeric suffix and whose leading prefix
+#   matches exactly are sorted according the numeric suffix
+#   in increasing numerical order.
+#
+# For example:
+# ~~~
+# tests += \
+#   test-a \
+#   test-b \
+#   test-b1 \
+#   test-b2 \
+#   test-b10 \
+#   test-b20 \
+#   test-b100 \
+#   # tests
+# ~~~
+# This example shows tests sorted alphabetically, followed
+# by a numeric suffix sort in increasing numeric order.
+#
+# Cleanups:
+# - Tests that end in "a" or "b" variants should be renamed to
+#   end in just the numerical value. For example 'tst-mutex7robust'
+#   should be renamed to 'tst-mutex12' (the highest numbered test)
+#   or 'tst-robust11' (the highest numbered test) in order to get
+#   reasonable ordering.
+# - Modules that end in "mod" or "mod1" should be renamed. For
+#   example 'tst-atfork2mod' should be renamed to 'tst-mod-atfork2'
+#   (test module for atfork2). If there are more than one module
+#   then they should be named with a suffix that uses [0-9] first
+#   then [A-Z] next for a total of 36 possible modules per test.
+#   No manually listed test currently uses more than that (though
+#   automatically generated tests may; they don't need sorting).
+# - Avoid including another test and instead refactor into common
+#   code with all tests including hte common code, then give the
+#   tests unique names.
+#
+# If you have a Makefile that needs converting, then you can
+# quickly split the values into one-per-line, ensure the start
+# and end markers are in place, and then run the script to
+# sort the values.
+
+import sys
+import locale
+import re
+import functools
+
+def glibc_makefile_numeric(string1, string2):
+    # Check if string1 has a numeric suffix.
+    var1 = re.search(r'([0-9]+) \\$', string1)
+    var2 = re.search(r'([0-9]+) \\$', string2)
+    if var1 and var2:
+        if string1[0:var1.span()[0]] == string2[0:var2.span()[0]]:
+            # string1 and string2 both share a prefix and
+            # have a numeric suffix that can be compared.
+            # Sort order is based on the numeric suffix.
+            return int(var1.group(1)) > int(var2.group(1))
+    # Default to strcoll.
+    return locale.strcoll(string1, string2)
+
+def sort_lines(lines):
+
+    # Use the C locale for language independent collation.
+    locale.setlocale (locale.LC_ALL, "C")
+
+    # Sort using a glibc-specific sorting function.
+    lines = sorted(lines, key=functools.cmp_to_key(glibc_makefile_numeric))
+
+    return lines
+
+def sort_makefile_lines():
+
+    # Read the whole Makefile.
+    lines = sys.stdin.readlines()
+
+    # Build a list of all start markers (tuple includes name).
+    startmarks = []
+    for i in range(len(lines)):
+        # Look for things like "var = \", "var := \" or "var += \"
+        # to start the sorted list.
+        var = re.search(r'^([a-zA-Z0-9-]*) [\+:]?\= \\$', lines[i])
+        if var:
+            # Remember the index and the name.
+            startmarks.append((i, var.group(1)))
+
+    # For each start marker try to find a matching end mark
+    # and build a block that needs sorting.  The end marker
+    # must have the matching comment name for it to be valid.
+    rangemarks = []
+    for sm in startmarks:
+        # Look for things like "  # var" to end the sorted list.
+        reg = r'^  # ' + sm[1] + r'$'
+        for j in range(sm[0] + 1, len(lines)):
+            if re.search(reg, lines[j]):
+                # Rembember the block to sort (inclusive).
+                rangemarks.append((sm[0] + 1, j))
+                break
+
+    # We now have a list of all ranges that need sorting.
+    # Sort those ranges (inclusive).
+    for r in rangemarks:
+        lines[r[0]:r[1]] = sort_lines(lines[r[0]:r[1]])
+
+    # Output the whole list with sorted lines to stdout.
+    [sys.stdout.write(line) for line in lines]
+
+
+def main(argv):
+    sort_makefile_lines ()
+
+if __name__ == '__main__':
+    main(sys.argv[1:])