[Bug 2152822] [NEW] comm and sort are incompatible in 26.04 LTS

[Serge]

Public bug reported:

After upgrading from 25.10 to 26.04, I've noticed one of my scripts
fail. It sorted some files with `sort` and then compared them with
`comm`, and now it fails with messages like `comm: input is not in
sorted order`.

Turns out the current version of `sort` supports locale-based collation,
so it have sorted the files correctly according to my
`LC_COLLATE=en_US.UTF-8` locale; while `comm` doesn't support collation,
and requires files sorted in `C` locale.

As most Ubuntu systems have locales other than `C`, this makes `sort`
and `comm` incompatible under default conditions.

Example: prepare two `en_US`-sorted files and compare them:

$ cat en_US_1.txt
aa
Aa
ab
Ab

$ cat en_US_2.txt
bb
Bb
bc
Bc

$ LC_COLLATE=en_US.UTF-8 comm -12 en_US_1.txt en_US_2.txt
comm: file 1 is not in sorted order
comm: file 2 is not in sorted order
comm: input is not in sorted order

Github issue: https://github.com/uutils/coreutils/issues/12253
A similar issue was mentioned in bug 2117711

** Affects: rust-coreutils (Ubuntu)
     Importance: Undecided
         Status: New

** Description changed:

  After upgrading from 25.10 to 26.04, I've noticed one of my scripts
  fail. It sorted some files with `sort` and then compared them with
  `comm`, and now it fails with messages like `comm: input is not in
  sorted order`.
  
  Turns out the current version of `sort` supports locale-based collation,
  so it have sorted the files correctly according to my
  `LC_COLLATE=en_US.UTF-8` locale; while `comm` doesn't support collation,
  and requires files sorted in `C` locale.
  
  As most Ubuntu systems have locales other than `C`, this makes `sort`
  and `comm` incompatible under default conditions.
  
  Example: prepare two `en_US`-sorted files and compare them:
- ```
- $ cat en_US_1.txt 
+ 
+ $ cat en_US_1.txt
  aa
  Aa
  ab
  Ab
  
- $ cat en_US_2.txt 
+ $ cat en_US_2.txt
  bb
  Bb
  bc
  Bc
  
  $ LC_COLLATE=en_US.UTF-8 comm -12 en_US_1.txt en_US_2.txt
  comm: file 1 is not in sorted order
  comm: file 2 is not in sorted order
  comm: input is not in sorted order
- ```
+ 
  Github issue: https://github.com/uutils/coreutils/issues/12253

** Description changed:

  After upgrading from 25.10 to 26.04, I've noticed one of my scripts
  fail. It sorted some files with `sort` and then compared them with
  `comm`, and now it fails with messages like `comm: input is not in
  sorted order`.
  
  Turns out the current version of `sort` supports locale-based collation,
  so it have sorted the files correctly according to my
  `LC_COLLATE=en_US.UTF-8` locale; while `comm` doesn't support collation,
  and requires files sorted in `C` locale.
  
  As most Ubuntu systems have locales other than `C`, this makes `sort`
  and `comm` incompatible under default conditions.
  
  Example: prepare two `en_US`-sorted files and compare them:
  
  $ cat en_US_1.txt
  aa
  Aa
  ab
  Ab
  
  $ cat en_US_2.txt
  bb
  Bb
  bc
  Bc
  
  $ LC_COLLATE=en_US.UTF-8 comm -12 en_US_1.txt en_US_2.txt
  comm: file 1 is not in sorted order
  comm: file 2 is not in sorted order
  comm: input is not in sorted order
  
  Github issue: https://github.com/uutils/coreutils/issues/12253
+ A similar issue was mentioned in #2117711

** Description changed:

  After upgrading from 25.10 to 26.04, I've noticed one of my scripts
  fail. It sorted some files with `sort` and then compared them with
  `comm`, and now it fails with messages like `comm: input is not in
  sorted order`.
  
  Turns out the current version of `sort` supports locale-based collation,
  so it have sorted the files correctly according to my
  `LC_COLLATE=en_US.UTF-8` locale; while `comm` doesn't support collation,
  and requires files sorted in `C` locale.
  
  As most Ubuntu systems have locales other than `C`, this makes `sort`
  and `comm` incompatible under default conditions.
  
  Example: prepare two `en_US`-sorted files and compare them:
  
  $ cat en_US_1.txt
  aa
  Aa
  ab
  Ab
  
  $ cat en_US_2.txt
  bb
  Bb
  bc
  Bc
  
  $ LC_COLLATE=en_US.UTF-8 comm -12 en_US_1.txt en_US_2.txt
  comm: file 1 is not in sorted order
  comm: file 2 is not in sorted order
  comm: input is not in sorted order
  
  Github issue: https://github.com/uutils/coreutils/issues/12253
- A similar issue was mentioned in #2117711
+ A similar issue was mentioned in bug 2117711

** Summary changed:

- comm and sort are incompatible
+ comm and sort are incompatible in 26.04 LTS

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https://bugs.launchpad.net/bugs/2152822

Title:
  comm and sort are incompatible in 26.04 LTS

Status in rust-coreutils package in Ubuntu:
  New

Bug description:
  After upgrading from 25.10 to 26.04, I've noticed one of my scripts
  fail. It sorted some files with `sort` and then compared them with
  `comm`, and now it fails with messages like `comm: input is not in
  sorted order`.

  Turns out the current version of `sort` supports locale-based
  collation, so it have sorted the files correctly according to my
  `LC_COLLATE=en_US.UTF-8` locale; while `comm` doesn't support
  collation, and requires files sorted in `C` locale.

  As most Ubuntu systems have locales other than `C`, this makes `sort`
  and `comm` incompatible under default conditions.

  Example: prepare two `en_US`-sorted files and compare them:

  $ cat en_US_1.txt
  aa
  Aa
  ab
  Ab

  $ cat en_US_2.txt
  bb
  Bb
  bc
  Bc

  $ LC_COLLATE=en_US.UTF-8 comm -12 en_US_1.txt en_US_2.txt
  comm: file 1 is not in sorted order
  comm: file 2 is not in sorted order
  comm: input is not in sorted order

  Github issue: https://github.com/uutils/coreutils/issues/12253
  A similar issue was mentioned in bug 2117711

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