cde/TODO

TODO for AT&T ksh93, 93u+m bugfix branch

______
Fix or remove broken default aliases:

- Remove alias times='{ { time;} 2>&1;}' which does not produce POSIX-
  compliant output; reimplement as a proper POSIX-compliant builtin.
  In any case, implementing a standard utility as an alias is unacceptable
  as 'unalias -a' (remove all aliases) should not remove standard utilities!
  Backport the builtin from the abandoned Vashisht/Rader branch:
  https://github.com/att/ast/pull/1332

- Remove alias command='command '. Continuing alias substitution after
  'command' (due to the final space in the alias) is inherently broken, as
  aliases may contain arbitrary shell grammar. For instance, when combining
  this default alias with the default 'times' alias ('command times'), which
  is perfectly valid per POSIX, you get a syntax error!

- Remove alias nohup='nohup '. Same reason as for 'command ' above.

- Remove pointless default aliases 'fc' and 'type'; these are already
  implemented as normal shell builtins. Add man page entries for these.

______
Fix currently known bugs affecting shell scripting. These are identified by
their modernish IDs. For exact details, see code/comments in:
https://github.com/modernish/modernish/tree/0.16/lib/modernish/cap/

- BUG_BRACQUOT: shell quoting within bracket patterns has no effect. This
  bug means the '-' retains it special meaning of 'character range', and an
  initial ! (and, on some shells, ^) retains the meaning of negation, even
  in quoted strings within bracket patterns, including quoted variables.

- BUG_CMDEXPAN: if the 'command' command results from an expansion, it acts
  like 'command -v', showing the path of the command instead of executing it.
  For example:
	v=command; "$v" ls
  or
	set -- command ls; "$@"
  don't work.

- BUG_CMDSPASGN: preceding a "special builtin"[*] with 'command' does not
  stop preceding invocation-local variable assignments from becoming global.
  [*] https://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_14

- BUG_CMDSPEXIT: preceding a "special builtin"[*] (other than 'eval', 'exec',
  'return' or 'exit') with 'command' does not always stop it from exiting
  the shell if the builtin encounters error.
  [*] https://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_14

- BUG_CSUBSTDO: If standard output (file descriptor 1) is closed before
  entering a $(command substitution), and any other file descriptors are
  redirected within the command substitution, commands such as 'echo' will
  not work within the command substitution, acting as if standard output is
  still closed.

- BUG_FNSUBSH: Function definitions within subshells (including command
  substitutions) are ignored if a function by the same name exists in the
  main shell, so the wrong function is executed. 'unset -f' is also silently
  ignored. This only applies to non-forked subshells.

- BUG_IFSGLOBS: In glob pattern matching (as in case or parameter
  substitution with # and %), if IFS starts with ? or * and the "$*"
  parameter expansion inserts any IFS separator characters, those characters
  are erroneously interpreted as wildcards when quoted "$*" is used as the
  glob pattern.

- BUG_IFSISSET: ${IFS+s} always yields 's' even if IFS is unset. This applies
  to IFS only.

- BUG_ISSETLOOP: Expansions like ${var+set} remain static when used within a
  'for', 'while' or 'until' loop; the expansions don't change along with the
  state of the variable, so they cannot be used to check whether a variable
  is set within a loop if the state of that variable may change in the
  course of the loop.

- BUG_KUNSETIFS: ksh93: Can't unset IFS under very specific circumstances.
  unset -v IFS is a known POSIX shell idiom to activate default field
  splitting. With this bug, the unset builtin silently fails to unset IFS
  (i.e. fails to activate field splitting) if we're executing an eval or a
  trap and a number of specific conditions are met.

- BUG_LOOPRET2: If a 'return' command is given without a status argument
  within the set of conditional commands in a 'while' or 'until' loop (i.e.,
  between 'while'/'until' and 'do'), the exit status passed down from the
  previous command is ignored and the function returns with status 0
  instead.

- BUG_MULTIBIFS: We're on a UTF-8 locale and the shell supports UTF-8
  characters in general (i.e. we don't have WRN_MULTIBYTE) – however, using
  multi-byte characters as IFS field delimiters still doesn't work. For
  example, "$*" joins positional parameters on the first byte of IFS instead
  of the first character.

- BUG_PUTIOERR: Shell builtins that output strings (echo, printf, ksh/zsh
  print), and thus also modernish put and putln, do not check for I/O errors
  on output. This means a script cannot check for them, and a script process
  in a pipe can get stuck in an infinite loop if SIGPIPE is ignored.

- BUG_TESTERR1A: test/[ exits with a non-error false status (1) if an
  invalid argument is given to an operator.