fix: Properly handle environments with unset IFS

Prior to this commit, the current state of `IFS` was stored into a local
variable `ifs`. Later, IFS is restored by setting `IFS=$ifs`. If the
user starts with either a set `IFS` or an empty `IFS`, then this
behavior is correct. If the user starts with an unset `IFS`, then
`IFS=$ifs` results in an empty `IFS`, which is not the original state.
Most of the time an empty `IFS` is not desired, and indeed it breaks
some things inside bash-completions. eg

```
unset IFS
local ifs=$IFS IFS=$' \t\n'
restore=$(shopt -po noglob)
IFS=$ifs
$restore
...
-bash: set -o noglob: command not found
```

With this commit, all instances of `local ifs=$IFS` have been removed.
Instead, the `local IFS` is dynamically unset.

Author: Seamus Connor

bash_completion

@@ -149,6 +149,23 @@ dequote()
     eval printf %s "$1" 2>/dev/null
 }
 
+# Unset the given variables across a scope boundary. Useful for unshadowing
+# global scoped variables. Note that simply calling unset on a local variable
+# will not unshadow the global variable. Rather, the result will be a local
+# variable in an unset state.
+# Usage: local IFS='|'; _comp_unlocal IFS
+# Param: $* Variable names to be unset
+_comp_unlocal()
+{
+    if ((BASH_VERSINFO[0] >= 5)) && shopt -q localvar_unset; then
+        shopt -u localvar_unset
+        unset -v "$@"
+        shopt -s localvar_unset
+    else
+        unset -v "$@"
+    fi
+}
+
 # Assign variable one scope above the caller
 # Usage: local "$1" && _upvar $1 "value(s)"
 # Param: $1  Variable name to assign value to
@@ -721,12 +738,12 @@ _comp_delimited()
         # glob char escaping issues to deal with. Do removals by hand instead.
         COMPREPLY=($(compgen "$@"))
         local -a existing
-        local x i ifs=$IFS IFS=$delimiter
+        local x i IFS=$delimiter
         existing=($cur)
         # Do not remove the last from existing if it's not followed by the
         # delimiter so we get space appended.
         [[ ! $cur || $cur == *"$delimiter" ]] || unset -v "existing[${#existing[@]}-1]"
-        IFS=$ifs
+        _comp_unlocal IFS
         if ((${#COMPREPLY[@]})); then
             for x in ${existing+"${existing[@]}"}; do
                 for i in "${!COMPREPLY[@]}"; do
@@ -1253,14 +1270,13 @@ else
         if [[ ${1-} == -s ]]; then
             procs=($(command ps ax -o comm | command sed -e 1d))
         else
-            local line i=-1 ifs=$IFS
-            IFS=$'\n'
+            local line i=-1 IFS=$'\n'
             # Some versions of ps don't support "command", but do "comm", e.g.
             # some busybox ones. Fall back
             local -a psout=($({
                 command ps ax -o command= || command ps ax -o comm=
             } 2>/dev/null))
-            IFS=$ifs
+            _comp_unlocal IFS
             for line in "${psout[@]}"; do
                 if ((i == -1)); then
                     # First line, see if it has COMMAND column header. For
@@ -1751,7 +1767,7 @@ _included_ssh_config_files()
 # Return: Completions, starting with CWORD, are added to COMPREPLY[]
 _known_hosts_real()
 {
-    local configfile flag prefix="" ifs=$IFS
+    local configfile flag prefix=""
     local cur suffix="" aliases i host ipv4 ipv6
     local -a kh tmpkh=() khd=() config=()
 
@@ -1817,7 +1833,7 @@ _known_hosts_real()
         #          spaces in their name work (watch out for ~ expansion
         #          breakage! Alioth#311595)
         tmpkh=($(awk 'sub("^[ \t]*([Gg][Ll][Oo][Bb][Aa][Ll]|[Uu][Ss][Ee][Rr])[Kk][Nn][Oo][Ww][Nn][Hh][Oo][Ss][Tt][Ss][Ff][Ii][Ll][Ee][ \t=]+", "") { print $0 }' "${config[@]}" | sort -u))
-        IFS=$ifs
+        _comp_unlocal IFS
     fi
     if ((${#tmpkh[@]} != 0)); then
         local j
@@ -1873,7 +1889,7 @@ _known_hosts_real()
                         # Add host to candidates
                         COMPREPLY+=($host)
                     done
-                    IFS=$ifs
+                    _comp_unlocal IFS
                 done <"$i"
             done
             ((${#COMPREPLY[@]})) &&
@@ -1935,7 +1951,6 @@ _known_hosts_real()
             $(compgen -A hostname -P "$prefix" -S "$suffix" -- "$cur"))
     fi
 
-    IFS=$' \t\n'
     $reset
 
     if ((${#COMPREPLY[@]})); then
@@ -2349,12 +2364,12 @@ complete -F _minimal ''
 __load_completion()
 {
     local -a dirs=(${BASH_COMPLETION_USER_DIR:-${XDG_DATA_HOME:-$HOME/.local/share}/bash-completion}/completions)
-    local ifs=$IFS IFS=: dir cmd="${1##*/}" compfile
+    local IFS=: dir cmd="${1##*/}" compfile
     [[ -n $cmd ]] || return 1
     for dir in ${XDG_DATA_DIRS:-/usr/local/share:/usr/share}; do
         dirs+=($dir/bash-completion/completions)
     done
-    IFS=$ifs
+    _comp_unlocal IFS
 
     if [[ $BASH_SOURCE == */* ]]; then
         dirs+=("${BASH_SOURCE%/*}/completions")

completions/7z

@@ -49,9 +49,9 @@ _7z()
             local reset=$(shopt -po noglob)
             set -o noglob
             compopt -o filenames
-            local ifs=$IFS IFS=$'\n'
+            local IFS=$'\n'
             COMPREPLY=($(compgen -d -P${cur:0:2} -S/ -- "${cur:2}"))
-            IFS=$ifs
+            _comp_unlocal IFS
             $reset
             compopt -o nospace
             return

completions/_umount.linux

@@ -25,9 +25,9 @@ _reply_compgen_array()
     ecur=${ecur//\'/\\\'}
 
     # Actually generate completions.
-    local ifs=$IFS
-    IFS=$'\n' eval 'COMPREPLY=(`compgen -W "$wlist" -- "${ecur}"`)'
-    IFS=$ifs
+    local IFS=$'\n'
+    COMPREPLY=($(compgen -W "$wlist" -- "${ecur}"))
+    _comp_unlocal IFS
 }
 
 # Unescape strings in the linux fstab(5) format (with octal escapes).
@@ -49,24 +49,23 @@ _linux_fstab()
 
     # Read and unescape values into COMPREPLY
     local fs_spec fs_file fs_other
-    local ifs="$IFS"
     while read -r fs_spec fs_file fs_other; do
         if [[ $fs_spec == [#]* ]]; then continue; fi
         if [[ ${1-} == -L ]]; then
             local fs_label=${fs_spec/#LABEL=/}
             if [[ $fs_label != "$fs_spec" ]]; then
                 __linux_fstab_unescape fs_label
-                IFS=$'\0'
+                local IFS=$'\0'
                 COMPREPLY+=("$fs_label")
-                IFS=$ifs
+                _comp_unlocal IFS
             fi
         else
             __linux_fstab_unescape fs_spec
             __linux_fstab_unescape fs_file
-            IFS=$'\0'
+            local IFS=$'\0'
             [[ $fs_spec == */* ]] && COMPREPLY+=("$fs_spec")
             [[ $fs_file == */* ]] && COMPREPLY+=("$fs_file")
-            IFS=$ifs
+            _comp_unlocal IFS
         fi
     done
 

completions/svcadm

@@ -44,10 +44,9 @@ _smf_complete_fmri()
             # we generate all possibles abbreviations for the FMRI
             # no need to have a generic loop as we will have a finite
             # number of components
-            local ifs="$IFS"
-            IFS="/"
+            local IFS="/"
             set -- $fmri
-            IFS=$ifs
+            _comp_unlocal IFS
             case $# in
                 1) fmri_part_list=" $1" ;;
                 2) fmri_part_list=" $2 $1/$2" ;;

test/t/unit/test_unit_unlocal.py

@@ -0,0 +1,18 @@
+import pytest
+
+from conftest import assert_bash_exec
+
+
+@pytest.mark.bashcomp(cmd=None, ignore_env=r"^\+(VAR=|declare -f foo)")
+class TestUnlocal:
+    def test_1(self, bash):
+        cmd = (
+            "foo() { "
+            "local VAR=inner; "
+            "_comp_unlocal VAR; "
+            "echo $VAR; "
+            "}; "
+            "VAR=outer; foo; "
+        )
+        res = assert_bash_exec(bash, cmd, want_output=True).strip()
+        assert res == "outer"