[builtin/completion_osh] Support SparseArray COMP_ARGV with compadjust

* SparseArray_GetValues is used to obtain comp_argv from the shell
  variable COMP_ARGV.  This ignores all the unset elements and only
  picks up the set elements.  Then the word index would be changed.
  This might not be desired.  Maybe it is better to first convert it
  to BashArray and use the member strs?

* Conversely, when there are unset elements in COMP_ARGV with
  BashArray, doesn't that cause problems in the later AdjustArg?

builtin/completion_osh.py

@@ -5,6 +5,7 @@
 from _devbuild.gen.syntax_asdl import loc
 from _devbuild.gen.value_asdl import (value, value_e)
 
+from core import bash_impl
 from core import completion
 from core import error
 from core import state
@@ -454,9 +455,13 @@ def Run(self, cmd_val):
         # TODO: How does the user test a completion function programmatically?  Set
         # COMP_ARGV?
         val = self.mem.GetValue('COMP_ARGV')
-        if val.tag() != value_e.BashArray:
+        if val.tag() == value_e.BashArray:
+            comp_argv = cast(value.BashArray, val).strs
+        elif val.tag() == value_e.SparseArray:
+            comp_argv = bash_impl.SparseArray_GetValues(
+                cast(value.SparseArray, val))
+        else:
             raise error.Usage("COMP_ARGV should be an array", loc.Missing)
-        comp_argv = cast(value.BashArray, val).strs
 
         # These are the ones from COMP_WORDBREAKS that we care about.  The rest occur
         # "outside" of words.

spec/ble-idioms.test.sh

@@ -1095,6 +1095,24 @@ compgen -F _set_COMPREPLY
 ## END
 
 
+#### SparseArray: compgen -F _set_COMPREPLY
+case $SH in bash|zsh|mksh|ash) exit ;; esac
+
+a=(echo 'Hello,' 'Bash' 'world!')
+var COMP_ARGV = _a2sp(a)
+compadjust cur prev words cword
+argv.py "$cur" "$prev" "$cword"
+argv.py "${words[@]}"
+
+## STDOUT:
+['world!', 'Bash', '3']
+['echo', 'Hello,', 'Bash', 'world!']
+## END
+
+## N-I bash/zsh/mksh/ash STDOUT:
+## END
+
+
 #### SparseArray (YSH): $[a1 === a2]
 case $SH in bash|zsh|mksh|ash) exit ;; esac