[spec/var-op-test] Enhance tests for ${array[@]+foo}

Part of issue #1884.

osh/word_eval.py

@@ -620,6 +620,7 @@ def _ApplyTestOp(
                     is_falsey = False
             elif case(value_e.BashArray):
                 val = cast(value.BashArray, UP_val)
+                # TODO: allow undefined
                 is_falsey = len(val.strs) == 0
             elif case(value_e.BashAssoc):
                 val = cast(value.BashAssoc, UP_val)

spec/array.test.sh

@@ -28,9 +28,10 @@ empty=()
 argv.py ${empty[@]:-not one} "${empty[@]:-not one}"
 ## stdout: ['not', 'one', 'not one']
 
-#### nounset with empty array (design bug, makes it hard to use arrays)
+#### nounset / set -u with empty array (bug in bash 4.3, fixed in 4.4)
+
 # http://lists.gnu.org/archive/html/help-bash/2017-09/msg00005.html
-# NOTE: This used to be a bug in bash 4.3, but is fixed in bash 4.4.
+
 set -o nounset
 empty=()
 argv.py "${empty[@]}"

spec/var-op-test.test.sh

@@ -103,7 +103,7 @@ argv.py "${with_icc+set}" = set
 ['', '=', 'set']
 ## END
 
-#### ${v+foo} and ${v:+foo} when set -u
+#### ${s+foo} and ${s:+foo} when set -u
 set -u
 v=v
 echo v=${v:+foo}
@@ -118,18 +118,49 @@ v=
 v=
 ## END
 
+#### "${array[@]} with set -u (bash is outlier)
+case $SH in dash) exit ;; esac
+
+set -u
+
+typeset -a empty
+empty=()
+
+echo empty /"${empty[@]}"/
+echo undefined /"${undefined[@]}"/
+
+## status: 1
+## STDOUT:
+empty //
+## END
+
+## BUG bash status: 0
+## BUG bash STDOUT:
+empty //
+undefined //
+## END
+
+# empty array is unset in mksh
+## BUG mksh status: 1
+## BUG mksh STDOUT:
+## END
+
+## N-I dash status: 0
+## N-I dash STDOUT:
+## END
+
+
 #### "${a[@]+foo}" and "${a[@]:+foo}" undefined, with set -u
 case $SH in dash) exit ;; esac
 
 set -u
 
-echo array="${array[@]+foo}"
-echo array="${array[@]:+foo}"
-## status: 0
+echo plus /"${array[@]+foo}"/
+echo plus colon /"${array[@]:+foo}"/
 
 ## STDOUT:
-array=
-array=
+plus //
+plus colon //
 ## END
 
 ## N-I dash STDOUT: