Fix regression involving command builtin

Fixes #1402

src/cmd/ksh93/bltins/command.c

@@ -57,7 +57,7 @@ int b_command(int argc, char *argv[], Shbltin_t *context) {
     while ((opt = getopt_long(true_argc, argv, short_options, long_options, NULL)) != -1) {
         switch (opt) {
             case 1: {
-                builtin_print_help(shp, cmd);
+                if (argc != 0) builtin_print_help(shp, cmd);
                 return 0;
             }
             case 'p': {
@@ -86,6 +86,7 @@ int b_command(int argc, char *argv[], Shbltin_t *context) {
                 return 2;
             }
             case '?': {
+                if (argc == 0) return 0;
                 builtin_unknown_option(shp, cmd, argv[opterr]);
                 return 2;
             }

src/cmd/ksh93/functions/_ksh_print_help

@@ -50,5 +50,5 @@ function _ksh_print_help {
                     /^[^ ]/b
                     p
                 }' |
-        uniq | "$ul"
+        uniq | "$ul" >&2
 }

src/cmd/ksh93/tests/b_command.sh

@@ -82,3 +82,12 @@ actual=$(
 )
 [[ $actual == "$expect" ]] ||
    log_error 'assignments to "command special_built-in" leaving side effects' "$expect" "$actual"
+
+# ========
+# Regression test for https://github.com/att/ast/issues/1402.
+#
+# We throw away stderr because we only want the value of `$t` not the error text from running
+# `command` with an invalid flag.
+expect='good'
+actual=$($SHELL -c 't=good; t=bad command -@; print $t' 2>/dev/null)
+[[ $expect == $actual ]] || log_error 'temp var assignment with `command`' "$expect" "$actual"

src/cmd/ksh93/tests/b_exit.sh

@@ -0,0 +1,54 @@
+#
+# Verify the `exit` command behaves as expected.
+#
+
+# =======
+actual=$($SHELL -c 'exit' 2>&1)
+status=$?
+expect=0
+[[ -z $actual ]] || log_error 'bare exit' "" "$actual"
+[[ $expect == $status ]] || log_error 'bare exit' "$expect" "$status"
+
+# =======
+actual=$($SHELL -c 'exit 0' 2>&1)
+status=$?
+expect=0
+[[ -z $actual ]] || log_error 'exit 0' "" "$actual"
+[[ $expect == $status ]] || log_error 'exit 0' "$expect" "$status"
+
+# =======
+actual=$($SHELL -c 'exit 1' 2>&1)
+status=$?
+expect=1
+[[ -z $actual ]] || log_error 'exit 1' "" "$actual"
+[[ $expect == $status ]] || log_error 'exit 1' "$expect" "$status"
+
+# =======
+actual=$($SHELL -c 'function e37 { return 37; } ; e37' 2>&1)
+status=$?
+expect=37
+[[ -z $actual ]] || log_error 'exit 37' "" "$actual"
+[[ $expect == $status ]] || log_error 'exit 37' "$expect" "$status"
+
+# =======
+actual=$($SHELL -c 'exit -1' 2>&1)
+status=$?
+expect=255
+[[ -z $actual ]] || log_error 'exit -1' "" "$actual"
+[[ $expect == $status ]] || log_error 'exit -1' "$expect" "$status"
+
+# =======
+actual=$($SHELL -c 'exit -2' 2>&1)
+status=$?
+expect=254
+[[ -z $actual ]] || log_error 'exit -2' "" "$actual"
+[[ $expect == $status ]] || log_error 'exit -2' "$expect" "$status"
+
+# =======
+$SHELL +E -i <<- \! && log_error 'interactive shell should not exit 0 after false'
+    false
+    exit
+!
+status=$?
+expect=1
+[[ $expect == $status ]] || log_error 'bare exit after false' "$expect" "$status"

src/cmd/ksh93/tests/builtins.sh

@@ -380,11 +380,6 @@ mkdir foo .bar
 cd foo
 cd ../.bar 2> /dev/null || log_error 'cd ../.bar when ../.bar exists should not fail'
 
-$SHELL +E -i <<- \! && log_error 'interactive shell should not exit 0 after false'
-    false
-    exit
-!
-
 unset ENV
 
 : ~root

src/cmd/ksh93/tests/meson.build

@@ -16,6 +16,7 @@ all_tests = [
     ['b_dirname'],
     ['b_echo.exp'],
     ['b_enum'],
+    ['b_exit'],
     ['b_grep'],
     ['b_head'],
     ['b_hist.exp'],