hush: partially fix wrong expansion on $IFS (bug 4027).

In the added testcase, before patch we failed 8 out of 9 tests,
now we fail only 2 (4th and 5th).

function                                             old     new   delta
expand_on_ifs                                        225     258     +33
expand_vars_to_list                                 1038    1054     +16
o_save_ptr_helper                                    115     119      +4
builtin_umask                                        132     133      +1
o_addQstr                                            165     161      -4
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 4/1 up/down: 54/-4)              Total: 50 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

3 files changed, 50 insertions, 9 deletions

diff --git a/shell/hush.c b/shell/hush.c
index 1082738a2..503cb770b 100644
--- a/shell/hush.c
+++ b/shell/hush.c
@@ -2281,7 +2281,7 @@ static void o_addqblock(o_string *o, const char *str, int len)
                         ordinary_cnt = len;
                 o_addblock(o, str, ordinary_cnt);
                 if (ordinary_cnt == len)
-                        return;
+                        return; /* NUL is already added by o_addblock */
                 str += ordinary_cnt;
                 len -= ordinary_cnt + 1; /* we are processing + 1 char below */
 
@@ -2295,8 +2295,8 @@ static void o_addqblock(o_string *o, const char *str, int len)
                 o_grow_by(o, sz);
                 o->data[o->length] = ch;
                 o->length++;
-                o->data[o->length] = '\0';
         }
+        o->data[o->length] = '\0';
 }
 
 static void o_addQblock(o_string *o, const char *str, int len)
@@ -2385,6 +2385,7 @@ static int o_save_ptr_helper(o_string *o, int n)
                                 n, string_len, string_start);
                 o->has_empty_slot = 0;
         }
+        o->has_quoted_part = 0;
         list[n] = (char*)(uintptr_t)string_len;
         return n + 1;
 }
@@ -4754,8 +4755,13 @@ static void o_addblock_duplicate_backslash(o_string *o, const char *str, int len
 static int expand_on_ifs(o_string *output, int n, const char *str)
 {
         while (1) {
-                int word_len = strcspn(str, G.ifs);
+                int word_len;
+
+                if (!*str)  /* EOL - do not finalize word */
+                        break;
+                word_len = strcspn(str, G.ifs);
                 if (word_len) {
+                        /* We have WORD_LEN leading non-IFS chars */
                         if (!(output->o_expflags & EXP_FLAG_GLOB)) {
                                 o_addblock(output, str, word_len);
                         } else {
@@ -4769,13 +4775,25 @@ static int expand_on_ifs(o_string *output, int n, const char *str)
                                 /*o_addqblock(output, str, word_len); - WRONG: "v='*'; echo Z$v" prints "Z*" instead of Z* files */
                         }
                         str += word_len;
+                        if (!*str)  /* EOL - do not finalize word */
+                                break;
+                        goto finalize; /* optimization (can just fall thru) */
+                }
+                /* Case "v=' a'; echo ''$v": we do need to finalize empty word */
+                if (output->has_quoted_part
+                /* Case "v=' a'; echo $v":
+                 * here nothing precedes the space in $v expansion,
+                 * therefore we should not finish the word
+                 * (IOW: if there *is* word to finalize, only then do it)
+                 */
+                 || (output->length && output->data[output->length - 1])
+                ) {
+ finalize:
+                        o_addchr(output, '\0');
+                        debug_print_list("expand_on_ifs", output, n);
+                        n = o_save_ptr(output, n);
                 }
-                if (!*str)  /* EOL - do not finalize word */
-                        break;
-                o_addchr(output, '\0');
-                debug_print_list("expand_on_ifs", output, n);
-                n = o_save_ptr(output, n);
-                str += strspn(str, G.ifs); /* skip ifs chars */
+                str += strspn(str, G.ifs); /* skip IFS chars */
         }
         debug_print_list("expand_on_ifs[1]", output, n);
         return n;
@@ -5270,11 +5288,13 @@ static NOINLINE int expand_vars_to_list(o_string *output, int n, char *arg)
                                         if (G.ifs[0])
                                                 o_addchr(output, G.ifs[0]);
                                 }
+                                output->has_quoted_part = 1;
                         }
                         break;
                 }
                 case SPECIAL_VAR_SYMBOL: /* <SPECIAL_VAR_SYMBOL><SPECIAL_VAR_SYMBOL> */
                         /* "Empty variable", used to make "" etc to not disappear */
+                        output->has_quoted_part = 1;
                         arg++;
                         cant_be_null = 0x80;
                         break;
@@ -5316,6 +5336,7 @@ static NOINLINE int expand_vars_to_list(o_string *output, int n, char *arg)
                                         val = NULL;
                                 }
                         } else { /* quoted $VAR, val will be appended below */
+                                output->has_quoted_part = 1;
                                 debug_printf_expand("quoted '%s', output->o_escape:%d\n", val,
                                                 !!(output->o_expflags & EXP_FLAG_ESC_GLOB_CHARS));
                         }
diff --git a/shell/hush_test/hush-vars/var_expand_on_ifs.right b/shell/hush_test/hush-vars/var_expand_on_ifs.right
new file mode 100644
index 000000000..2ed2069f7
--- /dev/null
+++ b/shell/hush_test/hush-vars/var_expand_on_ifs.right
@@ -0,0 +1,9 @@
+1 a b c
+2 a + b c
+3 a b c
+4 a  b c
+5 a  b c
+6 a b + c
+7 a b c
+8 a b  c
+9 a b  c
diff --git a/shell/hush_test/hush-vars/var_expand_on_ifs.tests b/shell/hush_test/hush-vars/var_expand_on_ifs.tests
new file mode 100755
index 000000000..a12ff8ec8
--- /dev/null
+++ b/shell/hush_test/hush-vars/var_expand_on_ifs.tests
@@ -0,0 +1,11 @@
+b=' b '
+e=''
+echo 1 a $b c
+echo 2 a +$b c
+echo 3 a $e$b c
+echo 4 a "$e"$b c
+echo 5 a ""$b c
+echo 6 a $b+ c
+echo 7 a $b$e c
+echo 8 a $b"$e" c
+echo 9 a $b"" c