ash: remove arithmetic expansion collapsing at parse time

Collapsing arithmetic expansion is incorrect when the inner arithmetic
expansion is a part of a parameter expansion.

Test case:
   unset a
   echo $((3 + ${a:=$((4 + 5))}))
   echo $a
Old result:
   12
   (4 + 5)
New result:
   12
   9

Based on commit bb777a6 from git://git.kernel.org/pub/scm/utils/dash/dash.git
by Herbert Xu

function                                             old     new   delta
readtoken1                                          3180    3163     -17

Signed-off-by: Ron Yorston <rmy@pobox.com>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

3 files changed, 11 insertions, 12 deletions

diff --git a/shell/ash.c b/shell/ash.c
index ee7642a64..33a477d80 100644
--- a/shell/ash.c
+++ b/shell/ash.c
@@ -11316,9 +11316,9 @@ readtoken1(int c, int syntax, char *eofmark, int striptabs)
                                 parenlevel--;
                         } else {
                                 if (pgetc() == ')') {
+                                        c = CTLENDARI;
                                         if (--arinest == 0) {
                                                 syntax = prevsyntax;
-                                                c = CTLENDARI;
                                         }
                                 } else {
                                         /*
@@ -11809,18 +11809,12 @@ parsearith: {
         if (++arinest == 1) {
                 prevsyntax = syntax;
                 syntax = ARISYNTAX;
-                USTPUTC(CTLARI, out);
-                if (dblquote)
-                        USTPUTC('"', out);
-                else
-                        USTPUTC(' ', out);
-        } else {
-                /*
-                 * we collapse embedded arithmetic expansion to
-                 * parenthesis, which should be equivalent
-                 */
-                USTPUTC('(', out);
         }
+        USTPUTC(CTLARI, out);
+        if (dblquote)
+                USTPUTC('"', out);
+        else
+                USTPUTC(' ', out);
         goto parsearith_return;
 }
 #endif
diff --git a/shell/ash_test/ash-vars/var-do-not-collapse-arithmetic-expansion-at-parse-time.right b/shell/ash_test/ash-vars/var-do-not-collapse-arithmetic-expansion-at-parse-time.right
new file mode 100644
index 000000000..81a15855c
--- /dev/null
+++ b/shell/ash_test/ash-vars/var-do-not-collapse-arithmetic-expansion-at-parse-time.right
@@ -0,0 +1,2 @@
+12
+9
diff --git a/shell/ash_test/ash-vars/var-do-not-collapse-arithmetic-expansion-at-parse-time.tests b/shell/ash_test/ash-vars/var-do-not-collapse-arithmetic-expansion-at-parse-time.tests
new file mode 100755
index 000000000..e97a08a57
--- /dev/null
+++ b/shell/ash_test/ash-vars/var-do-not-collapse-arithmetic-expansion-at-parse-time.tests
@@ -0,0 +1,3 @@
+unset a
+echo $((3 + ${a:=$((4 + 5))}))
+echo $a