[Bug rust/29859] New: Printing rust expressions with simple arithmetic gets wrong result

["bpeeluk at yahoo dot co.uk" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=29859

            Bug ID: 29859
           Summary: Printing rust expressions with simple arithmetic gets
                    wrong result
           Product: gdb
           Version: HEAD
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: rust
          Assignee: unassigned at sourceware dot org
          Reporter: bpeeluk at yahoo dot co.uk
  Target Milestone: ---

The rust parser doesn’t seem to handle expressions with multiple binary
operators but no parentheses correctly:

(gdb) p 3 - 2 - 1
$1 = 2
(gdb) p 5 * 4 / 3
$2 = 5

It seems to be calculating the answer as if the operators were right-to-left:

(gdb) p 3 - (2 - 1)
$3 = 2
(gdb) p 5 * (4 / 3)
$4 = 5

But it should be doing left-to-right:

(gdb) p (3 - 2) - 1
$5 = 0
(gdb) p (5 * 4) / 3
$6 = 6

I tested this with the current git master which is c8ea5e409b02cf7fa8.

Another way to test this could be to add the following lines to the bottom of
gdb/testsuite/gdb.rust/expr.exp:

gdb_test "print 3 - 2 - 1" " = 0"
gdb_test "print 5 * 4 / 3" " = 6"

and then run:

( cd gdb/testsuite && runtest gdb.rust/expr.exp )

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