Another Rust operator precedence bug

My earlier patch to fix PR rust/29859 introduced a new operator
precedence bug in the Rust parser.  Assignment operators are
right-associative in Rust.  And, while this doesn't often matter, as
Rust assignments always have the value (), still as a matter of
principle we should get this correct.

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

diff --git a/gdb/rust-parse.c b/gdb/rust-parse.c
index 337927219d55af668674b03fc47d39e10b746a89..f28514ab2dafd22182d77f282c87b665683e9c3c 100644 (file)
--- a/gdb/rust-parse.c
+++ b/gdb/rust-parse.c
@@ -1344,6 +1344,8 @@ rust_parser::parse_binop (bool required)
   OPERATION (ANDAND, 2, logical_and_operation) \
   OPERATION (OROR, 1, logical_or_operation)
 
+#define ASSIGN_PREC 0
+
   operation_up start = parse_atom (required);
   if (start == nullptr)
     {
@@ -1376,7 +1378,7 @@ rust_parser::parse_binop (bool required)
          compound_assign_op = current_opcode;
          /* FALLTHROUGH */
        case '=':
-         precedence = 0;
+         precedence = ASSIGN_PREC;
          lex ();
          break;
 
@@ -1398,7 +1400,11 @@ rust_parser::parse_binop (bool required)
          break;
         }
 
-      while (precedence <= operator_stack.back ().precedence
+      /* Make sure that assignments are right-associative while other
+        operations are left-associative.  */
+      while ((precedence == ASSIGN_PREC
+             ? precedence < operator_stack.back ().precedence
+             : precedence <= operator_stack.back ().precedence)
             && operator_stack.size () > 1)
        {
          rustop_item rhs = std::move (operator_stack.back ());

diff --git a/gdb/testsuite/gdb.rust/simple.exp b/gdb/testsuite/gdb.rust/simple.exp
index 3a010f30ea66bdbb8fd3cdcd3d29c7351ad7b44a..0fb06af9380e9d8dd0416ccce035895183d4feb5 100644 (file)
--- a/gdb/testsuite/gdb.rust/simple.exp
+++ b/gdb/testsuite/gdb.rust/simple.exp
@@ -416,3 +416,6 @@ if {[lindex $v 0] >= 8} {
 # The new parser introduced an operator precedence bug.
 gdb_test "print 5 * 7 / 5" " = 7"
 gdb_test "print 4 - 3 - 1" " = 0"
+
+# Another operator precedence bug.
+gdb_test "print \$one = \$two = 75" " = \\\(\\\)"