[RFA] Emit a warning for ineffective set VAR = EXP command

[Tristan Gingold <gingold@adacore.com>]

Hi,

the 'set VAR=EXP' command is a real trap for Ada (and maybe other languages such as Pascal users), because the '=' is interpreted as BINOP_EQUAL instead of BINOP_ASSIGN.  You often do not realize that the current language is not C where you are using to command for registers or convenience variables.

I simply propose to emit a warning if the expression is not an assignment (or a comma expression).

No regressions on x86_64 GNU/Linux.

Ok for trunk ?

2012-04-27  Tristan Gingold  <gingold@adacore.com>

	* printcmd.c (set_command): Emit a warning if the expression is not
	an assignment.

diff --git a/gdb/printcmd.c b/gdb/printcmd.c
index d441dfe..79e38f2 100644
--- a/gdb/printcmd.c
+++ b/gdb/printcmd.c
@@ -1080,6 +1080,12 @@ set_command (char *exp, int from_tty)
   struct cleanup *old_chain =
     make_cleanup (free_current_contents, &expr);
 
+  if (expr->nelts >= 1
+      && expr->elts[0].opcode != BINOP_ASSIGN
+      && expr->elts[0].opcode != BINOP_ASSIGN_MODIFY
+      && expr->elts[0].opcode != BINOP_COMMA)
+    warning (_("Expression is not an assignment (and might have no effect)"));
+
   evaluate_expression (expr);
   do_cleanups (old_chain);
 }