[Bug translator/20056] New: improve parse error message involving expect_op("...")

["fche at redhat dot com" <sourceware-bugzilla at sourceware dot org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=20056

            Bug ID: 20056
           Summary: improve parse error message involving expect_op("...")
           Product: systemtap
           Version: unspecified
            Status: NEW
          Severity: normal
          Priority: P2
         Component: translator
          Assignee: systemtap at sourceware dot org
          Reporter: fche at redhat dot com
  Target Milestone: ---

We have a number of constructs where peek_op() is followed by expect_op(), as
alternatives.  For example:

probe begin { println("2" }  }
                          ^ this is should be a ')' or ','

but the error message indicates only that a ',' was expected.  That's
because the parser::expect_op() doesn't take alternatives.  Maybe we need
an expect_op variant that takes a list of operators that are acceptable
there (like expect_known - but expressing alternation); that'd mean
reworking the control structures that look like

03826                   // Consume any subsequent arguments.                    
03827                   while (!peek_op (")"))
03828                     {
03829                       expect_op(",");
03830                       expression *e = parse_expression ();
03831                       fmt->args.push_back(e);
03832                     }
.....
03880           expect_op(")");

to consume "," or ")" early on.


A less coding-intensive alternative would be to give expect_op an extra
explanation-text parameter that expect_known could just append to its
PARSE_ERROR.

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