[Bug c++/15787] New: Poor error message

[igodard at pacbell dot net]

The actual problem in the test case is a missing "}", which fact appears nowhere in the message. The message talks about a "primary-expression", which is technically correct but reflects a compiler- and formal syntax-centric view. A user will in general neither know nor care what a primary-expression is; he wants to know what's wrong in terms of his code. The education, experience and knowledge of compiler users is *not* the same as of compiler writers :-)

The great bulk of syntactic arrors are bracket errors or missing semis. Now that you have a recursive descent parser, it is trivial to have the compiler suggest a plausible fix for these. For example, have the compiler keep a side stack of brackets entered and not exited. If you get a closer that matches the *second* item on the stack then your message offers the closers of the *top* item on the stack as suggestions. 

In the case of this code, the top item is "{" and the second is "if". When the parse error happens the cursor is on "else", which matches the "if". So you produce a message "expected primary-expression before 'else'; possibly a missing '}'?". This same stack can be used for repair.

Ivan

-- 
           Summary: Poor error message
           Product: gcc
           Version: 3.4.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: igodard at pacbell dot net
                CC: gcc-bugs at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=15787