[dmd-internals] Memory Leak

[Daniel Murphy]

This isn't a bug, dmd does not free memory (with some exceptions), it
assumes a garbage collector is present.

On Sun, Nov 11, 2012 at 6:26 PM, David Held <dmd at wyntrmute.com> wrote:

> While writing some unit tests for Dsymbol, I noticed that
> Dsymbol::toPrettyChars() leaks almost everywhere.  In the simple case where
> a symbol has no parent, it just returns toChars(), which does not leak (at
> least I don't think it does).  However, whenever the symbol has a parent
> (or many), the returned string is composed, which requires that it is
> allocated dynamically (via mem.malloc()). Even though the caller owns the
> string, and even though it is called dozens of times, it appears that none
> of the callers are properly disposing of the result.  Unfortunately, it is
> a bit messy to do so, because you must free the string *only* if it has a
> parent, which is a pretty bad implementation leak, IMO.  Here is a place
> where std::string would have worked nicely. ;)
>
> I suspect this has gone unnoticed because A) dmd probably has a relatively
> small memory footprint to begin with or B) most invokations of
> toPrettyChars() are during a call to error(), so the compiler is about to
> quit anyway.  What to do?  Leave it alone?  Try to fix it?  Note that
> fixing it without changing toPrettyChars() would require adding 2-3 lines
> of code to almost every call.
>
> Dave
>
>
> P.S.  Incidentally, this bug is one that is not easily caught with
> assertions (where would you place the assert that the string was freed?).
>  Fortunately, it is caught by unit testing; but it could also have been
> caught by documenting that the caller owns the string.  This is why you
> really want all 3 approaches to code quality.
>
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