Run dsymutil less on OSX

[alexcrichton]

Instead of running dsymutil for all builds, this changes it to only run the program for debug builds.

Closes #3495

[metajack]

I would be thrilled to get rid of this warning! 🐤

[jdm]

I'm pretty confident that this is necessary when debug symbols are generated.

[alexcrichton]

@jdm, do you have an example that I could test with? I'm having trouble getting any debug symbols at all (even with -Z extra-debug-info), so I may just not know what I'm doing.

[jdm]

@alexcrichton Why not try any of the debuginfo tests?

[alexcrichton]

It looks like debuginfo tests don't work at all on darwin. There's a few things that are all hindering it:

• gdb was removed from 10.9 by default
• debuginfo tests are all disabled on darwin (something about gdb needing root)
• If you run the debuginfo tests on this pull request, they all fail
• If you run the debuginfo tests before this pull request, they all fail.

Here's what I was getting: https://gist.github.com/alexcrichton/7256495. Note that I created the .dSYM folder manually in the middle (and got the same error both times)

[jdm]

Ok, I'll bust out my 10.6 machine tomorrow and see if I can spot a behaviour difference with this PR applied.

[alexcrichton]

From some small tests with C though, it looks like you're right in that the dSYM folder is used by gdb somehow (I get extra debugging symbols when the folder exists as opposed to when it doesn't).

I'm still not convinced though that our usage of dsymutil is useful at all. I looks like the warning: no debug symbols in executable is completely legitimate because maybe that's why darwin can't debug any rust executables...

[larsbergstrom]

@alexcrichton If you're still having trouble with debugging, you can download the Command Line Tools for Mountain Lion (from XCode 4.6.3, not 5.0) and mount it. Rather than installing, cd into /Volumes/Command Line Tools (Mountain Lion)/Packages and then install DeveloperToolsCLI.pkg, which will drop a less-not-working version of gdb in /usr/bin. In particular, that version will be able to set breakpoints and annotate frames with their source locations.

[jdm]

On 10.6 the warning does not appear when building rust programs with debug symbols enabled. So I'm pretty confident that we could solve the bit that annoys people by just not running dsymutil when no debug symbols are requested.

[alexcrichton]

I've updated to only run dsymutil in debug builds (those with -Z extra-debug-info on the command line). This still prints the warning on 10.9 (and I think 10.8 as well), so I'm curious why this works on 10.6 and not the current version. Regardless, that's a bug for another time.

[jdm]

Note that my last comment about the warning came from my memory of nearly two years ago; I'll investigate when I'm around my 10.6 machine this weekend.

[alexcrichton]

r? @jdm

[catamorphism]

@jdm @alexcrichton Can this merge?