Suggestion: Object filenames should be fully-qualified module names

[Bill Baxter]

Yes please!
I've spent the last week sending mail back and forth with some poor soul 
who was trying to use my Luigi GUI lib, but couldn't seem to link it for 
some reason.

Finally today I tracked it down to the only difference between my 
working build file and his not working one being his use of the -od 
flag.  I didn't know what -od was for, but after figuring it out, I 
remembered this thread.  -od flag and .obj files were silently being 
overwritten with other obj files of the same name.

EVIL!

Isn't Kirk's proposal also the way Java compilers do it?  I seem to 
recall a bunch of foo.bar.baz.class files appearing last time I played 
with Java.

--bb

Kirk McDonald wrote:
> I originally heard this idea proposed by Gregor Richards in #d, and I
> think it should become DMD's default behavior. If it is not the default 
> behavior, then it should at least be available as an option.
> 
> Perhaps my biggest grievance with both the DMD and GDC compilers is
> their handling of object files. DMD's default behavior is to dump all
> object files into the current directory. If the -od option is specified,
> the object files will be placed into the specified directory instead. If
> -op is specified, the object files are placed alongside the original 
> source files.
> 
> The default behavior and using -od on its own both fail if any two 
> source files in the project have the same name, even if they are in 
> different packages. Using -op by itself is unappealing for two reasons:
> 
> 1) It is not unreasonable to expect a system to place libraries in 
> directories to which the user does not have write access. Placing object 
> files alongside the source files would therefore fail.
> 
> 2) It pollutes the source directories with object files. I much prefer 
> keeping my object files somewhere to the side, in a designated "build" 
> directory. This makes keeping projects in version control much easier, 
> as I can simply exclude the one directory to keep object files out of 
> version control.
> 
> Specifying both -op and -od causes things to get a little more 
> interesting. Take the following:
> 
> test.d
> testpkg
>   test.d
> 
> // test.d
> module test;
> import testpkg.test : foo;
> void main() {
>     foo();
> }
> 
> // testpkg/test.d
> module testpkg.test;
> import std.stdio : writefln;
> void foo() { writefln("foo"); }
> 
> If we compile with this:
> 
> $ dmd test.d testpkg/test.d -op -odbuild
> 
> The "build" directory has the following structure:
> 
> build
>   test.obj
>   testpkg
>     test.obj
> 
> This is all and well. However, if we compile like this:
> 
> $ dmd test.d /path/to/testpkg/test.d -op -odbuild
> 
> Then DMD doesn't know what to do, and it places testpkg/test.obj 
> alongside the source file. (More specifically, the full path is "joined" 
> to the path specified by -od, which works out to just being the full path.)
> 
> This ambiguity can be disposed of if an object file's name is its 
> fully-qualified module name. If this were true, then we could just say
> 
> $ dmd test.d testpkg/test.d -odbuild
> 
> and the result would be the build directory looking like this:
> 
> build
>   test.obj
>   testpkg.test.obj
> 
> I find this very clean and simple. Since the compiler fails anyway if 
> two modules have the same name, there should not ever be overlaps in 
> object file names with this scheme. The -op option could probably be 
> safely deprecated.
> 
> As someone pointed out in #d, this would fail on NTFS if the module's 
> fully-qualified name exceeds 255 characters. Though I cannot recall ever 
> using a module whose name even approached that limit, this should be 
> solved in most cases by truncating the filename at the start. 
> (Hopefully, the last 255 characters are unique.) If the object file 
> would fail to be unique even then, it can probably be safely declared 
> the coder's fault for using a stupid naming scheme.
>