--dep-info doesn't reflect real output filename when using -c or --emit-llvm

[yuriks]

Usually, --dep-info would be used to generate dependency information to be included in a Makefile. However, when using the -c or --emit-llvm flags, along with --out-dir, the generated info doesn't have the correct names for the output files. When -c is used to compile foo.rs, it's output as foo.o, and when --emit-llvm is used, as foo.bc. On both cases the dependency info lists the full library name as it would've been output if none of the option were given. For example:

rustc --emit-llvm --staticlib --out-dir obj/ -L obj/ --dep-info obj/main.d src/main.rs

Outputs obj/main.bc, but obj/main.d has the following contents:

obj/libmain-66af34bf-0.0.a: src/main.rs src/efi.rs

The dependency info should be change to reflect the name of the files actually being output by the compiler for the given command.

EDIT: Realized it also doesn't track any external modules used by the crate as dependencies. (In this case libcore-2e829c2f-0.0.rlib and libextensions-d5bbcef2-0.0.so.) This might be on purpose, but doesn't seem ideal to me.

[alexcrichton]

I imagine that the restructuring of #7791 will address much of this. Right now dep-info doesn't track any dependencies, and I think that's more of a job for a package manager rather than rustc itself. I don't know what the makefile target dependency would be named. In theory it could be libstd-...rlib, but that doesn't actually correspond to anything because you'd then have to make a target saying that that points to (and things go on...)

[SiegeLord]

I don't know what the makefile target dependency would be named. In theory it could be libstd-...rlib, but that doesn't actually correspond to anything because you'd then have to make a target saying that that points to (and things go on...)

This also doesn't work if the dependency is also built as part of the build process. E.g. a library might have some examples which depend on the library being built. --dep-info will not be able to return that dependency because the library wasn't built yet and therefore the file doesn't exist yet.