When all the conditions are met:

• split-debuginfo=packed|unpacked, and
• -Zremap-path-scope=object is used,
• have at least one extern crate (dependency)

In the binary, DW_AT_GNU_dwo_name symbols from extern crates are not remapped. I haven't traced down why yet.

cc @Urgau, let me know if you need a better repro.

For the record: I tried reproducing the issue with rustc and failed to do. Maybe a Cargo specific thing.

$ rustc +nightly -C split-debuginfo=unpacked -g --remap-path-prefix=/tmp/split-rustc/=/remapped/path dep.rs --out-dir /tmp/split-rustc/target/ --crate-type lib -Zremap-path-scope=object
$ rustc +nightly -C split-debuginfo=unpacked -g --remap-path-prefix=/tmp/split-rustc/=/remapped/path main.rs --out-dir /tmp/split-rustc/target/ --extern=dep=/tmp/split-rustc/target/libdep.rlib -Zremap-path-scope=object
$ llvm-dwarfdump target/main | rg DW_AT_GNU_dwo_name
              DW_AT_GNU_dwo_name        ("/remapped/path/target/main.main.62a074bc4c4ee7d3-cgu.0.rcgu.dwo")
              DW_AT_GNU_dwo_name        ("/remapped/path/target/dep.dep.45866446ec9e29d2-cgu.0.rcgu.dwo")

I see something interesting in the Cargo test regarding the dependency, I don't think you are remapping the --out-dir, which would explain why the path isn't remapped, as I assume that the dwo/dwp would be in the target/ directory which isn't covered by those --remap-path-prefix (in the dependency rustc args).

    --remap-path-prefix=[ROOT]/home/.cargo/registry/src= \
    --remap-path-prefix=[..]/lib/rustlib/src/rust=/rustc/[..]

To me it seems like you are missing a --remap-path-prefix for the build.build-dir.

Really thank you very much Urgau! Excellent debugging skill!