Kcov is reporting 100% for Rust lib even though some methods are not covered

Question

I'm trying to add code coverage to my rust library. It's reporting that it is covered 100%, but when I look at the report a lot of lines are not counted: https://codecov.io/gh/JelteF/defaultmap/src/c878e108c61f270718c909e1500c4c2e865a33d1/src/lib.rs#L93...106

What is the reason for this and is it possible to fix this? I have already tried setting RUSTFLAGS to "-C link-dead-code" as suggested in this answer: https://stackoverflow.com/a/38371687/2570866 That didn't help however.

Answer 1

This is a known issue (https://github.com/rust-lang/rust/issues/39293), with no solutions implemented yet. Generics in Rust are similar to templates in C++, if you don't use the generic function, no code will be generated at all. Indeed those functions are not present:

$ nm target/debug/defaultmap-2fd0c3085042f647 | grep DefaultHashMap | cargo demangle
000000000002c350 t <defaultmap::hashmap::DefaultHashMap<K, V> as core::ops::Index<KB>>::index::h14fb5e24128b7e47
000000000002c390 t <defaultmap::hashmap::DefaultHashMap<K, V> as core::ops::Index<KB>>::index::h5c00e602e45f6925
000000000002c3d0 t <defaultmap::hashmap::DefaultHashMap<K, V> as core::ops::Index<KB>>::index::hc5dfb7b3478d945a
000000000002c420 t <defaultmap::hashmap::DefaultHashMap<K, V> as core::ops::IndexMut<K>>::index_mut::h8b298bf16464a070
000000000002c470 t <defaultmap::hashmap::DefaultHashMap<K, V> as core::ops::IndexMut<K>>::index_mut::hcc509def35f89759
000000000002bfc0 t <defaultmap::hashmap::DefaultHashMap<K, V>>::get::h6a0f4cb5c61c67e8
000000000002c060 t <defaultmap::hashmap::DefaultHashMap<K, V>>::get::ha5fdb528b5dd94a5
000000000002c110 t <defaultmap::hashmap::DefaultHashMap<K, V>>::get::hc1a5643986209ba6
000000000002c1b0 t <defaultmap::hashmap::DefaultHashMap<K, V>>::get_mut::h14f0ded6ba3206f3
000000000002c2a0 t <defaultmap::hashmap::DefaultHashMap<K, V>>::get_mut::h6ea36d917e778099
000000000002eaf0 t <defaultmap::hashmap::DefaultHashMap<K, V> as core::fmt::Debug>::fmt::h2cefa624bd18fcfe
000000000002e9e0 t <defaultmap::hashmap::DefaultHashMap<K, V> as core::default::Default>::default::h0b736edcd6ac228a
000000000002ea60 t <defaultmap::hashmap::DefaultHashMap<K, V> as core::default::Default>::default::hd09b7abe1e63b94f

I think, for now, the only practical solution is to manually inspect the coverage report, and add back missing tests for the ignored functions.