Significantly slower compilation times after #3969

[tomusdrw]

I've noticed an increased compilation time recently and bisected the commit that caused it.
The issue is not super severe on a powerful server (8 x i9), the compilation time goes from 6m18s to 8m52s, but on a decent laptop it goes from 17m13s to 25m17s. It seems consistently increased by ~30%.

It's not very obvious for me what change exactly in #3969 causes this, it would be good to investigate.

[gnunicorn]

Confirming. Seeing the same issue here from ~13min -> ~16:50min ...

cargo clean && time cargo build:

@ 1fa9b541a409228cde567d6118afa4f517b3078f:

    Finished dev [unoptimized + debuginfo] target(s) in 12m 56s
cargo build  3809,30s user 169,40s system 512% cpu 12:57,04 total


----

@ fc563644f2d36af9cdd26b0f8125cb5da2a6180e:

    Finished dev [unoptimized + debuginfo] target(s) in 16m 49s
cargo build  5060,85s user 227,63s system 521% cpu 16:54,45 total

----

[bkchr]

I have looked at the build graph before and after the change.

Before this commit we had the following targets when running cargo build:

substrate 2.0.0 (bin "substrate")

After the commit, we have the following targets:

srml-contracts 2.0.0 (lib)
node-cli 2.0.0 (bin "substrate", lib)
substrate-cli 2.0.0 (lib)
transaction-factory 0.0.1 (lib)
substrate-primitives 2.0.0 (lib)
srml-support 2.0.0 (lib)
node-rpc-client 2.0.0 (bin "node-rpc-client")
srml-session 2.0.0 (lib)
substrate-session 2.0.0 (lib)
node-executor 2.0.0 (lib)
substrate-test-runtime-client 2.0.0 (lib)
substrate-network 2.0.0 (lib)
srml-authority-discovery 0.1.0 (lib)
substrate-service 2.0.0 (lib)
srml-staking 2.0.0 (lib)
substrate-rpc-primitives 2.0.0 (lib)
node-rpc 2.0.0 (lib)
substrate-test-client 2.0.0 (lib)
substrate-offchain 2.0.0 (lib)
substrate-offchain-primitives 2.0.0 (lib)
substrate-consensus-common 2.0.0 (lib)
srml-support-test 2.0.0 (lib)
srml-grandpa 2.0.0 (lib)
substrate-consensus-aura 2.0.0 (lib)
sr-primitives 2.0.0 (lib)
srml-offences 1.0.0 (lib)
srml-democracy 2.0.0 (lib)
srml-utility 2.0.0 (lib)
substrate-consensus-babe 2.0.0 (lib)
substrate-consensus-rhd 2.0.0 (lib)
srml-transaction-payment-rpc-runtime-api 2.0.0 (lib)
sr-std 2.0.0 (lib)
substrate-inherents 2.0.0 (lib)
substrate-authority-discovery-primitives 2.0.0 (lib)
... (probably every crate in the workspace)

It seems that we just need to run cargo build -p node-runtime, when we really want to find the commit that blow up the compilations times :D

[tomaka]

As mentioned, cargo build didn't compile for instance node-template before. Now it does.

[eddyb]

Looking at the previous comments and the Cargo.toml changes in #3969, it seems like cargo build before is equivalent to cargo build -p node-cli after the change.

Would cargo build -p node-cli be considered a viable replacement?

If not, default-members = ["node/cli"] could be added to [workspace] (see relevant documentation) to restore the original behavior for cargo build, cargo run, etc.

[bkchr]

Yeah, I think its time to close this issue. The reported slowdown was a false positive.