Usage of cargo tree to debug unnecessary rebuilds

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#1

I have workspace and two particular crates in it: lib1 and lib2.
And lib2 depend on lib1. The problem is that when I run
cargo build -p lib2 and then cargo build -p lib1 the rebuild happens.
I mean lib1 build during build of lib2 and then it rebuilds again after cargo build -p lib1.

My only idea is features, I mean the one of dependency of lib1 should have feature set1,
when I run cargo build -p lib1 and feature set2 when build lib2, and feature set1 != feature set2.
But which one?

I try cargo +beta tree -e features -p for lib1 and lib2,
but I can not automate comparing of features set,
and manual checking is showing that they are the same.
May be I missing something, and for example cargo +beta tree -e features not work as expecting,
and doesn't show set of feature for particular crate, instead it shows feature set for whole tree?

#2

What's your workspace's Cargo.toml look like

#3

Something like this:

[workspace]
members = ["lib1", "lib2"]

[profile.release]
debug = true

[profile.dev.build-override]
opt-level = 2

[profile.test.build-override]
opt-level = 2
#4

I think this does come down to features, does lib2 use any features that are different from the default feature set of lib1?

#5

I think this does come down to features, does lib2 use any features that are different from the default
feature set of lib1?

That is my question, why you asking me? :slight_smile:

Directly in Cargo.toml of lib1 and lib2 - no, but indirectly who knows,
I can not find way how to get from cargo +beta tree the list, with crates and features instead of tree,
to run just diff to compare all dependicies.

#6

I found way to get list: cargo +beta tree --prefix none, but looks like deps are the same. This drive me nuts, though I not completly sure, because of cargo tree print each feature on the new line,
instead of near crate name.

#7

I found culprit: it is chrono and num-traits.
chrono use

num-traits = { version = "0.2", default-features = false }

while other dependency rstar use with default-features on.

But I am not sure what is really going on,

looks like:

[features]
default = ["std"]
std = []
i128 = []

And I build std code anyway, why cargo think that num-traits = default = false, and num-traits = deafult = true is the different thing?
For std build it should be the same thing?

#8

Cargo doesn't know anything special about that "std" feature, and treats it just like any other. So in building one of the libraries, it sees a subset of crates that include num-traits without default features, so it builds without. In your other library it sees num-traits required with default features enabled, so it does.

One way to see this is cargo build --verbose, and look for --cfg for the feature. I agree it would be nice to get cargo tree to show this though.