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Provide opt-out feature=from_source to use serde_derive source #2580

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Provide opt-out feature=from_source to use serde_derive source #2580

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3cb80db
Add derive_compiled feature to force full compilation of derive
sagudev Aug 19, 2023
b12293e
Add cfg opt-in for the precompiled binary
pinkforest Aug 19, 2023
8d54439
Remove redundant features
pinkforest Aug 19, 2023
2e5bba0
Use opt-out instead and provide doc
pinkforest Aug 20, 2023
10a0210
Add simplified gating via build.rs
pinkforest Aug 20, 2023
81e79c1
Provide the opt-out gate without build.rs
pinkforest Aug 20, 2023
6bccee7
Fix the manifest gate for opt-out - thanks @sagudev
pinkforest Aug 20, 2023
5854820
Provide opt-out source compilation by feature `from_source
pinkforest Aug 20, 2023
23059f7
Provide another opt-out alternative w/ nightly with cross-compile
pinkforest Aug 20, 2023
cb23de9
Switch back to opt-out `feature=from_source` override.
pinkforest Aug 20, 2023
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19 changes: 19 additions & 0 deletions README.md
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Expand Up @@ -73,6 +73,25 @@ fn main() {
}
```

## Note about serde_derive Binary
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@oli-obk Sadly with either CARGO_ENCODED_RUSTFLAGS or given these .cargo/config neither work 😭

build.target

[build]
target = "wasm32-unknown-unknown"

[target.wasm32-unknown-unknown]
rustflags = ['--cfg=serde_derive_build="source"']

build.rustflags

[build]
rustflags = ['--cfg=serde_derive_build="source"']

Both set the options but it doesn't get seen at serde_derive procmacro level still

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To get rustflags into build script builds you need to use -Zhost-config and

[host]
rustflags = [...]

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Oh we have a winner! Thanks @Nemo157 ❤️

$ cargo -Zhost-config build
error: the -Zhost-config flag requires the -Ztarget-applies-to-host flag to be set
[foobar@localhost whatever]$ cargo -Ztarget-applies-to-host -Zhost-config build
   Compiling proc-macro2 v1.0.66
   Compiling unicode-ident v1.0.11
   Compiling whatever v0.1.0 (/home/foobar/code/whatever)
warning: "x86_64-unknown-linux-gnu"
   Compiling quote v1.0.33
   Compiling syn v2.0.29
   Compiling serde_derive v1.0.183 (/home/foobar/code/pushpush/serde/precompiled/serde_derive)
    Finished dev [unoptimized + debuginfo] target(s) in 2.84s
[foobar@localhost whatever]$ cargo -Ztarget-applies-to-host -Zhost-config build --target wasm32-unknown-unknown
   Compiling proc-macro2 v1.0.66
   Compiling unicode-ident v1.0.11
   Compiling whatever v0.1.0 (/home/foobar/code/whatever)
warning: "wasm32-unknown-unknown"
   Compiling quote v1.0.33
   Compiling syn v2.0.29
   Compiling serde_derive v1.0.183 (/home/foobar/code/pushpush/serde/precompiled/serde_derive)
    Finished dev [unoptimized + debuginfo] target(s) in 3.43s
[foobar@localhost whatever]$ cat .cargo/config
[host]
rustflags = ['--cfg=serde_derive_build="source"']

When were these -Z introduced ? 🤔 so we can document it as required version if using this opt-out ?

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I think using an unstable option for the opt-out is wrong. Also it still has the same issue of getting overriden by other ways to specify rustflags rather than appending to it.

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Thanks for trying it out

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It's fragile (or rather: easy to get wrong). Is there some solution to the resolver=2 problem?

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Good question need to build a test-case for it and prove it works I'll do that shortly.

EDIT: Yeah so I've replicated the resolver problem. Maybe we can just document this ?
This was the repro for it: https://github.com/pinkforest/serde_optout_unification_proof

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Alright with me. Is there something that can be done to ensure build dependencies also have the feature enabled?

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It seems I didn't clear the target properly between my repro previously

and it seems I can't replicate the problem with feature unification

e.g. I don't see anything wrong with the feature approach ?

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@Nemo157 Nemo157 Aug 20, 2023 •
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That's because it's a proc-macro crate, which is its own kind of dependency similar to a build-dependency, which is built for a single target: the host; so both the build-dep and normal-dep refer to the same proc-macro-dependency and their features get unified in it. A more accurate cargo tree would look like

top-bin v0.1.0 (/tmp/tmp.mNq6xeO1Ms/serde_optout_unification_proof/top-bin)
└── some-lib v0.1.0 (/tmp/tmp.mNq6xeO1Ms/serde_optout_unification_proof/some-lib)
    [proc-macro-dependencies]
    └── serde_derive v1.0.183 (proc-macro) (https://github.com/serde-rs/serde?rev=cb23de92e7f479139add329e8629eb3b179109f6#cb23de92)
        ├── proc-macro2 v1.0.66
        │   └── unicode-ident v1.0.11
        ├── quote v1.0.33
        │   └── proc-macro2 v1.0.66 (*)
        └── syn v2.0.29
            ├── proc-macro2 v1.0.66 (*)
            ├── quote v1.0.33 (*)
            └── unicode-ident v1.0.11
[build-dependencies]
└── some-build-lib v0.1.0 (/tmp/tmp.mNq6xeO1Ms/serde_optout_unification_proof/some-build-lib)
    [proc-macro-dependencies]
    └── serde_derive v1.0.183 (proc-macro) (https://github.com/serde-rs/serde?rev=cb23de92e7f479139add329e8629eb3b179109f6#cb23de92) (*)

EDIT: And by switching both dependencies to serde = { features = ["derive"] } instead of being direct you can see that there are two versions of serde built (because no (*)), one for host one for target, that both link against the same serde_derive (because (*)):

> cargo tree --features=from_source
warning: skipping duplicate package `serde_derive` found at `/home/nemo157/.cargo/git/checkouts/serde-1cbd136c2e06ab68/cb23de9/precompiled/serde_derive`
top-bin v0.1.0 (/tmp/tmp.mNq6xeO1Ms/serde_optout_unification_proof/top-bin)
└── some-lib v0.1.0 (/tmp/tmp.mNq6xeO1Ms/serde_optout_unification_proof/some-lib)
    └── serde v1.0.183 (https://github.com/serde-rs/serde?rev=cb23de92e7f479139add329e8629eb3b179109f6#cb23de92)
        [proc-macro-dependencies]
        └── serde_derive v1.0.183 (proc-macro) (https://github.com/serde-rs/serde?rev=cb23de92e7f479139add329e8629eb3b179109f6#cb23de92)
            ├── proc-macro2 v1.0.66
            │   └── unicode-ident v1.0.11
            ├── quote v1.0.33
            │   └── proc-macro2 v1.0.66 (*)
            └── syn v2.0.29
                ├── proc-macro2 v1.0.66 (*)
                ├── quote v1.0.33 (*)
                └── unicode-ident v1.0.11
[build-dependencies]
└── some-build-lib v0.1.0 (/tmp/tmp.mNq6xeO1Ms/serde_optout_unification_proof/some-build-lib)
    └── serde v1.0.183 (https://github.com/serde-rs/serde?rev=cb23de92e7f479139add329e8629eb3b179109f6#cb23de92)
        [proc-macro-dependencies]
        └── serde_derive v1.0.183 (proc-macro) (https://github.com/serde-rs/serde?rev=cb23de92e7f479139add329e8629eb3b179109f6#cb23de92) (*)


When using `serde_derive` either directly or via `serde` with `derive` feature.

Please note that `serde_derive` may be distributed from within pre-compiled binary
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To force building `serde_derive` from source, an override is provided:

```sh
RUSTFLAGS='--cfg serde_derive_build="source"'
```

Alternatively in `~/.cargo/config`:
```toml
rustflags = ['--cfg serde_derive_build="source"']
```

More info from [cargo reference](https://doc.rust-lang.org/cargo/reference/config.html#buildrustflags).

## Getting help

Serde is one of the most widely used Rust libraries so any place that Rustaceans
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2 changes: 1 addition & 1 deletion precompiled/serde_derive/Cargo.toml
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Expand Up @@ -21,7 +21,7 @@ deserialize_in_place = []
[lib]
proc-macro = true

[target.'cfg(not(all(target_arch = "x86_64", target_os = "linux", target_env = "gnu")))'.dependencies]
[target.'cfg(not(all(serde_derive_build = "precompiled", target_arch = "x86_64", target_os = "linux", target_env = "gnu")))'.dependencies]
proc-macro2 = "1"
quote = "1"
syn = "2.0.28"
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14 changes: 12 additions & 2 deletions precompiled/serde_derive/src/lib.rs
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Expand Up @@ -15,8 +15,18 @@

#![doc(html_root_url = "https://docs.rs/serde_derive/1.0.183")]

#[cfg(not(all(target_arch = "x86_64", target_os = "linux", target_env = "gnu")))]
#[cfg(all(
serde_derive_build = "source",
target_arch = "x86_64",
target_os = "linux",
target_env = "gnu"
))]
include!("lib_from_source.rs");

#[cfg(all(target_arch = "x86_64", target_os = "linux", target_env = "gnu"))]
#[cfg(all(
not(serde_derive_build = "source"),
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target_arch = "x86_64",
target_os = "linux",
target_env = "gnu"
))]
include!("lib_precompiled.rs");