Assume `build.rs` in the same directory as `Cargo.toml` is a build script (unless explicitly told not to) #3361

pwoolcoc · 2016-12-02T19:22:16Z

So, in May I posted a question in the #cargo IRC room: https://botbot.me/mozilla/cargo/2016-05-26/?msg=66770068&page=1

This PR does what was discussed there. If cargo sees a build.rs in the same directory as the Cargo.toml, it will assume build.rs is a build script unless package.build = false. Just for completeness I also made build = true mean the same as build = "build.rs" but I'm not sure if that is okay or not.

rust-highfive · 2016-12-02T19:22:27Z

r? @brson

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This change makes cargo assume `build = "build.rs"` if there is a `build.rs` file in the same directory as `Cargo.toml`. However, you can set `build = false` to prevent this.

steveklabnik · 2016-12-02T21:08:50Z

yessssssss i asked @alexcrichton about this a while back and he was 👍 at the time. I think this is great.

pwoolcoc · 2016-12-02T21:16:17Z

src/cargo/util/toml.rs

@@ -540,7 +546,11 @@ impl TomlManifest {
        }

        // processing the custom build script
-        let new_build = project.build.as_ref().map(PathBuf::from);
+        let manifest_file = util::important_paths::find_root_manifest_for_wd(None, &layout.root)


Looking this over again, I'm wondering if I actually have to do this, or if I can just assume base_dir == layout.root?

pwoolcoc · 2016-12-02T21:17:11Z

@steveklabnik :) everyone who commented in #cargo seemed to support it, but it was a while ago, so I'm hoping the support is still there.

alexcrichton · 2016-12-02T23:27:31Z

Thanks for the PR! The implementation looks great to me as well.

My only hesitation here is that we risk breaking projects when this lands. Projects can fix builds with build = false in Cargo.toml, but I think that'll end up getting rejected on the stable/beta channels. In that sense, if a crate has a build.rs but it's not a build script, then you can't keep that layout and continue to work on stable/beta/nightly.

I'd also want to think through the backcompat story here with all crates published on crates.io. It may be worth doing a survey there to see how many crates have a build.rs file which isn't a build script, if any. If that number is 0, then our lives are much easier! If that number is greater, we may want to proactively reach out to authors to head off the breakage.

@pwoolcoc would you be willing to scrape crates.io and test for build.rs scripts in roots which aren't build scripts?

pwoolcoc · 2016-12-03T00:41:59Z

@alexcrichton sure, I can do that.

Would it preferable to change it slightly to only print a deprecation warning when there is a build.rs that isn't a build script, and land the rest of the change after a couple releases?

steveklabnik · 2016-12-03T01:09:44Z

I haven't read the patch, but to be clear, the way in which this would break is if someone had specially configured a `build.rs` at the top level to be source, correct? I'd imagine this would be very, very tiny, given almost all source files are in `src`, generally speaking.

…

On Fri, Dec 2, 2016 at 7:42 PM, Paul Woolcock ***@***.***> wrote: @alexcrichton <https://github.com/alexcrichton> sure, I can do that. Would it preferable to change it slightly to only print a deprecation warning when there is a build.rs that isn't a build script, and land the rest of the change after a couple releases? — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub <#3361 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AABsik8uKsZgLWAKElRYJ8Opr2UGLQtcks5rELrYgaJpZM4LC5aC> .

pwoolcoc · 2016-12-03T03:02:26Z

@steveklabnik yea, if someone has a crate with a build.rs file in the same directory as Cargo.toml, and the build.rs is not a build script, then this patch will try to treat it as a build script. The user would have to add build = false to the package section of their Cargo.toml in order to prevent this.

alexcrichton · 2016-12-03T20:22:52Z

@pwoolcoc

Would it preferable to change it slightly to only print a deprecation warning when there is a build.rs that isn't a build script, and land the rest of the change after a couple releases?

If we have no existing build.rs scripts that aren't build scripts, I think we can avoid this. Otherwise yeah I think we'll need to take this route. I figure we should just get a handle on the situation first so we can categorize our options.

@steveklabnik

the way in which this would break is if someone had specially configured a build.rs at the top level to be source, correct?

Indeed! I agree that it should be rare if ever, but I just want to make sure!

pwoolcoc · 2016-12-05T20:22:51Z

@alexcrichton ok, I'm finishing up the few crates that my script couldn't automatically check, but here are the preliminary results. There are 12 crates that have a build.rs in the same directory as a Cargo.toml, without an accompanying build = "build.rs" in the Cargo.toml file. However, all of the build.rs are build scripts that are just not being used. None of them are actually source code for the project. However, this still means that their builds might break from this change.

The 12 crates are:

pcb https://github.com/ubsan/pcb/pcb-c
libsqlite3-sys https://github.com/jgallagher/rusqlite
sphinxad-sys https://github.com/TrionProg/sphinxad-sys
webkitten https://github.com/kattrali/webkitten
core-nightly https://github.com/rust-lang/rust (lol)
al-sys https://github.com/jpernst/alto/
roboime-next https://github.com/roboime/roboime-next/
hoodlum https://github.com/tcr/hoodlum
static-server https://github.com/DenisKolodin/static-server
strcursor https://github.com/DanielKeep/strcursor
rustproof https://github.com/Rust-Proof/rustproof
openal-rs https://github.com/jpernst/alto

alexcrichton · 2016-12-06T19:34:28Z

@pwoolcoc thanks for the investigation! Looking at those thought I think that this change would break most of those crates unfortunately. Most of the build scripts have an extern crate directive which isn't listed in [build-dependencies].

Given that we may need to pursue a strategy like:

Add knowledge of build = <bool>
If build isn't specified and build.rs exists, generate a warning

We probably need to let that bake for quite some time, and then after that's in we can enable the auto-detection. What do you think?

pwoolcoc · 2016-12-06T19:47:16Z

@alexcrichton sounds good, I suspected as much, so I have a patch ready to go for this. So to be clear, the new behavior would be:

If build = "build.rs" is present, same behavior as today
if build = true is present, it is equivalent to build = "build.rs", regardless of the existence of build.rs
If build = false is present, it is equivalent to not having a build value at all, regardless of the existence of build.rs
If build = ... is not present, and a build.rs file is present, a warning would be printed.

Does that sound right? I'll push my last commit so you can look it over, too.

alexcrichton · 2016-12-06T19:48:46Z

@pwoolcoc sounds exactly right to me!

pwoolcoc · 2016-12-06T21:07:46Z

r? @alexcrichton

alexcrichton · 2016-12-07T08:06:11Z

@bors: r+

Thanks!

bors · 2016-12-07T08:06:12Z

📌 Commit 1b99491 has been approved by alexcrichton

bors · 2016-12-07T08:06:17Z

⌛ Testing commit 1b99491 with merge 333a798...

Assume `build.rs` in the same directory as `Cargo.toml` is a build script (unless explicitly told not to) So, in May I posted a question in the #cargo IRC room: https://botbot.me/mozilla/cargo/2016-05-26/?msg=66770068&page=1 This PR does what was discussed there. If `cargo` sees a `build.rs` in the same directory as the `Cargo.toml`, it will assume `build.rs` is a build script unless `package.build = false`. Just for completeness I also made `build = true` mean the same as `build = "build.rs"` but I'm not sure if that is okay or not.

bors · 2016-12-07T09:13:04Z

☀️ Test successful - status-appveyor, status-travis
Approved by: alexcrichton
Pushing 333a798 to master...

pwoolcoc · 2016-12-09T15:29:50Z

@alexcrichton sorry to revive the old thread, just had a question about this. What is the procedure for going back to finish features like this a few releases down the line? Should I open a tracking issue for it? Or just put a reminder in my calendar for March and ping you again after a couple release cycles?

alexcrichton · 2016-12-10T01:13:41Z

@pwoolcoc oh we unfortunately don't have a super principled way of handling this in Cargo. For now though want to open a tracking issue here?

rust-highfive assigned brson Dec 2, 2016

Paul Woolcock added 2 commits December 2, 2016 14:57

Assume build = 'build.rs' by default

ea2c6e8

This change makes cargo assume `build = "build.rs"` if there is a `build.rs` file in the same directory as `Cargo.toml`. However, you can set `build = false` to prevent this.

Tests for new package.build behavior

73e0244

pwoolcoc force-pushed the default-build-script branch from 9016053 to 73e0244 Compare December 2, 2016 19:57

pwoolcoc commented Dec 2, 2016

View reviewed changes

Paul Woolcock added 2 commits December 5, 2016 09:41

Using layout.root here should be sufficient

e409049

correct typo

d998dba

pwoolcoc force-pushed the default-build-script branch from be5ef11 to 3846a15 Compare December 6, 2016 20:01

change this to only emit a warning right now

1b99491

pwoolcoc force-pushed the default-build-script branch from 9bf77ef to 1b99491 Compare December 6, 2016 20:51

rust-highfive assigned alexcrichton and unassigned brson Dec 6, 2016

alexcrichton added the relnotes Release-note worthy label Dec 7, 2016

bors merged commit 1b99491 into rust-lang:master Dec 7, 2016

pwoolcoc mentioned this pull request Dec 12, 2016

Tracking issue for PR #3361 #3391

Closed

brson mentioned this pull request Mar 1, 2017

Multiple crates can't find pkg_config in 1.17 rust-lang/rust#40183

Closed

ehuss added this to the 1.15.0 milestone Feb 6, 2022

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Assume `build.rs` in the same directory as `Cargo.toml` is a build script (unless explicitly told not to) #3361

Assume `build.rs` in the same directory as `Cargo.toml` is a build script (unless explicitly told not to) #3361

pwoolcoc commented Dec 2, 2016

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Assume build.rs in the same directory as Cargo.toml is a build script (unless explicitly told not to) #3361

Assume build.rs in the same directory as Cargo.toml is a build script (unless explicitly told not to) #3361

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Assume `build.rs` in the same directory as `Cargo.toml` is a build script (unless explicitly told not to) #3361

Assume `build.rs` in the same directory as `Cargo.toml` is a build script (unless explicitly told not to) #3361

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