The new version causes build issues

[BlackDex]

Hello there,

I'm building a musl based rust build container with some pre-compiled C libraries, including libxml2.
All previous versions seem to work perfectly and build without issues.

But since the release of the new version this now breaks.
Not specifically sure why this is happening though, as i have not yet look into it deeply.
But maybe somebody here knows a way to fix it, or see what the issues more quickly :)

The error can be viewed here:
https://github.com/BlackDex/rust-musl/actions/runs/14512752243/job/40714970804#step:33:324

Any pointers would be great.

[dginev]

Pity, since a significant part of the contribution for the new release was exactly an improved build process which could work on more OS-es. Thank you for reporting this so quickly!

[dginev]

@BlackDex on an Ubuntu CI toolchain, this crate would depend on libxml2-dev. It is hard to quickly notice if your builds add that in already, our CI does that here:

rust-libxml/.github/workflows/CI.yml

Line 16 in 34028d5

packages: "libxml2-dev"

This has always been the case, and the recent change in PR #143 makes even better use of that.

[BlackDex]

Hmm, if i understand it correctly, it should be looking for either the libxml-2.0 pkg-config/pc file or it looks at the LIBXML2 variable which should be pointing to the library it self.

Lets see if i build/provide the pc file or not, and else i need to define the LIBXML2 variable.

[BlackDex]

Ok, it looked like i used a make command which did not installed the .c and .h files.

I now get the following error:

error[E0308]: mismatched types
   --> /usr/local/cargo/registry/src/index.crates.io-1949cf8c6b5b557f/libxml-0.3.4/src/c_helpers.rs:112:57
    |
112 |     xmlSetStructuredErrorFunc(ctxt as *mut c_void, Some(_ignoreInvalidTagsErrorFunc));
    |                                                    ---- ^^^^^^^^^^^^^^^^^^^^^^^^^^^ types differ in mutability
    |                                                    |
    |                                                    arguments to this enum variant are incorrect
    |
    = note: expected fn pointer `unsafe extern "C" fn(_, *const _xmlError)`
                  found fn item `unsafe extern "C" fn(_, *mut _xmlError) {_ignoreInvalidTagsErrorFunc}`
help: the type constructed contains `unsafe extern "C" fn(*mut c_void, *mut _xmlError) {_ignoreInvalidTagsErrorFunc}` due to the type of the argument passed
   --> /usr/local/cargo/registry/src/index.crates.io-1949cf8c6b5b557f/libxml-0.3.4/src/c_helpers.rs:112:52
    |
112 |     xmlSetStructuredErrorFunc(ctxt as *mut c_void, Some(_ignoreInvalidTagsErrorFunc));
    |                                                    ^^^^^---------------------------^
    |                                                         |
    |                                                         this argument influences the type of `Some`
note: tuple variant defined here
   --> /rustc/05f9846f893b09a1be1fc8560e33fc3c815cfecb/library/core/src/option.rs:580:5

error[E0308]: mismatched types
   --> /usr/local/cargo/registry/src/index.crates.io-1949cf8c6b5b557f/libxml-0.3.4/src/tree/node.rs:418:14
    |
418 |     unsafe { xmlNodeSetContent(self.node_ptr_mut()?, c_content.as_bytes().as_ptr()) }
    |              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^- help: consider using a semicolon here: `;`
    |              |
    |              expected `()`, found `i32`

error[E0308]: mismatched types
  --> /usr/local/cargo/registry/src/index.crates.io-1949cf8c6b5b557f/libxml-0.3.4/src/schemas/parser.rs:82:14
   |
82 |         Some(common::structured_error_handler),
   |         ---- ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ types differ in mutability
   |         |
   |         arguments to this enum variant are incorrect
   |
   = note: expected fn pointer `unsafe extern "C" fn(_, *const _xmlError)`
                 found fn item `unsafe extern "C" fn(_, *mut _xmlError) {structured_error_handler}`
help: the type constructed contains `unsafe extern "C" fn(*mut c_void, *mut _xmlError) {structured_error_handler}` due to the type of the argument passed
  --> /usr/local/cargo/registry/src/index.crates.io-1949cf8c6b5b557f/libxml-0.3.4/src/schemas/parser.rs:82:9
   |
82 |         Some(common::structured_error_handler),
   |         ^^^^^--------------------------------^
   |              |
   |              this argument influences the type of `Some`
note: tuple variant defined here
  --> /rustc/05f9846f893b09a1be1fc8560e33fc3c815cfecb/library/core/src/option.rs:580:5

error[E0308]: mismatched types
   --> /usr/local/cargo/registry/src/index.crates.io-1949cf8c6b5b557f/libxml-0.3.4/src/schemas/validation.rs:104:14
    |
104 |         Some(common::structured_error_handler),
    |         ---- ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ types differ in mutability
    |         |
    |         arguments to this enum variant are incorrect
    |
    = note: expected fn pointer `unsafe extern "C" fn(_, *const _xmlError)`
                  found fn item `unsafe extern "C" fn(_, *mut _xmlError) {structured_error_handler}`
help: the type constructed contains `unsafe extern "C" fn(*mut c_void, *mut _xmlError) {structured_error_handler}` due to the type of the argument passed
   --> /usr/local/cargo/registry/src/index.crates.io-1949cf8c6b5b557f/libxml-0.3.4/src/schemas/validation.rs:104:9
    |
104 |         Some(common::structured_error_handler),
    |         ^^^^^--------------------------------^
    |              |
    |              this argument influences the type of `Some`
note: tuple variant defined here
   --> /rustc/05f9846f893b09a1be1fc8560e33fc3c815cfecb/library/core/src/option.rs:580:5

For more information about this error, try `rustc --explain E0308`.
error: could not compile `libxml` (lib) due to 4 previous errors

Caused by:
  process didn't exit successfully: `CARGO=/usr/local/rustup/toolchains/stable-x86_64-unknown-linux-gnu/bin/cargo CARGO_CRATE_NAME=libxml CARGO_MANIFEST_DIR=/usr/local/cargo/registry/src/index.crates.io-1949cf8c6b5b557f/libxml-0.3.4 CARGO_MANIFEST_PATH=/usr/local/cargo/registry/src/index.crates.io-1949cf8c6b5b557f/libxml-0.3.4/Cargo.toml CARGO_PKG_AUTHORS='Andreas Franzén <andreas@devil.se>:Deyan Ginev <deyan.ginev@gmail.com>:Jan Frederik Schaefer <j.schaefer@jacobs-university.de>' CARGO_PKG_DESCRIPTION='A Rust wrapper for libxml2 - the XML C parser and toolkit developed for the Gnome project' CARGO_PKG_HOMEPAGE='' CARGO_PKG_LICENSE=MIT CARGO_PKG_LICENSE_FILE='' CARGO_PKG_NAME=libxml CARGO_PKG_README=README.md CARGO_PKG_REPOSITORY='https://github.com/KWARC/rust-libxml' CARGO_PKG_RUST_VERSION='' CARGO_PKG_VERSION=0.3.4 CARGO_PKG_VERSION_MAJOR=0 CARGO_PKG_VERSION_MINOR=3 CARGO_PKG_VERSION_PATCH=4 CARGO_PKG_VERSION_PRE='' LD_LIBRARY_PATH='/home/rust/src/target/debug/deps:/usr/local/rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib' OUT_DIR=/home/rust/src/target/x86_64-unknown-linux-musl/debug/build/libxml-0b891eab3728ee47/out /usr/local/rustup/toolchains/stable-x86_64-unknown-linux-gnu/bin/rustc --crate-name libxml --edition=2021 /usr/local/cargo/registry/src/index.crates.io-1949cf8c6b5b557f/libxml-0.3.4/src/lib.rs --error-format=json --json=diagnostic-rendered-ansi,artifacts,future-incompat --diagnostic-width=268 --crate-type lib --emit=dep-info,metadata,link -C embed-bitcode=no -C debuginfo=2 --check-cfg 'cfg(docsrs,test)' --check-cfg 'cfg(feature, values())' -C metadata=808ef9371f6be4e5 -C extra-filename=-9aa406fe2004f28c --out-dir /home/rust/src/target/x86_64-unknown-linux-musl/debug/deps --target x86_64-unknown-linux-musl -C linker=x86_64-unknown-linux-musl-ld -L dependency=/home/rust/src/target/x86_64-unknown-linux-musl/debug/deps -L dependency=/home/rust/src/target/debug/deps --extern libc=/home/rust/src/target/x86_64-unknown-linux-musl/debug/deps/liblibc-eb5d845088983b4e.rmeta --cap-lints warn -Clink-arg=-s -L native=/usr/local/musl/lib -l static=xml2 -l m` (exit status: 1)
warning: build failed, waiting for other jobs to finish...

Also, not looked deeply into this yet.

[BlackDex]

@BlackDex on an Ubuntu CI toolchain, this crate would depend on libxml2-dev. It is hard to quickly notice if your builds add that in already, our CI does that here:

rust-libxml/.github/workflows/CI.yml

Line 16 in 34028d5
packages: "libxml2-dev"

This has always been the case, and the recent change in PR #143 makes even better use of that.

That will not work for my build-images i think, as those are using static build versions.
But pkg-config seems to extract the correct locations, so that is good.

But the above error still persists.
The error regarding src/tree/node.rs:418:14 can simply be solved by adding the ; where suggested.
But the others i have no quick clue on how to solve those.

[BlackDex]

I just run cargo +nightly clippy on the codebase, and it returns an error regarding those items too.

error[E0308]: mismatched types
   --> src/c_helpers.rs:112:57
    |
112 |     xmlSetStructuredErrorFunc(ctxt as *mut c_void, Some(_ignoreInvalidTagsErrorFunc));
    |                                                    ---- ^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected fn pointer, found fn item
    |                                                    |
    |                                                    arguments to this enum variant are incorrect
    |
    = note: expected fn pointer `unsafe extern "C" fn(*mut libc::c_void, _)`
                  found fn item `unsafe extern "C" fn(libc::c_void, _) {c_helpers::_ignoreInvalidTagsErrorFunc}`
help: the type constructed contains `unsafe extern "C" fn(libc::c_void, *mut bindings::_xmlError) {c_helpers::_ignoreInvalidTagsErrorFunc}` due to the type of the argument passed
   --> src/c_helpers.rs:112:52
    |
112 |     xmlSetStructuredErrorFunc(ctxt as *mut c_void, Some(_ignoreInvalidTagsErrorFunc));
    |                                                    ^^^^^---------------------------^
    |                                                         |
    |                                                         this argument influences the type of `Some`
note: tuple variant defined here
   --> /home/mathijs/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/option.rs:580:5
    |
580 |     Some(#[stable(feature = "rust1", since = "1.0.0")] T),
    |     ^^^^

For more information about this error, try `rustc --explain E0308`.
error: could not compile `libxml` (lib) due to 1 previous error

[dginev]

Interesting, which toolchain versions are those? I haven't encountered this, but I am tracking the most recent nightly.

Checked with rustc 1.88.0-nightly (a15cce269 2025-04-17) and rustc 1.88.0-nightly (38c560ae6 2025-04-15). And with the latest stable rustc 1.86.0 (05f9846f8 2025-03-31). At commit 34028d5 .

$ cargo +nightly clippy
warning: use `std::ptr::eq` when comparing raw pointers
  --> src/tree/node.rs:57:5
   |
57 |     self.node_ptr() == other.node_ptr()
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `std::ptr::eq(self.node_ptr(), other.node_ptr())`
   |
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#ptr_eq
   = note: `#[warn(clippy::ptr_eq)]` on by default

warning: use `std::ptr::eq` when comparing raw pointers
  --> src/readonly/tree.rs:25:5
   |
25 |     self.0 == other.0
   |     ^^^^^^^^^^^^^^^^^ help: try: `std::ptr::eq(self.0, other.0)`
   |
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#ptr_eq

warning: `libxml` (lib) generated 2 warnings (run `cargo clippy --fix --lib -p libxml` to apply 2 suggestions)
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.04s

I should clean this up as well, but I'd like to know the exact conditions that lead to the errors you're seeing.

Edit: Well, more interestingly, can you attach the bindings.rs which was generated during your local build, at target/debug/build/libxml-[id]/out/bindings.rs, since that is likely different from mine.

[BlackDex]

I'm using:

cargo +nightly -vV
cargo 1.88.0-nightly (864f74d4e 2025-04-11)
release: 1.88.0-nightly
commit-hash: 864f74d4eadcaea3eeda37a2e7f4d34de233d51e
commit-date: 2025-04-11
host: x86_64-unknown-linux-gnu
libgit2: 1.9.0 (sys:0.20.0 vendored)
libcurl: 8.12.1-DEV (sys:0.4.80+curl-8.12.1 vendored ssl:OpenSSL/3.4.1)
ssl: OpenSSL 3.4.1 11 Feb 2025
os: Ubuntu 22.4.0 (jammy) [64-bit]

I did a new clone, and for some reason it doesn't complain about the previous items right now, and only the same you also see.

The only pending items which prevent me from using 0.3.4 are these:

error[E0308]: mismatched types
   --> .artifacts/rust-libxml/src/c_helpers.rs:112:57
    |
112 |     xmlSetStructuredErrorFunc(ctxt as *mut c_void, Some(_ignoreInvalidTagsErrorFunc));
    |                                                    ---- ^^^^^^^^^^^^^^^^^^^^^^^^^^^ types differ in mutability
    |                                                    |
    |                                                    arguments to this enum variant are incorrect
    |
    = note: expected fn pointer `unsafe extern "C" fn(_, *const _xmlError)`
                  found fn item `unsafe extern "C" fn(_, *mut _xmlError) {_ignoreInvalidTagsErrorFunc}`
help: the type constructed contains `unsafe extern "C" fn(*mut c_void, *mut _xmlError) {_ignoreInvalidTagsErrorFunc}` due to the type of the argument passed
   --> .artifacts/rust-libxml/src/c_helpers.rs:112:52
    |
112 |     xmlSetStructuredErrorFunc(ctxt as *mut c_void, Some(_ignoreInvalidTagsErrorFunc));
    |                                                    ^^^^^---------------------------^
    |                                                         |
    |                                                         this argument influences the type of `Some`
note: tuple variant defined here
   --> /rustc/05f9846f893b09a1be1fc8560e33fc3c815cfecb/library/core/src/option.rs:580:5

error[E0308]: mismatched types
  --> .artifacts/rust-libxml/src/schemas/parser.rs:82:14
   |
82 |         Some(common::structured_error_handler),
   |         ---- ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ types differ in mutability
   |         |
   |         arguments to this enum variant are incorrect
   |
   = note: expected fn pointer `unsafe extern "C" fn(_, *const _xmlError)`
                 found fn item `unsafe extern "C" fn(_, *mut _xmlError) {structured_error_handler}`
help: the type constructed contains `unsafe extern "C" fn(*mut c_void, *mut _xmlError) {structured_error_handler}` due to the type of the argument passed
  --> .artifacts/rust-libxml/src/schemas/parser.rs:82:9
   |
82 |         Some(common::structured_error_handler),
   |         ^^^^^--------------------------------^
   |              |
   |              this argument influences the type of `Some`
note: tuple variant defined here
  --> /rustc/05f9846f893b09a1be1fc8560e33fc3c815cfecb/library/core/src/option.rs:580:5

error[E0308]: mismatched types
   --> .artifacts/rust-libxml/src/schemas/validation.rs:104:14
    |
104 |         Some(common::structured_error_handler),
    |         ---- ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ types differ in mutability
    |         |
    |         arguments to this enum variant are incorrect
    |
    = note: expected fn pointer `unsafe extern "C" fn(_, *const _xmlError)`
                  found fn item `unsafe extern "C" fn(_, *mut _xmlError) {structured_error_handler}`
help: the type constructed contains `unsafe extern "C" fn(*mut c_void, *mut _xmlError) {structured_error_handler}` due to the type of the argument passed
   --> .artifacts/rust-libxml/src/schemas/validation.rs:104:9
    |
104 |         Some(common::structured_error_handler),
    |         ^^^^^--------------------------------^
    |              |
    |              this argument influences the type of `Some`
note: tuple variant defined here
   --> /rustc/05f9846f893b09a1be1fc8560e33fc3c815cfecb/library/core/src/option.rs:580:5

For more information about this error, try `rustc --explain E0308`.
error: could not compile `libxml` (lib) due to 3 previous errors

[dginev]

I did a new clone, and for some reason it doesn't complain about the previous items right now, and only the same you also see.

There seem to be subtle differences between the generated bindings.rs files then. The *mut _xmlError vs *const _xmlError seems to be such an example. The c_helpers expect a generated declaration that matches exactly:

 pub type xmlErrorPtr = *mut xmlError;

If that is instead a *const, you'd get the type error. But I find it surprising the same toolchain could produce such a difference.

[BlackDex]

Maybe it's because a different version of libxml2?
I get this both using stable or nightly btw, doesn't matter which toolchain.

The libxml2 version I'm using is v2.14.2 (But 2.14.1 also failed).