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bindgen::ParseCallbacks: support tracking env variable usage for cargo #2400

Merged
merged 4 commits into from
Apr 10, 2023
Merged

bindgen::ParseCallbacks: support tracking env variable usage for cargo #2400

merged 4 commits into from
Apr 10, 2023

Commits on Apr 10, 2023

  1. bindgen::ParseCallbacks: support tracking env variable usage for cargo 

    bindgen currently has a `bindgen/build.rs` which attempts to have cargo
rebuild bindgen when TARGET specific env variables change, specifically
`BINDGEN_EXTRA_CLANG_ARGS_<target>`. Unfortunately, this doesn't have
the desired effect in most cases.

Specifically, when a crate `A` has `bindgen` in `build-dependencies`,
and we're cross compiling `A` for target `T` on a host `H`, `bindgen`'s
`build.rs` will observe `TARGET` set to `H` (the host target name)
instead of `T` (because `bindgen` itself is being built for `H` and not
`T`). Then, within the build script of crate `A`, one would use
`bindgen` to generate bindings, and now `TARGET` is set to `T`, so
different env variables are used.

Allow crates using `bindgen` in build scripts to correctly handle env
variable changes by adding `ParseCallbacks::read_env_var()` to track
env var reads and adding a basic implementation to `CargoCallbacks` to
emit `cargo:rerun-if-env-changed` lines.
    @codyps @pvdrz
    codyps authored and pvdrz committed Apr 10, 2023
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  2. Run rustfmt

    @pvdrz
    pvdrz committed Apr 10, 2023
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  3. Update docs

    @pvdrz
    pvdrz committed Apr 10, 2023
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  4. Update changelog

    @pvdrz
    pvdrz committed Apr 10, 2023
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