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[vello_shaders] Bring back the Bazel build hack #621

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Jun 28, 2024
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22 changes: 21 additions & 1 deletion vello_shaders/src/compile/mod.rs
Original file line number Diff line number Diff line change
Expand Up @@ -274,5 +274,25 @@ fn postprocess(wgsl: &str) -> String {
// NOTE: Embedding build environment info into the code makes reproducible builds trickier.
pub fn shader_dir() -> &'static PathBuf {
static SHADER_DIR: OnceLock<PathBuf> = OnceLock::new();
SHADER_DIR.get_or_init(|| Path::new(env!("CARGO_MANIFEST_DIR")).join("shader"))
SHADER_DIR.get_or_init(|| manifest_dir().join("shader"))
}

// In a regular cargo build the manifest directory is simply given by CARGO_MANIFEST_DIR.
//
// Skia, an external consumer of this crate, uses Bazel rules to compile Rust code. Due to
// limitations in Bazel's rust support, Skia maintains its own build definitions
// (https://source.chromium.org/chromium/chromium/src/+/main:third_party/skia/bazel/external/vello/BUILD.bazel).
//
// Because of the current setup, Bazel sets CARGO_MANIFEST_DIR to the workspace root instead of the
// actual crate being built. This could be improved but until then, we work around this by allowing
// the absolute path to the vello_shader crate's manifest to be specified using the
// `UNSTABLE_BAZEL_VELLO_SHADERS_CRATE_MANIFEST_PATH` build script environment variable.
//
// This should never be set when using cargo.
fn manifest_dir() -> PathBuf {
use std::env;
env::var_os("UNSTABLE_BAZEL_VELLO_SHADERS_CRATE_MANIFEST_PATH")
.and_then(|p| Path::new(&p).parent().map(|p| p.to_owned()))
.unwrap_or_else(|| PathBuf::from(env!("CARGO_MANIFEST_DIR")))
.to_path_buf()
}