Move to a builder struct for spirv-builder (#59)

This allows the print_metadata option

examples/example-runner/build.rs

@@ -1,8 +1,8 @@
-use spirv_builder::build_spirv;
+use spirv_builder::SpirvBuilder;
 use std::error::Error;
 
 fn main() -> Result<(), Box<dyn Error>> {
     // This will set the env var `example-shader.spv` to a spir-v file that can be include!()'d
-    build_spirv("../example-shader")?;
+    SpirvBuilder::new("../example-shader").build()?;
     Ok(())
 }

spirv-builder/src/lib.rs

@@ -24,12 +24,35 @@ impl fmt::Display for SpirvBuilderError {
 
 impl Error for SpirvBuilderError {}
 
-pub fn build_spirv(path_to_crate: impl AsRef<Path>) -> Result<(), SpirvBuilderError> {
-    let spirv_module = invoke_rustc(path_to_crate.as_ref())?;
-    let spirv_path: &Path = spirv_module.as_ref();
-    let env_var = spirv_path.file_name().unwrap().to_str().unwrap();
-    println!("cargo:rustc-env={}={}", env_var, spirv_module);
-    Ok(())
+pub struct SpirvBuilder {
+    path_to_crate: PathBuf,
+    print_metadata: bool,
+}
+impl SpirvBuilder {
+    pub fn new(path_to_crate: impl AsRef<Path>) -> Self {
+        Self {
+            path_to_crate: path_to_crate.as_ref().to_owned(),
+            print_metadata: true,
+        }
+    }
+
+    /// Whether to print build.rs cargo metadata (e.g. cargo:rustc-env=var=val). Defaults to true.
+    pub fn print_metadata(&mut self, v: bool) -> &mut Self {
+        self.print_metadata = v;
+        self
+    }
+
+    /// Builds the module. Returns the path to the built spir-v file. If print_metadata is true,
+    /// you usually don't have to inspect the path, as the environment variable will already be
+    /// set.
+    pub fn build(self) -> Result<PathBuf, SpirvBuilderError> {
+        let spirv_module = invoke_rustc(self.path_to_crate.as_ref(), self.print_metadata)?;
+        let env_var = spirv_module.file_name().unwrap().to_str().unwrap();
+        if self.print_metadata {
+            println!("cargo:rustc-env={}={}", env_var, spirv_module.display());
+        }
+        Ok(spirv_module)
+    }
 }
 
 // https://github.com/rust-lang/cargo/blob/1857880b5124580c4aeb4e8bc5f1198f491d61b1/src/cargo/util/paths.rs#L29-L52
@@ -64,7 +87,7 @@ fn find_rustc_codegen_spirv() -> PathBuf {
     panic!("Could not find {} in library path", filename);
 }
 
-fn invoke_rustc(path_to_crate: &Path) -> Result<String, SpirvBuilderError> {
+fn invoke_rustc(path_to_crate: &Path, print_metadata: bool) -> Result<PathBuf, SpirvBuilderError> {
     // Okay, this is a little bonkers: in a normal world, we'd have the user clone
     // rustc_codegen_spirv and pass in the path to it, and then we'd invoke cargo to build it, grab
     // the resulting .so, and pass it into -Z codegen-backend. But that's really gross: the user
@@ -93,7 +116,9 @@ fn invoke_rustc(path_to_crate: &Path) -> Result<String, SpirvBuilderError> {
     if build.status.success() {
         let stdout = String::from_utf8(build.stdout).unwrap();
         let artifact = get_last_artifact(&stdout);
-        print_deps_of(&artifact);
+        if print_metadata {
+            print_deps_of(&artifact);
+        }
         Ok(artifact)
     } else {
         Err(SpirvBuilderError::BuildFailed)
@@ -106,7 +131,7 @@ struct RustcOutput {
     filenames: Option<Vec<String>>,
 }
 
-fn get_last_artifact(out: &str) -> String {
+fn get_last_artifact(out: &str) -> PathBuf {
     let last = out
         .lines()
         .filter_map(|line| match serde_json::from_str::<RustcOutput>(line) {
@@ -128,11 +153,11 @@ fn get_last_artifact(out: &str) -> String {
         .filter(|v| v.ends_with(".spv"));
     let filename = filenames.next().expect("Crate had no .spv artifacts");
     assert_eq!(filenames.next(), None, "Crate had multiple .spv artifacts");
-    filename
+    filename.into()
 }
 
-fn print_deps_of(artifact: &str) {
-    let deps_file = Path::new(artifact).with_extension("d");
+fn print_deps_of(artifact: &Path) {
+    let deps_file = artifact.with_extension("d");
     let mut deps_map = HashMap::new();
     depfile::read_deps_file(&deps_file, |item, deps| {
         deps_map.insert(item, deps);
@@ -149,5 +174,5 @@ fn print_deps_of(artifact: &str) {
             None => println!("cargo:rerun-if-changed={}", artifact),
         }
     }
-    recurse(&deps_map, artifact.into());
+    recurse(&deps_map, artifact.to_str().unwrap().into());
 }