wgsl: add spirv-unknown-naga-wgsl target, transpiling with naga 29

Author: Firestar99

Cargo.lock

@@ -61,6 +61,8 @@ itertools = "0.14.0"
 tracing.workspace = true
 tracing-subscriber.workspace = true
 tracing-tree = "0.4.0"
+naga = { version = "29.0.1", features = ["spv-in", "wgsl-out"] }
+strum = { version = "0.27.2", features = ["derive"] }
 
 [dev-dependencies]
 pretty_assertions = "1.0"

crates/rustc_codegen_spirv/Cargo.toml

@@ -127,6 +127,7 @@ mod custom_decorations;
 mod custom_insts;
 mod link;
 mod linker;
+mod naga_transpile;
 mod spirv_type;
 mod spirv_type_constraints;
 mod symbols;

crates/rustc_codegen_spirv/src/lib.rs

@@ -3,6 +3,7 @@ use crate::maybe_pqp_cg_ssa as rustc_codegen_ssa;
 
 use crate::codegen_cx::{CodegenArgs, SpirvMetadata};
 use crate::linker;
+use crate::naga_transpile::should_transpile;
 use crate::target::{SpirvTarget, SpirvTargetVariant};
 use ar::{Archive, GnuBuilder, Header};
 use rspirv::binary::Assemble;
@@ -319,6 +320,10 @@ fn post_link_single_module(
 
         drop(save_modules_timer);
     }
+
+    if let Some(transpile) = should_transpile(sess) {
+        transpile(sess, cg_args, &spv_binary, out_filename).ok();
+    }
 }
 
 fn do_spirv_opt(

crates/rustc_codegen_spirv/src/link.rs

@@ -0,0 +1,79 @@
+use crate::codegen_cx::CodegenArgs;
+use crate::target::{NagaTarget, SpirvTarget};
+use rustc_session::Session;
+use rustc_span::ErrorGuaranteed;
+use std::path::Path;
+
+pub type NagaTranspile = fn(
+    sess: &Session,
+    cg_args: &CodegenArgs,
+    spv_binary: &[u32],
+    out_filename: &Path,
+) -> Result<(), ErrorGuaranteed>;
+
+pub fn should_transpile(sess: &Session) -> Option<NagaTranspile> {
+    let target = SpirvTarget::parse_target(sess.opts.target_triple.tuple())
+        .expect("parsing should fail earlier");
+    match target {
+        SpirvTarget::Naga(NagaTarget::NAGA_WGSL) => Some(transpile::wgsl_transpile),
+        _ => None,
+    }
+}
+
+mod transpile {
+    use crate::codegen_cx::CodegenArgs;
+    use naga::error::ShaderError;
+    use naga::valid::Capabilities;
+    use rustc_session::Session;
+    use rustc_span::ErrorGuaranteed;
+    use std::path::Path;
+
+    pub fn wgsl_transpile(
+        sess: &Session,
+        _cg_args: &CodegenArgs,
+        spv_binary: &[u32],
+        out_filename: &Path,
+    ) -> Result<(), ErrorGuaranteed> {
+        // these should be params via spirv-builder
+        let opts = naga::front::spv::Options::default();
+        let capabilities = Capabilities::all();
+        let writer_flags = naga::back::wgsl::WriterFlags::empty();
+
+        let module = naga::front::spv::parse_u8_slice(bytemuck::cast_slice(spv_binary), &opts)
+            .map_err(|err| {
+                sess.dcx().err(format!(
+                    "Naga failed to parse spv: \n{}",
+                    ShaderError {
+                        source: String::new(),
+                        label: None,
+                        inner: Box::new(err),
+                    }
+                ))
+            })?;
+        let mut validator =
+            naga::valid::Validator::new(naga::valid::ValidationFlags::default(), capabilities);
+        let info = validator.validate(&module).map_err(|err| {
+            sess.dcx().err(format!(
+                "Naga validation failed: \n{}",
+                ShaderError {
+                    source: String::new(),
+                    label: None,
+                    inner: Box::new(err),
+                }
+            ))
+        })?;
+
+        let wgsl_dst = out_filename.with_extension("wgsl");
+        let wgsl = naga::back::wgsl::write_string(&module, &info, writer_flags).map_err(|err| {
+            sess.dcx()
+                .err(format!("Naga failed to write wgsl : \n{err}"))
+        })?;
+
+        std::fs::write(&wgsl_dst, wgsl).map_err(|err| {
+            sess.dcx()
+                .err(format!("failed to write wgsl to file: {err}"))
+        })?;
+
+        Ok(())
+    }
+}