Trick Cargo into adding shader files as dependencies

Add the context of the shader sources with include_bytes!() so that
Cargo will recompile the rust source if the shader source changes.

src/lib.rs

@@ -3,26 +3,26 @@
 use {
     naga::front::wgsl,
     proc_macro::TokenStream,
-    quote::quote,
-    std::fs,
+    quote::{format_ident, quote},
     syn::{parse, LitStr},
 };
 
 mod source_reader;
 
 struct ShaderModule {
-    source_text: String,
+    source_file: source_reader::SourceFile,
     naga_module: naga::Module,
 }
 
 impl ShaderModule {
-    fn try_new(source_file: impl Into<std::path::PathBuf>) -> Result<Self, Error> {
-        let source_filename = source_file.into();
-        let source_file = source_reader::read_source_file(source_filename)?;
-        let source_text = source_file.full_text().to_string();
+    fn try_new(
+        source_dir: &std::path::Path,
+        source_filename: &std::path::Path,
+    ) -> Result<Self, Error> {
+        let source_file = source_reader::read_source_file(source_dir, source_filename)?;
 
-        let naga_module = wgsl::parse_str(&source_text).map_err(|err| {
-            if let Some(location) = err.location(&source_text) {
+        let naga_module = wgsl::parse_str(&source_file.full_text()).map_err(|err| {
+            if let Some(location) = err.location(&source_file.full_text()) {
                 let (inner_source_filename, inner_line_num) =
                     source_file.map_source_line_num(location.line_number as usize);
                 Error::Message(format!(
@@ -41,17 +41,35 @@ impl ShaderModule {
             }
         })?;
         Ok(Self {
-            source_text,
+            source_file,
             naga_module,
         })
     }
 
     fn emit_rust_code(&self) -> TokenStream {
-        let source_text = &self.source_text;
+        // We include the text of all the source files into the generated code
+        // with include_bytes!() so that Cargo recognizes them as
+        // dependencies. It's not pretty but it works. Since the file contents
+        // are just stored in unused local variables, they should be removed by
+        // the optimizer and not affect the compiled code.
+        let source_text = &self.source_file.full_text();
+        let dependencies: Vec<_> = self
+            .source_file
+            .all_filenames()
+            .iter()
+            .map(|path| path.as_os_str().to_string_lossy())
+            .collect();
+        let dummy_var: Vec<_> = (0u32..)
+            .map(|n| format_ident!("_{}", n))
+            .take(dependencies.len())
+            .collect();
         quote! {
-            wgpu::ShaderModuleDescriptor {
-                label: None,
-                source: wgpu::ShaderSource::Wgsl(Cow::Borrowed(#source_text)),
+            {
+                #(let #dummy_var = include_bytes!(#dependencies);)*
+                wgpu::ShaderModuleDescriptor {
+                    label: None,
+                    source: wgpu::ShaderSource::Wgsl(Cow::Borrowed(#source_text)),
+                }
             }
         }
         .into()
@@ -60,7 +78,7 @@ impl ShaderModule {
 
 struct WgslModuleMacroInput {
     source_dir: std::path::PathBuf,
-    filename: String,
+    filename: std::path::PathBuf,
 }
 
 enum Error {
@@ -89,7 +107,7 @@ fn parse_input(token_stream: TokenStream) -> Result<WgslModuleMacroInput, Error>
 
     let source_dir = token.span().source_file().path().parent().unwrap().into();
     let literal: LitStr = parse(token_stream)?;
-    let filename = literal.value();
+    let filename = std::path::Path::new(&literal.value()).into();
     Ok(WgslModuleMacroInput {
         source_dir,
         filename,
@@ -98,8 +116,7 @@ fn parse_input(token_stream: TokenStream) -> Result<WgslModuleMacroInput, Error>
 
 fn wgsl_module_inner(input_token_stream: TokenStream) -> Result<TokenStream, Error> {
     let input = parse_input(input_token_stream)?;
-    let full_filename = input.source_dir.join(&input.filename);
-    let module = ShaderModule::try_new(full_filename)?;
+    let module = ShaderModule::try_new(&input.source_dir, &input.filename)?;
     Ok(module.emit_rust_code())
 }
 

src/source_reader.rs

@@ -29,10 +29,14 @@ impl SourceFile {
     pub fn map_source_line_num(&self, line_num: usize) -> (&Path, usize) {
         (&self.source_map.filename, line_num)
     }
+
+    pub fn all_filenames(&self) -> Vec<&Path> {
+        vec![&self.source_map.filename]
+    }
 }
 
-pub fn read_source_file(filename: PathBuf) -> Result<SourceFile, Error> {
-    let source_text = fs::read_to_string(&filename).map_err(|err| {
+pub fn read_source_file(source_dir: &Path, filename: &Path) -> Result<SourceFile, Error> {
+    let source_text = fs::read_to_string(&source_dir.join(filename)).map_err(|err| {
         Error::from_message(format!(
             "Could not open \"{}\": {}",
             &filename.as_os_str().to_string_lossy(),
@@ -42,7 +46,7 @@ pub fn read_source_file(filename: PathBuf) -> Result<SourceFile, Error> {
     Ok(SourceFile {
         source_text,
         source_map: SourceMap {
-            filename,
+            filename: filename.into(),
             offset: 0,
             total_lines: 0,
             insertions: vec![],