feat(render): Generate Rust perfect hash (#423)

Add Rust support for perfect hashes generated by Render.

(cherry picked from commit 86feed5)

Author: yonch

cmake/render.cmake

@@ -89,6 +89,7 @@ function(render_compile INPUT_DIR)
         # Rust per-app crate files live under src/
         "${OUTPUT_DIR}/${PACKAGE}/${APP}/src/wire_messages.rs"
         "${OUTPUT_DIR}/${PACKAGE}/${APP}/src/encoder.rs"
+        "${OUTPUT_DIR}/${PACKAGE}/${APP}/src/hash.rs"
         "${OUTPUT_DIR}/${PACKAGE}/${APP}/Cargo.toml"
         "${OUTPUT_DIR}/${PACKAGE}/${APP}/src/lib.rs"
         # Headers that are also generated alongside sources
@@ -296,6 +297,7 @@ function(render_compile INPUT_DIR)
       COMMAND ${CMAKE_COMMAND} -E copy_if_different "${_src_dir}/src/lib.rs" "${_dest_dir}/src/lib.rs"
       COMMAND ${CMAKE_COMMAND} -E copy_if_different "${_src_dir}/src/encoder.rs" "${_dest_dir}/src/encoder.rs"
       COMMAND ${CMAKE_COMMAND} -E copy_if_different "${_src_dir}/src/wire_messages.rs" "${_dest_dir}/src/wire_messages.rs"
+      COMMAND ${CMAKE_COMMAND} -E copy_if_different "${_src_dir}/src/hash.rs" "${_dest_dir}/src/hash.rs"
       DEPENDS render_compile_${PACKAGE}
       VERBATIM
     )

renderc/io.opentelemetry.render/src/io/opentelemetry/render/generator/HashGenerator.xtend

@@ -11,6 +11,7 @@ import static io.opentelemetry.render.generator.RenderGenerator.generatedCodeWar
 import static extension io.opentelemetry.render.extensions.AppExtensions.hashName
 import static extension io.opentelemetry.render.extensions.AppExtensions.hashSize
 import static extension io.opentelemetry.render.extensions.AppExtensions.hashFunctor
+import static extension io.opentelemetry.render.extensions.AppExtensions.pkg
 
 class HashGenerator {
 
@@ -20,6 +21,8 @@ class HashGenerator {
 
     fsa.generateFile(outputPath(app, "hash.c"), generateC(app, hash))
     fsa.generateFile(outputPath(app, "hash.h"), generateH(app, hash))
+    // Rust port: generate perfect hash for rpc_id into src/hash.rs
+    fsa.generateFile(outputPath(app, "src/hash.rs"), generateRust(app, hash))
   }
 
   private def generateC(App app, PerfectHash hash) {
@@ -71,4 +74,36 @@ class HashGenerator {
     '''
   }
 
+  private def generateRust(App app, PerfectHash hash) {
+    '''
+    «generatedCodeWarning()»
+    // Perfect hash for RPC IDs for «app.pkg.name»::«app.name»
+    //
+    // g_type: «hash.g_type»
+    // g_size: «hash.g_size»
+    // g_shift: «hash.g_shift»
+    // hash_shift: «hash.hash_shift»
+    // hash_mask: «hash.hash_mask»
+    // n_keys: «hash.n_keys»
+    // multiplier: «hash.multiplier»
+    // hash_seed: «hash.hash_seed»
+
+    #[allow(dead_code)]
+    pub const «app.hashSize»: u32 = «hash.hash_mask + 1»u32;
+
+    #[allow(dead_code)]
+    pub static G_ARRAY: [«hash.g_type»; «hash.g_size»] = [
+        «hash.g_array.map[toString].join(",")»
+    ];
+
+    #[inline]
+    #[allow(dead_code)]
+    pub fn «app.hashName»(rpc_id: u32) -> u32 {
+        let k = (rpc_id ^ «hash.hash_seed»u32).wrapping_mul(«hash.multiplier»u32);
+        let g = G_ARRAY[(k >> «hash.g_shift») as usize] as u32;
+        (k >> «hash.hash_shift»).wrapping_add(g) & «hash.hash_mask»u32
+    }
+    '''
+  }
+
 }

renderc/io.opentelemetry.render/src/io/opentelemetry/render/generator/RustCargoGenerator.xtend

@@ -86,6 +86,11 @@ class RustCargoGenerator {
     pub mod encoder {
         include!(concat!(env!("CARGO_MANIFEST_DIR"), "/src/encoder.rs"));
     }
+
+    #[allow(dead_code)]
+    pub mod hash {
+        include!(concat!(env!("CARGO_MANIFEST_DIR"), "/src/hash.rs"));
+    }
     '''
   }