fix: add wasmtime flags macro support (#1327)

Signed-off-by: James Sturtevant <jsturtevant@gmail.com>

Author: jsturtevant

Justfile

@@ -238,10 +238,13 @@ test-isolated target=default-target features="" :
     {{ cargo-cmd }} test {{ if features =="" {''} else if features=="no-default-features" {"--no-default-features" } else {"--no-default-features -F function_call_metrics," + features } }} --profile={{ if target == "debug" { "dev" } else { target } }} {{ target-triple-flag }} -p hyperlight-host --lib -- metrics::tests::test_metrics_are_emitted --exact
 
 # runs integration tests
-test-integration target=default-target features="":
+test-integration target=default-target features="": (witguest-wit)
     @# run execute_on_heap test with feature "executable_heap" on (runs with off during normal tests)
     {{ cargo-cmd }} test {{ if features =="" {"--features executable_heap"} else if features=="no-default-features" {"--no-default-features --features executable_heap"} else {"--no-default-features -F executable_heap," + features } }} --profile={{ if target == "debug" { "dev" } else { target } }} {{ target-triple-flag }} --test integration_test execute_on_heap
 
+    @# run component-util integration tests that depend on generated WIT inputs
+    {{ cargo-cmd }} test -p hyperlight-component-util --profile={{ if target == "debug" { "dev" } else { target } }} {{ target-triple-flag }} --test wasmtime_guest_codegen
+
     @# run the rest of the integration tests
     {{ cargo-cmd }} test -p hyperlight-host {{ if features =="" {''} else if features=="no-default-features" {"--no-default-features" } else {"--no-default-features -F " + features } }} --profile={{ if target == "debug" { "dev" } else { target } }} {{ target-triple-flag }} --test '*'
 

src/hyperlight_component_util/src/emit.rs

@@ -763,6 +763,21 @@ pub fn kebab_to_imports_name(trait_name: &str) -> Ident {
 pub fn kebab_to_exports_name(trait_name: &str) -> Ident {
     format_ident!("{}Exports", kebab_to_type(trait_name))
 }
+/// Convert a kebab name to a SCREAMING_SNAKE_CASE identifier suitable
+/// for use as a constant in a `wasmtime::component::flags!` invocation.
+pub fn kebab_to_flags_const(n: &str) -> Ident {
+    let s: String = n
+        .chars()
+        .map(|c| {
+            if c == '-' {
+                '_'
+            } else {
+                c.to_ascii_uppercase()
+            }
+        })
+        .collect();
+    format_ident!("{}", s)
+}
 
 /// The kinds of names that a function associated with a resource in
 /// WIT can have

src/hyperlight_component_util/src/hl.rs

@@ -18,7 +18,7 @@ use itertools::Itertools;
 use proc_macro2::{Ident, TokenStream};
 use quote::{format_ident, quote};
 
-use crate::emit::{ResolvedBoundVar, State, kebab_to_cons, kebab_to_var};
+use crate::emit::{ResolvedBoundVar, State, kebab_to_cons, kebab_to_flags_const, kebab_to_var};
 use crate::etypes::{self, Defined, Handleable, Tyvar, Value};
 use crate::rtypes;
 
@@ -91,16 +91,37 @@ pub fn emit_hl_unmarshal_toplevel_value(
         }
         Value::Flags(ns) => {
             let bytes = usize::div_ceil(ns.len(), 8);
+            let result_var = format_ident!("{}_flags", id);
             let fields = ns.iter().enumerate().map(|(i, n)| {
                 let byte_offset = i / 8;
                 let bit_offset = i % 8;
-                let fieldid = kebab_to_var(n.name);
-                quote! {
-                    #fieldid: (#id[#byte_offset] >> #bit_offset) & 0x1 == 1,
+                let is_set = quote! { (#id[#byte_offset] >> #bit_offset) & 0x1 == 1 };
+                if s.is_wasmtime_guest {
+                    let const_name = kebab_to_flags_const(n.name);
+                    quote! {
+                        if #is_set {
+                            #result_var |= #tname::#const_name;
+                        }
+                    }
+                } else {
+                    let fieldid = kebab_to_var(n.name);
+                    quote! {
+                        #fieldid: #is_set,
+                    }
                 }
             });
-            quote! {
-                (#tname { #(#fields)* }, #bytes)
+            if s.is_wasmtime_guest {
+                quote! {
+                    {
+                        let mut #result_var = #tname::empty();
+                        #(#fields)*
+                        (#result_var, #bytes)
+                    }
+                }
+            } else {
+                quote! {
+                    (#tname { #(#fields)* }, #bytes)
+                }
             }
         }
         Value::Variant(vcs) => {
@@ -434,9 +455,15 @@ pub fn emit_hl_marshal_toplevel_value(
                 .map(|(i, n)| {
                     let byte_offset = i / 8;
                     let bit_offset = i % 8;
-                    let fieldid = kebab_to_var(n.name);
+                    let is_set = if s.is_wasmtime_guest {
+                        let const_name = kebab_to_flags_const(n.name);
+                        quote! { #id.contains(#tname::#const_name) }
+                    } else {
+                        let fieldid = kebab_to_var(n.name);
+                        quote! { #id.#fieldid }
+                    };
                     quote! {
-                        bytes[#byte_offset] |= (if #id.#fieldid { 1 } else { 0 }) << #bit_offset;
+                        bytes[#byte_offset] |= (if #is_set { 1 } else { 0 }) << #bit_offset;
                     }
                 })
                 .collect::<Vec<_>>();

src/hyperlight_component_util/src/rtypes.rs

@@ -24,9 +24,9 @@ use quote::{format_ident, quote};
 use syn::Ident;
 
 use crate::emit::{
-    FnName, ResourceItemName, State, WitName, kebab_to_cons, kebab_to_exports_name, kebab_to_fn,
-    kebab_to_getter, kebab_to_imports_name, kebab_to_namespace, kebab_to_type, kebab_to_var,
-    split_wit_name,
+    FnName, ResourceItemName, State, WitName, kebab_to_cons, kebab_to_exports_name,
+    kebab_to_flags_const, kebab_to_fn, kebab_to_getter, kebab_to_imports_name, kebab_to_namespace,
+    kebab_to_type, kebab_to_var, split_wit_name,
 };
 use crate::etypes::{
     self, Component, Defined, ExternDecl, ExternDesc, Func, Handleable, ImportExport, Instance,
@@ -409,21 +409,41 @@ fn emit_value_toplevel(s: &mut State, v: Option<u32>, id: Ident, vt: &Value) ->
             }
         }
         Value::Flags(ns) => {
-            let (vs, toks) = gather_needed_vars(s, v, |_| {
-                let ns = ns
+            if s.is_wasmtime_guest {
+                let flags = ns
                     .iter()
                     .map(|n| {
                         let orig_name = n.name;
-                        let id = kebab_to_var(orig_name);
-                        quote! { pub #id: bool }
+                        let const_name = kebab_to_flags_const(orig_name);
+                        quote! {
+                            #[component(name = #orig_name)]
+                            const #const_name;
+                        }
                     })
                     .collect::<Vec<_>>();
-                quote! { #(#ns),* }
-            });
-            let vs = emit_type_defn_var_list(s, vs);
-            quote! {
-                #[derive(Debug, Clone, PartialEq)]
-                pub struct #id #vs { #toks }
+                quote! {
+                    ::wasmtime::component::flags! {
+                        #id {
+                            #(#flags)*
+                        }
+                    }
+                }
+            } else {
+                let (vs, toks) = gather_needed_vars(s, v, |_| {
+                    let ns = ns
+                        .iter()
+                        .map(|n| {
+                            let id = kebab_to_var(n.name);
+                            quote! { pub #id: bool }
+                        })
+                        .collect::<Vec<_>>();
+                    quote! { #(#ns),* }
+                });
+                let vs = emit_type_defn_var_list(s, vs);
+                quote! {
+                    #[derive(Debug, Clone, PartialEq)]
+                    pub struct #id #vs { #toks }
+                }
             }
         }
         Value::Variant(vcs) => {

src/hyperlight_component_util/tests/wasmtime_guest_codegen.rs

@@ -0,0 +1,47 @@
+/*
+Copyright 2026 The Hyperlight Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+use hyperlight_component_util::{emit, guest, rtypes, util};
+
+#[test]
+fn wasmtime_guest_codegen_emits_wasmtime_flags_macro() {
+    let generated = util::read_wit_type_from_file(
+        "../tests/rust_guests/witguest/interface.wasm",
+        None,
+        |kebab_name, ct| {
+            // Mirrors the hyperlight-wasm guest-bindgen expansion path:
+            // https://github.com/hyperlight-dev/hyperlight-wasm/blob/81e72f5920ebc23584097abfe24d05a40bf084cc/src/hyperlight_wasm_macro/src/lib.rs#L37-L38
+            emit::run_state(true, true, |s| {
+                rtypes::emit_toplevel(s, &kebab_name, ct);
+                guest::emit_toplevel(s, &kebab_name, ct);
+            })
+        },
+    );
+    let generated: syn::File = syn::parse2(generated).expect("generated Rust should parse");
+    let generated = prettyplease::unparse(&generated);
+
+    assert!(generated.contains("::wasmtime::component::flags! {"));
+    assert!(generated.contains("Smallflags {"));
+    assert!(generated.contains("\"flag-a\""));
+    assert!(generated.contains("const FLAG_A;"));
+    assert!(generated.contains("\"flag-b\""));
+    assert!(generated.contains("const FLAG_B;"));
+    assert!(generated.contains("\"flag-c\""));
+    assert!(generated.contains("const FLAG_C;"));
+    assert!(!generated.contains("pub flag_a: bool"));
+    assert!(!generated.contains("pub flag_b: bool"));
+    assert!(!generated.contains("pub flag_c: bool"));
+}