support variant, enum, and union derives (#4359)

* support variant, enum, and union derives

This is the second stage of implementing #4308.  It adds support for deriving
variant, enum, and union impls for `ComponentType`, `Lift`, and `Lower`.  It
also fixes derived record impls for generic `struct`s, which I had intended to
support in my previous commit, but forgot to test.

Signed-off-by: Joel Dice <joel.dice@fermyon.com>

* deduplicate component-macro code

Thanks to @jameysharp for the suggestion!

Signed-off-by: Joel Dice <joel.dice@fermyon.com>

crates/wasmtime/src/component/func/typed.rs

@@ -1492,6 +1492,95 @@ pub fn typecheck_record(
     }
 }
 
+/// Verify that the given wasm type is a variant with the expected cases in the right order and with the right
+/// names.
+pub fn typecheck_variant(
+    ty: &InterfaceType,
+    types: &ComponentTypes,
+    expected: &[(&str, fn(&InterfaceType, &ComponentTypes) -> Result<()>)],
+) -> Result<()> {
+    match ty {
+        InterfaceType::Variant(index) => {
+            let cases = &types[*index].cases;
+
+            if cases.len() != expected.len() {
+                bail!(
+                    "expected variant of {} cases, found {} cases",
+                    expected.len(),
+                    cases.len()
+                );
+            }
+
+            for (case, &(name, check)) in cases.iter().zip(expected) {
+                check(&case.ty, types)
+                    .with_context(|| format!("type mismatch for case {}", name))?;
+
+                if case.name != name {
+                    bail!("expected variant case named {}, found {}", name, case.name);
+                }
+            }
+
+            Ok(())
+        }
+        other => bail!("expected `variant` found `{}`", desc(other)),
+    }
+}
+
+/// Verify that the given wasm type is a enum with the expected cases in the right order and with the right
+/// names.
+pub fn typecheck_enum(ty: &InterfaceType, types: &ComponentTypes, expected: &[&str]) -> Result<()> {
+    match ty {
+        InterfaceType::Enum(index) => {
+            let names = &types[*index].names;
+
+            if names.len() != expected.len() {
+                bail!(
+                    "expected enum of {} names, found {} names",
+                    expected.len(),
+                    names.len()
+                );
+            }
+
+            for (name, expected) in names.iter().zip(expected) {
+                if name != expected {
+                    bail!("expected enum case named {}, found {}", expected, name);
+                }
+            }
+
+            Ok(())
+        }
+        other => bail!("expected `enum` found `{}`", desc(other)),
+    }
+}
+
+/// Verify that the given wasm type is a union with the expected cases in the right order.
+pub fn typecheck_union(
+    ty: &InterfaceType,
+    types: &ComponentTypes,
+    expected: &[fn(&InterfaceType, &ComponentTypes) -> Result<()>],
+) -> Result<()> {
+    match ty {
+        InterfaceType::Union(index) => {
+            let union_types = &types[*index].types;
+
+            if union_types.len() != expected.len() {
+                bail!(
+                    "expected union of {} types, found {} types",
+                    expected.len(),
+                    union_types.len()
+                );
+            }
+
+            for (index, (ty, check)) in union_types.iter().zip(expected).enumerate() {
+                check(ty, types).with_context(|| format!("type mismatch for case {}", index))?;
+            }
+
+            Ok(())
+        }
+        other => bail!("expected `union` found `{}`", desc(other)),
+    }
+}
+
 unsafe impl<T> ComponentType for Option<T>
 where
     T: ComponentType,

crates/wasmtime/src/component/mod.rs

@@ -24,7 +24,8 @@ pub use wasmtime_component_macro::{ComponentType, Lift, Lower};
 #[doc(hidden)]
 pub mod __internal {
     pub use super::func::{
-        align_to, next_field, typecheck_record, MaybeUninitExt, Memory, MemoryMut, Options,
+        align_to, next_field, typecheck_enum, typecheck_record, typecheck_union, typecheck_variant,
+        MaybeUninitExt, Memory, MemoryMut, Options,
     };
     pub use crate::map_maybe_uninit;
     pub use crate::store::StoreOpaque;