support dynamic function calls in component model (#4442)

* support dynamic function calls in component model

This addresses #4310, introducing a new `component::values::Val` type for
representing component values dynamically, as well as `component::types::Type`
for representing the corresponding interface types. It also adds a `call` method
to `component::func::Func`, which takes a slice of `Val`s as parameters and
returns a `Result<Val>` representing the result.

Note that I've moved `post_return` and `call_raw` from `TypedFunc` to `Func`
since there was nothing specific to `TypedFunc` about them, and I wanted to
reuse them.  The code in both is unchanged beyond the trivial tweaks to make
them fit in their new home.

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

* order variants and match cases more consistently

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

* implement lift for String, Box<str>, etc.

This also removes the redundant `store` parameter from `Type::load`.

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

* implement code review feedback

This fixes a few issues:

- Bad offset calculation when lowering
- Missing variant padding
- Style issues regarding `types::Handle`
- Missed opportunities to reuse `Lift` and `Lower` impls

It also adds forwarding `Lift` impls for `Box<[T]>`, `Vec<T>`, etc.

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

* move `new_*` methods to specific `types` structs

Per review feedback, I've moved `Type::new_record` to `Record::new_val` and
added a `Type::unwrap_record` method; likewise for the other kinds of types.

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

* make tuple, option, and expected type comparisons recursive

These types should compare as equal across component boundaries as long as their
type parameters are equal.

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

* improve error diagnostic in `Type::check`

We now distinguish between more failure cases to provide an informative error
message.

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

* address review feedback

- Remove `WasmStr::to_str_from_memory` and `WasmList::get_from_memory`
- add `try_new` methods to various `values` types
- avoid using `ExactSizeIterator::len` where we can't trust it
- fix over-constrained bounds on forwarded `ComponentType` impls

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

* rearrange code per review feedback

- Move functions from `types` to `values` module so we can make certain struct fields private
- Rename `try_new` to just `new`

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

* remove special-case equality test for tuples, options, and expecteds

Instead, I've added a FIXME comment and will open an issue to do recursive
structural equality testing.

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

crates/component-macro/Cargo.toml

@@ -17,6 +17,7 @@ proc-macro = true
 proc-macro2 = "1.0"
 quote = "1.0"
 syn = { version = "1.0", features = ["extra-traits"] }
+wasmtime-component-util = { path = "../component-util", version = "=0.40.0" }
 
 [badges]
 maintenance = { status = "actively-developed" }

crates/component-macro/src/lib.rs

@@ -5,6 +5,7 @@ use std::fmt;
 use syn::parse::{Parse, ParseStream};
 use syn::punctuated::Punctuated;
 use syn::{braced, parse_macro_input, parse_quote, Data, DeriveInput, Error, Result, Token};
+use wasmtime_component_util::{DiscriminantSize, FlagsSize};
 
 #[derive(Debug, Copy, Clone)]
 enum VariantStyle {
@@ -147,64 +148,6 @@ fn add_trait_bounds(generics: &syn::Generics, bound: syn::TypeParamBound) -> syn
  generics
 }
 
-#[derive(Debug, Copy, Clone)]
-enum DiscriminantSize {
- Size1,
- Size2,
- Size4,
-}
-
-impl DiscriminantSize {
- fn quote(self, discriminant: usize) -> TokenStream {
- match self {
- Self::Size1 => {
- let discriminant = u8::try_from(discriminant).unwrap();
- quote!(#discriminant)
- }
- Self::Size2 => {
- let discriminant = u16::try_from(discriminant).unwrap();
- quote!(#discriminant)
- }
- Self::Size4 => {
- let discriminant = u32::try_from(discriminant).unwrap();
- quote!(#discriminant)
- }
- }
- }
-}
-
-impl From<DiscriminantSize> for u32 {
- fn from(size: DiscriminantSize) -> u32 {
- match size {
- DiscriminantSize::Size1 => 1,
- DiscriminantSize::Size2 => 2,
- DiscriminantSize::Size4 => 4,
- }
- }
-}
-
-impl From<DiscriminantSize> for usize {
- fn from(size: DiscriminantSize) -> usize {
- match size {
- DiscriminantSize::Size1 => 1,
- DiscriminantSize::Size2 => 2,
- DiscriminantSize::Size4 => 4,
- }
- }
-}
-
-fn discriminant_size(case_count: usize) -> Option<DiscriminantSize> {
- if case_count <= 0xFF {
- Some(DiscriminantSize::Size1)
- } else if case_count <= 0xFFFF {
- Some(DiscriminantSize::Size2)
- } else if case_count <= 0xFFFF_FFFF {
- Some(DiscriminantSize::Size4)
- } else {
- None
- }
-}
-
 struct VariantCase<'a> {
  attrs: &'a [syn::Attribute],
  ident: &'a syn::Ident,
@@ -288,7 +231,7 @@ fn expand_variant(
  ));
  }
 
- let discriminant_size = discriminant_size(body.variants.len()).ok_or_else(|| {
+ let discriminant_size = DiscriminantSize::from_count(body.variants.len()).ok_or_else(|| {
  Error::new(
  input.ident.span(),
  "`enum`s with more than 2^32 variants are not supported",
@@ -417,7 +360,7 @@ fn expand_record_for_component_type(
  const SIZE32: usize = {
  let mut size = 0;
  #sizes
- size
+ #internal::align_to(size, Self::ALIGN32)
  };
 
  const ALIGN32: u32 = {
@@ -439,6 +382,23 @@ fn expand_record_for_component_type(
  Ok(quote!(const _: () = { #expanded };))
 }
 
+fn quote(size: DiscriminantSize, discriminant: usize) -> TokenStream {
+ match size {
+ DiscriminantSize::Size1 => {
+ let discriminant = u8::try_from(discriminant).unwrap();
+ quote!(#discriminant)
+ }
+ DiscriminantSize::Size2 => {
+ let discriminant = u16::try_from(discriminant).unwrap();
+ quote!(#discriminant)
+ }
+ DiscriminantSize::Size4 => {
+ let discriminant = u32::try_from(discriminant).unwrap();
+ quote!(#discriminant)
+ }
+ }
+}
+
 #[proc_macro_derive(Lift, attributes(component))]
 pub fn lift(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
  expand(&LiftExpander, &parse_macro_input!(input as DeriveInput))
@@ -523,7 +483,7 @@ impl Expander for LiftExpander {
  for (index, VariantCase { ident, ty, .. }) in cases.iter().enumerate() {
  let index_u32 = u32::try_from(index).unwrap();
 
- let index_quoted = discriminant_size.quote(index);
+ let index_quoted = quote(discriminant_size, index);
 
  if let Some(ty) = ty {
  lifts.extend(
@@ -666,7 +626,7 @@ impl Expander for LowerExpander {
  for (index, VariantCase { ident, ty, .. }) in cases.iter().enumerate() {
  let index_u32 = u32::try_from(index).unwrap();
 
- let index_quoted = discriminant_size.quote(index);
+ let index_quoted = quote(discriminant_size, index);
 
  let discriminant_size = usize::from(discriminant_size);
 
@@ -989,19 +949,6 @@ impl Parse for Flags {
  }
 }
 
-enum FlagsSize {
- /// Flags can fit in a u8
- Size1,
- /// Flags can fit in a u16
- Size2,
- /// Flags can fit in a specified number of u32 fields
- Size4Plus(usize),
-}
-
-fn ceiling_divide(n: usize, d: usize) -> usize {
- (n + d - 1) / d
-}
-
 #[proc_macro]
 pub fn flags(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
  expand_flags(&parse_macro_input!(input as Flags))
@@ -1010,13 +957,7 @@ pub fn flags(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
 }
 
 fn expand_flags(flags: &Flags) -> Result<TokenStream> {
- let size = if flags.flags.len() <= 8 {
- FlagsSize::Size1
- } else if flags.flags.len() <= 16 {
- FlagsSize::Size2
- } else {
- FlagsSize::Size4Plus(ceiling_divide(flags.flags.len(), 32))
- };
+ let size = FlagsSize::from_count(flags.flags.len());
 
  let ty;
  let eq;

crates/component-util/Cargo.toml

@@ -0,0 +1,11 @@
+[package]
+name = "wasmtime-component-util"
+version = "0.40.0"
+authors = ["The Wasmtime Project Developers"]
+description = "Utility types and functions to support the component model in Wasmtime"
+license = "Apache-2.0 WITH LLVM-exception"
+repository = "https://github.com/bytecodealliance/wasmtime"
+documentation = "https://docs.rs/wasmtime-component-util/"
+categories = ["wasm"]
+keywords = ["webassembly", "wasm"]
+edition = "2021"

crates/component-util/src/lib.rs

@@ -0,0 +1,75 @@
+/// Represents the possible sizes in bytes of the discriminant of a variant type in the component model
+#[derive(Debug, Copy, Clone)]
+pub enum DiscriminantSize {
+ /// 8-bit discriminant
+ Size1,
+ /// 16-bit discriminant
+ Size2,
+ /// 32-bit discriminant
+ Size4,
+}
+
+impl DiscriminantSize {
+ /// Calculate the size of discriminant needed to represent a variant with the specified number of cases.
+ pub fn from_count(count: usize) -> Option<Self> {
+ if count <= 0xFF {
+ Some(Self::Size1)
+ } else if count <= 0xFFFF {
+ Some(Self::Size2)
+ } else if count <= 0xFFFF_FFFF {
+ Some(Self::Size4)
+ } else {
+ None
+ }
+ }
+}
+
+impl From<DiscriminantSize> for u32 {
+ /// Size of the discriminant as a `u32`
+ fn from(size: DiscriminantSize) -> u32 {
+ match size {
+ DiscriminantSize::Size1 => 1,
+ DiscriminantSize::Size2 => 2,
+ DiscriminantSize::Size4 => 4,
+ }
+ }
+}
+
+impl From<DiscriminantSize> for usize {
+ /// Size of the discriminant as a `usize`
+ fn from(size: DiscriminantSize) -> usize {
+ match size {
+ DiscriminantSize::Size1 => 1,
+ DiscriminantSize::Size2 => 2,
+ DiscriminantSize::Size4 => 4,
+ }
+ }
+}
+
+/// Represents the number of bytes required to store a flags value in the component model
+pub enum FlagsSize {
+ /// Flags can fit in a u8
+ Size1,
+ /// Flags can fit in a u16
+ Size2,
+ /// Flags can fit in a specified number of u32 fields
+ Size4Plus(usize),
+}
+
+impl FlagsSize {
+ /// Calculate the size needed to represent a value with the specified number of flags.
+ pub fn from_count(count: usize) -> FlagsSize {
+ if count <= 8 {
+ FlagsSize::Size1
+ } else if count <= 16 {
+ FlagsSize::Size2
+ } else {
+ FlagsSize::Size4Plus(ceiling_divide(count, 32))
+ }
+ }
+}
+
+/// Divide `n` by `d`, rounding up in the case of a non-zero remainder.
+fn ceiling_divide(n: usize, d: usize) -> usize {
+ (n + d - 1) / d
+}

crates/wasmtime/Cargo.toml

@@ -20,6 +20,7 @@ wasmtime-cache = { path = "../cache", version = "=0.40.0", optional = true }
 wasmtime-fiber = { path = "../fiber", version = "=0.40.0", optional = true }
 wasmtime-cranelift = { path = "../cranelift", version = "=0.40.0", optional = true }
 wasmtime-component-macro = { path = "../component-macro", version = "=0.40.0", optional = true }
+wasmtime-component-util = { path = "../component-util", version = "=0.40.0", optional = true }
 target-lexicon = { version = "0.12.0", default-features = false }
 wasmparser = "0.87.0"
 anyhow = "1.0.19"
@@ -115,4 +116,5 @@ component-model = [
  "wasmtime-cranelift?/component-model",
  "wasmtime-runtime/component-model",
  "dep:wasmtime-component-macro",
+ "dep:wasmtime-component-util",
 ]