wiggle-generate: always pass GuestPtr by reference

with the prev approach, it would be passed by reference sometimes
(e.g. when used as an Array argument) but by value most of the time.
this was inconsistient.

theres no need to pass the owned version, all operations are &self.

crates/wiggle/crates/generate/src/funcs.rs

@@ -2,6 +2,7 @@ use proc_macro2::TokenStream;
 use quote::quote;
 
 use crate::lifetimes::anon_lifetime;
+use crate::module_trait::passed_by_reference;
 use crate::names::Names;
 
 pub fn define_func(names: &Names, func: &witx::InterfaceFunc) -> TokenStream {
@@ -67,10 +68,10 @@ pub fn define_func(names: &Names, func: &witx::InterfaceFunc) -> TokenStream {
         .map(|p| marshal_arg(names, p, error_handling(p.name.as_str())));
     let trait_args = func.params.iter().map(|param| {
         let name = names.func_param(&param.name);
-        match param.tref.type_().passed_by() {
-            witx::TypePassedBy::Value { .. } => quote!(#name),
-            witx::TypePassedBy::Pointer { .. } => quote!(&#name),
-            witx::TypePassedBy::PointerLengthPair { .. } => quote!(&#name),
+        if passed_by_reference(&*param.tref.type_()) {
+            quote!(&#name)
+        } else {
+            quote!(#name)
         }
     });
 

crates/wiggle/crates/generate/src/module_trait.rs

@@ -5,6 +5,21 @@ use crate::lifetimes::{anon_lifetime, LifetimeExt};
 use crate::names::Names;
 use witx::Module;
 
+pub fn passed_by_reference(ty: &witx::Type) -> bool {
+    let passed_by = match ty.passed_by() {
+        witx::TypePassedBy::Value { .. } => false,
+        witx::TypePassedBy::Pointer { .. } | witx::TypePassedBy::PointerLengthPair { .. } => true,
+    };
+    match ty {
+        witx::Type::Builtin(b) => match &*b {
+            witx::BuiltinType::String => true,
+            _ => passed_by,
+        },
+        witx::Type::Pointer(_) | witx::Type::ConstPointer(_) | witx::Type::Array(_) => true,
+        _ => passed_by,
+    }
+}
+
 pub fn define_module_trait(names: &Names, m: &Module) -> TokenStream {
     let traitname = names.trait_name(&m.name);
     let traitmethods = m.funcs().map(|f| {
@@ -25,10 +40,10 @@ pub fn define_module_trait(names: &Names, m: &Module) -> TokenStream {
         let args = f.params.iter().map(|arg| {
             let arg_name = names.func_param(&arg.name);
             let arg_typename = names.type_ref(&arg.tref, lifetime.clone());
-            let arg_type = match arg.tref.type_().passed_by() {
-                witx::TypePassedBy::Value { .. } => quote!(#arg_typename),
-                witx::TypePassedBy::Pointer { .. } => quote!(&#arg_typename),
-                witx::TypePassedBy::PointerLengthPair { .. } => quote!(&#arg_typename),
+            let arg_type = if passed_by_reference(&*arg.tref.type_()) {
+                quote!(&#arg_typename)
+            } else {
+                quote!(#arg_typename)
             };
             quote!(#arg_name: #arg_type)
         });

crates/wiggle/tests/flags.rs

@@ -14,7 +14,7 @@ impl<'a> flags::Flags for WasiCtx<'a> {
     fn configure_car(
         &self,
         old_config: types::CarConfig,
-        other_config_ptr: GuestPtr<types::CarConfig>,
+        other_config_ptr: &GuestPtr<types::CarConfig>,
     ) -> Result<types::CarConfig, types::Errno> {
         let other_config = other_config_ptr.read().map_err(|e| {
             eprintln!("old_config_ptr error: {}", e);

crates/wiggle/tests/pointers.rs

@@ -13,9 +13,9 @@ impl<'a> pointers::Pointers for WasiCtx<'a> {
     fn pointers_and_enums<'b>(
         &self,
         input1: types::Excuse,
-        input2_ptr: GuestPtr<'b, types::Excuse>,
-        input3_ptr: GuestPtr<'b, types::Excuse>,
-        input4_ptr_ptr: GuestPtr<'b, GuestPtr<'b, types::Excuse>>,
+        input2_ptr: &GuestPtr<'b, types::Excuse>,
+        input3_ptr: &GuestPtr<'b, types::Excuse>,
+        input4_ptr_ptr: &GuestPtr<'b, GuestPtr<'b, types::Excuse>>,
     ) -> Result<(), types::Errno> {
         println!("BAZ input1 {:?}", input1);
         let input2: types::Excuse = input2_ptr.read().map_err(|e| {
@@ -52,7 +52,7 @@ impl<'a> pointers::Pointers for WasiCtx<'a> {
         println!("input4 {:?}", input4);
 
         // Write ptr value to mutable ptr:
-        input4_ptr_ptr.write(input2_ptr).map_err(|e| {
+        input4_ptr_ptr.write(*input2_ptr).map_err(|e| {
             eprintln!("input4_ptr_ptr error: {}", e);
             types::Errno::InvalidArg
         })?;

crates/wiggle/tests/structs.rs

@@ -44,10 +44,13 @@ impl<'a> structs::Structs for WasiCtx<'a> {
 
     fn return_pair_of_ptrs<'b>(
         &self,
-        first: GuestPtr<'b, i32>,
-        second: GuestPtr<'b, i32>,
+        first: &GuestPtr<'b, i32>,
+        second: &GuestPtr<'b, i32>,
     ) -> Result<types::PairIntPtrs<'b>, types::Errno> {
-        Ok(types::PairIntPtrs { first, second })
+        Ok(types::PairIntPtrs {
+            first: *first,
+            second: *second,
+        })
     }
 }
 

crates/wiggle/tests/wasi.rs

@@ -23,7 +23,7 @@ impl<'a> GuestErrorType<'a> for types::Errno {
 }
 
 impl<'a> crate::wasi_snapshot_preview1::WasiSnapshotPreview1 for WasiCtx<'a> {
-    fn args_get(&self, _argv: GuestPtr<GuestPtr<u8>>, _argv_buf: GuestPtr<u8>) -> Result<()> {
+    fn args_get(&self, _argv: &GuestPtr<GuestPtr<u8>>, _argv_buf: &GuestPtr<u8>) -> Result<()> {
         unimplemented!("args_get")
     }
 
@@ -33,8 +33,8 @@ impl<'a> crate::wasi_snapshot_preview1::WasiSnapshotPreview1 for WasiCtx<'a> {
 
     fn environ_get(
         &self,
-        _environ: GuestPtr<GuestPtr<u8>>,
-        _environ_buf: GuestPtr<u8>,
+        _environ: &GuestPtr<GuestPtr<u8>>,
+        _environ_buf: &GuestPtr<u8>,
     ) -> Result<()> {
         unimplemented!("environ_get")
     }
@@ -153,7 +153,7 @@ impl<'a> crate::wasi_snapshot_preview1::WasiSnapshotPreview1 for WasiCtx<'a> {
     fn fd_prestat_dir_name(
         &self,
         _fd: types::Fd,
-        _path: GuestPtr<u8>,
+        _path: &GuestPtr<u8>,
         _path_len: types::Size,
     ) -> Result<()> {
         unimplemented!("fd_prestat_dir_name")
@@ -175,7 +175,7 @@ impl<'a> crate::wasi_snapshot_preview1::WasiSnapshotPreview1 for WasiCtx<'a> {
     fn fd_readdir(
         &self,
         _fd: types::Fd,
-        _buf: GuestPtr<u8>,
+        _buf: &GuestPtr<u8>,
         _buf_len: types::Size,
         _cookie: types::Dircookie,
     ) -> Result<types::Size> {
@@ -260,7 +260,7 @@ impl<'a> crate::wasi_snapshot_preview1::WasiSnapshotPreview1 for WasiCtx<'a> {
         &self,
         _fd: types::Fd,
         _path: &GuestPtr<'_, str>,
-        _buf: GuestPtr<u8>,
+        _buf: &GuestPtr<u8>,
         _buf_len: types::Size,
     ) -> Result<types::Size> {
         unimplemented!("path_readlink")
@@ -295,8 +295,8 @@ impl<'a> crate::wasi_snapshot_preview1::WasiSnapshotPreview1 for WasiCtx<'a> {
 
     fn poll_oneoff(
         &self,
-        _in_: GuestPtr<types::Subscription>,
-        _out: GuestPtr<types::Event>,
+        _in_: &GuestPtr<types::Subscription>,
+        _out: &GuestPtr<types::Event>,
         _nsubscriptions: types::Size,
     ) -> Result<types::Size> {
         unimplemented!("poll_oneoff")
@@ -314,7 +314,7 @@ impl<'a> crate::wasi_snapshot_preview1::WasiSnapshotPreview1 for WasiCtx<'a> {
         unimplemented!("sched_yield")
     }
 
-    fn random_get(&self, _buf: GuestPtr<u8>, _buf_len: types::Size) -> Result<()> {
+    fn random_get(&self, _buf: &GuestPtr<u8>, _buf_len: types::Size) -> Result<()> {
         unimplemented!("random_get")
     }