Fully qualify uses of Result in scaffolding/macro code

PR mozilla#1469 introduced an incompatibility with a local `type Result<T> =
std::result::Result<T, MyError>` type alias. As can be seen with the included
test without the fix applied:

```
error[E0107]: this type alias takes 1 generic argument but 2 generic arguments were supplied
  --> /mounted_workdir/target/debug/build/unary-result-alias-f408c03f1955dadd/out/unary-result-alias.uniffi.rs:79:1
   |
79 | / #[::uniffi::ffi_converter_error(
80 | |     tag = crate::UniFfiTag,
81 | |     flat_error,
82 | |
83 | | )]
   | |  ^
   | |  |
   | |__expected 1 generic argument
   |    help: remove this generic argument
   |
note: type alias defined here, with 1 generic parameter: `T`
  --> fixtures/regressions/unary-result-alias/src/lib.rs:7:10
   |
7  | pub type Result<T> = std::result::Result<T, MyError>;
   |          ^^^^^^ -
   = note: this error originates in the macro `::uniffi::ffi_converter_default_return` which comes from the expansion of the attribute macro `::uniffi::ffi_converter_error` (in Nightly builds, run with -Z macro-backtrace for more info)
```

Fixing the macros in `uniffi_core` to use `::std::result::Result` fixes that.

This exposes a further case in the generated code:

```
error[E0107]: this type alias takes 1 generic argument but 2 generic arguments were supplied
   --> /mounted_workdir/target/debug/build/unary-result-alias-f408c03f1955dadd/out/unary-result-alias.uniffi.rs:108:40
    |
108 |     uniffi::rust_call(call_status, || <Result<(), r#MyError> as ::uniffi::FfiConverter<crate::UniFfiTag>>::lower_return(
    |                                        ^^^^^^     --------- help: remove this generic argument
    |                                        |
    |                                        expected 1 generic argument
    |
note: type alias defined here, with 1 generic parameter: `T`
   --> fixtures/regressions/unary-result-alias/src/lib.rs:7:10
    |
7   | pub type Result<T> = std::result::Result<T, MyError>;
    |          ^^^^^^ -
```

So the same change is required to the output produced by bindgen.

Cargo.toml

@@ -46,6 +46,7 @@ members = [
  "fixtures/regressions/missing-newline",
  "fixtures/regressions/swift-callbacks-omit-labels",
  "fixtures/regressions/swift-dictionary-nesting",
+ "fixtures/regressions/unary-result-alias",
  "fixtures/uitests",
  "fixtures/uniffi-fixture-time",
  "fixtures/version-mismatch",

fixtures/regressions/unary-result-alias/Cargo.toml

@@ -0,0 +1,20 @@
+[package]
+name = "unary-result-alias"
+version = "0.1.0"
+edition = "2021"
+license = "MPL-2.0"
+publish = false
+
+[lib]
+name = "uniffi_unary_result_alias"
+crate-type = ["lib", "cdylib"]
+
+[dependencies]
+uniffi = { path = "../../../uniffi" }
+thiserror = "1.0"
+
+[build-dependencies]
+uniffi = {path = "../../../uniffi", features = ["build"] }
+
+[dev-dependencies]
+uniffi = {path = "../../../uniffi", features = ["bindgen-tests"] }

fixtures/regressions/unary-result-alias/README.md

@@ -0,0 +1,7 @@
+Ensure that generated bindings are compatible with crates which have a
+local
+
+```rust
+pub enum MyError { ... };
+pub type Result<T> = std::result::Result<T, MyError>
+```

fixtures/regressions/unary-result-alias/build.rs

@@ -0,0 +1,7 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+fn main() {
+ uniffi::generate_scaffolding("./src/unary-result-alias.udl").unwrap();
+}

fixtures/regressions/unary-result-alias/src/lib.rs

@@ -0,0 +1,13 @@
+#[derive(Debug, thiserror::Error)]
+pub enum MyError {
+ #[error("Badness has happened")]
+ AllGoneWrong,
+}
+
+pub type Result<T> = std::result::Result<T, MyError>;
+
+pub fn returns_unary_result_alias() -> Result<()> {
+ Ok(())
+}
+
+include!(concat!(env!("OUT_DIR"), "/unary-result-alias.uniffi.rs"));

fixtures/regressions/unary-result-alias/src/unary-result-alias.udl

@@ -0,0 +1,9 @@
+[Error]
+enum MyError {
+ "AllGoneWrong",
+};
+
+namespace unary_result_alias {
+ [Throws=MyError]
+ void returns_unary_result_alias();
+};

fixtures/regressions/unary-result-alias/tests/bindings/test.kts

@@ -0,0 +1,7 @@
+// This is just a basic "it compiled and ran" test.
+// What we're really guarding against is failure to
+// compile the bindings as a result of buggy codegen.
+
+import uniffi.unary_result_alias.*
+
+returnsUnaryResultAlias()

fixtures/regressions/unary-result-alias/tests/bindings/test.py

@@ -0,0 +1,7 @@
+# This is just a basic "it loaded and ran" test.
+# What we're really guarding against is failure to
+# load the bindings as a result of buggy codegen.
+
+from unary_result_alias import *
+
+returns_unary_result_alias()

fixtures/regressions/unary-result-alias/tests/bindings/test.swift

@@ -0,0 +1,7 @@
+// This is just a basic "it compiled and run" test.
+// What we're really guarding against is failure to
+// compile the bindings as a result of buggy codegen.
+
+import unary_result_alias
+
+try returnsUnaryResultAlias()

fixtures/regressions/unary-result-alias/tests/test_generated_bindings.rs

@@ -0,0 +1,5 @@
+uniffi::build_foreign_language_testcases!(
+ "tests/bindings/test.py",
+ "tests/bindings/test.kts",
+ "tests/bindings/test.swift",
+);

uniffi_bindgen/src/scaffolding/mod.rs

@@ -108,7 +108,7 @@ mod filters {
  };
  Ok(match callable.throws_type() {
  Some(e) => format!(
- "<Result<{}, {}> as ::uniffi::FfiConverter<crate::UniFfiTag>>",
+ "<std::result::Result<{}, {}> as ::uniffi::FfiConverter<crate::UniFfiTag>>",
  result_type,
  type_rs(&e)?
  ),

uniffi_core/src/lib.rs

@@ -288,7 +288,7 @@ macro_rules! ffi_converter_default_return {
  ($uniffi_tag:ty) => {
  type ReturnType = <Self as $crate::FfiConverter<$uniffi_tag>>::FfiType;
 
- fn lower_return(v: Self) -> Result<Self::FfiType, $crate::RustBuffer> {
+ fn lower_return(v: Self) -> ::std::result::Result<Self::FfiType, $crate::RustBuffer> {
  Ok(<Self as $crate::FfiConverter<$uniffi_tag>>::lower(v))
  }
  };
@@ -338,7 +338,7 @@ macro_rules! ffi_converter_forward {
  <$T as $crate::FfiConverter<$existing_impl_tag>>::lower(obj)
  }
 
- fn lower_return(v: Self) -> Result<Self::ReturnType, $crate::RustBuffer> {
+ fn lower_return(v: Self) -> ::std::result::Result<Self::ReturnType, $crate::RustBuffer> {
  <$T as $crate::FfiConverter<$existing_impl_tag>>::lower_return(v)
  }