Add UI test for invalid module items (#124)

This commit introduces a compile time error for invalid module items.

For example, the following will now give a descriptive compile time
error:

```rust
#[swift_bridge::bridge]
mod ffi {
    use std;
    fn foo() {}
}

// error: Only `extern` blocks, structs and enums are supported.
//  --> tests/ui/invalid-module-item.rs:6:5
//   |
// 3 |     use std;
//   |     ^^^^^^^^
//
// error: Only `extern` blocks, structs and enums are supported.
//  --> tests/ui/invalid-module-item.rs:7:5
//   |
// 4 |     fn foo() {}
//   |     ^^^^^^^^^^^
//
```

Before this commit we would simply panic with an unhelpful message.

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "swift-bridge"
-version = "0.1.41"
+version = "0.1.42"
 edition = "2021"
 keywords = ["swift", "ffi", "bindings", "ios", "mac"]
 description = "Generate FFI bindings for safe interop between Rust and Swift."
@@ -14,10 +14,10 @@ default = []
 async = ["tokio", "once_cell"]
 
 [build-dependencies]
-swift-bridge-build = {version = "0.1.41", path = "crates/swift-bridge-build"}
+swift-bridge-build = {version = "0.1.42", path = "crates/swift-bridge-build"}
 
 [dependencies]
-swift-bridge-macro = {version = "0.1.41", path = "crates/swift-bridge-macro"}
+swift-bridge-macro = {version = "0.1.42", path = "crates/swift-bridge-macro"}
 
 ################################################################################
 # Optional features used for async function support.

crates/swift-bridge-build/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "swift-bridge-build"
-version = "0.1.41"
+version = "0.1.42"
 edition = "2021"
 keywords = ["swift", "ffi", "bindings", "ios", "mac"]
 description = "Parse Rust files for swift-bridge modules and generate the corresponding Swift and C code for them."
@@ -9,6 +9,6 @@ license = "Apache-2.0/MIT"
 
 [dependencies]
 proc-macro2 = "1"
-swift-bridge-ir = {version = "0.1.41", path = "../swift-bridge-ir"}
+swift-bridge-ir = {version = "0.1.42", path = "../swift-bridge-ir"}
 syn = {version = "1"}
 tempfile = "3.3"

crates/swift-bridge-cli/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "swift-bridge-cli"
-version = "0.1.41"
+version = "0.1.42"
 edition = "2021"
 keywords = ["swift", "ffi", "bindings", "ios", "mac"]
 description = "Parse Rust files for swift-bridge modules and generate the corresponding Swift and C code for them."
@@ -9,4 +9,4 @@ license = "Apache-2.0/MIT"
 
 [dependencies]
 clap = "3"
-swift-bridge-build = { version = "0.1.41", path = "../swift-bridge-build" }
+swift-bridge-build = { version = "0.1.42", path = "../swift-bridge-build" }

crates/swift-bridge-ir/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "swift-bridge-ir"
-version = "0.1.41"
+version = "0.1.42"
 edition = "2021"
 keywords = ["swift", "ffi", "bindings", "ios", "mac"]
 description = "Holds the data structures and logic for bridge module parsing and code generation."

crates/swift-bridge-ir/src/errors/parse_error.rs

@@ -1,6 +1,6 @@
 use proc_macro2::Ident;
 use quote::ToTokens;
-use syn::{Error, FnArg, Receiver};
+use syn::{Error, FnArg, Item, Receiver};
 use syn::{ForeignItemType, LitStr};
 use syn::{Token, Type};
 
@@ -19,46 +19,35 @@ pub(crate) enum ParseError {
     },
     /// `fn foo (&self)`
     ///           ----
-    AmbiguousSelf {
-        self_: Receiver,
-    },
+    AmbiguousSelf { self_: Receiver },
     /// fn foo (bar: &Bar);
     /// If Bar wasn't declared using a `type Bar` declaration.
-    UndeclaredType {
-        ty: Type,
-    },
+    UndeclaredType { ty: Type },
     /// Declared a type that we already support.
     /// Example: `type u32`
-    DeclaredBuiltInType {
-        ty: ForeignItemType,
-    },
+    DeclaredBuiltInType { ty: ForeignItemType },
     /// A bridge module struct with one or more fields must have a
     /// `#\[swift_bridge(swift_repr ="...")\[\]` attribute so that we know whether to create a
     /// `struct` or `class` on the Swift side.
-    StructMissingSwiftRepr {
-        struct_ident: Ident,
-    },
+    StructMissingSwiftRepr { struct_ident: Ident },
     /// Only "class" and "struct" can be used as swift_repr.
-    StructInvalidSwiftRepr {
-        swift_repr_attr_value: LitStr,
-    },
+    StructInvalidSwiftRepr { swift_repr_attr_value: LitStr },
     /// A struct was declared with an unrecognized attribute.
-    StructUnrecognizedAttribute {
-        attribute: Ident,
-    },
+    StructUnrecognizedAttribute { attribute: Ident },
     /// There is no reason to use `swift_repr = "class"` on an empty struct.
     /// It's extra overhead with no advantages.
     EmptyStructHasSwiftReprClass {
         struct_ident: Ident,
         swift_repr_attr_value: LitStr,
     },
+    /// See [`FunctionAttributeParseError`]
     FunctionAttribute(FunctionAttributeParseError),
     /// The function argument is a mutable reference to a Copy opaque type.
     /// We do not currently support passing mutable references to Copy opaque types across FFI.
     // Would need to Box the copy type and pass a pointer between languages.
-    ArgCopyAndRefMut {
-        arg: FnArg,
-    },
+    ArgCopyAndRefMut { arg: FnArg },
+    /// There was an unsupported item in the module, such as a `use` statement.
+    InvalidModuleItem { item: Item },
 }
 
 /// An error while parsing a function attribute.
@@ -191,6 +180,10 @@ struct {struct_name};
                     format!(r#"Mutable references to opaque Copy types are not yet supported."#);
                 Error::new_spanned(arg, message)
             }
+            ParseError::InvalidModuleItem { item } => {
+                let message = format!(r#"Only `extern` blocks, structs and enums are supported."#);
+                Error::new_spanned(item, message)
+            }
         }
     }
 }

crates/swift-bridge-ir/src/parse.rs

@@ -105,13 +105,9 @@ impl Parse for SwiftBridgeModuleAndErrors {
                             TypeDeclaration::Shared(SharedTypeDeclaration::Enum(shared_enum)),
                         );
                     }
-                    _ => {
-                        todo!(
-                            r#"
-                        Push an error that the module may only contain `extern` blocks, structs
-                        and enums
-                        "#
-                        )
+                    invalid_item => {
+                        let error = ParseError::InvalidModuleItem { item: invalid_item };
+                        errors.push(error);
                     }
                 };
             }
@@ -146,7 +142,7 @@ impl Parse for SwiftBridgeModuleAndErrors {
 #[cfg(test)]
 mod tests {
     use super::*;
-    use crate::test_utils::parse_ok;
+    use crate::test_utils::{parse_errors, parse_ok};
 
     /// Verify that we can parse a cfg feature from a module.
     #[test]
@@ -167,4 +163,26 @@ mod tests {
             }
         };
     }
+
+    /// Verify that we get an error when parsing an unsupported module item, such as a
+    /// `use` statement.
+    #[test]
+    fn invalid_module_item() {
+        let tokens = quote! {
+            #[swift_bridge::bridge]
+            mod foo {
+                use std;
+            }
+        };
+
+        let errors = parse_errors(tokens);
+
+        assert_eq!(errors.len(), 1);
+        match &errors[0] {
+            ParseError::InvalidModuleItem { item } => {
+                assert!(matches!(item, Item::Use(_)))
+            }
+            _ => panic!(),
+        }
+    }
 }

crates/swift-bridge-macro/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "swift-bridge-macro"
-version = "0.1.41"
+version = "0.1.42"
 edition = "2021"
 keywords = ["swift", "ffi", "bindings", "ios", "mac"]
 description = "Powers swift-bridge module code generation."
@@ -14,7 +14,7 @@ proc-macro = true
 proc-macro2 = "1"
 quote = "1"
 syn = { version = "1", features = ["full"] }
-swift-bridge-ir = {version = "0.1.41", path = "../swift-bridge-ir"}
+swift-bridge-ir = {version = "0.1.42", path = "../swift-bridge-ir"}
 
 [dev-dependencies]
 swift-bridge = {path = "../../"}

crates/swift-bridge-macro/tests/ui/invalid-module-item.rs

@@ -0,0 +1,10 @@
+//! # To Run
+//! cargo test -p swift-bridge-macro -- ui trybuild=invalid-module-item.rs
+
+#[swift_bridge::bridge]
+mod ffi {
+    use std;
+    fn foo() {}
+}
+
+fn main() {}

crates/swift-bridge-macro/tests/ui/invalid-module-item.stderr

@@ -0,0 +1,11 @@
+error: Only `extern` blocks, structs and enums are supported.
+ --> tests/ui/invalid-module-item.rs:6:5
+  |
+6 |     use std;
+  |     ^^^^^^^^
+
+error: Only `extern` blocks, structs and enums are supported.
+ --> tests/ui/invalid-module-item.rs:7:5
+  |
+7 |     fn foo() {}
+  |     ^^^^^^^^^^^