Support serde flatten for Typescript

cli/src/main.rs

@@ -257,12 +257,13 @@ fn main() {
         .filter_map(|dir_entry| dir_entry.path().to_str().map(String::from))
         .collect();
 
+    let supports_flatten = lang.supports_flatten();
     let mut generated_contents = vec![];
     let parsed_data = glob_paths
         .par_iter()
         .map(|filepath| {
             let data = std::fs::read_to_string(filepath).unwrap();
-            let parsed_data = typeshare_core::parser::parse(&data);
+            let parsed_data = typeshare_core::parser::parse(&data, supports_flatten);
             if parsed_data.is_err() {
                 panic!("{}", parsed_data.err().unwrap());
             }

core/src/language/go.rs

@@ -154,6 +154,10 @@ impl Language for Go {
 
         writeln!(w, "}}")
     }
+
+    fn supports_flatten(&self) -> bool {
+        false
+    }
 }
 
 impl Go {

core/src/language/kotlin.rs

@@ -181,6 +181,10 @@ impl Language for Kotlin {
 
         writeln!(w, "}}\n")
     }
+
+    fn supports_flatten(&self) -> bool {
+        false
+    }
 }
 
 impl Kotlin {

core/src/language/mod.rs

@@ -294,4 +294,6 @@ pub trait Language {
 
         Ok(())
     }
+    /// whether `#[serde(flatten)]` macro attribute is supported or not
+    fn supports_flatten(&self) -> bool;
 }

core/src/language/scala.rs

@@ -209,6 +209,10 @@ impl Language for Scala {
         self.write_enum_variants(w, e)?;
         writeln!(w, "}}\n")
     }
+
+    fn supports_flatten(&self) -> bool {
+        false
+    }
 }
 
 impl Scala {

core/src/language/swift.rs

@@ -506,6 +506,10 @@ impl Language for Swift {
 
         writeln!(w, "}}")
     }
+
+    fn supports_flatten(&self) -> bool {
+        false
+    }
 }
 
 impl Swift {

core/src/language/typescript.rs

@@ -110,13 +110,33 @@ impl Language for TypeScript {
 
     fn write_struct(&mut self, w: &mut dyn Write, rs: &RustStruct) -> std::io::Result<()> {
         self.write_comments(w, 0, &rs.comments)?;
+        let mut inheritance = "".to_string();
+        let mut count = 0;
+        for field in rs.fields.iter() {
+            if field.flattened {
+                let ts_ty = match self.format_type(&field.ty, rs.generic_types.as_slice()) {
+                    Ok(v) => v,
+                    Err(e) => return Err(std::io::Error::new(std::io::ErrorKind::InvalidInput, e)),
+                };
+                if count >= 1 {
+                    inheritance.push_str(", ");
+                }
+                inheritance.push_str(ts_ty.as_str());
+                count += 1;
+            }
+        }
         writeln!(
             w,
-            "export interface {}{} {{",
+            "export interface {}{}{} {{",
             rs.id.renamed,
             (!rs.generic_types.is_empty())
                 .then(|| format!("<{}>", rs.generic_types.join(", ")))
-                .unwrap_or_default()
+                .unwrap_or_default(),
+            if !inheritance.is_empty() {
+                format!(" extends {inheritance}")
+            } else {
+                "".to_string()
+            }
         )?;
 
         rs.fields
@@ -160,6 +180,10 @@ impl Language for TypeScript {
             }
         }
     }
+
+    fn supports_flatten(&self) -> bool {
+        true
+    }
 }
 
 impl TypeScript {
@@ -230,6 +254,9 @@ impl TypeScript {
         field: &RustField,
         generic_types: &[String],
     ) -> std::io::Result<()> {
+        if field.flattened {
+            return Ok(());
+        }
         self.write_comments(w, 1, &field.comments)?;
         let ts_ty = self
             .format_type(&field.ty, generic_types)

core/src/lib.rs

@@ -30,7 +30,7 @@ pub fn process_input(
     language: &mut dyn Language,
     out: &mut dyn Write,
 ) -> Result<(), ProcessInputError> {
-    let parsed_data = parser::parse(input)?;
+    let parsed_data = parser::parse(input, language.supports_flatten())?;
     language.generate_types(out, &parsed_data)?;
     Ok(())
 }

core/src/parser.rs

@@ -78,7 +78,7 @@ pub enum ParseError {
 }
 
 /// Parse the given Rust source string into `ParsedData`.
-pub fn parse(input: &str) -> Result<ParsedData, ParseError> {
+pub fn parse(input: &str, supports_flatten: bool) -> Result<ParsedData, ParseError> {
     let mut parsed_data = ParsedData::default();
 
     // We will only produce output for files that contain the `#[typeshare]`
@@ -94,7 +94,7 @@ pub fn parse(input: &str) -> Result<ParsedData, ParseError> {
     for item in flatten_items(source.items.iter()) {
         match item {
             syn::Item::Struct(s) if has_typeshare_annotation(&s.attrs) => {
-                parsed_data.push_rust_thing(parse_struct(s)?);
+                parsed_data.push_rust_thing(parse_struct(s, supports_flatten)?);
             }
             syn::Item::Enum(e) if has_typeshare_annotation(&e.attrs) => {
                 parsed_data.push_rust_thing(parse_enum(e)?);
@@ -131,7 +131,7 @@ fn flatten_items<'a>(
 ///
 /// This function can currently return something other than a struct, which is a
 /// hack.
-fn parse_struct(s: &ItemStruct) -> Result<RustItem, ParseError> {
+fn parse_struct(s: &ItemStruct, supports_flatten: bool) -> Result<RustItem, ParseError> {
     let serde_rename_all = serde_rename_all(&s.attrs);
 
     let generic_types = s
@@ -156,6 +156,7 @@ fn parse_struct(s: &ItemStruct) -> Result<RustItem, ParseError> {
         }));
     }
 
+    let mut flattened: bool = false;
     Ok(match &s.fields {
         // Structs
         Fields::Named(f) => {
@@ -170,9 +171,14 @@ fn parse_struct(s: &ItemStruct) -> Result<RustItem, ParseError> {
                         RustType::try_from(&f.ty)?
                     };
 
-                    if serde_flatten(&f.attrs) {
-                        return Err(ParseError::SerdeFlattenNotAllowed);
-                    }
+                    flattened = if serde_flatten(&f.attrs) {
+                        if !supports_flatten {
+                            return Err(ParseError::SerdeFlattenNotAllowed);
+                        }
+                        true
+                    } else {
+                        false
+                    };
 
                     let has_default = serde_default(&f.attrs);
                     let decorators = get_field_decorators(&f.attrs);
@@ -183,6 +189,7 @@ fn parse_struct(s: &ItemStruct) -> Result<RustItem, ParseError> {
                         comments: parse_comment_attrs(&f.attrs),
                         has_default,
                         decorators,
+                        flattened,
                     })
                 })
                 .collect::<Result<_, ParseError>>()?;
@@ -380,6 +387,7 @@ fn parse_enum_variant(
                         comments: parse_comment_attrs(&f.attrs),
                         has_default,
                         decorators,
+                        flattened: false,
                     })
                 })
                 .collect::<Result<Vec<_>, ParseError>>()?,

core/src/rust_types.rs

@@ -77,6 +77,9 @@ pub struct RustField {
     /// Language-specific decorators assigned to a given field.
     /// The keys are language names (e.g. SupportedLanguage::TypeScript), the values are decorators (e.g. readonly)
     pub decorators: HashMap<SupportedLanguage, HashSet<String>>,
+    /// Whether the field should be flattened or not,
+    /// as per `#[serde(flatten)]` definition.
+    pub flattened: bool,
 }
 
 /// A Rust type.

core/tests/snapshot_tests.rs

@@ -67,7 +67,7 @@ fn check(
     )?;
 
     let mut typeshare_output: Vec<u8> = Vec::new();
-    let parsed_data = typeshare_core::parser::parse(&rust_input)?;
+    let parsed_data = typeshare_core::parser::parse(&rust_input, lang.supports_flatten())?;
     lang.generate_types(&mut typeshare_output, &parsed_data)?;
 
     let typeshare_output = String::from_utf8(typeshare_output)?;