Pretty-display return types.

CHANGELOG.md

@@ -11,6 +11,11 @@ Bug fixes
 * `set_bit` for bit-flags with negative index now works correctly.
 * Misnamed `params` field `name` in the JSON output of `Engine::gen_fn_metadata_to_json` is fixed (was incorrectly named `type`).
 
+Enhancements
+------------
+
+* Formatting of return types in functions metadata info is improved.
+
 
 Version 1.4.0
 =============

src/module/mod.rs

@@ -87,6 +87,27 @@ pub struct FuncInfo {
 }
 
 impl FuncInfo {
+    /// Format a return type to be display-friendly.
+    ///
+    /// `()` is cleared.  
+    /// [`RhaiResult`][crate::RhaiResult] and [`RhaiResultOf<T>`] are expanded.
+    pub fn format_return_type(typ: &str) -> std::borrow::Cow<str> {
+        const RHAI_RESULT_TYPE: &str = "RhaiResult";
+        const RHAI_RESULT_TYPE_EXPAND: &str = "Result<Dynamic, Box<EvalAltResult>>";
+        const RHAI_RESULT_OF_TYPE: &str = "RhaiResultOf<";
+        const RHAI_RESULT_OF_TYPE_EXPAND: &str = "Result<{}, Box<EvalAltResult>>";
+
+        match typ {
+            "" | "()" => "".into(),
+            RHAI_RESULT_TYPE => RHAI_RESULT_TYPE_EXPAND.into(),
+            ty if ty.starts_with(RHAI_RESULT_OF_TYPE) && ty.ends_with(">") => {
+                RHAI_RESULT_OF_TYPE_EXPAND
+                    .replace("{}", ty[RHAI_RESULT_OF_TYPE.len()..ty.len() - 1].trim())
+                    .into()
+            }
+            ty => ty.into(),
+        }
+    }
     /// Generate a signature of the function.
     /// Exported under the `metadata` feature only.
     #[cfg(feature = "metadata")]
@@ -94,6 +115,8 @@ impl FuncInfo {
     pub fn gen_signature(&self) -> String {
         let mut sig = format!("{}(", self.metadata.name);
 
+        let return_type = Self::format_return_type(&self.metadata.return_type);
+
         if !self.metadata.params_info.is_empty() {
             let params: StaticVec<_> = self
                 .metadata
@@ -102,14 +125,11 @@ impl FuncInfo {
                 .map(|s| s.as_str())
                 .collect();
             sig.push_str(&params.join(", "));
-            sig.push_str(")");
+            sig.push(')');
 
-            match self.metadata.return_type.as_str() {
-                "" | "()" => (),
-                ty => {
+            if !return_type.is_empty() {
                 sig.push_str(" -> ");
-                    sig.push_str(ty);
-                }
+                sig.push_str(&return_type);
             }
         } else {
             for x in 0..self.metadata.params {
@@ -119,14 +139,14 @@ impl FuncInfo {
                 }
             }
 
-            if self.func.is_script() {
             sig.push(')');
-            } else {
-                sig.push_str(")");
 
-                match self.metadata.return_type.as_str() {
-                    "()" => (),
-                    _ => sig.push_str(" -> ?"),
+            if !self.func.is_script() {
+                sig.push(')');
+
+                if !return_type.is_empty() {
+                    sig.push_str(" -> ");
+                    sig.push_str(&return_type);
                 }
             }
         }

src/serde/metadata.rs

@@ -70,8 +70,11 @@ struct FnMetadata<'a> {
     pub num_params: usize,
     #[serde(default, skip_serializing_if = "Vec::is_empty")]
     pub params: Vec<FnParam<'a>>,
+    // No idea why the following is needed otherwise serde comes back with a lifetime error
     #[serde(default, skip_serializing_if = "Option::is_none")]
-    pub return_type: Option<&'a str>,
+    pub _dummy: Option<&'a str>,
+    #[serde(default, skip_serializing_if = "String::is_empty")]
+    pub return_type: String,
     pub signature: String,
     #[serde(default, skip_serializing_if = "Vec::is_empty")]
     pub doc_comments: Vec<&'a str>,
@@ -126,10 +129,8 @@ impl<'a> From<&'a FuncInfo> for FnMetadata<'a> {
                     FnParam { name, typ }
                 })
                 .collect(),
-            return_type: match info.metadata.return_type.as_str() {
-                "" | "()" => None,
-                ty => Some(ty),
-            },
+            _dummy: None,
+            return_type: FuncInfo::format_return_type(&info.metadata.return_type).into_owned(),
             signature: info.gen_signature(),
             doc_comments: if info.func.is_script() {
                 #[cfg(feature = "no_function")]