Make API for exporting JS content more explicit (#4333)

Author: RunDevelopment

crates/cli-support/src/js/mod.rs

@@ -120,6 +120,18 @@ struct FieldAccessor {
     is_optional: bool,
 }
 
+/// Different JS constructs that can be exported.
+enum ExportJs<'a> {
+    /// A class of the form `class Name {...}`.
+    Class(&'a str),
+    /// An anonymous function expression of the form `function(...) {...}`.
+    ///
+    /// Note that the function name is not included in the string.
+    Function(&'a str),
+    /// An arbitrary JS expression.
+    Expression(&'a str),
+}
+
 const INITIAL_HEAP_VALUES: &[&str] = &["undefined", "null", "true", "false"];
 // Must be kept in sync with `src/lib.rs` of the `wasm-bindgen` crate
 const INITIAL_HEAP_OFFSET: usize = 128;
@@ -163,38 +175,46 @@ impl<'a> Context<'a> {
     fn export(
         &mut self,
         export_name: &str,
-        contents: &str,
+        export: ExportJs,
         comments: Option<&str>,
     ) -> Result<(), Error> {
         let definition_name = self.generate_identifier(export_name);
-        if contents.starts_with("class") && definition_name != export_name {
+        if matches!(export, ExportJs::Class(_)) && definition_name != export_name {
             bail!("cannot shadow already defined class `{}`", export_name);
         }
 
-        let contents = contents.trim();
+        // write out comments
         if let Some(c) = comments {
             self.globals.push_str(c);
         }
+
         let global = match self.config.mode {
-            OutputMode::Node { module: false } => {
-                if contents.starts_with("class") {
-                    format!("{}\nmodule.exports.{1} = {1};\n", contents, export_name)
-                } else {
-                    format!("module.exports.{} = {};\n", export_name, contents)
+            OutputMode::Node { module: false } => match export {
+                ExportJs::Class(class) => {
+                    format!("{}\nmodule.exports.{1} = {1};\n", class, export_name)
                 }
-            }
-            OutputMode::NoModules { .. } => {
-                if contents.starts_with("class") {
-                    format!("{}\n__exports.{1} = {1};\n", contents, export_name)
-                } else {
-                    format!("__exports.{} = {};\n", export_name, contents)
+                ExportJs::Function(expr) | ExportJs::Expression(expr) => {
+                    format!("module.exports.{} = {};\n", export_name, expr)
                 }
-            }
+            },
+            OutputMode::NoModules { .. } => match export {
+                ExportJs::Class(class) => {
+                    format!("{}\n__exports.{1} = {1};\n", class, export_name)
+                }
+                ExportJs::Function(expr) | ExportJs::Expression(expr) => {
+                    format!("__exports.{} = {};\n", export_name, expr)
+                }
+            },
             OutputMode::Bundler { .. }
             | OutputMode::Node { module: true }
             | OutputMode::Web
-            | OutputMode::Deno => {
-                if let Some(body) = contents.strip_prefix("function") {
+            | OutputMode::Deno => match export {
+                ExportJs::Class(class) => {
+                    assert_eq!(export_name, definition_name);
+                    format!("export {}\n", class)
+                }
+                ExportJs::Function(function) => {
+                    let body = function.strip_prefix("function").unwrap();
                     if export_name == definition_name {
                         format!("export function {}{}\n", export_name, body)
                     } else {
@@ -203,14 +223,12 @@ impl<'a> Context<'a> {
                             definition_name, body, definition_name, export_name,
                         )
                     }
-                } else if contents.starts_with("class") {
-                    assert_eq!(export_name, definition_name);
-                    format!("export {}\n", contents)
-                } else {
+                }
+                ExportJs::Expression(expr) => {
                     assert_eq!(export_name, definition_name);
-                    format!("export const {} = {};\n", export_name, contents)
+                    format!("export const {} = {};\n", export_name, expr)
                 }
-            }
+            },
         };
         self.global(&global);
         Ok(())
@@ -1169,10 +1187,10 @@ __wbg_set_wasm(wasm);"
 
         self.write_class_field_types(class, &mut ts_dst);
 
-        dst.push_str("}\n");
+        dst.push('}');
         ts_dst.push_str("}\n");
 
-        self.export(name, &dst, Some(&class.comments))?;
+        self.export(name, ExportJs::Class(&dst), Some(&class.comments))?;
 
         if class.generate_typescript {
             self.typescript.push_str(&class.comments);
@@ -2872,7 +2890,11 @@ __wbg_set_wasm(wasm);"
                             self.typescript.push_str(";\n");
                         }
 
-                        self.export(name, &format!("function{}", code), Some(&js_docs))?;
+                        self.export(
+                            name,
+                            ExportJs::Function(&format!("function{}", code)),
+                            Some(&js_docs),
+                        )?;
                         self.globals.push('\n');
                     }
                     AuxExportKind::Constructor(class) => {
@@ -3995,7 +4017,7 @@ __wbg_set_wasm(wasm);"
 
         self.export(
             &enum_.name,
-            &format!("Object.freeze({{\n{}}})", variants),
+            ExportJs::Expression(&format!("Object.freeze({{\n{}}})", variants)),
             Some(&docs),
         )?;