Merge pull request #863 from napi-rs/const-var

feat(napi-derive): support const export

crates/backend/src/ast.rs

@@ -1,5 +1,5 @@
 use proc_macro2::Ident;
-use syn::{Attribute, Type};
+use syn::{Attribute, Expr, Type};
 
 #[derive(Debug, Clone)]
 pub struct NapiFn {
@@ -93,3 +93,11 @@ pub struct NapiEnumVariant {
   pub val: i32,
   pub comments: Vec<String>,
 }
+
+#[derive(Debug, Clone)]
+pub struct NapiConst {
+  pub name: Ident,
+  pub js_name: String,
+  pub type_name: Type,
+  pub value: Expr,
+}

crates/backend/src/codegen.rs

@@ -2,6 +2,7 @@ use proc_macro2::{Ident, Span, TokenStream};
 
 use crate::BindgenResult;
 
+mod r#const;
 mod r#enum;
 mod r#fn;
 mod r#struct;

crates/backend/src/codegen/const.rs

@@ -0,0 +1,41 @@
+use proc_macro2::{Literal, TokenStream};
+use quote::ToTokens;
+
+use crate::{codegen::get_register_ident, BindgenResult, NapiConst, TryToTokens};
+
+impl TryToTokens for NapiConst {
+  fn try_to_tokens(&self, tokens: &mut TokenStream) -> BindgenResult<()> {
+    let register = self.gen_module_register();
+    (quote! {
+      #register
+    })
+    .to_tokens(tokens);
+
+    Ok(())
+  }
+}
+
+impl NapiConst {
+  fn gen_module_register(&self) -> TokenStream {
+    let name_str = self.name.to_string();
+    let name_ident = self.name.clone();
+    let js_name_lit = Literal::string(&self.js_name);
+    let register_name = get_register_ident(&name_str);
+    let type_name = &self.type_name;
+    quote! {
+      #[allow(non_snake_case)]
+      #[allow(clippy::all)]
+      #[napi::bindgen_prelude::ctor]
+      fn #register_name() {
+        use std::ffi::CString;
+        use std::ptr;
+
+        unsafe fn cb(env: napi::sys::napi_env) -> napi::Result<napi::sys::napi_value> {
+          <#type_name as napi::bindgen_prelude::ToNapiValue>::to_napi_value(env, #name_ident)
+        }
+
+        napi::bindgen_prelude::register_module_export(#js_name_lit, cb);
+      }
+    }
+  }
+}

crates/backend/src/lib.rs

@@ -53,4 +53,5 @@ napi_ast_impl! {
  (Struct, NapiStruct),
  (Impl, NapiImpl),
  (Enum, NapiEnum),
+ (Const, NapiConst),
 }

crates/backend/src/typegen.rs

@@ -1,3 +1,4 @@
+mod r#const;
 mod r#enum;
 mod r#fn;
 pub(crate) mod r#struct;

crates/backend/src/typegen/const.rs

@@ -0,0 +1,17 @@
+use super::{ToTypeDef, TypeDef};
+
+use crate::{ty_to_ts_type, NapiConst};
+
+impl ToTypeDef for NapiConst {
+  fn to_type_def(&self) -> TypeDef {
+    TypeDef {
+      kind: "const".to_owned(),
+      name: self.js_name.to_owned(),
+      def: format!(
+        "export const {}: {}",
+        &self.js_name,
+        ty_to_ts_type(&self.type_name, false).0
+      ),
+    }
+  }
+}

crates/macro/src/parser/mod.rs

@@ -9,8 +9,9 @@ use attrs::{BindgenAttr, BindgenAttrs};
 
 use convert_case::{Case, Casing};
 use napi_derive_backend::{
-  BindgenResult, CallbackArg, Diagnostic, FnKind, FnSelf, Napi, NapiEnum, NapiEnumVariant, NapiFn,
-  NapiFnArgKind, NapiImpl, NapiItem, NapiStruct, NapiStructField, NapiStructKind,
+  BindgenResult, CallbackArg, Diagnostic, FnKind, FnSelf, Napi, NapiConst, NapiEnum,
+  NapiEnumVariant, NapiFn, NapiFnArgKind, NapiImpl, NapiItem, NapiStruct, NapiStructField,
+  NapiStructKind,
 };
 use proc_macro2::{Ident, TokenStream, TokenTree};
 use quote::ToTokens;
@@ -296,7 +297,7 @@ fn extract_doc_comments(attrs: &[syn::Attribute]) -> Vec<String> {
     })
 }
 
-// Unescapes a quoted string. char::escape_debug() was used to escape the text.
+// Unescaped a quoted string. char::escape_debug() was used to escape the text.
 fn try_unescape(s: &str) -> Option<String> {
   if s.is_empty() {
     return Some(String::new());
@@ -584,6 +585,7 @@ impl ParseNapi for syn::Item {
       syn::Item::Struct(s) => s.parse_napi(tokens, opts),
       syn::Item::Impl(i) => i.parse_napi(tokens, opts),
       syn::Item::Enum(e) => e.parse_napi(tokens, opts),
+      syn::Item::Const(c) => c.parse_napi(tokens, opts),
       _ => bail_span!(
         self,
         "#[napi] can only be applied to a function, struct, enum or impl."
@@ -625,6 +627,14 @@ impl ParseNapi for syn::ItemEnum {
   }
 }
 
+impl ParseNapi for syn::ItemConst {
+  fn parse_napi(&mut self, tokens: &mut TokenStream, opts: BindgenAttrs) -> BindgenResult<Napi> {
+    let napi = self.convert_to_ast(opts);
+    self.to_tokens(tokens);
+    napi
+  }
+}
+
 fn fn_kind(opts: &BindgenAttrs) -> FnKind {
   let mut kind = FnKind::Normal;
 
@@ -910,3 +920,22 @@ impl ConvertToAST for syn::ItemEnum {
     })
   }
 }
+
+impl ConvertToAST for syn::ItemConst {
+  fn convert_to_ast(&mut self, opts: BindgenAttrs) -> BindgenResult<Napi> {
+    match self.vis {
+      Visibility::Public(_) => Ok(Napi {
+        comments: vec![],
+        item: NapiItem::Const(NapiConst {
+          name: self.ident.clone(),
+          js_name: opts
+            .js_name()
+            .map_or_else(|| self.ident.to_string(), |(s, _)| s.to_string()),
+          type_name: *self.ty.clone(),
+          value: *self.expr.clone(),
+        }),
+      }),
+      _ => bail_span!(self, "only public const allowed"),
+    }
+  }
+}

examples/napi/__test__/typegen.spec.ts.md

@@ -8,7 +8,8 @@ Generated by [AVA](https://avajs.dev).
 
 > Snapshot 1
 
-    `export function getWords(): Array<string>␊
+    `export const DEFAULT_COST: number␊
+    export function getWords(): Array<string>␊
     export function getNums(): Array<number>␊
     export function sumNums(nums: Array<number>): number␊
     export function readFileAsync(path: string): Promise<Buffer>␊

examples/napi/__test__/values.spec.ts

@@ -3,6 +3,7 @@ import { join } from 'path'
 import test from 'ava'
 
 import {
+  DEFAULT_COST,
   add,
   fibonacci,
   contains,
@@ -48,6 +49,10 @@ import {
   createSymbol,
 } from '../'
 
+test('export const', (t) => {
+  t.is(DEFAULT_COST, 12)
+})
+
 test('number', (t) => {
   t.is(add(1, 2), 3)
   t.is(fibonacci(5), 5)

examples/napi/index.d.ts

@@ -1,3 +1,4 @@
+export const DEFAULT_COST: number
 export function getWords(): Array<string>
 export function getNums(): Array<number>
 export function sumNums(nums: Array<number>): number

examples/napi/src/lib.rs

@@ -3,6 +3,9 @@ extern crate napi_derive;
 #[macro_use]
 extern crate serde_derive;
 
+#[napi]
+pub const DEFAULT_COST: u32 = 12;
+
 mod array;
 mod r#async;
 mod bigint;