implement export default

spec/eslint.ts

@@ -0,0 +1,90 @@
+// this file comes from https://github.com/msgpack/msgpack-javascript/blob/main/.eslintrc.js
+
+export default {
+  root: true,
+  extends: [
+    // https://eslint.org/docs/rules/
+    "eslint:recommended",
+    // https://github.com/typescript-eslint/typescript-eslint/blob/master/packages/eslint-plugin/src/configs/recommended.ts
+    "plugin:@typescript-eslint/recommended",
+
+    // https://github.com/benmosher/eslint-plugin-import
+    "plugin:import/recommended",
+    "plugin:import/typescript",
+
+    // https://prettier.io/docs/en/integrating-with-linters.html
+    // > Make sure to put it last, so it gets the chance to override other configs.
+    "prettier",
+  ],
+  plugins: [
+    "@typescript-eslint/eslint-plugin",
+    "eslint-plugin-tsdoc"
+  ],
+  parser: "@typescript-eslint/parser",
+  parserOptions: {
+    project: "./tsconfig.json",
+  },
+  settings: {},
+  rules: {
+    "no-constant-condition": ["warn", { checkLoops: false }],
+    "no-useless-escape": "warn",
+    "no-console": "warn",
+    "no-var": "warn",
+    "no-return-await": "warn",
+    "prefer-const": "warn",
+    "guard-for-in": "warn",
+    "curly": "warn",
+    "no-param-reassign": "warn",
+    "prefer-spread": "warn",
+
+    "import/no-unresolved": "off", // cannot handle `paths` in tsconfig
+    "import/no-cycle": "error",
+    "import/no-default-export": "warn",
+
+    "tsdoc/syntax": "warn",
+
+    "@typescript-eslint/await-thenable": "warn",
+    "@typescript-eslint/array-type": ["warn", { default: "generic" }],
+    "@typescript-eslint/naming-convention": [
+      "warn",
+      { "selector": "default", "format": ["camelCase", "UPPER_CASE", "PascalCase"], "leadingUnderscore": "allow" },
+      { "selector": "typeLike", "format": ["PascalCase"], "leadingUnderscore": "allow" },
+    ],
+    "@typescript-eslint/restrict-plus-operands": "warn",
+    "@typescript-eslint/no-throw-literal": "warn",
+    "@typescript-eslint/unbound-method": "warn",
+    "@typescript-eslint/explicit-module-boundary-types": "warn",
+    "@typescript-eslint/no-extra-semi": "warn",
+    "@typescript-eslint/no-extra-non-null-assertion": "warn",
+    "@typescript-eslint/no-unused-vars": ["warn", { "argsIgnorePattern": "^_" }],
+    "@typescript-eslint/no-use-before-define": "warn",
+    "@typescript-eslint/no-for-in-array": "warn",
+    "@typescript-eslint/no-unsafe-argument": "warn",
+    "@typescript-eslint/no-unsafe-call": "warn",
+    // "@typescript-eslint/no-unsafe-member-access": "warn", // too strict, especially for testing
+    "@typescript-eslint/no-unnecessary-condition": ["warn", { "allowConstantLoopConditions": true }],
+    "@typescript-eslint/no-unnecessary-type-constraint": "warn",
+    "@typescript-eslint/no-implied-eval": "warn",
+    "@typescript-eslint/no-non-null-asserted-optional-chain": "warn",
+    "@typescript-eslint/no-invalid-void-type": "warn",
+    "@typescript-eslint/no-loss-of-precision": "warn",
+    "@typescript-eslint/no-confusing-void-expression": "warn",
+    "@typescript-eslint/no-redundant-type-constituents": "warn",
+    "@typescript-eslint/prefer-for-of": "warn",
+    "@typescript-eslint/prefer-includes": "warn",
+    "@typescript-eslint/prefer-string-starts-ends-with": "warn",
+    "@typescript-eslint/prefer-readonly": "warn",
+    "@typescript-eslint/prefer-regexp-exec": "warn",
+    "@typescript-eslint/prefer-nullish-coalescing": "warn",
+    "@typescript-eslint/prefer-optional-chain": "warn",
+    "@typescript-eslint/prefer-ts-expect-error": "warn",
+
+    "@typescript-eslint/indent": "off",
+    "@typescript-eslint/no-explicit-any": "off",
+    "@typescript-eslint/no-empty-interface": "off",
+    "@typescript-eslint/no-empty-function": "off",
+    "@typescript-eslint/no-var-requires": "off",
+    "@typescript-eslint/no-non-null-assertion": "off",
+    "@typescript-eslint/ban-ts-comment": "off",
+  },
+};

spec/eslint.ts.stdout

@@ -0,0 +1,112 @@
+{
+  "default": {
+    "root": true,
+    "extends": [
+      "eslint:recommended",
+      "plugin:@typescript-eslint/recommended",
+      "plugin:import/recommended",
+      "plugin:import/typescript",
+      "prettier"
+    ],
+    "plugins": [
+      "@typescript-eslint/eslint-plugin",
+      "eslint-plugin-tsdoc"
+    ],
+    "parser": "@typescript-eslint/parser",
+    "parserOptions": {
+      "project": "./tsconfig.json"
+    },
+    "settings": {},
+    "rules": {
+      "no-constant-condition": [
+        "warn",
+        {
+          "checkLoops": false
+        }
+      ],
+      "no-useless-escape": "warn",
+      "no-console": "warn",
+      "no-var": "warn",
+      "no-return-await": "warn",
+      "prefer-const": "warn",
+      "guard-for-in": "warn",
+      "curly": "warn",
+      "no-param-reassign": "warn",
+      "prefer-spread": "warn",
+      "import/no-unresolved": "off",
+      "import/no-cycle": "error",
+      "import/no-default-export": "warn",
+      "tsdoc/syntax": "warn",
+      "@typescript-eslint/await-thenable": "warn",
+      "@typescript-eslint/array-type": [
+        "warn",
+        {
+          "default": "generic"
+        }
+      ],
+      "@typescript-eslint/naming-convention": [
+        "warn",
+        {
+          "selector": "default",
+          "format": [
+            "camelCase",
+            "UPPER_CASE",
+            "PascalCase"
+          ],
+          "leadingUnderscore": "allow"
+        },
+        {
+          "selector": "typeLike",
+          "format": [
+            "PascalCase"
+          ],
+          "leadingUnderscore": "allow"
+        }
+      ],
+      "@typescript-eslint/restrict-plus-operands": "warn",
+      "@typescript-eslint/no-throw-literal": "warn",
+      "@typescript-eslint/unbound-method": "warn",
+      "@typescript-eslint/explicit-module-boundary-types": "warn",
+      "@typescript-eslint/no-extra-semi": "warn",
+      "@typescript-eslint/no-extra-non-null-assertion": "warn",
+      "@typescript-eslint/no-unused-vars": [
+        "warn",
+        {
+          "argsIgnorePattern": "^_"
+        }
+      ],
+      "@typescript-eslint/no-use-before-define": "warn",
+      "@typescript-eslint/no-for-in-array": "warn",
+      "@typescript-eslint/no-unsafe-argument": "warn",
+      "@typescript-eslint/no-unsafe-call": "warn",
+      "@typescript-eslint/no-unnecessary-condition": [
+        "warn",
+        {
+          "allowConstantLoopConditions": true
+        }
+      ],
+      "@typescript-eslint/no-unnecessary-type-constraint": "warn",
+      "@typescript-eslint/no-implied-eval": "warn",
+      "@typescript-eslint/no-non-null-asserted-optional-chain": "warn",
+      "@typescript-eslint/no-invalid-void-type": "warn",
+      "@typescript-eslint/no-loss-of-precision": "warn",
+      "@typescript-eslint/no-confusing-void-expression": "warn",
+      "@typescript-eslint/no-redundant-type-constituents": "warn",
+      "@typescript-eslint/prefer-for-of": "warn",
+      "@typescript-eslint/prefer-includes": "warn",
+      "@typescript-eslint/prefer-string-starts-ends-with": "warn",
+      "@typescript-eslint/prefer-readonly": "warn",
+      "@typescript-eslint/prefer-regexp-exec": "warn",
+      "@typescript-eslint/prefer-nullish-coalescing": "warn",
+      "@typescript-eslint/prefer-optional-chain": "warn",
+      "@typescript-eslint/prefer-ts-expect-error": "warn",
+      "@typescript-eslint/indent": "off",
+      "@typescript-eslint/no-explicit-any": "off",
+      "@typescript-eslint/no-empty-interface": "off",
+      "@typescript-eslint/no-empty-function": "off",
+      "@typescript-eslint/no-var-requires": "off",
+      "@typescript-eslint/no-non-null-assertion": "off",
+      "@typescript-eslint/ban-ts-comment": "off"
+    }
+  }
+}

src/ast.rs

@@ -98,6 +98,7 @@ pub enum Statement<'src> {
     },
     Return(Expression<'src>),
     Yield(Expression<'src>),
+    ExportDefault(Expression<'src>),
     Export(Statements<'src>), // stmts.len() == 1
 }
 
@@ -111,6 +112,7 @@ impl<'src> Statement<'src> {
             FnDef { name, stmts, .. } => calc_offset(*name, stmts.span()),
             Return(ex) => ex.span,
             Yield(ex) => ex.span,
+            ExportDefault(ex) => ex.span,
             Export(stmts) => stmts[0].span().unwrap(),
         })
     }

src/compiler.rs

@@ -334,6 +334,15 @@ impl Compiler {
                     self.add_inst(OpCode::Yield, (self.target_stack.len() - res.0 - 1) as u8);
                     self.target_stack.pop();
                 }
+                Statement::ExportDefault(ex) => {
+                    // `export default expr` is a syntactic sugar for `export const default = expr`.
+                    let res = self.compile_expr(ex)?;
+
+                    let name_id = self.add_literal(Value::Str("default".to_string()));
+                    self.add_load_literal_inst(name_id);
+                    self.add_copy_inst(res);
+                    self.add_inst(OpCode::Export, 0);
+                }
                 Statement::Export(stmts) => {
                     assert!(stmts.len() == 1);
 

src/parser.rs

@@ -568,6 +568,13 @@ fn fn_def_statement(i: Span) -> IResult<Span, Statement> {
     ))
 }
 
+fn export_default_statement(i: Span) -> IResult<Span, Statement> {
+    let (i, _) = space_delimited(tag("export"))(i)?;
+    let (i, _) = space_delimited(tag("default"))(i)?;
+    let (i, ex) = space_delimited(expr)(i)?;
+    Ok((i, Statement::ExportDefault(ex)))
+}
+
 fn export_statement(i: Span) -> IResult<Span, Statement> {
     let (i, _) = space_delimited(tag("export"))(i)?;
     let (i, stmt) = statement(i)?;
@@ -613,6 +620,7 @@ fn general_statement<'a>(last: bool) -> impl Fn(Span<'a>) -> IResult<Span<'a>, S
             fn_def_statement,
             return_statement,
             yield_statement,
+            export_default_statement,
             export_statement,
             terminated(expr_statement, terminator),
         ))(input)

src/type_checker.rs

@@ -280,6 +280,9 @@ pub fn type_check<'src>(
                 tc_expr(e, ctx)?;
                 // TODO: check type with the return type, but don't escape from this function.
             }
+            Statement::ExportDefault(e) => {
+                res = tc_expr(e, ctx)?;
+            }
             Statement::Export(stmts) => {
                 res = type_check(stmts, ctx)?;
             }