fix(es/parser) Throw a syntax error for const without initializer i…

…n strict mode (#3742)

Co-authored-by: Donny/강동윤 <kdy1997.dev@gmail.com>

.github/workflows/cargo.yml

@@ -16,6 +16,8 @@ env:
   CARGO_INCREMENTAL: 0
   RUST_LOG: "debug"
   DIFF: 0
+  # https://github.com/swc-project/swc/pull/3742
+  RUST_MIN_STACK: 4194304
 
 jobs:
   check-license:

crates/swc_ecma_codegen/src/stmt.rs

@@ -42,13 +42,11 @@ mod tests {
     fn declaration_statement() {
         assert_min("var foo;", "var foo");
         assert_min("let foo;", "let foo");
-        assert_min("const foo;", "const foo");
         assert_min("var foo = 10;", "var foo=10");
         assert_min("let foo = 10;", "let foo=10");
         assert_min("const foo = 10;", "const foo=10");
         assert_min("var foo, bar;", "var foo,bar");
         assert_min("let foo, bar;", "let foo,bar");
-        assert_min("const foo, bar;", "const foo,bar");
         assert_min("var foo = 10, bar = 20;", "var foo=10,bar=20");
         assert_min("let foo = 10, bar = 20;", "let foo=10,bar=20");
         assert_min("const foo = 10, bar = 20;", "const foo=10,bar=20");

crates/swc_ecma_parser/src/error.rs

@@ -183,6 +183,8 @@ pub enum SyntaxError {
     ImportBindingIsString(JsWord),
     ExportBindingIsString,
 
+    ConstDeclarationsRequireInitialization,
+
     TS1003,
     TS1005,
     TS1009,
@@ -487,6 +489,10 @@ impl SyntaxError {
                 "A string literal cannot be used as an exported binding without `from`.".into()
             }
 
+            SyntaxError::ConstDeclarationsRequireInitialization => {
+                "'const' declarations must be initialized".into()
+            }
+
             SyntaxError::TS1003 => "Expected an identifier".into(),
             SyntaxError::TS1005 => "Expected a semicolon".into(),
             SyntaxError::TS1009 => "Trailing comma is not allowed".into(),

crates/swc_ecma_parser/src/parser/stmt.rs

@@ -727,7 +727,7 @@ impl<'a, I: Tokens> Parser<I> {
                 break;
             }
 
-            decls.push(self.with_ctx(ctx).parse_var_declarator(for_loop)?);
+            decls.push(self.with_ctx(ctx).parse_var_declarator(for_loop, kind)?);
         }
 
         if !for_loop && !eat!(self, ';') {
@@ -748,7 +748,11 @@ impl<'a, I: Tokens> Parser<I> {
         })
     }
 
-    fn parse_var_declarator(&mut self, for_loop: bool) -> PResult<VarDeclarator> {
+    fn parse_var_declarator(
+        &mut self,
+        for_loop: bool,
+        kind: VarDeclKind,
+    ) -> PResult<VarDeclarator> {
         let start = cur_pos!(self);
 
         let mut name = self.parse_binding_pat_or_ident()?;
@@ -798,6 +802,13 @@ impl<'a, I: Tokens> Parser<I> {
                 // Destructuring bindings require initializers, but
                 // typescript allows `declare` vars not to have initializers.
                 if self.ctx().in_declare {
+                    None
+                } else if kind == VarDeclKind::Const && self.ctx().strict {
+                    self.emit_err(
+                        span!(self, start),
+                        SyntaxError::ConstDeclarationsRequireInitialization,
+                    );
+
                     None
                 } else {
                     match name {
@@ -2214,4 +2225,36 @@ export default function waitUntil(callback, options = {}) {
         let src = "export { 'foo' };";
         test_parser(src, Syntax::Es(Default::default()), |p| p.parse_module());
     }
+
+    #[test]
+    #[should_panic(expected = "'const' declarations must be initialized")]
+    fn ts_error_for_const_declaration_not_initialized() {
+        let src = r#"
+"use strict";
+const foo;"#;
+
+        test_parser(
+            src,
+            Syntax::Typescript(TsConfig {
+                ..Default::default()
+            }),
+            |p| p.parse_script(),
+        );
+    }
+
+    #[test]
+    #[should_panic(expected = "'const' declarations must be initialized")]
+    fn es_error_for_const_declaration_not_initialized() {
+        let src = r#"
+"use strict";
+const foo;"#;
+
+        test_parser(
+            src,
+            Syntax::Es(EsConfig {
+                ..Default::default()
+            }),
+            |p| p.parse_script(),
+        );
+    }
 }